Thursday, July 10, 2008

Taking Soundings with a Lead Line

Soundings (measuring the depth of water) are taken when going into or out of port or approaching an anchorage, shoal, or rock. The usual method of taking soundings is by the depth sounder, although the hand lead must always be available. The hand lead consists of a narrow block of lead, weighing from 7 to 14 pounds, which is attached to a marked line. With the ship making 12 knots, a good leadsman can get reliable soundings down to 7 fathoms. At slower speeds, of course, the lead has time to sink even deeper before the ship moves up to it. The leadline may also be used for determining the direction in which a ship practically dead in the water is moving. Direction of movement is found by placing the lead on the bottom, directly below the leadsman, and noting the direction of the motion of the ship as shown by the change of direction of the leadline from the up and down.
Before heaving, the leadsman takes station in the chains, which usually are platforms projecting over each side at the after end of the forecastle. The lead is then lowered over the side and is supported in the heaving hand by a wooden toggle, inserted in the leadline about 2 fathoms from the lead. The spare line is coiled in the other hand, free for running. To make the heave, start by swinging the lead in a fore-and-aft direction outboard of the chains, in order to gain momentum, then swing the lead in a complete circle. When the force is great enough, let go the lead as it swings forward and at a point about level with the deck. This action makes it fly forward on a line a little above and practically parallel to the deck.
As the ship moves ahead, heave in the spare line rapidly. The marker should be read when the lead is on the bottom and the line hauled just taut, up and down. Ability to heave the lead can be acquired only by practice. It is necessary to practice in both chains, because the right hand is used for heaving from the starboard chain, the left hand for heaving from the port chain.
A good heave has no value unless the depth can be read correctly and quickly. Learn the markings of the line, which are as follows:
1. At 2 fathoms, 2 strips of leather.
2. AU fathoms, 3 strips of leather.
3. At 5 fathoms, a white rag.
4. At 7 fathoms, a red rag.
5. At 10 fathoms, a piece of leather with a hole in it.
6. At 13 fathoms, the same as at 3 fathoms.
7. At 15 fathoms, the same as at 5 fathoms.
8. At 17 fathoms, the same as at 7 fathoms.
9. At 20 fathoms, 2 knots.
10. At 25 fathoms, 1 knot.
Leadlines often are marked also at each half fathom over the range of depth used most, and may even have foot markings around the more important depths. Some leadlines are so fixed that the depth may be read at the level of the chains instead of at less than 3 fathoms of water, 1/4 fathom more than 4, and 1/2 fathom more than 4. If bottom is not reached, report "No bottom at."