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rudder cavitation

I have been told that if i fit a cavitation plate on the rudder of my 40 ft narrowboat I will use less fuel as the thrust from the prop will push out more under water. not loosing some of the thrust pushing water above the water level off the stern?.I have seen this fitted to a number of boat rudders. Any thoughts please. thank you. Regards Arthur

Asked by: Arthur  | 10.23am, Friday 23 July

WW says:

I can understand the theory behind this but we are talking about narrowboats, not Formula 1 racing cars. The number of other places where inefficiencies can creep in are so great that I would have thought any advantage gained would be minute. If it was worth doing, I suspect that many more people would have tried it by now.

Graham Booth  | 10.05AM, Sunday 25 July

An anti cavition plate is a plate fitted to prevent the propeller sucking in air. This will be seen in the form of lots of bubbles in the wash and a lot of propeller noise. If your boat has a short swim, and is shallow draught with a small propeller, this might be the case. Flat or slightly downward angled plates fitted near the top of the rudder will direct the wash downwards, preventing the 'hump' of water often seen at the back of boats when under way. This will also in theory make the boat more efficient.
I don't know wether you would notice the difference on a narrowboat, but if you do decide to give it a go, please let me know the results.

Rupert Smedley  | 2.55PM, Wednesday 11 August

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