1. Take, for example, the process of sallying the ice-bound ship for relieving her of any remediable pressure, and giving free action to the power of wind or “warps” for promoting her progress. And in this we have an adaptation of a previously unapprehended mean and provision, always at hand, possessing extraordinary capabilities as a mechanical force. It may not be uninteresting to elucidate this fact.
Suppose a ship, navigating the Arctic seas, to be held firmly on the sides by the contact of two large sheets, or numerous compacted pieces, of ice. The ice just a-head may be less compact, or there may be a proximate channel, available for “boring” or sailing, if the existing pressure could be relieved so that the ship might be free to move. For the relief of this lateral pressure, no mechanical force, except the action of the wind on the sails when coming somewhat in the direction of “the beam,” had heretofore been considered as available, or had been applied. But my Father’s device afforded a novel, as well as a powerfully available, agency. In what degree powerful is easily estimated. The ship, in the case referred to, we will suppose is tolerably flat-sided (like the Resolution), and floats, ordinarily, at the depth of the greatest width. Now the power yielded by sallying may be considered as corresponding with that obtained by a wedge acted on by a heavy weight; the wedge, in this case, being the portion of the ship’s side that becomes depressed, operating by virtue of the expansion of the ship’s width when heeling, and the force acting on the wedge being the weight transferred from an even distribution with an upright position of the ship, to an accumulation of weight on one side, inducing a heeling position. Let the extent of heeling be considered as a “streak” of nine inches, in which case, as the opposite side will be proportionally and equally raised, the width of the line of flotation will be increased, altogether (in a main breadth of 26 feet), about half an inch, or a quarter inch on either side. The depressed side, then, in its progress under water, as far as nine inches, will have expanded a quarter of an inch in width, and the raised side an equal quantity; and both sides will act on the contiguous ices with the mechanical force of a wedge of nine inches long and a quarter-inch at the thick end,—exhibiting, on the ordinary mode of calculating the power of the wedge, a gain of power for either side in the proportion of twice the length of the wedge,[O] or 18 inches, to a quarter inch, or as 72 to 1.
The force acting on these wedges is that of the weight of the men employed in sallying, when all are placed on one side of the deck right over the head or back of one of the wedges. In a whaler carrying fifty men, the weight available for this purpose, say that of forty-six or forty-eight of the crew, may be estimated at about three tons, one half of which only would act downward, the other half being expended in the resistance upward, of the opposite side.
Hence the mechanical force hereby derived, as represented by these data, would appear to be that of two wedges of a power of seventy-two to one, each acted on by a weight of a ton and a half, that is, a force of the weight of 108 tons acting towards the separation of the ice and ship on each side. But only half the amount of these two forces, it will be obvious, comes effectively into operation; for the wedges, being on opposite sides of the ship, act antagonistically, thus spending one-half of their power against each other, in the compressing of the opposite sides of the ship together. The force really in operation, then, serving to push off the ice from each side, or tending to separate the compressing masses of ice, will be equivalent to two weights of fifty-four or altogether to a weight of 108 tons.
If there were no resistance either from the friction of the ice on the ship’s sides, or from the stability of the ship, the estimated mechanical force, for the case assumed, would no doubt take effect. The resistance from friction cannot, it is evident, be determined; but that of the ship’s stability might be easily represented. At the commencement of the heeling position, however, the resistance from this source would be but trifling. In its actual influence, in ordinary cases, the stability might abstract, perhaps, a quarter or a third part from the entire force exerted, but still leaving a free action equivalent to the weight of seventy or eighty tons towards the separation of the ices, right and left.
But the force ultimately brought into operation, after a sallying motion is once obtained, becomes still greater and more effective,—acting now and then, in the nature of concussion from the momentum of a portion of the ship’s weight, as thus may be illustrated:—
The weight of the crew, in the outset of the operation, being placed all on one side of the deck, and then suddenly transferred to the other, will, after the overcoming of the friction originally induced by the ice, cause the ship to heel, and, on the reversing of the action (by the men running back again across the deck) the direction of the heeling will be also reversed. The process being carried on with a strict attention to the adjustment of the moment of the running of the men (indicated by the word of command, “over”) to the time of change in the natural oscillations of the ship,—these oscillations (supposing the ice to be gradually receding) will increase to a maximum, whilst the incidental concussions of the ship’s sides against the contiguous ices will act as a “ram” on the wedge-like expansion of the width of her two broadsides. The additional force thus incidentally applied, it is evident, may be enormous. Hence the wonderful effects sometimes produced by my Father’s ingenious device of sallying,—effects not less important and striking when “clawing” to windward of masses of ice in boring, when, by the mere action of the wind on the sails the ship may have come to a stand, as when stuck fast betwixt equally compressing ices on both broadsides at once. The moment the sallying is perceived, the ship realises such relief from both pressure and friction, as to start a-head as if acted on by a magical power!
It hardly requires, perhaps, to be explained, that our investigations of the operation of sallying in urging a path through encumbering ices, are, strictly, only illustrative. For the action of the ship’s side which we have considered as that of a regular straight wedge is, in reality, curvilinear, and, ordinarily, would be unusually thin at the apex, thus giving, at the commencement of the heeling movement, a much higher degree of mechanical power. The extent of the compression on the ship’s sides, too, we could only consider in a particular case, such as one of thin ice, or ice touching the sides to no great depth. In case of compression from thick ice, having contact with the ship’s sides to a considerable depth, the resistance to the sallying would, of course, be much increased, and, by consequence, the operation less effective.
It may just be added that the principle of sallying is evidently capable of still more powerful application by aiding the weight of the men, in the first instance of movement, by auxiliary loads of guns, chains, casks, or other heavy bodies transferred to one side of the deck; or, in a still higher degree, by an auxiliary mechanical force derived from a “purchase” from the ship’s lowermast, or top-mast head, to an anchor fixed in a distant part of the ice on either side. An enormous power, it is evident, might be derived from a leverage of this kind, sufficient almost to compress or squeeze in the very timbers of the hull.