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ContinuousWave: Whaler Performance
Can Dole-Fins cause purposing
|Author||Topic: Can Dole-Fins cause purposing|
posted 10-24-2002 05:51 PM ET (US)
I have bought a 1996 17 foot Outrage w/ 1996 115hp Yamy. Rig has a T-Top. I am repitching from a 17" Alum to a 19" SS prop. Out of the hole with 17 is great but high end speeds under full or 1/2 load causes the boat to purpose bad unless engine is trimmed down a great deal. Would removing this devise help alleviate that problem. I know that it says it reduces it but it cant get worse. Thanks, Stan
posted 10-24-2002 05:56 PM ET (US)
sorry got to love/hate spell check "porpoising" Stan :)
posted 10-24-2002 05:57 PM ET (US)
when you run look and see if they are out of the water, most of the time they are only in the water when you try and plan then as you trim they come out. I think that it is improper load distrobution or the trim of the engine, I have never heard of them making it worse.
posted 10-24-2002 09:13 PM ET (US)
So when trimed they should be out of the water? Stan
posted 10-24-2002 09:43 PM ET (US)
At least in smooth water, when you are well planed your cavitation plate will be above the surface of the water if your motor height is set for maximum performance and efficiency. If your cavitation plate is above the surface of the water, your DoelFins will be too.
posted 10-24-2002 11:48 PM ET (US)
Some time ago I began a thread on the topic of "General Theory of Porpoising" ( http://continuouswave.com/ubb/Forum4/HTML/001015.html ). I was surprised to learn that naval architects and designers had been studying this phenomenon for many years and had not isolated the cause of it.
Based on that revelation, I gave up thinking that random advice from on-line participants would be able to resolve the cause of porpoising.
posted 10-25-2002 10:01 AM ET (US)
Jim....I hear ya. I have owned the same boat and with one engine she would porpoise like hell. With the new Johnson I could trim it so high I would shoot a 5' rooster tail and never porpoise. No doel-fin either. I think the engine mounting and prop make a BIG difference.
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