The ballast is composed of iron and sheet lead; the former, a fixture to the wooden bottom of the torpedo; the latter, screwed on with long screws into the iron. A thin sheet of lead is always kept on the bottom, affording a soft material for moving them about on, removing the objection that may be made to the friction caused by an iron bottom in the moving of them in the torpedo-room. By taking out these screws, several more thicknesses of sheet-lead can be screwed on, the same screws binding all together. On leaving the manufacturers, there is sufficient lead placed on the bottom for a speed between three and ten knots. A very large increase of ballast would require another buoy to be strung on over and above the usual complement. [Illustration: (T)] The proper adjustment of the slings is most important, as the divergence depends upon it. The after legs of the slings, when stretched out alongside the torpedo, should extend one foot beyond the stem iron of the torpedo for the large torpedo, and eight inches for the small one; the distance on the slings being reckoned from the seizing round the thimble. This first adjustment is near enough if within two inches of the regulation. The thimble of the slings is made suitable for wire or hemp rope, the fore surface of it being bell-mouthed, to prevent chafe of the tow-rope; the thimble is so constructed that the parts of the slings cannot escape from the groove should the seizing become slack; it will be observed that by this arrangement the edge of the thimble is not brought in contact when rounding the stem or stern of a vessel, the nip after leaving the tow-rope coming direct on to the fore span, and thence to the projecting curve of the side lever. When all four legs are pulled out, in direction of the tow-rope, they bear an equal strain; the junction of the four legs should be on a level with the upper towing-irons, at the same time the upper fore span should make an angle between 80° and 85° with the near side of the torpedo. This arrangement gives the best divergence with the least strain on the tow-rope, and is suitable when the torpedo is kept at short scope, as well as when a long length of tow-line is out. The slings are made of the best Italian hemp (not laid up too hard), the rope being of the same strength as the tow-rope; for although in towing four legs divide the strain, yet during collision the strain might be brought on one or two.[2] [2] It may be here remarked, the small rudder on the stern of the torpedo is not for the purpose of increasing the divergence, but to control the direction of the torpedo when the tow-rope is suddenly slacked. [Illustration: (U)] [Illustration: (V)] The tow-rope for large torpedo can be of 2½ in. or 3 in. hemp, or 1½ in. flexible galvanized iron wire. For small torpedo, 1½ in. to 2 in. hemp, or ⅞ in. wire.