Exh Relief Hole Question

[SRP71]

I have two stainless steel props, (1) Ron Hill 22 and (1) Raker 20. The 22 is a little too much pitch for hole shot when pulling a skiier with a fully loaded boat. (Several passengers) So I purchased a used 20 Raker last fall. The 20 let motor rev up and you can definatley tell its a 20 by the amount of slip when hitting it hard while going 30 mph or higher.

I understand that having exh relief holes in front of the blades allows prop to slip more out of the hole but does it also affect the prop slip while under way on plane?

The exh relief holes are larger than a 3/8" drill bit but not larger than 7/16". I am suspecting the previous owner enlarged holes so his motor could handle the prop.

I am running a 235 crossflow on a fairly light skiboat. Prop shaft is about 1 1/2" below the lowest point on the hull. Running boat at an altitude of 4500ft plus..

The Ron hill also has relief holes but they are much smaller.
22 works great if its just me , the wife and the kids. Pulls me out of the water fairly fast.

Do the have such a thing as plugs for props? want to experiment with plugging off the relief holes or decreasing the size of the relief holes to see if I can gain some extra bite.

One other interesting note the blade surface area on the Ron Hill is smaller than the Raker.

Thanks for the help
SRP71 :)

[chris_lacey]

I wouldn't think the holes would have much of an effect at/over 30mph. I run a Predator over/through hub on my V-King with a 235 it has very large vent holes but once it hooks, it's hooked. I also ran a Raker on this boat with a V4 OMC, and again, once it hooked it was hooked.
Are the blades in good shape? Engine height sounds about right for a 'Stream, sorry don't know about the Lavey.

[hsbob]

my old lazer II seam like it had !/2 sq holes. Epoxy the holes in and redrill to the new size.

[Reese]

1 1/2" below the pad is too high for most props. It's probably a good height for top end but not with two or three guys and a skier. My water ski setup uses a 21 deg, heavy cupped 14" dia four blade that is never any higher than 3- 3 1/2 below the pad.

Once I found the best height, I played with the vent holes....actually had a machine shop mill 3/4" vent slots on the leading edge of the hub. Vent holes or slots really only effect hole shot.

[SRP71]

I have tried playing with the motor height and it doesn't help. All it does is create a second wake on the motor from the cav plave. Gains werer very minor if at All.. Only noticed slight improvement when turning very sharp at speeds less than 30. The rear of the Hull I am running is rather shallow, makes it great for skiing. The tansom bracket I am running has about 8" of setback with a negative angle. I can actually tuck the motor under quite a bit if needed.

The prop is in good condition, but I dont think it has been cupped. My other prop has been re worked and works great at about any height.

I guess I will have to live with the slip I guess... :mad:

Or just keep my foot out of it when accelerating... Gas prices should help that issue!!!!

Just thought I should get a littl better bite with this prop, Acts like an Alum prop.

Might think about having it cupped if it would be worth the expense..


SRP71

[SRP71]

I will see if I can find a local prop shop that can add some cupping to the prop.

Just thought that only decreasing pitch form 22 to a 20 would have such negative results. Sounds like cupping is my solution.

SRP71 :)