Other late discoveries for the prevention of Shipwreck, and preservation of Mariners.
[From American and Batavian correspondence.]
1. An expert American seaman recommends to mariners the experiment of hanging out a line of cable over the stern of a small vessel, or boat, in a rough sea, as this appendage serves to make a long wake, and will be found to enable the vessel (according to the sea term) to live much longer in a heavy gale. Little danger, he observes, is to be apprehended from a long sweeping swell of the sea; the mischief generally arises from overhanging surges, which at once break in and overwhelm the vessel. Having often experienced, in stormy weather, the beneficial effects of a long coil of rope fixed to a flat piece of wood, and appended to vessels, he thence endeavours to explain the extraordinary efficacy of the tow-line in balancing the ship, and lowering the high-swelling surge.
2. From the Transactions of the Philosophical Society, at Philadelphia, we learn, that Mr. Hopkinson has invented an instrument, with a graduated tube, which, from the difference of specific gravity between oil and water, by its rise and fall, accurately measures the ship’s progress. Also, a curious spring block, by which sailing is greatly expedited; for which useful invention he obtained the Society’s gold medal.
3. Mr. Gearson, of York-town, Pennsilvania, has lately obtained a patent for an important invention, by means of which, we are informed, that a vessel whose bottom is so shattered, that the ordinary pumps could not, for one hour, prevent her sinking, will be effectually kept buoyant; and, though under a press of sail, be incapable of being overset by the heaviest gale.
4. A gentleman of Rotterdam has invented a new floating machine, which, though small, is capable of holding four men commodiously, and may be enlarged sufficiently to accommodate fifty, if required. So curious is its construction, we are told, as to enable it to withstand the utmost fury of the winds and seas. It can neither overset, nor sink, and may therefore, in the most stormy weather, be steered whatever course the pilot shall see necessary. These last may be considered as different modifications of the life-boat, constructed with the same humane views, though probably without any communication between the respective artists. Were packet-boats destined to convey important dispatches thus constructed, many unfortunate accidents might be prevented.
The comparative value of these and other laudable inventions, whether produced by foreigners, or our own countrymen, must rest with their ingenious authors, at least, till their respective merits be fully ascertained by actual experiment. Were models of every new and useful contrivance, of this nature, consigned to the board of Naval Architecture, for public inspection, the display of such an assemblage of mechanism would excite emulation, and the result of satisfactory trials, if communicated from time to time, might prove highly important to the maritime world.
To ascertain the ship’s burthen.
5. It is certain, that a ship will carry a weight equal to that of a quantity of water, of the same bulk with itself, deducting, however, the weight of metal employed in its construction; for the wood is nearly of the same weight with water. Were it not for the iron, or other metal, a ship might float though full of water. However it be loaded, therefore, it will not entirely sink as long as the weight of its cargo is less than that of an equal bulk of water.
Now, to ascertain this, the capacity of the ship must be measured. Suppose it to be 1000 cubical feet, multiply that by 73 pounds, the average weight of a cubical foot of sea-water (taken at a proper distance from shore), which gives in the product 73,000 pounds for the weight of a bulk of water equal to that of the ship, the burthen of the ship being 73,000 pounds, or 36 ton and a half, reckoning a ton 2000 pounds, that being the weight of a ton of sea-water. If the cargo exceeds 36 ton and half, the ship will sink; if just 73,000 pounds, she will swim, though very deep in the water, and on the very point of sinking. And though she may float at sea, she will sink on entering the mouth of a river; fresh water being specifically lighter than sea-water, and in the proportion of about 63 to 73.