The grapnel
hooks a rock, a large increase of strain is indicated on the
dynamometer, and it becomes doubtful whether the cable as well is hooked
or not. Again, it frequently happens in grappling over a rocky bottom
that one or more prongs are broken off, the grapnel thus becoming
useless, great waste of time being thus occasioned. Fully realizing all
the difficulties herein enumerated, it occurred to me that a grapnel
might be constructed in such a manner as to automatically signal by
electrical means the hooking of the cable, while it would ignore all
strain that external causes might bring to bear on it, and thereby
obviate the uncertainties attached to the use of the grapnels at present
in vogue. To effect this, I designed early in 1881 a grapnel fitted in
each prong with an insulated conducting surface, and a plunger and pin
so arranged that the cable, when hooked, should, by the pressure that
it would bring to bear on any of the plungers, cause the pin to come in
contact with the conducting surface, itself in electrical communication
with any suitable current detecter and battery on board the repairing
ship, and thereby complete the circuit.
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