Friday, 7 September 2012

The Jet Propelled Ironclad

The 1860s were a time of great experimentation in ship design, perhaps nowhere more so than with HMS Waterwtich. Most modern warships of the time used steam power to drive a single screw propeller. The Waterwitch didn't have any propeller at all, she was jet powered.

The Waterwitch's two steam engines powered a huge 19ft, 8 ton, rotary pump, which sucked water through valves in the bottom of the boat, and forced it out through adjustable nozzles, pushing the ship along. She wasn't a toy either, she displaced 1,200 tons, and had a crew of 80, many of whom were working her 6 furnaces. It has to be said that she also had a full set of very traditional barquetine rigged sails.

But she worked, the Waterwitch not only moved, but in fact was highly manoeuvrable. The biggest concern was that she didn´t move very fast, only 9 knots as most, when HMS Warrior, for example, could reach 14.5 knots. This was in part due to the inefficiency of the process, only a quarter to a third of the engine power transferred to propelling the vessel according to the engineering press of the time, if it had been 100% she would have whizzed along at 24 knots. There was also the question of the huge amount of space the machinery took up in the hull compared to a screw driven ship.

In the Waterwitch's defence it should be said that she was intended as a gunboat, not an oceangoing battleship, and it was here that her advantages would be most evident. The idea was firstly that she would be extremely manoeuvrable, simply changing the direction of the water jets pivoting her around. But secondly, she could also operate in very shallow water, far more so than any propeller driven ship. Infact she could apparently dig herself into, and out of, sand banks, or so it was claimed. The water jets could be directed forwards or backwards, and there were rudders at either end.

There was also the question of armour - in the debate of speed vs protection, British gunboat doctrine tended to the former, whilst HMS Waterwitch was very much of the latter, with an armoured central casement in the middle 60 feet of her 162 ft length, protected by 4.5 inches of armour and 10 inches of teak. This central box had gun ports in front and back as well as each side for her 2x 7 inch muzzle loading, and 2x 20 pounder breech loading guns.

The Waterwitch could therefore navigate in waters normally inaccessible to warships, attacking areas previously considered invulnerable, and bypassing defences, She could also direct her fire in the most opportune manner available. Whatever the reason, jet propulsion wasn't considered worth pursuing, but maybe HMS Waterwitch was ahead of her time. The Finns and Israelis both now operate patrol boats using a similar process.

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