Holes in Prop

[MarkAB]

I have been advised that instead of decreasing prop pitch, drilling a hole in each of the prop blades will have the same effect. The hole is apparently drilled in the centre of the blade.<br /><br />As to the hydrofoil issue - will I see a benefit on a 8hp motor? I cannot get my boat to plane!!

 

[cobra 3.0]

Re: Holes in Prop

Check out this site.<br /><br /> http://www.marinemechanic.com/site/page76.html

 

[JasonJ]

Re: Holes in Prop

I have the holes mentioned in that website on my 14x17 prop. I have no idea if they helped, they appear to have been part of the manufacturing process, thus being stock for that prop. I had a 13x17 on and put this 14x17 on and it made dramatic improvements, but I cannot attest to how much was the holes and how much was the 1 inch increase in diameter. My application is slightly different than the original posters (125 horse), but I can at least vouch that the holes don't seem to hurt anything.

 

[Hooty]

Re: Holes in Prop

Ya don't drill holes in the prop blades, if it's a through the hub exhaust, ya drill 'em in front of the blades. It acts kinda like slipping a clutch. That attached link explains it.<br /><br />c/6<br />Hooty

 

[cobra 3.0]

Re: Holes in Prop

I've put these holes in, with mixed results. I find there is more cavitation now in turns.

 

[WillyBWright]

Re: Holes in Prop

MarkAB, sorry, you're not likely to plane a boat with an 8Hp. 9.9s might plane a small aluminum fishing boat with one person, with a 15Hp it'll probably plane with two people.<br /><br />Depends a lot on the boat, too. One place I worked had a 20' Jon workboat with an 8' beam. I could plane it off with an old 7 1/2Hp Scott Atwater Bail-A-Matic. Might have just been 5Hp. I don't remember for sure.<br /><br />I don't think ventilating the prop or adding a hydrofoil would help an 8Hp.

 

[cobra 3.0]

Re: Holes in Prop

What kind of boat do you have? Also, is the tilt angle set correctly?

 

[MarkAB]

Re: Holes in Prop

Cobra,<br /><br />I have a 10ft fiberglass tri hull dingy. It weighs in at approx (190 lb). By tilt, I assume you mean trim. The motor only has four holes and the two nearest the transom work best.<br /><br />My last option (besides having to upgrade) is to change the prop. The current one is a 9x9 and I can't find out what the standard is. The motor is a '79 Yamaha.