Harbor targets may be anchored, or supported on stakes; but it would conduce to good practice to stretch a screen of sufficient length to show, distinctly, four or six ports, with the proper intervals between. This will the better exhibit the lateral effect of the firing of each gun, and of the concentration of fire from several guns at known distances.
PACKING-BOXES.
223. Cartridges for small arms, primers, spur-tubes, percussion-caps, spare fuzes, false-fires, blue-lights, port-fires, and signal-rockets, will generally be supplied to vessels in boxes, in which they can be kept with little liability to injury, until wanted for use. (See [Part I., Page 10, Art. 42.])
These boxes are to be safely kept and returned into store, or accounted for in the same manner as other articles of Ordnance stores, by those persons in whose charge they may be placed. They will be held pecuniarily responsible for their loss.
GUN-SLINGS
224. Must be made of chain of 3/4-inch iron, and tested, to secure proper strength; the rings are to be of 1 1/4-inch iron. The length of the slings should exceed by one foot that of the longest gun on board. The two parts should be parcelled and marled together for a space of two feet before and one foot behind the trunnions of the longest gun, and a piece of three-inch rope spliced around both parts in the wake of the parcelling, long enough to take four or five turns round the chase of the largest gun.
TRUNNION-SIGHT FOR MORTARS AND PIVOT-GUNS.
225. The trunnion-sight is designed to be used only when the required elevation passes the limits of the other sights. It is formed of a bar of mahogany, or other hard wood not liable to warp, of about forty inches in length, two inches wide, and one inch thick, with a brass notch at the rear end and a point at the other, fixed in, and parallel to, the upper edge. It is attached, by a stout thumb-screw, to the axis of the left trunnion, around which it revolves when the screw is slack.
A semicircular plate, graduated to degrees, is attached to the bar, so that the sight may be used with the tables showing the corresponding ranges of the several classes of guns with their distant firing-charge. (See [Tables of Ranges, Appendix D.])
The upper edge of the sight-bar corresponds with 0° when the line of sight is parallel to the axis of the bore. A small level let into the upper surface of the rear end of the bar shows when the bar is level.