Lloyd's give an additional year to all ships or yachts that are fastened from the keel upwards (to within one-fifth the depth of hold amidships from the deck) with yellow metal or copper bolts and dumps, or trenails ; in such case the fastenings for the upper strakes of plank to the deck must be properly galvanised, it being also understood that the iron bolts for frames, beams, &c., are to be galvanised. And a further two years are granted if no trenails are used at all.* Whether trenails or bolts are used, one is to be put in each plank or strake at every timber ; two-thirds of the trenails are required to be driven through, and the butts of the plank must be through-bolted with copper or yellow metal ; and the bilge strakes and limber strake should be through-bolted.
Trenails are scarcely adapted for vessels of less than 50 tons, on account of the small size of the timbers ; and even in these they should • be very sparingly used (and only in the bottom plank), as a 3in. timber must be very considerably weakened if it is bored with holes to receive l in. trenails.
Some ten years ago it seemed likely that composite vessels would quite supersede those entirely of wood construction ; but so far the composite plan has not advanced in favour. This is really a matter for surprise, as the composite build offers this advantage over the wood structure : so very much more room is obtainable inside on the same weight or displacement. The great question was ten years ago, could a composite vessel be so fastened as to be insured against the possibility of the fastenings giving out ? We think the question has now, after ten years, been satisfactorily answered by such vessels as Oimara, Selene, Nyanza, or Garrion, built by Steele and Co., of Greenock ; the Sunbeam and Modwena, built by Bowdler and Chaffler, at Liverpool ; the Bella Donna and Seabird, built by Hatcher ; and many others. None of these vessels have, so far as we know, ever shown the slightest signs of straining, nor have their fastenings decayed ; in fact, so far there seems every chance of their out-enduring any of the wood yachts which were constructed at about the same period. For a composite yacht it is best that all the planking (excepting, of course, the deck) should be of hard wood, and that the plank fastenings should be of Muntz' metal screw bolts sunk in the plank, and so insulated that galvanic action could not be set up with the outside copper, the bolts, and the frames. Mr. J. S. White, of East Cowes, has, within the last two years, provided the necessary plant for composite construction, and has built three large yachts according to that system of construction. We may perhaps take this as evidence that composite vessels are gradually coming into general use.
Lloyd's have compiled a table of scantlings for composite and iron yachts, and will in future class such as are built up to their rules. Steel,
however, is likely to supersede iron, as Lloyd's will give the same class for one-fifth less weight.
A great many experiments have from time to time been made with compositions for preventing the fouling of the bottom of ships; but up to the present time no specific has been discovered, and the opportunity for someone to realise a large fortune still exists. So far as yachts are con cerned, they are generally sheathed with copper ; and, for these waters at least, the bottom can be kept clean enough by a couple of scrubbings throughout the season. One of the compositions, such as Jesty's, Day's, Peacock's, or Martin's, is sometimes put over the copper; but, for racing at least, we prefer the copper without the composition, as clean copper has a smoother surface than either of the compositions imparts. Of course, for a racing yacht, the copper cannot very well be cleaned too often; and a month is quite long enough for the vessel to be without a scrub, although there are but few who get one so often. The Admiralty have been making some experiments with zinc as a sheathing for iron ships (the iron being first protected by a slight wood skin), but so far zinc does not appear to offer many advantages. Copper, on the other band— if the ship be kept constantly moving, or moored, say, in a five-knot tide —will keep comparatively clean, on account of the extensive exfoliation which goes on of the oxychlorides and other soluble salts produced by the action of the salt water on the copper. Oxychlorides are similarly and much more rapidly formed on zinc, but are not so readily soluble ; hence very little exfoliation takes place, and a corroded and rough surface is the result, the zinc being finally eaten through. Zinc, therefore, we may conclude, is unsuitable as a sheathing for yachts, especially as evidence exists that such sheathing }in. thick has been eaten through in one year. An alloy of copper (2) and zinc (3), popularly known as Muntz' metal, is largely used as a sheathing for ships; but it is scarcely so good as copper for yachts, as, owing to its greater stiffness, it cannot be laid so well. Another objection to Muntz' metal sheathing is that it does not exfoliate to the extent copper does, and that after being under the influence of salt water any considerable time—say three or four years—the metal becomes rotten ; but this defect, it is said, can be remedied by an addition of a small quantity of tin to the alloy. For composite ships Muntz' metal sheathing has some advantage, as it sets up very little, if any, galvanic action with iron ; hut the risk of galvanic action from copper sheathing in a well-constructed composite ship is so remote that copper is to be preferred even to these, if the difference in cost is not a consideration.