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History of the Atlantic Cable & Undersea Communications
from the first submarine cable of 1850 to the worldwide fiber optic network

Flume Tanks
by George Smith

Introduction: George Smith sailed on HMTS/CS Alert (4) as third engineer from January 1967 to October 1973. Here he explains a stability device used on cable ships—the flume tank. See also George's notes and photos on cable laying on the Alert.

--Bill Burns

Flume Tanks

The flume tank on the Alert was basically a rectangular box mounted on the top deck of the ship and fitted with internal baffles. The tank extended across the full width of the ship; it was about 6 feet high (I'm 5’ 6” and I remember being able to stand upright in it), and about 8 feet fore and aft. Inside the tank was a series of baffle plates with various size holes cut in them.

Diagram of CS Alert showing the ship's flume tank and ballast tanks trimmed for a load of lightweight cable. Taken from a report of loading and ballasting tests performed on the Alert in Glasgow in 1972.
Image courtesy of George Smith

Once the vessel was loaded, a calculated amount of water was pumped into the flume tank. The amount of water varied with how the ship was loaded, and also with the density of the water being pumped in. 100% sea water weighs about  64.5 lbs/cubic foot, fresh about 62, estuarial water varies between those two.

When the ship rolled the baffles “held back” the water in the tank from flowing freely, thus cutting down both the amount you rolled and how fast. The flume tank thus acted as a form of stabiliser.

When a ship is under way the same thing could be achieved with hydraulically controlled stabilising fins, and I believe that they are more efficient, but fins do not work when the ship is stationary or proceeding very slowly, as is often the case when laying cable. Hence a flume tank on a cable ship.

The tank certainly worked; it allowed us to carry out repairs in seas which would otherwise have made cable work impossible. But don't think it would let you work in a raging hurricane!

It also made life more bearable when crossing the North Atlantic in winter—a large whisky and heavy weather do not go together, spillages must be avoided.

Copyright © 2007 FTL Design

Last revised: 14 September, 2007

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