Prop cavitation

[redagain]

Ive got a vintage 58' alumacraft "deep-C". has a real good running low time 66 merc 35 hp on it. Just got it this spring. Over the weekend, at our cabin, i pulled my kids with it for the first time on a tube. My kids are young girls and very light. Boat motor/prop would cavitate terribly whenever id turn, sometimes sharp or even a moderately tight turn. Only does this under load(pulling someone). Would a different prop solve the problem?

 

[jestor68]

What tilt pin hole are you using on the motor?

If you have it set too far out, it will ventilate the prop, because it brings it closer to the surface.

When you turn and the boat heels over, the prop comes even closer to the surface and ventilates. Moving the tilt pin closer to the transom should help, since this lowers the prop in the water.

 

[redagain]

I will check it out this weekend. Thanks for the advice.

 

[Sea Rider]

If you run a well ballanced boat, engine trimmed to remain a 90° while on planing parallel to water surface, you need a engine/transom height optimization specially if ventilating at close tight turns, choppy, windy, wavy waters. Raise engine 1-2 holes up if that's possible untill ventilation disappears.

Happy Boating

 

[jestor68]

Raise engine 1-2 holes up if that's possible untill ventilation disappears.

Happy Boating

You don't wanna do that with a old Alumacraft deep C boat.

 

[Sea Rider]

You don't wanna do that with a old Alumacraft deep C boat.

Why is that so ? Being a 35 HP engine surely has clamp screws, if so, could shim transom to raise engine accordingly. Which other method would you recommend to raise engine, as trimming it out of 90° is not the way to go, will lose best prop thrust performance.

Happy Boating

 

[jestor68]

Why is that so ? Being a 35 HP engine surely has clamp screws, if so, could shim transom to raise engine accordingly. Which other method would you recommend to raise engine, as trimming it out of 90° is not the way to go, will lose best prop thrust performance.

Happy Boating

Think about it. You don't raise the motor to reduce ventilation.

 

[Sea Rider]

Think about it. You don't raise the motor to reduce ventilation.

Redagain definitely will not be pleased with that vague answer. To enlighten us all, would you recommend installing a clever type prop or doel fins on LU to reduce ventilation on AV Plate.?

Happy Boating

 

[Texasmark]

Got lost in the exchange. On "Ventilating" while under the load of the skiis sounds like physics to me. The engine turns the prop but the boat doesn't move (per se) due to the load of the skiers. The turning blade generates a suction vortex. The easiest way out is to the low resistance (air) on/above the surface. My solution would be to drop the tilt pin down to the next lower notch.

Mark