SPEED RECORDER 137
Walker's Patent "Cherub" or ''Neptune" Tafirail Log is one greatly
used nowadays, and most candidates will have had more or less experi-
ence in its working. It consists of a cylindrical brass case with a dial,
the case containing the registering machinery.
The dial is marked round its edges from 0 to 100, these figures repre-
senting miles. A brass hand points to the number of miles run. There
is also a smaller hand, like the seconds hand of a watch, which indicates
the quarter miles. A bell within the brass case is struck as each sixth
part of a mile is recorded, that is, the bell is struck six times during a
run of one mile.
In the latest type of "Cherub" log the small hand indicates tenths
of miles instead of quarters, and the bell is not fitted.
A rotator is towed by means of a patent log line. This revolves
according to the speed of the ship, and works the mechanism in the
brass case, the distance covered being read from the dial. A "governor"
is attached to the line just abaft the rail; this helps to make the log
work at a uniform speed.
The figures show an electric "Cherub" log fitted to the taffrail and
connected up to a repeater log in the chartroom. A common practice
is to tow the log from a boom amidships as shown in Figure 8, the speed
indicator being in the chartroom or on the bridge.
L Having "streamed the log," what attention will you give it while
in usel
See that the line is clear, the governor is acting properly, and that
there is nothing foul of the rotator. Take every opportunity of testing
the accuracy of its readings, not forgetting that it indicates the distance
travelled through the water, not the distance made good ovei the
ground. Give the mechanism a drop or two of good oil occasionally.
Take care to haul it in before stopping, or when likely to have to go
astern on the engines.
2. Does the dial indicate the speed at which the ship is travelling at
the time you look at it, or does it only record the number of
miles run?
It only records the number of miles and quarters or tenths of B^
mile which the ship has run.