Grantville Gazette.Volume 22 Read online

  Some of the intensive methods popular in modern times, with raised beds, etc., are likely to gain a following-especially as industrialization gains speed and both truck-gardening and allotments became relevant. University students and other people without an independent household had generally rented rooms without kitchen access and eaten their meal in taverns, but an infrastructure able to support the families of industrial workers living in apartment blocks would not be something just occurring overnight. There would also be the more psychological aspect of how a "proper" household was defined, and that would to the large majority of the new workers include at least a rented plot of land for a kailyard.

  A few plants were likely to spread far and fast, and first, last and always would have been the potato. Potatoes along with many other American plants had already arrived in Europe, but they were being regarded as curiosa or grown as ornamental plants in manor gardens. To have an entire group of influential new people spread all over Europe taking potatoes for granted as a part of their daily diet, missing them when not available, and mentioning how easy and reliable a crop they made, was bound to have gardeners and farmers wanting to try growing them. Potatoes obviously would have potential as a field crop-especially on poor soil-but few gardeners would be able to resist growing a tasty vegetable, which would reliably produce a crop from midsummer onwards to the autumn, and could be stored without problems all winter.

  The second fastest group of plants to spread would probably have been the modern continuously-blooming roses. Roses were hugely popular and a major status symbol, but the only types available were those now called historical roses. Historical roses have wonderful fragrances, but they blooms only for about a month every year, and their color-scale is fairly much limited to pink, red and white. An owner of a modern bright yellow climbing rose would literally be able to set any price he wanted on his spring cuttings. Rose cuttings must be grafted immediately after cutting and transported as whole living plants, which would be expensive, but once the wealthiest household in an area had a rose, it was of course much easier for the rose to spread to the entire region.

  Fruit trees were already being grafted all over Europe, and while most gardeners made do with the locally available types, there was also a certain amount of international trading going on. That the cuttings used for grafting are cut in winter or very early spring, while the trees are still dormant, means that there are a few months every year where a bundle of fruit tree cuttings may be wrapped in burlap and transported easily by wagon. At their destination, the cuttings would be grafted onto a locally grown root and eventually become a French pear in Germany or a German apple in France. That the fruit tree cutting could be moved so easily, meant that they were available also to people of only moderate means-such as village parsons or small town craft masters-and at least some of the traders leaving Grantville around the month of March would certainly have a bundle of cuttings tucked beneath their wagon seat to sell along their route.

  Other vegetables, herbs and ornamental plants would eventually spread from Grantville as well, but as with the potatoes the main impact would probably come simply from Americans mentioning them abroad, and thus creating a demand. The Grantville plant stock would of course have had several centuries of breeding for improvement, but without people to advocate the growing of, for example, tomatoes, corn, peanuts, chiles, and pumpkins, these would have remain curiosa for decades if not centuries.

  How soon and how many items intended for especially for gardens would go into production is anybody's guess, but as in our world it would probably follow the farming items. Artificial fertilizers and more efficient pesticides would immediately have a market, but Victorian glass cloches and mobile watering wagons would also set local gardeners drooling. In fact anything able to increase a garden's yield or-as servants became industrial workers-save labor, would have a market.

  ***

  The Wind is Free: Sailing Ship Design, Part 2, Seaworthiness

  Iver P. Cooper

  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. (Gle
te 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.