Part II: Goals of Sailing Ship Design
The designer of a sailing ship must give it sufficient capacity and speed to carry out its mission, yet without unduly compromising its seaworthiness. And seaworthiness itself is a complex concept, embracing watertightness, buoyancy, stability, hull strength, weatherliness, handiness, and freedom to enter shallow or constricted waters.
Capacity and Displacement
The ship buyer, be he king or commoner, doesn't specify the hydrodynamic parameters. Instead, he says, "I want a warship of 100 guns" or "I want a merchant ship, capable of voyages to the Indies, which will carry 500 tons of cargo".
Capacity ("burden") is the ability to cram in crew, passengers, provisions, cargo, cannon (and their shot and powder) and miscellaneous supplies (e.g., spare sails). It's limited both in terms of volume (by the dimensions and layout of the ship) and weight (too much, and the ship sinks). Until the nineteenth century, it was probably the single most important desideratum for a ship (other than staying afloat). The different demands on capacity compete with each other; for example, putting on more cannon (and the crews to man them) increases fighting ability but reduces the space for cargo and crew provisions.
The formula developed (1582) by the Elizabethan shipwright Matthew Baker, and one of several formulae in use in the 1630s, was keel length X maximum beam X depth of hold, all in feet, divided by 100.
The result was a value in tuns burden; a tun was a volume measurement, a container of 252 gallons of wine, about 40 cubic feet, weighing about one English long ton (2240 pounds). Thus, the original meaning of "burden" was the number of tuns of wine that the ship could carry.
There was also something called "tons and tonnage." That added to the burden ("tons") an estimate (typically, one-third of the burden) of the miscellaneous goods ("tonnage") which could be carried. A ship with a burden of 300 tons has a "tons and tonnage" of 400. (BakerCV, 25-6). When "burden" is quoted in the literature it often really means "tons and tonnage," the total cargo capacity (modern "net tonnage").
The largest of the seventeenth-century merchant ships were the Portuguese nao, which were rated as high as 2000 tons burden. (Brigadier 12).
Passenger capacity can be estimated from burden. The tendency was to stuff the ship for maximum profit. A 1534 Spanish ordinance limited New World-bound ships to 60 passengers per 100 tons burden, but some carried almost one per ton (Perez-Mallaina, 130). In the Irish emigration to America, the average was 0.4/ton in 1769-70, and 0.66 in 1771 (Wokeck 185). In 1819, US ships were limited to 0.40/ton. (Blunt 314). Bear in mind that these ships carried cargo, too.
Of course, slave ships were packed even more densely. The average was reportedly 4 slaves/ton for 1600-1650 (Thornton 118). A 1684 Portuguese ordinance limited carriage to 2.5-3.5 slaves/ton (depending on portholes). (Rawley 252).
Displacement is a somewhat slippery concept, as it can be expressed in both weight and volume terms. The sum of the lightship weight (hull, rigging, armament, superstructure) and the deadweight (crew, provisions, stores, and cargo) is the load, which causes the ship to sink until the underwater portion has displaced a volume of water of equal weight. If that comes at a point at which the ship's deck is still above water, then the ship is floating (and if not, you need a new designer). Multiply the burden of a down-time ship by 1.67 (Wikipedia/BOM) or 1.3-5 (warships; Glete 529) to crudely estimate its displacement.
For a ship to be buoyant, the designer has to limit the ratio of its mass to its volume so that its overall density less than that of water. And that means that a steel hulled ship has to have a greater volume than a wooden hulled one of the same surface area, to compensate for the greater density of the hull. Even so, they tend to ride lower in the water. (McCutchan 110).
A battleship by definition must have a large displacement, and that would also be typical of a long-distance trader. There was a tendency to overload long-distance traders to increase profitability. Matters were exacerbated by the nonchalant distribution of weight; heavy cargo often ended up on the upper deck. The Cosmographer Royal said that overloading was one of the reasons the nao Santo Alberto (sunk 1593) "and many others lie buried at the bottom of the sea." (Brigadier 13). Warships also were victims of overloading; excessive armament contributed to the capsizing of the Vasa.
In nineteenth-century wooden warships, about half of the load displacement was attributable to the hull. For merchantmen, the hull was only 35-45% (wood) or 30-35% (iron) displacement. (White 384).
The development of integral calculus in the second half of the seventeenth century made possible the calculation of the underwater volume corresponding to various waterlines and thus the calculation of the waterline corresponding to a particular load. (Glete 50ff), and for that matter, the location of the center of buoyancy for a particular angle of heel.
In Weber's "In the Navy" (Ring of Fire), Eddie tells Mike, "I don't have the least idea how to figure displacements or allow for stability requirements, and I know the designers screwed up the displacement calculations big time for a lot of the real ironclads built during the Civil War. There was one class of monitor that would've sunk outright if they'd ever tried to mount their turrets!"
Draft and Freeboard
The ship's draft (distance from waterline to bottom of the keel), and also the waterline length and breadth, will change depending on how heavily it's loaded, and how salty and warm the water is. Shallowness of draft is desirable if the captain wants to negotiate rivers and coastal waters (perhaps to escape a deep-drafted pursuer which would, if it followed, run aground). The great draft of the Constitution -class ships limited which ports they could use. (ChapelleHASN 130). But a deep draft ship can sail closer to the wind, and is less likely to drift to leeward (Anderson 88; ChapelleHASS 46). And it's less susceptible to wave action (Walton 168).
A ship with high freeboard (distance from waterline to deck) will suffer from windage, and be driven to leeward, but one with low freeboard is also easier for hostiles in small craft to board, and will be more likely to take on water if the sea state is high. (The Egyptians have the colorful term, "sailing with your coffin.") (Hollander 58). Freeboard on early nineteenth century British frigates was usually 6-9', with drafts of 15-20'. (Gardiner 143). Lloyd's rule was to provide 2-3 inches freeboard per foot of depth (White 33).
Speed and Resistance
The wind exerts a force on the sails, which cause the ship to accelerate. But there are forces which oppose the motion of the ship through the water (and air).
Frictional resistance, which is dominant at low speeds, is the result of friction between the hull and the water it contacts, and is proportional to the "wetted surface" of the hull, and the hull roughness. It increases as the square, or nearly so, of the speed (Baker 19ff). It's usually 80-90% of total resistance for ships at 6-8 knots; 50-60% at twice that speed. (White 448).
Form (pressure) resistance is the result of the hull pushing water out of its way, and the water returning to form a turbulent wake (eddies). It is proportional to the cross-sectional area of the underwater portion of the hull, and affected by the shape of the bow and stern. For ships with easy curves at bow and stern, eddymaking resistance is about 8% of the frictional resistance (White 449).
Air resistance is the result of the ship's above-water structure pushing air out of the way, and thus is akin to form resistance, but much weaker. The resistance is increased if there is a headwind.
Wavemaking resistance is simple in concept but difficult to quantify. As it moves through the water, the ship makes waves, which cost energy. In general, the faster the ship is going, the greater the resistance, roughly as the square of the speed.
However, there is also a periodic fluctuation in resistance, depending on speed. The bow waves and stern wave systems interact, and, depending on the speed, they may reinforce each other or partially cancel each other out. The distance (wavelength) between the waves increases as the square of the ship speed, and when the wavelength is near the waterline length, the waves reinforce each other. The wavelength equals the waterline length when the ship is traveling at "hull speed" (in knots, 1.34 times the square root of the waterline length). At speeds near the hull speed; this reinforcement means that the resistance increases faster than the square of the ship speed-indeed, as the third, fourth or fifth power.
Wave (added) resistance, as the name implies, is the result of ocean wave action. It is roughly proportional to the square of the wave height. (Nabergoj), which in turn depends on the wind speed and fetch. The direction of wave motion is also important, with "head seas" being the worst. Long, heavy ships are less affected. (Prpic-Orsic).
Stability
A ship can heel over as a result of wind or wave action, making a turn, or firing a broadside. What happens next depends on the relative positions of the center of gravity (whose position is dependent on how the ship is loaded, and whether it carries ballast) and the center of buoyancy (which depends on the hull form). The ship can right itself, remain at a "list," or be driven over further until it passes the "angle of vanishing stability" (AVS) and capsizes. The effect of the design parameters on stability can be complex.
Sailing ships typically had a maximum safe heel of 45-65њ, depending on hull form, loading, and the possibility of flooding. (ChapelleSSUS 213).
A ship can be stiff, that is, have too high an initial stability. If there is a sudden gust, and it doesn't timely reduce sail, then since the ship doesn't heel much, the sails take the full force of the wind, and "the topsails are often carried away, or the sails torn to shreds." (Walton, 215). Worse, if the ship heels and then rights itself too quickly, it could be dismasted (as happened repeatedly with the 1800 Akbar -Gardiner 137). Stiffness can be reduced by "winging" weights out to the ship's sides or raising the center of gravity. (Walton 168).
For a warship, you want a slow and easy roll, limited in angle, to make it easy to aim.(ChapelleHASN 24).
Stability predictions are inherently more difficult to make for wooden ships because of the great variation in the specific gravity of wood. (Reed 360).
The Swedish crown had an unpleasant reminder that even kings are subject to the laws of physics. The pride of the Swedish navy, the Vasa, sank in 1628, on its maiden voyage, blown over by a gentle wind gust estimated as being just eight knots. Fairley says that according to modern calculations, four knots would have been enough to capsize it. Its maximum angle of heel was just ten degrees.
The basic problem was that the Vasa was top-heavy. It was the first Swedish warship with two enclosed gundecks. This was not part of the original plans, but rather a last minute development in the Swedish-Danish arms race. There were also several upward revisions, during construction, of the number and weight of the cannon. All this meant that the ship was not only taller, but wider. Since the Vasa 's keel had already been laid, the width had to be added mostly in the upper part of the hull, which further raised the center of gravity. The keel was found to be a bit thin for supporting all the added weight so additional braces were added in the hold. With space reduced, Vasa could only carry about 120 tons of ballast, and Fairley says it would have needed more than twice that amount to be stable. (But it was impossible to add more since the gunports were already only 3.5 feet above the waterline-Franzen 19)
It is interesting to note that the Vasa underwent a crude stability ("lurch") test. Thirty men ran side to side three times. The result? The ship rocked back and forth like crazy. The outcome was not reported to the shipyard or the king. Curiously, the admiral who witnessed the experiment concluded that the ship was carrying too much ballast because the gunports were close to the water.
Hull Strength
The hull of a ship has to be strong enough to withstand the stresses imposed by the opposing forces of gravity and buoyancy, as well as those added, once it ventures out of harbor, by wind and wave. It is obvious that a warship must also be able to endure enemy gunfire. But the warship's own broadside can deliver a considerable recoil shock. (Glete 35).
The resistance to these stresses is the compound effect of the ship's frames, decks, deck supports (beams and knees) and longitudinal or diagonal stiffeners.
The hull bends as a result of variations in the local ratio of weight to buoyancy along the length of the hull. When a ship hogs, the center droops; when it sags, its ends droop. In the hogged state, the main deck is compressed and the bottom is stretched; sagging has the opposite effect.
Hogging and sagging can occur even in still water because of the narrowing of the ends (reducing buoyancy) and the non-uniform loading of the ship. Hogging and sagging is even more pronounced when a ship encounters waves, because buoyancy is increased at the crests and reduced at the troughs. The worst situation is when the waves have a wavelength equal to the hull length. (Thearle 312). Moreover, as the center of the ship passes from crest to trough, its state changes from sagging to hogging, at a frequency of perhaps a few seconds (315). Obviously, this challenges hull integrity. If the bending is too great, the ship snaps. Goodbye ship. Even if the stress isn't catastrophic, the strains tend to reduce the speed and increase leakage. (Glete 36).
Once the relationship of hull length to speed potential was recognized, there was an incentive to build longer hulls. (ChapelleSSUS 412). But hogging and sagging stresses are typically proportional to the square of the hull length.
However, lengthening the hull has compensations. In the nineteenth century, designers took advantage of longer hulls by repositioning the foremast further aft, reducing the bow load and thus reducing hogging. (McCuchan 36). Also, a very long hull might not often encounter waves whose wavelength equals the hull length.
Increasing breadth and depth increases the weight, and therefore the tendency to bend, but also the ability of the hull to resist the bending forces.
The usual antidote to bending was reinforcement. The thickness of the main deck and the keel could be increased (McCutchan 37). The French frigate L'Oiseau (1772) had diagonal planking (ChapelleSSUS 207), and the USS Constitution (1797) had diagonal risers (Otton), both to inhibit hogging. This became common in early nineteenth century. (ChapelleHASN 365).
Since hogging was feared more than sagging, from time to time, builders experimented with laying the keel with a slight sag in the middle. This expedient was recommended by Griffith in the 1850s. (ChappelleSSUS 366).
Handiness
The longer the ship, the slower it turns (Laing 32) and the larger its turning radius. A ship half the length is probably about four times as maneuverable. It also helps to have fine ends, and weight concentrated amidships. (Atwood).
Weatherliness
When the force of the wind upon the sail is not parallel to the keel, the ship will be pushed, not just in the direction its bow is pointing, but also laterally. This undesirable lateral motion is called leeway and a ship with minimal leeway when traveling upwind is said to be weatherly. The resistance to leeway increases with the draft and underwater length of the hull.
Windage (the force of the wind other than on the sails) is also important, and it is strongest when the wind is on the beam. In general, the ship with the higher freeboard or greater superstructure is going to suffer more leeway. If a single and a double decker were both making five knots close-hauled, in an hour the former might be pushed two miles to leeward, and the latter three. (Laing 75).
Weatherliness is especially important for fighting ships because it determines who obtains the weather gage. (ChapelleHASS 47).
Hull Dimensions.
The basic dimensions of the hull are its length, breadth (beam), and depth, all of which vary as a result of the curves of the hull.
Length. Seventeenth-century sources generally quote the keel length. The length of the gun deck limits the number of guns which can be carried upon it. (MurrayS 6). A late seventeenth-century naval regulation required a minimum spacing of 6.5 feet between gunports to accommodate the gun crew. (Grieco 110). Based on data for nineteenth-century British warships (Creuze 53), the length on the gun deck is perhaps 20% greater than the keel length. For the waterline length, which affects wavemaking resistance and pitch stability, I would split the difference.
Raleigh advised against building ships much longer than 100 feet (Creuze 17). For large warships launched between 1600 and 1640, a typical keel length would be 100-130 feet (Temmu). A first rate in Nelson's navy might have a 175 foot keel. (Longridge 7).
Breadth. For large warships launched between 1600 and 1640, a typical maximum beam (B) would be 35-45 feet, usually closer to 35.
Length/Breadth Ratio. This ratio determines the overall shape. Chapelle says that a ship with too wide a hull was slow, and one too narrow was an unsteady gun platform and couldn't carry sail well, presumably because of lack of stability. (ChapelleHASS 46). Vasa had a ratio of about 4:1. (Franzen 74ff).
The Portuguese nao had a length: beam ratio of 3:1 (Brigadier 11; Konstam 7). William Burroughs, the controller of the British Royal Navy, around 1596 suggested relative proportions for three "orders" of ships: (1) pure merchant ship, keel length twice breadth amidships, depth in hold half breadth; (2) all-purpose, length 2-2.25 times breadth, depth 11/24ths breadth; and (3) warship, length three times breadth, depth 0.4 times breadth. Looking at seven merchantmen (1582-1627) of 130-200 tons "burden" (see Capacity, below), these had length/breadth ratios of 2.14-2.92, and depth/breadth of 0.42-0.5. (BakerNM 8-9; Myers 106). The anonymous Treatise on Shipbuilding (c1620) called for length to be 2-3 times breadth, and depth 0.33-0.5 times breadth, and said the ideal warship was KL/B 2.78, D/B 0.43 (107).
"By 1634 it was very difficult to find a [British war]ship with a keel/beam ratio of less than 2.90, and there were several higher than 3.00." (Myers) In 1841, the typical length/breadth ratio for an English warship was 3.15, whereas in America, even merchant ships averaged 4.6. The extreme clippers which developed later in the nineteenth century reached a ratio of 5.7. (Laing 54).
Depth/breadth ratio. The depth determines the number of decks (Glete 52), the height of the gun deck, and the amount of freeboard. Duhamel (1764) says that the depth of a warship is usually 0.5B; but in the list of warships he provides, it is usually a bit less than that (4-6). In nineteenth-century British ships, depth was 0.55B for sloops and smacks, 0.58-0.75B for schooners and brigs, and 0.66-0.75B for large schooners and ships. This evolved under tonnage rules which penalized breadth and ignored depth. (Creuze 36).
Body
The body of the ship consists of the hull, deck, and any superstructures other than rigging. The hull is the backbone of the ship. It's partly out of sight, beneath the waves, but it should never be out of mind. Without a hull, you're swimming!
Frame vs. Monocoque Construction
In the classic truss frame construction, an internal skeleton carries the load, and the skin of the structure just keeps out wind and water. In a monocoque ("single shell") construction, it is the skin that bears all or most of the load.
Generally speaking, the truss frame is superior (on weight and cost basis) for resisting compression and bending, and the monocoque shell for resisting shear and torsion. In the Thirties, airplanes got large enough and fast enough for the monocoque strategy to prevail. (Gordon 311-3).
While classical ships were monocoque, their construction was labor- and timber-intensive, and hence this construction strategy was gradually abandoned. By the seventeenth century, the transition to frame construction was almost complete. The principal exception was that the Dutch used a hybrid process in building flutes; a few bottom strakes were attached to the keel before doing any framing.
Chinese junks have been characterized as monocoques because they lack the keel, stem and sternpost, but their strength is not attributable just to their skin; they are reinforced by transverse bulkheads. (Thomas). Modern European monocoques are mostly open boats made of plywood or fiberglass, but there are also some monocoque minesweepers.
The backbone of the framed ship was formed by the keel, stem and sternpost. The length of these pieces determined the length and depth of the ship. Beginning in the early eighteenth century, there was a false keel under the true one. The idea was that if the ship ran aground, the false keel would absorb the impact, like the bumper on an automobile. (Mondfeld 74).
If a ship has a strongly tapered stern profile, it may have "deadwood," a vertical extension of the keel, to connect the aft end of the keel to the buttock of the ship. (After 1860, the bow was tapered enough so deadwood was needed in front, too.) The sternpost is connected to the aft end of the deadwood and the rudder mechanism is attached to the sternpost. Both the stem and sternpost are likely to be made of a single log of first class oak. (Longridge 11). Deadwood reduces leeway but increases frictional resistance. (Winters).
Transverse vs. Longitudinal Framing
There are two basic framing methods. In transverse framing, curved ribs run up from the keel, forming the load-bearing elements of the sides of the ship, and then deck beams bridge the tops of the ribs. It is called transverse because the ribs are (viewed from above) perpendicular to the keel.
The alternative is longitudinal framing, in which the sides of the ship are established by longitudinal (parallel to the keel) stiffeners. This was introduced in the nineteenth century (Young).
Bear in mind that a ship would not be purely transversely or purely longitudinally framed. Even if a ship has transverse ribs, they are attached to a longitudinal keel. And if a ship has longitudinal girders, then these must be linked by transverse "webs."
In wooden sailing ships, and early steel ships, transverse framing predominated. However, that meant that most of the structure did not offer any resistance to longitudinal bending. (NavArchWeb). That's fine for an accordion, but not good for a ship.
Bulkheads
These divide the ship into watertight compartments, and also increase its hull strength and its stability after being damaged. However, they also make it more time-consuming to load and unload cargo. Both transverse and longitudinal bulkheads were used regularly in Chinese junks since at least the second century (Temple 190), but prior to the nineteenth century, their use in European ships appears to have been spottier. Bulkheads were initially made of wood, but iron ones were introduced in the 1830s. (Young; Gould 79).
Planking
The framing must be covered with wooden planks or iron plates. There are two basic construction methods. In both, the planks run fore-and-aft. Carvel construction, invented in the ancient Mediterranean, fitted the planks or plates so they met edge to edge, forming a smooth surface. In clinker (lapstrake) building, used in northern Europe and in China, the planks or plates overlap their edges. (Svensson, 8). Clinker is not as streamlined as carvel, but it is stronger, and hence the planks can be made thinner.
Gould contends that the adoption of gunports favored the adoption of carvel planking (Gould 215). In the seventeenth century, the English used carvel planking everywhere, but the Dutch used clinker for their upper works. (Anderson 153).
John Smith's Sea Grammar (1627) says that a ship of 400 tuns requires four inch planking; one of 300, three inch; and smaller ships two inch.
Waterproofing
Wooden ships are made watertight by caulking them. Traditionally European ships were caulked by filling the seams with oakum (fibers from old ropes) soaked in pitch. The pitch can be distilled from pine resin, or from asphalt. Lime was sometimes used in place or in addition to pitch. The Chinese instead used tung oil or fish oil. Modern sealants include silicone and polyurethane.
Deck
In profile, the deck of a ship may be flush (horizontal), or it may have a sheer (upward curve) toward either or both ends. Judging from contemporary illustrations, seventeenth-century vessels will most likely have a very pronounced stern sheer. The sheer was gradually flattened out over the course of the eighteenth century.
Viewed from the front, the deck will usually be either flat or slightly cambered (convex upward). Camber slightly increases the structural strength, and reduces the recoil distance of the cannon (Dodds 89). Sheer and camber both permit water to drain away.
Hull Material
Wood has the advantage of being naturally buoyant; wrought iron and steel, that of considerably greater tensile strength and stiffness, both absolutely and in proportion to weight. Wood is vulnerable to biological attack; metal, to corrosion.
Wood. The deck could be made of any of variety of woods, such as pine (BakerCV 95). The materials requirements for the hull were more stringent. The official march of the eighteenth century British Navy proclaimed, "Heart of oak are our ships…" Oak was the principal hull wood for European navies in the seventeenth century, too. Pine was used, especially in the cost-conscious Dutch flutes, when oak was unavailable or deemed too pricey. (Unger), but it was definitely inferior.
However, beginning in the sixteenth century, Portuguese ships built in Goa shipyards used teak. The teak hulls lasted a decade longer than those made of oak or pine, perhaps because of its resistance to teredo worms. (Brigadier). Moreover, oak contains tannic acid, which corrodes iron, and teak doesn't (Jordan). Teak requires less seasoning than oak, it doesn't expand significantly when heated, and it is extremely durable. (Bowen 143). The British displaced the Portuguese, but it wasn't until the early nineteenth century that the British permitted warship construction in India. Soon thereafter, the British use of teak surpassed that of oak. (Schlich, 578).
Mahogany was used by the Spanish in the New World, it being readily available in Cuba and the Honduras. It is more buoyant than oak, easy to bend and carve, and resistant to dry rot. It also doesn't burn or splinter as easily as oak. (Glete 31; Fine Woodworking 25).
As commemorated by a Bermuda postage stamp, native Red cedar ( Juniperus bermudiana) was used to build the Deliverance and Patience , which went to the rescue of the Jamestown colony in 1610. Many sloops for the West Indian and African trade were constructed from this wood. (ChapelleSSUS 65).
Long, straight timbers are used for the keel, and are also sawn to make planking. For large ships, several pieces had to be "scarfed" together; HMS Thunderer needed seven baulks, each 26' (Dodds 58).
There is also a demand for "compass" (curved) timber for use in framing. Foresters would survey forests and mark the trees which had branches of a particular desired curve. In like manner, they looked for "knee" (angled) timber, taking it from the junction of branch and trunk. The knee timbers secured the deck beams to the frame (BakerCV 95). Warships had a particular need for crooked timber for reinforcement (Glete 52).
Wooden planking can be curved, but the curves must be gentle. If the curve is too sharp, the wood will break rather than bend. (Henderson 118). In the seventeenth century, "green planks were often scorched or heated in wet sand to render them pliable enough to be fitted around the customary bluff bows…" (BakerCV 31).
The natural supply of compass and knee timber was gradually depleted, and hence means were sought to produce it artificially. Unfortunately, the heavier the timber, the harder it is to bend. According to Baker, "the steam bending of frames was unknown" in the seventeenth century, and Griffiths (16) says, "from time immemorial shipbuilders have bent their planks by a due application of heat and moisture but it is not… until the present [nineteenth] century, that any of them discovered how to bend frame timbers and knees."
Another issue was how to attach the planking to the frame, and indeed the various frame elements to each other. Baker says that in the early seventeenth century, there was extensive use of "treenails" (wooden pegs), with iron nails being used mainly in fastening down the planking of the superstructure. (BakerCV 33). However, the Portuguese apparently just used iron nails in the hull, and the Spanish San Martin (sunk 1618) used both kinds on the same planking (Crisman). Treenails were cheaper than iron ones even in the mid-eighteenth century (Dodds 24).
The great enemy of the wooden ship was dry rot. (Dodds 13). Three expedients were used to minimize it. First, shipbuilders selected resistant woods. Teak and greenheart are good for perhaps twelve years but weren't used by Europeans (except as noted) in the early seventeenth century. Oak is durable if seasoned (English practice was three years), lasting perhaps a decade, but unseasoned oak can be destroyed in a few months. (Which didn't stop the American colonists from using unseasoned wood for smugglers and privateers, ChapelleSSUS 13.) The heartwood was preferred even though that meant that the tree had to be allowed to grow longer to get enough of it. Elm doesn't rot if it's constantly immersed in water and hence it was used for the keel and the lowest planks. (Dodds 18; Murray 72). The Sparrowhawk (wrecked 1626) had an elm keel (Riess 71).
Secondly, at least by the nineteenth century, they experimented with various preservatives. Metallic salts didn't work well, but cresoted timber was resistant to both rot and marine worms. (161).
Finally, they grudgingly recognized that they needed to hold down the moisture level in the wood by forced ventilation. (162). In the nineteenth century, steam fans were available (Lewis 112).
Iron. Iron use in seventeenth-century ships was mostly in cannon, bolts, hinges, chainplates, hooks and the like. (ChapelleSSUS 14). Iron knees were used in the first rate Royal James in the 1670s, but weren't routinely used in England until after 1800. At first the knees were a hybrid of iron and wood. The complete iron knee appeared in the Unicorn (1824). (Goodwin) By the end of the eighteenth century, iron had also been used in the cross-bracings of warships. (Dodds 7).
An iron-hulled pleasure boat was built as early as 1777, but little is known about it. Wilkinson's Trial (1787) weighed eight tons yet drew only eight inches empty. Unfortunately, it and the three additional barges he constructed in 1788 cost at least three times as much as its wooden counterparts. (Barker)
In 1810, Sir Samuel Bentham unsuccessfully urged the Admiralty to switch to iron-hulled warships, in view of the shortage of timber. (It took 2-3 loads, each fifty cubic feet or one "standard" oak tree, per ton of ship, to build a warship, and 1-1.5 for a merchant ship, and the cost even in the 1750s was almost 10?/load. Dodds 13)..
Nonetheless, iron hulls started popping up a few decades later. The Aaron Manby, a wrought iron steamship, was built in 1820, and the 218 ton bark Ironsides in 1838 (McCutchan 111; Young). Ma Roberts (1858) was the first steel paddle steamer, and the 1271 ton Formby (1863) the first steel square-rigger. It cost twenty pounds to the ton. (McCutchan 36). The first iron warship was HMS Warrior (1860).
Iron had advantages other than availability, of course. It was stronger than wood, and hence could be used to build longer (hence faster) ships. While iron was more costly per unit volume, its strength meant that less was needed, so 19c iron ships were 10-25% cheaper. Iron hulls also lasted two or three times longer than wood ones (White 412).
Iron ships usually came in two basic flavors, the all-iron ship, and the composite, which had an iron frame and wooden planking and decking. (Svensson 62). Composites were favored for tropical waters, where copper sheathing was necessary to protect against marine borers; iron set against copper would experience bimetallic corrosion (Lewis 117). Another variation was seen in the Great Republic (1853), 335' long; it was mainly wood, but its hull was reinforced with diagonal strips of iron.
It is important to recognize that there wasn't a rapid transition from wooden to iron ships; the two types co-existed for decades. Iron ships were not only more expensive to construct than unsheathed wooden ships, they had nasty effects on ship's compasses. The bottom of the all-iron ship was a haven for barnacles and seaweed, increasing skin drag if not cleaned frequently. So their maintenance cost was higher than for sheathed wooden ships. And iron corroded three times as fast as copper. (McCutchan 110, Atwood 299, White 415).
An advantage of iron plating, over wood planking and decking, was that the iron plates could be bent easily. But of course the iron added more weight to the hull.
Mild steel was 25-30% stronger than iron, allowing a saving of 20% in weight of scantling and 13-15% overall, but in 1880 it was 50% more expensive (White 429ff).
Hull Form
As the ship moves, water is parted by the bow, and passes around and under the hull, rejoining at the stern. If there is separation of the flow from the hull, eddies will form where the water returns. The energy to form these eddies comes from the ship's propulsion, so these flow disturbances are felt as "form resistance". Separation tends to occur where there is an abrupt change in underwater hull form. (ChapelleSSUS 49).
The choice of hull shape isn't easy. For example, the 3D shape which would yield the minimum wetted surface for a given volume, and thus the least skin drag for its displacement, would be a hemisphere. However, the fluid flow at the fore and aft "ends" would be kinked, creating significant form drag. (Gougeon 32).
To reduce form drag, water must be moved out of the way and back again more gently, i.e., the ship needs a streamlined shape. Fish bodies have offered inspiration to ship designers for centuries (and there are old plans which actually depict a fish body beneath the hull diagram).
Tapered shapes reduce form drag and frictional resistance, but also reduce both capacity and the ratio of capacity to resistance.
Midship Section Position. Imagine that the ship is sliced into vertical sections, like a loaf of bread. The section with the largest beam is called, somewhat misleadingly, the "midship section."
A good ship, old salts said, should have a "cod's head and a mackerel's tail" (a teardrop shape, with the midship section forward). In keeping with the adage, the seventeenth-century midship section was actually located about one-third keel length from the fore end of the keel. That yielded a short full (broad) bow and a long fine (narrow) stern. (BakerCV 20-21). A Dutch merchantman shown in Furttenbach's Architectura Navalis (1629) exemplifies this shape. I would estimate that quarter-length from the bow, it is a third broader than a quarter-length from the stern. (Landstrom 146). On the Mayflower replica, based on Matthew Baker's manuscript, the midship section was placed 21 feet from the forward end of the 58 foot keel. (BakerNM 80).
In later centuries, the midship section was moved aft, to true midships, or even somewhat aft (the "wedge" shape), the latter being touted by EB11 "Yachting." For our purposes, the key point is that the position of the midship section is something that the designers are going to argue about.
Midship Section Shape. On a ship plan, the sectional view of the ship is the view from the front. We need to consider both the underwater portion (the bottom) and the abovewater lines (the sides).
Bottom. A semicircular underwater section requires the least "wetted area" (which determines frictional drag) for a given capacity, and this was recognized by Georges Fournier (1595-1652) in his treatise Hydrographie (1643)(Laing 162). Unfortunately, it provides no stability, and hence is practical only on a multihull or if there is substantial ballast. Rounding makes the hull "tender"; a small degree of tilt produces only a small righting tendency so the hull heels easily and recovers slowly. However, if deep-ballasted (see below), then its resistance to heeling will increase as the angle of heel becomes larger.
The bottom may instead have one or more chines (angles). A simple-V bottom has one chine, a square bottom two, and a shallow-V has three. A square (flat) bottom maximizes capacity and also makes it easier to shelve the ship on a beach, if need be. Additionally, if the bottom is flat (or a shallow-V), the hull is "stiff"; the center of buoyancy moves sharply in the direction of a small tilt and thus creates a strong righting moment. However, if the tilt continues to increase, the righting moment will decrease once more. (Gougeon 39-42). Generally speaking, flat bottomed hulls experience more leeway than V-shaped ones.
In the early seventeenth century, most "blue water" ships had a short flat portion at the bottom (the floor), then a nearly circular underbody. (BakerCV 20; BakerNM 31). The Dutch merchantman shown in Furttenbach's Architectura Navalis (1629) had a more pronounced flat bottom, almost as wide as the maximum beam (Langstrom 146). Square bottoms were found on colonial workboats since they made the boats easier for neophytes to build.
However, there were ships, such as the Dufyken (1595), whose bottoms were partially V-shaped, not flat. The slope and rise of the "V" is called deadrise, and in later years there was much disagreement as to how much was desirable. (Duhamel 7, ChapelleHASN 406). Deadrise reduced resistance, but at the cost of stability.
The sides of the ship may be vertical (wall-sided), or, as they near the top, they may creep in (tumblehome) or out (flare). Tumblehome reduces topside weight, and also might make the ship more difficult to board (Millar 20). If taxes are based on breadth on deck, then tumblehome gives you a bit of "free" cargo capacity. It lowers the center of gravity (Millar 20), but it reduces the reserve of buoyancy and the "righting arm" at large angles of heel (Walton 144ff). The curved section also increases strength in compression, which may be helpful in supporting heavy guns. (Harland 44). Flare has the reverse effects. Both tumblehome and flare increase the cost of the hull.
In the early seventeenth century, the ships usually had, starting above the level of maximum beam, itself a little above the load waterline, a straight tumblehome at about twenty degrees from the vertical. (Baker).
Eighteenth-century British warships also had substantial tumblehome. After the Napoleonic wars, the British found themselves short of compass timber suitable for curved futtocks (or at least of the funds for buying such timber), and switched to "wall-sided" ships. (Kirby 98). Modern ships, while made of metal, also tend to have vertical walls. However, icebreakers curve inward both above and below the waterline, to protect them from ice pressure. (Rogers 28).
Full and Sharp Ends. To reduce form resistance, the hull tapers as you move from the midship section to the ends. The seventeenth-century shipbuilder determined what taper to use where by a combination of geometrical rising and narrowing algorithms, and judgment by eye (the latter assisted, in so-called "whole moulding," by the use of flexible wooden ribbands to ensure that the curves were smooth and plankable).
The combination of the bow (and stern) shape (horizontal) and profile (vertical) determines whether the ends are "full" (boxy) or "sharp" ("fine", tapered). The sharpness reduces form drag but also reduces local buoyancy; the ends will sag if local buoyancy is inadequate to support their weight. (ChapelleHASS 44; Darcangelo 1-3; Villiers 105). As to stability, a wall-sided ship with a diamond shape would have half the buoyancy, but only one quarter the metacentric height (and thus, roughly, initial stability) of a ship of rectangular shape. (Simpson 36ff). Sharpness of profile likewise reduces stability.
The sharpness of the design may be summarized in terms of the midship section coefficient (ratio of actual underwater area of midship section to that of the corresponding rectangle), prismatic coefficient (ratio of underwater volume to that of a prism with the same midship section and length, but without any taper), and block coefficient (ratio of actual underwater volume to that of the corresponding block).
We know that the wargamers in Grantville have several of Chappelle's books. They aren't identified, but given the nature of their hobby, they almost certainly own The History of the American Sailing Navy (ChapelleHASN) and The Search for Speed Under Sail (ChapelleSSUS). These books are valuable in that they detail the "lines" of numerous successful sailing ships, both warships and merchantmen.
While the designers of the 1632verse will no doubt be fascinated by the data in this book, it is hard to extract from them any overarching principles. A fast ship can have a full midsection (high midship coefficient), and relatively fine ends (low prismatic coefficient), or the reverse.
Looking at the fast ships of ChapelleSSUS chapters 6-8, which include clippers and their predecessors, the block coefficients are. 30-. 76, the midship section coefficients. 53-. 93, and the prismatic coefficients. 56-. 82 (ChapelleSSUS 406ff). The Surprise (1850), despite a. 82 prismatic, was considered a "fast sailor." The Eckford Webb (1855), with a. 72 prismatic, is known to have made 16 knots. (385), for an SLR of 1.43! (411), although it might have been blessed with a light load at the time. The most that can be said is that the short-term speed champs Sovereign of the Seas, Lighting and Sweepstakes had lower prismatics:. 62,. 61 and. 64, respectively. (409).
ChapelleSSUS teaches that for fast sailing downwind, a low prismatic coefficient (implying a ship with relatively fine ends) is desirable, but on other points of sail, a higher prismatic is better. (45ff). And the effective hull length of the ship, for computing hull speed, is the product of the actual hull length and the prismatic coefficient, implying that with enough wind power, ships with full ends will go faster.
The displacement volume can be estimated if the length ("between perpendiculars"), beam and draft are known; multiply these by an assumed block coefficient (. 6-. 7 for a merchant,. 5-. 6 for a battleship,. 4-. 6 for a cruiser; White 4; Ridler 62).
Bow Shape. A curious practice, lasting the entire seventeenth and eighteenth centuries, was a cutoff upper bow. The lower bow was round, but above the beakhead, the upper deck had a square Which should have carried a sign which read "Shoot Me!" since it was a weak point, vulnerable to raking. Nelson's flagship, the Victory, when brought in for repairs, was much more heavily damaged in its upper bow than its lower bow (Fincham 203). The English shipwrights smacked their collective foreheads, and English ships constructed after 1811 featured a complete round bow. (Anderson 181).
Stern Shape. In medieval times, big ships had rounded sterns. Beginning around 1500, such ships were given a flat, square, "transom" stern, which the Dutch called spiegel (looking-glass), perhaps because of the reflection from the windows set in the stern cabin.
Hydrodynamically speaking, the transom stern was inferior to its predecessor, the round stern. The water pushed out of the way by the bow reunited abruptly behind the stern, creating a turbulent wake. This increased drag, reducing speed. Moreover, part of the rudder was in the area of turbulence, and hence steering was impaired. (As a palliative, at some point the aft edge of the rudder was thickened.)(BakerCV 19).
In the seventeenth century, the English created a hybrid stern, in which the lower part was rounded and the upper part square. This can be seen in Sovereign of the Seas (1637), whose stern flattened out about ten feet above the waterline, but it wasn't common on English ships until the 1650s (Anderson 144; Langstrom 152; Millar 17). The hybrid stern solved the hydrodynamic problem, but bear in mind that the transom upper stern was probably a weak point in combat. The English made the final step to a round stern in the 1820s. (Millar 20), and the Americans followed suit. Besides being stronger, the round stern offered the prospect of placing gunports in the rear quarters, eliminating that blind spot.
Unfortunately, the change also eliminated the traditional quarter galleries for the ship's officers, and this wasn't borne (especially by senior officers) in silence. The plans for the early round stern warships were revised so as to mask the new sterns with quarter galleries. (ChapelleHASN 365).
Bow Profile. Usually, the bow and stern overhang, that is, they rake outward as you go upward. Compared to a ship of the same deck length but without an overhang, the raked ship will have less frictional drag because the water flows under it more readily, but also less resistance to leeway, reserve buoyancy, and cargo capacity. A ship with an excessively raked stern or bow might not be able to carry guns at those ends (ChappelleBC 43).
Bow profiles may be plumb (vertical), "V" (straight; slanting outward); clipper ("concave"; "hollow"; starts vertical and arcs outward); spoon ("convex"; starts horizontal and arcs upward) or tumblehome (spoon bow which ultimately curves inward).
John Smith wrote in 1627, "fore Rake is that which gives the ship good way, and makes her keep a good wind, but if she have not a full Bow, it will make her pitch her head much into the Sea; if but a small Rake forward, the sea will meet her so fast upon the Bowes, she will make small way…" (226).
The seventeenth-century bow was typically a "V" bow terminating in a beakhead, a structure similar in appearance to the ram of the ancient galley. It wasn't used for ramming, of course, but rather to provide a platform for sailors working on the bowsprit. It also "shattered the seas at each plunge and kept them from sweeping fore and aft." (Masefield; AndersonRS xvi, xvii) You could also find spoon bows (xv).
As ships got longer, a pronounced rake became problematic from a strength standpoint. Rake went out of fashion in the 1820s and 1830s, and packet ships sometimes had almost vertical stem and sternpost. (ChapelleHASN 423).
The clipper bow was popularized by John Griffiths, who argued that such bows would have minimal head-on resistance, and would resisting burying when the ship plunged in a heavy sea. He tested his ideas in tank experiments, but the proof of the pudding was his Rainbow (1845), which made the round trip from New York to China in 7 months, 17 days. (Laing 170-9).
A twentieth-century variation is the bulbous bow. Above the water line, you have a clipper bow. Below it, there is a protruding bulb which creates its own bow wave. If properly designed, it reduces the normal bow wave at speeds near the hull speed (GlobalSecurity).
Unfortunately, it's more useful on powered ships, since they can consistently maintain the right speed. A sailing ship is at the mercy of the winds, and at speeds much different from the "design speed," the bulb increases drag. For a Napoleonic era warship (say, 170'LWL, hull speed 13 knots, 0.60 block coefficient), you would need to reach a speed of 10 knots to see a 10% reduction in resistance.
With short ships, there will also be increased pitching at high speeds, and the bulb does no good when it's out of the water and actually creates drag on each reentry.
Finally, at all speeds, the bulb increases turning resistance. (Killing 37-9), and frictional resistance, so light wind performance will be poorer.
Stern Profile. In the seventeenth century, the most common stern profiles were rounded or slightly vee'd sterns (AndersonRS xv, xvii), and one which angled or curved outward and then turned vertical to create a transom (xvi).
Subsequently, shipbuilders constructed ships with "finer" sterns, the theory being that this reduced the turbulence behind the ship and thus reduced form drag. The trend was reversed by Griffiths, who favored matching his sharp bow with a blunt stern (leading detractors to suggest that his ship would sail better backward).(Laing 176).
Girdling. As early as 1622, the English added an extra layer of planking (girdling, furring) at the waterline to increase stability. (BakerNM 6; OED). For example, the 76-gun Royal Katherine (1664) had a normal beam of 39'8" and a girdled beam of 41' (Temmu). Lewis (200) says that this substantially increases stability while adding "very little" to the draft.
Ballast
The height of the center of gravity is determined not by how much weight is being carried, but where it is located. In general, the lower the center of gravity, the greater the stability of the ship. Merchant vessels have the luxury of stowing heavy cargo deep in the hold. Warships have the problem that guns are heavy, and needed to be high enough on the hull to be above the wave action. They therefore need to carry ballast to compensate; ballast and water was typically 12-14% displacement (White 84).
Ballasting lowers the center of gravity, and thus increases stability, but at the cost of increased mass and thus reduced speed. Also, too much ballast will make the ship too stiff. (Walton 168ff). Ballast is most effective when deep in the hull, and so as more ballast is added, the return in stability diminishes.
The most commonly used ballasts were gravel, coarse shingle, sand and rock. (ChapelleHASS 247). They had the advantage that they could be laid wherever desired.
Iron and lead were only rarely used as ballast in the seventeenth century, most likely on account of their cost (Lavery 186). In the late eighteenth century; cast iron ballast cost?27-5s/ton (Dodds 23). The most efficient ballast would be lead, because of its high density, but on account of its cost it was then limited to royal yachts.
In 1796, Samuel Bentham had iron ballast bolted outside the hull, beside the protruding keel. That moved the CoG more than the same weight of internal ballast would have. This deep ballasting eventually evolved into the uncapsizable hull. (This has a deep fin with ballast attached at the end; a completely watertight hull is uncapsizable if the external ballast moves the CoG below the center of buoyancy.)(Gougeon 39, 51; ChapelleHASN 236).
The crew's water and victuals may also be placed low in the hull, to augment the ballast, but of course they diminish over the course of the cruise. HMS Endymion (1797) carried 120 tons iron, 26 shingle, and 124 water. (Gardiner 145).
Cargo can also serve as ballast, if dense enough, and has the advantage of earning revenue. The Portuguese found Chinese porcelain to be a useful ballast for their East Indiamen. (Brigadier 54). Madeira is a fortified wine, and in the eighteenth century it was recognized that unlike other wines, its taste is improved if it spends, say, three months "cooking" as ballast for a ship traversing the tropics. (NewScientist 114). The improved Madeira was called vinho da roda ("wine of the round trip"). The nineteenth century frozen water trade from New England to the American South, the Caribbean, and even India, was profitable because the ice served in place of stone ballast (which had to be paid for).
1911EB "Ballast" notes that "in modern vessels the place of ballast is taken by water-tanks which are filled more or less as required to trim the ship." For example, a tank in the bottom of the screw-propelled icebreaker Ermack (1898) held 800 tons of water. Pumps could be used to shift this water to tanks fore, aft, port or starboard. (Rogers 29-30). Simpson's ironclads appear to have a similar feature. (1633, Chap. 4; 1634: TBW, Chaps. 31, 44, 48, 60,61)
With water ballasting, it is very important to keep the tanks full; any partially full tank of liquid is subject to the "free surface effect"; the liquid sloshes in the direction of the tilt and moves the center of gravity in the "wrong" direction. Likewise, solid ballast, whether sand or cargo, must be kept from shifting.
Fins
You can increase lateral resistance by placing a fin below the main body of the hull. The fin increases the lateral area and simultaneously lowers the center of lateral resistance. This improves resistance to leeway. Unfortunately, fins increase wetted area (thus, skin drag) and draft.
These disadvantages are somewhat muted by use of retractable fins. Seventeenth-century Dutch coasters were equipped with leeboards. These were fins which hung on either side of the boat and could be let down as needed. A centerboard is a retractable fin mounted in a (hopefully) watertight cabinet inside the hull. It could slide up and down (daggerboard, drop keel) or pivot on a bolt at one end (pivot keel). (Gougeon 33-6). The centerboard first appeared in 1774 (ChappelleHASS 166-8), and the pivoted type around 1809 (360), but wasn't really popular until the nineteenth century.
Chapelle says that the centerboard made it possible for a coaster to sail well when light. (ChapelleSSUS 279). He is also of the opinion that "extremely high speed-length ratios became possible only after the centerboard was introduced (412). Simpson's ironclads have two big centerboards (1634: TBW, Chap. 44).
Bilge keels are fins which are mounted at the boundary between the bottom and the sides. When the ship heels, the leeward bilge keel is submerged, and then resists further rolling. However, the submerged keel also increases resistance to forward motion.
Hydrodynamic Lift
If the underwater form of the ship is chosen appropriately, it can behave somewhat like an airplane wing, generating lift as it picks up speed. This lift, in turn, reduces frictional resistance, permitting the ship to travel even faster.
The necessary hydrodynamic structure can be the shape of the ship's hull itself (a "planing hull"), or a fin-like device ("hydrofoil") below the hull.
Unfortunately, this "planing" becomes significant only when the ship reaches very high speeds-an SLR of 2.5. (Teale 7). The only sailing hulls which reach that kind of speed are those with very large sail areas and very low displacement-essentially, high-performance racers. That kind of performance can't be expected from a pure sailing ship carrying substantial cargo or armament. We could nonetheless see it in a military courier ship, or a ship which has auxiliary power.
Hull Protection
Wood was coated with various substances to ward off marine borers (which damaged the ship) and fouling organisms (which slowed it down). Fouling can double or even triple the frictional resistance of a ship. (Baker, Ship Form 30; White 449; Millar 21).
One such coating was a mixture of tallow and sulfur (sometimes also including ground glass)(BakerCV 98). If this were insufficient, the hull could be scraped or singed to remove the nautical nasties. In the late sixteenth century, Sir Richard Hawkins advocated double planking with a layer of hair and tar in-between. The teredo worm won't tunnel through tar. (Millar 21).
Lead sheathing has a confusing history. It was used on Mediterranean hulls, as early as the fourth century B.C., to make the hulls watertight, but of course also afforded some protection from marine parasites. It fell into disuse after the first century A.D. (except for patching), but it made a comeback after the Europeans had their first Close Encounter with Teredo Worms. As early as 1513, Spanish caravels plated their bottoms with one or two tons of lead. (Crisman 261; BakerCV 97). The 480-ton galleon Santa Margarita (lost 1622) had 325 square meters of lead sheathing, less than 1 mm thick, yet weighing 4706 pounds (Malcolm).
Hawkins didn't think much of the idea; the lead was heavy, costly and easily damaged (especially if the ship got grounded). Nonetheless, the British used it on some warships in the mid-seventeenth century. Milled sheet lead, which was thinner and thus lighter than the earlier plates, was patented in 1670. Unfortunately, it was soft, and also tended to cause corrosion of the rudder irons. (GlobalSecurity) Nonetheless, British use continued for another century.
Another concept was sacrificial planking, that is, put a cheap wood over the good wood; Hawkins liked to put elm over tarred oak. The Dutch East Indiaman Mauritius (1601-9) went to the extreme of having sacrificial pine over lead, but that was to protect the lead from rocks. While sacrificial wood conserves the structural strength of the hull, the hull surface still gets fouled.
Copper sheathing was introduced in the 1760s and was initially disastrous (the iron parts, such as rudder hinges, disintegrated)(Millar 21; ChapelleSSUS 207ff). By the 1770s, the problem had been solved; bronze or copper fastenings were used. (Dodds 18). Copper sheathing was used in thicknesses which weighed 22-32 ounces per square foot, depending on the ship and the location. HMS Victory had 3500 4' x 14" sheets, weighing almost 13 tons. (Callcut).
Cost was also an issue, at least until after the War of 1812. (ChapelleSSUS 277).
The cost of sheathing the 1890 Edgar, 7350 tons displacement, was 17,000? (Atwood, Warships 145).
The development of copper sheathing encouraged the use of detailed plans, so that the cost of sheathing could be estimated accurately. (ChapelleHASN 21).
De Roche's Moonraker (Karen Bergstralh's story, Grantville Gazette , Volume 9), is copper clad. The timing is a bit vague; Karen told me to assume 1634-35. In 163x OTL, the price of copper in Amsterdam was 60 guilders per 100 pounds (Posthumus).
Copper is gradually corroded by seawater (Brigadier 12). Cathodic protection (that is, the sacrificial use of a more active and hopefully cheaper metal) was introduced in the early nineteenth century… tin, iron and zinc were used to protect copper. (Morgan). Zinc was also used as a sheathing in its own right, but it was even more vulnerable than copper.
Naturally, copper or zinc sheathing can't be used directly with an iron hull (or for that matter with iron nails and fittings), because there would be an electrochemical reaction between them, mediated by the salt water. One trick used in the British navy after 1887 was to use an inner sheathing of teak and an outer one of copper. (Atwood, Warships 143). There was even experimentation with rubber sheathing (Hebert).
Sheathing didn't merely protect the hull from fouling organisms, it also could increase smoothness and thus lower resistance. However, copper-sheathed hulls weren't as smooth as you might expect; "the plates were laid over tarred felt and the fastening nails dented the whole surface in a manner best described as 'quilting.'" (ChappelleSSUS 402).
Rudder and Steering
When the rudder is pivoted to one side, it creates a drag force that acts perpendicularly to the rudder surface. That drag force acts partially to slow the ship down, and also to cause the ship to turn. The ship will also heel over. (Sinisi).
Small ships were steered with a tiller, which is simply a lever connected to a pivotable rudder post, which in turn bears the rudder. The tiller was swung horizontally, clockwise or counter-clockwise. Flint, 1634: The Baltic War, Chap. 31 comments, "Unfortunately, the length of the tiller had to be in direct proportion to the forces required to shift the rudder, and its maximum length was restricted by the width of the ship itself."
On larger, multi-decked ships, the tiller needed to be worked from above. In the seventeenth century, this was done using a rather improbable contrivance known as a whipstaff. The whipstaff was a long pole which reached down through a small slot, which acted as a pivot point, to the level of the tiller, where it fitted into a ring fastened to the end of the tiller. To turn the tiller in one direction, the helmsman had to push the upper end of the whipstaff the other way, and also push downward. (Anderson 156-7). (While Flint says the helmsman stood on the quarter-deck, Anderson said that "the helmsman was still below-deck as a general rule," just not at the tiller level.)
Flint continues, the whipstaff "provided the helmsmen with a powerful mechanical advantage, but meant that the rudder's range of movement was even more sharply restricted. As a result, a large sailing ship… found it impossible to apply more than five or six degrees of rudder." (Cp. Phillips-Birt 155).
Because of the limitation of the rudder angle, to make a sharp course change, the sails had to be trimmed accordingly. (Landstrom 122)
The earliest evidence of a steering wheel is in the English Ossory (1711). Naval historians aren't entirely sure how long the whipstaff survived after that, but there is reason to believe that it was still in use in the mid-eighteenth century (Anderson 169).
The steering wheel is connected by two opposed pulley systems to the tiller. Turn the wheel one way, and one pulley system tightens while the other slackens, moving the tiller in the appropriate direction.
In the Baltic War, Admiral Simpson insisted that all of his ships be equipped with steering wheels (actually, a more modern form than the one described above). "The use of a geared quadrant system to shift the rudder not only permitted him to build in a much greater mechanical advantage for the helmsman, but also offered a substantially greater amount of maneuverability… Simpson's ships
… could apply up to eighty degrees of rudder…"
Superstructures
Sixteenth-century warships had fort-like towers, the forecastle and aftcastle, to serve much like the towers of a castle on land. They were essentially infantry platforms, which gave their inhabitants a height advantage for missile and melee combat, and also some shielding from hostile fire. The problem, of course, was that they reduced the ship's speed, weatherliness, and stability. (Although Glete 38 says that they were of rather light construction, and thus not as adverse to stability as their height suggested.)
Raleigh warned against the "high charging" of ships, which "brings them all ill quality." They were phased out over the course of the seventeenth century (ChapelleSSUS 80), but it was a halting process. There was a concern that with most of the crew below deck manning the guns, the enemy could board amidships and trap the crew. Keeping the "castles" meant that the crew would have rallying points for launching counterattacks. (GleteWS, 30). These concerns ebbed, presumably as a result of both the steady increase in firepower and the provision of fighting platforms in the masts.
The three-deck battleship Sovereign of the Seas (1637) was in service until 1696, but at some point the superstructure was cut down because otherwise her draft was so great that in even a light air she couldn't open the lowest leeward gunports. (Langstrom 153).
Even merchant ships had substantial superstructure. Typically, the afterbody had two levels above the main deck, the half deck and the quarterdeck. (BakerCV 29). The poop deck is part of, aft of, or above the quarter deck, depending on the period.
Monohulls vs. Multihulls
The conventional sailing ship has a single hull. However, multihulls-two or more hulls joined together by a deck or struts-can be found in the seventeenth century in both the Indian Ocean and the South Pacific. The catamaran has two hulls, and the trimaran has three.
European experiments with catamaran designs date back at least to 1662.
According to canon (1633, Chap. 4), the timberclads used in the Baltic War campaign are catamarans, with paddle wheels positioned in-between their hulls. While these were steamships, their success will give the catamaran design a certain degree of credibility that it would not have possessed previously.
I intend to discuss the advantages and disadvantages of multihulls, and the problems peculiar to multihulls in a later article.
Shipbuilding
Plans. The first known printed plans for ships appeared in Instrucion Nautica (1587)(BakerSS 8). In 1650, the British Admiralty began requiring the preservation of warship plans but it took until 1675 to achieve compliance (ChapelleHASS 17). Plans weren't used in merchant shipbuilding until the mid-nineteenth century (McGee).
If you "take off the lines" of a ship (usually a captured vessel whose sailing performance impressed you), it means you reverse-engineer a plan for it. This required a specially-fitted dry dock (ChapelleSSUS 38).
Models. The English shipwright Pett is known to have made ship models as early as 1596. Ship models could be made, before the ship was built, for a variety of purposes-to please a customer (a model of the Prince Royal was given to Prince Henry in 1607), to persuade an prospective customer to approve the construction, as a teaching tool for apprentice shipwrights, or as a guide to the actual construction. . Reading multiview ship plans is something of an art, and the models no doubt had a more visceral impact on laymen.
In Britain, the Lords of the Admiralty were aristocrats and civil servants, not shipwrights, and they couldn't read plans. Hence, they demanded models, as well as plans, before engaging a contractor, and Admiralty models from the 1650s have survived. Their standard scale is 1:48, and they show the hull in detail. Decks were sometimes omitted so that the deck beams could be seen. (Anderson 145, 159; King 113; Davis 17; Grimwood 20). The lift model (layers of wood, held together by dowels, showing successive waterlines) appeared at the end of the eighteenth century. (Edwin 266; ChapelleSSUS 150ff).
Lofting. In the mold loft, thin pieces of wood were laid down to show, full size, the curve of the principal pieces of the hull. The purpose of this was to facilitate selection of which timbers to use where, and to guide the cutting of those timbers. Lofting is described in Fernandez' Livro de tracas de carpinataria (1616)(Schwarz) and Sutherland's Shipbuilder's Assistant (1711)(OED), and I suspect lofting predates the use of formal plans.
Cost and Time. The shipyard you pick makes a big difference. In 1669, Dutch cargo ships cost 40% less than English. (Unger 125). By building its own ships at Deptford, the East India Company reduced its costs in 1607 from?45 to?10/ton. (Gardner 29).
The Transportation Costs Addendum (1632. org) provides costs/ton for ships of various periods. In 163x, a 40-gun warship might cost 6000 pounds (Langstrom 149).
Ridler (62) suggests that for mid-nineteenth century warships, the number of man-days work required to build it and equip it for sea can be estimated by the formula 0.4*B^ 3*L/100, and the cost in dollars by multiplying the number of days by four. The cost breakdown, he says, is 72% hull, 5.4% spars, 4.6% sails, 4.8% rigging, 2.5% boats, 3.5% gun carriages, 0.5% outfits and sea stores, and 2.2% furniture. But Laing (54) says that as you increase the length/breadth ratio, while keeping capacity constant, the cost of construction increases.
Revenue. A merchant ship might reasonably hope to recover its cost in two trading voyages (Millar 3). Long-distance traders of course would need to carry more valuable cargoes for this to be the case.
Lifespan. Rot was the main enemy of the wooden ship, but of course navigational hazards, storms and hostile vessels also took their toll. On the Lisbon-Goa route, about one-sixth of the ships were lost, in either passage (Brigadier 14). The typical lifespan for a merchantman was 5-20 years, but some ships were flimsily built in the expectation that they would be used for just a few high profit, high risk voyages. Warships had a longer life, but required expensive rebuilds (at least half the original cost) every decade or so. (ChappelleHASN 47).
Up-Time Knowledge
In terms of books, the public and school libraries don't have much (see Addendum). But the "Four Musketeers," the teenage wargamers, were able to assemble "two tall piles" of books on naval history. In particular, we know Eddie Cantrell has "Chapelle's books on American sailing ship designs." And that "Chapelle's books had been pounced upon by the Swedish shipwrights as if Eddie had been Galahad, returning to King Arthur with Holy Grail in hand," and used to design a new sloop-of-war (1633, Chaps. 4, 28). EB11 "Shipbuilding" describes basic stability calculations.
Practical knowledge is important, but hard to find in a town that is over two hundred miles from the nearest ocean. Fortunately, we have John Chandler Simpson, a Naval Academy graduate with a bachelor's degree in engineering, and combat experience in Vietnam. Who was able to look at Eddie's plans for a riverine ironclad, and immediately realize that the displacement estimate was way too low, and that the ship would have twice the draft Eddie hoped for. (Weber, "In the Navy," Ring of Fire).
We also have Jack Clements, a retired Coast Guard boat pilot) who owns a large power boat (Century 3200), and Louie Tillman, a thirty year Navy veteran with another (Cris Craft). (1633, Chap. 35). Then there's Ernie Trelli, who served with the Navy in the Gulf War (Grid), but hasn't yet appeared in a story.
While there aren't many "old salts" in Grantville, the new USE navy is going to need physicists, engineers and mathematicians to reconstruct the sciences of aerodynamics and hydrodynamics, and to modernize construction methods and materials, and there at least we have a respectable pool of talent.
Experimentation
Even if some engineers or physicists have basic texts on aerodynamics and hydrodynamics, there are going to be a lot of gaps in their knowledge. Those gaps will need to be filled by experimentation, at first with models and then with full-scale ships.
Early hydrodynamic experiments included towing wooden blocks (Christian Huygens and collaborators, 1668), simple geometric solids (Samuel Fortrey, 1675; Fredrik Chapman, 1775, 1794), planks cut to the waterlines of actual ships (Henry Sheeres and Anthony Dean, 1685; Pieter van Zwijndregt, 1750s), models constructed by joining circular sections to facilitate changes in shape (Bird, 1750s), and finally three-dimensional ship models (William Shipley, 1758-63).
There were several pitfalls. The first was ensuring that the models were towed at a constant speed, and accurately timing their performance. Another problem was avoiding blockage. Finally, for ship model studies to bear any relevance to the real world, they must be scaled properly. Usually, the scaling is chosen so the model accurately duplicates real-world wavemaking resistance, and the frictional resistances for ship versus model are determined by calculation.
In the 1820s, the British went so far as to invite competitive designs and assemble the resulting full-scale ships into experimental squadrons which underwent sailing trials. However, the competition rules didn't prohibit "tuning-up," and that limited what could be learned. (ChapelleHASN 369).