Holes in propeller?

[titaniumneck]

Hello again, well I drilled 1/4 inch holes on the aluminum prop which is a 11 pitch, and the other prop is a 12 pitch s/s. The motor again is a 40 hp tohatsu m40c, on a 15 foot sprint fiberglass boat. The 11 pitch aluminum prop with holes did a little better hole shot, top in speed was the same, but the motor sounded better, running a little higher rpms, more like she use to on my aluminum boat. With the stainless prop it sounded bogged down.
So I guess my next step is to get stainless prop to prop shop and have prop dropped down to 11 pitch with vent holes. What yall think?

 

[titaniumneck]

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[walleyehed]

I know it's cost-prohibitive to just buy an 11P SS when you have a 12P, but it's really hard to remove pitch from a prop without losing efficiency, effectively killing the reason for going SS. Blade geometry is hard to "take back". You can go the other way with no issues but it's truly a gamble to try and remove (drop) pitch on an existing SS.

 

[Texasmark]

more like she use to on my aluminum boat. With the stainless prop it sounded bogged down.
So I guess my next step is to get stainless prop to prop shop and have prop dropped down to 11 pitch with vent holes. What yall think?

On the "more like part", sure you aren't blaming your prop for a powerhead degradation? On bogging with the 12P SS it's probably cupped making your SS selection 2" more in pitch. 2/11= 18% more pitch. Yes that would be/should be noticeable at WOT.

 

[titaniumneck]

So for cost and performance, should I get old s/s prop dropped down in pitch. Prop shop I have seen some beautiful work done said he can do it for about $75 to $90. Or just buying new prop work better. Old prop is in good condition.

 

[Texasmark]

So for cost and performance, should I get old s/s prop dropped down in pitch. Prop shop I have seen some beautiful work done said he can do it for about $75 to $90. Or just buying new prop work better. Old prop is in good condition.

This is from Walleyehed just above in case you missed it. Also incase you missed it he authored at least one Sticky at the top of this section. Pays to heed his advice. Wink.

And I quote: "I know it's cost-prohibitive to just buy an 11P SS when you have a 12P, but it's really hard to remove pitch from a prop without losing efficiency, effectively killing the reason for going SS. Blade geometry is hard to "take back". You can go the other way with no issues but it's truly a gamble to try and remove (drop) pitch on an existing SS."

 

[jimmbo]

Twisting the blades to a different pitch is along the lines of Voodoo magic. I guess a bit of added cup would be about the only way to increase the effective pitch of a prop. Anytime I have seen a 'repitched' prop, the blade contours never looked right, and unless the prop shop really knows and understands propellers, the end result is usually disappointing. Bronze is probably the best metal for a prop if you are trying to alter pitch. AL just breaks, and SS is very stiff

 

[SeaRay Seville]

Okay guys, my interest is peaked! Can anyone post or send pics of a drilled prop? Someone mentioned this in my post as well and I would like some pics of where exactly these holes are being drilled. Furthermore how crucial is the centering/spacing of the holes? I have access and some experience with a mill at work. I'd imagine the holes need to be very precise to function correctly> Thanks guys.

 

[jimmbo]

Lousy pic, but it shows the vent

 

[SeaRay Seville]

Crazy something so small can make such a big difference! Do you start with just 1 or do all 3? This would be on my 100HP Mercury with ballistic 13.5x17P prop, start with 3/16' hole on one and move to 2 and 3 if little or no performance is gained? or just open up the one hole larger? I tried you tubing this and only found model plane props. Thanks again Jimmbo!

 

[jimmbo]

On a 3 blade prop, you would have to do all three. On a 4 blade, you might be able to do two
The holes in that prop are probably about 5/16 or 3/8 of an inch. Finding the right size is like getting the waiter to salt and pepper your food. More, more, more, more TOO Much!!!