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Author Topic:   Can Dole-Fins cause purposing
eaglet1122 posted 10-24-2002 05:51 PM ET (US)   Profile for eaglet1122   Send Email to eaglet1122  
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
eaglet1122 posted 10-24-2002 05:56 PM ET (US)     Profile for eaglet1122  Send Email to eaglet1122     
sorry got to love/hate spell check "porpoising" Stan :)
thebone12 posted 10-24-2002 05:57 PM ET (US)     Profile for thebone12  Send Email to thebone12     
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.
eaglet1122 posted 10-24-2002 09:13 PM ET (US)     Profile for eaglet1122  Send Email to eaglet1122     
So when trimed they should be out of the water? Stan
kingfish posted 10-24-2002 09:43 PM ET (US)     Profile for kingfish  Send Email to kingfish     
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.
jimh posted 10-24-2002 11:48 PM ET (US)     Profile for jimh  Send Email to jimh     
Some time ago I began a thread on the topic of "General Theory of Porpoising" ( ). 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.

Bigshot posted 10-25-2002 10:01 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
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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