or 51 feet 1.95 inches. 1 fathom = 5.11629 feet, or 5 feet 1.395 inches.
If a 28″ glass is used, and 8 divisions, then —
1 knot = 47 feet 9.024 inches.
1 fathom = 5 feet 11.627 inches.
The line should be about 150 fathoms long, having 10 fathoms between the chip and first knot for strayline.
Bowditch gives 6,120 feet in a sea-mile, which, if taken as the length, with a 28″ glass, will make the divisions 47.6 feet and 5.95 feet.
Some logs, the earliest of which, perhaps, was Massey's, are actuated by wings on a rotating rod, which turns as the vessel passes through the water, operating, by means of an endless screw, a series of multiplying wheels, which register the total distance run between the time the log was thrown overboard and that at which it was taken from the water.
These are only taken in when the ship's course is changed, or when the speed is below two or three knots per hour.
They are somewhat liable to turn up missing, owing probably to their being bitt<
h the tube containing the line.
This instrument consists of a delicately pivoted helix, which is turned by the action of the water, and registers the number of revolutions made on a series of dials.
Two of these helices are employed, turning in opposite directions for the purpose of eliminating any error which might occur from the twisting of the line or other similar cause.
Arrangements are provided for disconnecting the registering apparatus when the lead reaches bottom.
The helix of Massey, such as that employed in his patent log, has also been used, but owing to its want of delicacy does not give as satisfactory results as those of Saxton's current meter.
In sounding at extreme depths, it is not expected to recover the plummet, but arrangements are made for detaching the registering apparatus or the devices for obtaining specimens of bottom, which may then be hauled up with comparative ease and safety.
It has been proposed to dispense with the sounding-line altogether,