THK N E W - Y O R K EXHIBITION ILLUSTRATED
ing and facility in meeting the waves. The same considerations of pitching andscending apply to the stern, which should possess the requisite fulness above thewater graduated to avoid the occurrence of violent and sudden shocks, and be re-lieved of all unnecessary weight, which, in such a place, is renderedmore injuriousV its leverage. The water filling into the vacuity left by the passage of a vessel,does so with a rapidity proportioned to the pressure or depth, and consequentlyWith a velocity decreasing towards the surface where it should be quieseent. Tofacilitate this action, the upper water-lines require to be full, and the lower ones® n e]y tapered, so that the diagonal lines representing the probable course of the
quick, but require a ready eye and hand to meet the seas on either bow, whichwould cause her to fall from her course. A great difference in the draft for-ward and aft, is objectionable on account of the necessity for deep water, but isnecessary in vessels of this class to counteract the effect of the preponderatingafter sails.
A beautifully executed model of the clipper-ship, N. B. Palmer, as constructedby Jacob A. Westervelt & Co., shows the disposition of the timber and bracing,and forms a complete study. If a ship were divided in its length into a numberof sections, those in the middle would rise, and at the ends would sink from the
Water, have a quick ascent from the keel and approach the horizontasurface. It was found that the steamboat John Neilson, which has a pecu 1floor gradually rising aft, for the purpose of retaining a stratum. o air Punder her bottom to lessen its friction, is improved by an application of fa sin conformity with the principle above recorded; which is not a genera ynized one, although carried out to some extent in the yacht America, anrecently modelled clippers. By the courtesy of her modeller, George Steel s, sq.,we are enabled to furnish a drawing of the after-body of the “ America, exempfying the various water lines and diagonals used in the draught o a s up.
The calculations of the sizeand position of the sails requirea knowledge merely of the simpleproblems of resolution and com-position of forces, and may be ea-sily examined in detail; but, as inthose of the hull, although the ab-stract principles are simple whenexamined singly, their combina-tion to produce the desired resultinvolves a sagacity and powers.°f observation, analysis, and ap-plication, not surpassed in anyother profession, and not at alllessened by the fact that they arenot made to apply to particular cir-cumstances, but must correspondto the varying requirements oftrade and travel frequently in-volving an antagonism of princi-ples. Take, for instance, the con-sideration of steering qualities:—
It is desirable on account of safety ^that a vessel should carry a wea-ther-helm to .counteract a ten-dency to come nearer the wind,a nd there is no doubt but it ma-terially assists the progress of thev ®ssel by diminishing the leeway;but when the sails and hull are sobadly adapted, that they requirea constant and material correc- „„r,QHlp™hle
tive action of the helm, the retarding effect of the rudder” J 10 best in the
A model of the pilot boat Enchantress, b\ D. Lb ’
common level, producing the effect termed “ hogging: ” again, when a ship isheeled in a wind, the action of the water on the inclined surface of the bow occa-sions a lateral curvature, amounting, in an English man-of-war, where provisionwas made for observing with accuracy, to a departure of one inch and a half froma straight line, or a variation of three inches on the two tacks. These, and variousother strains, and the necessity for discarding useless material, require a scientificdisposition of timber. The tendency to hogging is guarded against by solid floorsto resist the compression below, and direct connections above, extending thewhole length, to sustain the tension which obtains there as in a beam loaded at
the ends and supported in themiddle. The iron braces whichare frequently used to strengthenthe hull, and when double forma lattice work crossing on thesides at right angles, might bemore advantageously disposed asan arch springing from the un-supported ends and rising as highas possible amidships.
Clipper ship Whirlwind, mod-elled by Robert Underhill.Length 200 feet; breadth 40feet and depth 20 feet. Clippership Vision , of 750 tons custom-house measurement. Length ondeck, 150 feet; moulded breadthof beam, 32 feet 4 inches, anddepth 20 feet; modelled by An-anias Dekke, of Boston. The“Vision” has full water-lines aft,but is also full below, and is inthis respect inferior to the“Whirlwind.” The latter hassteamboat ends, and being pro-portionably longer, has moreacute angles.
U. S. Mail Steamer Illinois,built by Smith & Dimon. Themidship section of this model isplaced aft the middle of thelength, and it is likely the bodywould be improved by shifting a portion of the buoyancy at the foremast to aboutthe mizen. She has something of the English full after-body, but not carried
Exhibition to illustrate the steering qualities of a ship.
flow to rise readily over the waves, and a deep,
lean stern, she will
With a light, buoyant I out so completely as in the “ Georgia” by the same builders, and would be more easi-
steer easily and j ly steered and propelled had the rise of the lower after-lines been earlier commenced
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