Int14200 Col2520
Protecting the Vitals
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This section looks at the ‘vital’ elements of HMS Colossus – the items that must be protected from enemy gunfire if the ship is to remain an effective fighting unit.


The ship is designed with a double bottom, for strength, rigidity and to minimise the risk of flowing. Bulkheads divide the ship into watertight compartments, although there are many watertight doors between compartments, and these are not always effective or quick to close (as was the problem when the Victoria was rammed and sunk by HMS Camperdown in 1893).

MOVE - Propulsion

Colossus is fitted with two Maudsley compound engines developing 7,488 Indicated Horse Power (IHP) driving two 4 bladed propellers of 17’8” diameter and giving a maximum speed of 16.5 knots per hour (as speed was frequently expressed in the 1880s).[2]

The high pressure (HP) cylinder has a diameter of 58”, and the two low pressure (LP) cylinders have 74” diameters. The stroke is stroke 39”. Steam is exhausted to surface condensers. Thrust blocks are situated just aft of the engine couplings.

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“Float” – Colossus is designed as a central armoured citadel box with a watertight raft extending forward and aft protected by a 3 inch armoured deck lying a few feet below the waterline. At the ranges these ships are expecting to fight (about 1,000 yards), gunfire trajectories will be almost horizontal, so shells hitting the water would be exploded or retarded before doing much damage below the waterline.

The spaces above the armoured deck are filled with stores, coal etc., and wing compartments are filled with cork. The intention being that if these unarmoured ends are penetrated not much water would be able to flow in (since the spaces will already be full), and the ship will remain buoyant and stable.

“Move”: the boilers, and engines are placed within the armoured citadel. Additionally, coal bunkers are placed outboard of the machinery spaces. Tests show that 2 foot of coal is equivalent to an inch of armour.



“Fight”. This means that the ship can continue to supply, aim and fire her guns. The loading mechanism and turret bases are protected inside the central citadel. The magazines and shell rooms as I shall show now, are located deep below the water line, with the lifts to the guns within the armoured citadel.

(place the mouse over the boilers to see the turret positions)

There are 8 main and 2 auxiliary elliptical boilers in four boiler rooms. Working pressure is 64 pounds on the square inch.

The main boilers each have three grates, the auxiliary boilers only two. Coal bunkers are situated outboard of the boilers and engines giving added protection.

(c) Rob.b1904 2008