Can-Buoys; these are in the form of a cone, (see plate [II]. fig. 8.) and of this construction are all the buoys which are floated over dangerous banks and shallows, as a warning to passing ships, that they may avoid them. They are extremely large, that they may be seen at a distance, and are fastened by strong chains to the anchors which are sunk for this purpose at such places.
Nun-Buoys, are shaped like the middle frustum of two cones, abutting upon one common base, (plate [II]. fig. 9.) being casks, which are large in the middle, and tapering, nearly to a point, at each end.
Wooden Buoys, are solid pieces of timber, sometimes in the shape of a cylinder, and sometimes of a nun-buoy; they are furnished with one or two holes, in which to fix a short piece of rope, whose two ends being spliced together make a sort of circle or ring called the strop.
Cable-Buoys, common casks employed to buoy up the cable in different places from any rocky ground. In the harbour of Alexandria, in Egypt, every ship is moored with at least three cables, and has three or four of these buoys on each cable for this purpose.
BUOY-ROPE, the rope which fastens the buoy to the anchor: it should be little more than equal in length to the depth of the water where the anchor lies, as it is intended to float near, or immediately above the bed of it, that the pilot may at all times know the situation thereof. See plate [I]. fig. 6. b is the anchor, c the buoy-rope, and d the buoy floating on the surface of the water.
The Buoy-Rope is often extremely useful otherways, in drawing up the anchor when the cable is broke. It should therefore be always of sufficient strength for this purpose, or else the anchor may be lost through negligence.
Slings of the Buoy, the ropes which are fastened about it, and by which it is hung: they are curiously spliced round it, something resembling the braces of a drum.
To stream the Buoy, is to let it fall from the ship’s side into the water, which is always done before they let go the anchor, that it may not be retarded by the buoy-rope as it sinks to the bottom.
BURTHEN, or Burden, port, (byrthen, Sax.) the weight or measure of any species of merchandize that a ship will carry when fit for sea.
To determine the burthen, or, in other words, the tonnage, of a ship, it is usual to multiply the length of the keel into the extreme breadth of the ship within-board, taken along the midship-beam, and multiply the product by the depth in the hold from the plank joining to the kelson upwards, to the main-deck, and divide the last product by 94, then will the quotient be the burden required, in tons.