Pronblems with hydrofoil (whale-tail)

[Pharcta2]

Hi all - I have a Merc. 75 OB, and recently installed a Hydrofoil (black whale tail thingy). It puts me up on plane reallllly quick now! However, when I hi about 25-27 MPH the boat takes a hard, and I mean sudden, no warning, steering wheel not bucking ro anything, HARD left, placing the gunwale below the water line. I'm pretty sure I need to adjust the tabs on the hydrofoil, but I'm not sure which direction. Currently, they are on the 1st hole, which I think is 10 degrees. It looks like this from the bottom (the slashes are the tabs):

<---/-()-\--->

Any ideas?

Thanks!

[united jigsticker]

If everything is symetrical, you wouldn't get a pull one way or another suddenly from the tabs. And also, I think the tabs are simply for trim purposes, allowing the boat to either plane higher or lower in the water.

A sudden turn at a certain speed to me would indicate there has to be a drag on one side and not the other. I am not sure how this could be possible, but you may want to check your installation.

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Good fishing,
UJ
[email protected]

[Surface Tension]

UJ, What I meant by out of water is sort of what you mentioned, into cavitation or interrupted water. In either case the fin isn't getting the bite it had and therefore the pull. Some boats without a foil can produce a pull when trimmed up at times but a foil seems to make the situation more common. I've noticed when using a foil that you need less trim out because your not solely relying on the props angle of trust anymore to get the same amount of attitude.
Foils will get out on plane faster and keep you there at lower speeds but with some drawbacks. The pull is one of them.
A better alternitive with no negitives are adjustable trim tabs.

[Pharcta2]

Thanks for the input - Maybe I'm not used to the foil yet, and am trying to trim the motor like I used to do without the foil. I'll play around with the trimming next trip out.

[Surface Tension]

The foil is lifting your boat out of the water higher now. When at full lift your trim tab isn't in the water any more and the torque from your props rotation is pulling on the steering wheel. Trim your motor down a little and the pull will go away.

[united jigsticker]

ST,

If the foil is mounted properly, shouldn't it be mounted above the trim tab level with the factory trim plate on the motor? And for the foil to be effective, it would have to be submersed in the water at all times, otherwise it would cause the boat to porpose, wouldn't it?

The only thing that could possibly cause the trim tab to come out of the water would be the foil causing cavitation at the trim tab. However, if that was the case, I'd expect the prop to also cavitate and at that point the motor would rev higher or even over rev., or cause one side of the foil to drag in the water if the boat is not perfectly level from side to side, and that could cause the pull.

Huh. After all that, your point seems to be an excellent one ST. So either trim the motor down further, adjust your trim pin so you can trim the motor down further, inspect the height of the foil, or perhaps your motor now is mounted just a bit too high on the transom for the foil to ride coorectly in the water on full plane.

Keep in mind that the further down you trim the motor, you start to put an angle back onto it which will force the front of the boat down in the water. This will decrease the speed of the boat if it is too significant.

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Good fishing,
UJ
[email protected]

[This message has been edited by united jigsticker (edited 06-07-2004).]