A NEW PROTECTIVE AGAINST TORPEDOES.

Otago Daily Times, Issue 7335, 19 August 1885, Page 4

A NEW PROTECTIVE AGAINST TORPEDOES.

When, some years ago, the masonry of the quays in the Seychelles Islands was found to be constantly needing repairs at great ex- ■ pense, in consequence of the deterioration due to -violent seas, a plan was devised of protecting the portions exposed to the action of the waves by a palisade of bamboo canes, the space between which and the structure of the quay itself was filled in with the fibre forming the husk of the c'dSoahut: This cellulose, or cofferdam, as it is called,- was found to behave like a sponge, and offer the most effectual shield to the masonry of the quays. The great success of .this expedient has led to some experiments,.w"hich have just been conducted at Toulon, with a view of utilising cofferdam as a protective against projectiles, shells, and torpedoes in naval warfare, and with a result that seems to indicate what may become a very extensive employment for the cocoanut fibre, which lias' already found so many uses in commerce, and the trade in which has recently been largely developed in the South Sea Islands. " ■-•■■■■ - : . ; .

Cofferdam, copra, or coir are various commercial terms for the ligneous envelope of the cocoanut. This is disintegrated and comminuted by various mechanical processes, which we need not here describe. The cellulose itself is one of the lightest substances known, weighing about five times less than cork. The material used for the experiments was in every case a mixture of 14 parts of pulverised cellulose and one part of fibres, the latter acting like hair in mortar or cement as a binder. This mixture was compressed so as to form a kind of felting, of the density of 120 kilogrammes to.the cubic metre, and thus condensed was placed in a case, which was covered with boarding about Sin thick, the depth of the cofferdam being about 2ft. These particular thicknesses were chosen as of dimensions practically applicable to vessels which it might be desired to protect by this means.

The first experiment was designed to test the effect of an ordinary projectile which was fired from a cannon of Din calibre, at a distance of only 60 yards,,against, the case of cofferdam above described. , The projectile pierced the case through and through, carrying away a quantity of the cellulose, but a remarkably small quantity, when the cubic content of the projectile is considered. The most important feature, however, of this experiment was that, immediately after the shot, the perforation was found to be filled up by the cofferdam, so that it was impossible for a man to thrust his arm through the place penetrated by the projectile. It was, then attempted to force water through the place where the shot had passed, but even after several minutes only drops were found to ooze through. In proportion as if absorbs liquid, the cellulose augments in volume and density, and tends thereby to withstand the further entrance of water.

The next experiment was made with a view to show the incombustibility of the cofferdam, ahd its power to resist or extinguish explosive projectiles and shells. First, a portion of its contents was removed from the abovementioned case, and a .large quantity of burning charcoal was placed in it, and covered with the cellulose to the depth of from three to four inches, when the charcoal was speedily extinguished. Next, from the former distance of 60 yards, shells of nine inches in diameter were shot into the case of cofferdam and burst there—the fragments nearly all remaining in the cellulose, into which no water was found to have entered. Moreover, the material is said to have offered such obstruction to the few splinters of the shell which passed through it, that they would scarcely retain velocity enough to be dangerous. \

The third experiment was one for testing the resistance of the cofferdam to the effects of torpedoes. Here the case used to contain the cellulose was of sheet-iron. The torpedo was attached to it on the under side, and exploded. In this instance the effects were more violent—a side was blown off the case, and the mass of the cofferdam was found to have been pierced through aud tlirough with a small longitudinal perforation. But even in this case it is considered that the force of the blow inflicted by the torpedo was considerably attenuated. The question is now under serious consideration whether vessels of war should not have a protecting envelope of this cofferdam, which, in conjunction with water-tight compartments, would, it is thought, prove the best defence against all kinds of artillery.—Chambers' Journal.