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On the Loss of HMS Captain by Andrew A.W. Drew, M.A.
(Possible source -The Mariner's Mirror)
In his article, Captain Drew argues that the low freeboard was irrelevant to the stability of the ship; indeed it was the narrow, shallow and consequently poorly ballasted design that gave Captain the instability she showed. The article is summarised as follows –
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“You can’t have everything in a
ship's design – speed, weight, dimensions, carrying capacity, and stability.
In Captain’s case great speed under steam, lightness of draught, and great carrying capacity “are antagonistic” to stability due to the form of the hull under water needed to achieve the first three.
Stability under sail is obtainable two ways – the shape of the hull below the water, and use of low down ballast.
A ship which is unstable without ballast and not under sail can be made perfectly stable with ballast, even when under sail.
Similarly, a naturally safe hull form becomes unsafe if the centre of gravity is raised through turrets and armour plating. So such a ship must have a hull that naturally resists lateral pressure.
The hull design of the Captain was ”such that no sane man would ever dream of calling suitable for a sailing ship”
was a design suitable for carrying enormous weights, upon a comparatively small draught of water, and obtained a high rate of speed under steam; but she could not resist sail pressure.
The low freeboard did not come into it, indeed if the ship had been higher out of the water as the design intended, the higher centre of gravity would have made her even more unstable. This point was made by EJ Reed who expressed his concern that when the ship was light of coal and stores, i.e. her freeboard increased and her stability decreased. A deeply laden merchant ship, despite a low freeboard, does not capsize; an insufficiently ballasted one with a high freeboard will be capsized in a squall of wind.
A naval architect will know that to increase stability, you increase her beam; but the ship loses speed. Or a mechanic would say increase the draught and lower the weights; this will also decrease speed.
But HMS Captain had neither of these – she had a very narrow beam, and a shallower draught than any other ship of her tonnage; and she had a double skinned bottom, thus preventing ballast from being very low.
Ironclads have abandoned the good old fashioned keel, but for ships such as Captain they should revert to the hull used by sailing frigates, albeit at the cost of a further 1000 tons. Commercial yacht builders stick to this design of deep keels because “they can make their vessels do the work under sail which Whitehall never does”.” |
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HMS Captain
1870