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Old 31 March 2004, 06:34   #1
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Rooster Tail

I was reading some of the earlier posts about spray at the transom.

I've always noticed quite a big rooster tail (spray coming up out of the water a couple of feet behind the prop)

It happens mainly at lowish speeds 15 knots or so.

Boat seems to perform and handle well and I don't get any spray into the boat

Is this normal?
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Old 31 March 2004, 08:26   #2
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I used to get it on my old boat when the boat had just dropped off planing speeds. I never really knew why it occured though...
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Old 31 March 2004, 08:39   #3
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- possibly because you're still trimmed out?
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Old 31 March 2004, 08:47   #4
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no, it happens trimmed in
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Old 31 March 2004, 08:51   #5
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Yes happened while trimmed in too.
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Old 31 March 2004, 08:55   #6
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Dunno then. I suppose there will be all sorts of effects with different hull geometries, engine positions, etc...
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Old 31 March 2004, 09:55   #7
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Could it be when the engine is fully trimmed in and the back of the boat is low in the water the propeller isn't square to the water and because of that it throws water up aswell as out?
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Old 31 March 2004, 11:25   #8
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Hydrodynamics...

This could all be rubbish - but...

When accelerating your boat up onto the plane, once you have got there, you can throttle back slightly and stay on the plane.

This is because a hull just before it planes - or as it comes up onto the plane - has more drag than the same boat on the plane (which is the whole point - as well as being able to go faster).

SO...going the other way, if you are just on the plane, and throttle back just enough to drop off the plane - as you decelerate your drag increases rapidly as you begin to displace (and speed decays), but your prop/engine will still be trying to go faster. Water is incompressible (pretty much), so the only place for it to go is up.

Sound reasonable? Or a load of old cobblers?



Dylan...
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Old 31 March 2004, 11:40   #9
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Hmm, sounds interesting, who knows.

I'm not unduly bothered about my Rooster Tail, in fact I'm quite proud of it.
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Old 31 March 2004, 13:32   #10
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