i drilled holes in my prop, guess what happened?

[phatmanmike]

boat - 1960 glasspar 16' citation runabout<br />motor- 1976 merc 115<br />prop- merc 13.5 x 21p 3blade aluminum<br /><br />boat was hard to get on plane, wouldnt rev as easily as i wanted.drilled 3 holes 1/2 inch from edge of prop/gearcase, 3/16" in size.<br /><br />with me, my wife and our 3 year old daughter in boat, i could immediatly tell a difference.<br /><br />this had NO effect on top speed other than the fact that it got there quicker.<br /><br />boat still idles and cruises nicely at slow speeds.<br /><br />i have a OMC service bulletin that JOE REEVES sent me detailing the process... email me if you want a copy.

 

[cobra 3.0]

Re: i drilled holes in my prop, guess what happened?

...was it something like this?<br /><br /> http://marinemechanic.com/site/page76.html

 

[bubbakat]

Re: i drilled holes in my prop, guess what happened?

you have mail

 

[TwoBallScrewBall]

Re: i drilled holes in my prop, guess what happened?

Isn't this dangerous from a balancing perspective?<br /><br />-Edit- <br /><br />Looked at the link above, I thought you were drilling the blades. Balance should not be affected here if the holes are equally spaced. <br /><br />I think I might try this on my 19 foot bowrider with 140hp 3.0 I/O and 14X19 prop. I like the prop and it gets on plane OK with 2 in the boat, but with 3 of 4 people it works up a sweat to get out of the hole. Hopefully this will help.

 

[cobra 3.0]

Re: i drilled holes in my prop, guess what happened?

Steve, I have the same situation with my 140 hp 3.0 and a 19" pitch stainless. The 17" aluminum gives me way better hole shot and close to the same top speed...and it really rips for tubing!

 

[imported_JD__]

Re: i drilled holes in my prop, guess what happened?

Friendly advice:<br />It will definitely help the hole shot. Don't do what I did. Thinking that more + more was better, I kept enlarging the holes to 7/16, 1/2 then oops! My prop would ventilate and not even plane the boat out. If you get close to good performance and want just a little more, only enlarge one of the holes at a time and then test. Don't enlarge all three at the same time. It is surprising how 1/16" enlargement will effect your hole shot. Worse case scenario, if you overdo it by making the holes too large take your prop to a machine shop and have it prepped for the Mercury PVS plugs.<br />JD

 

[TwoBallScrewBall]

Re: i drilled holes in my prop, guess what happened?

Thanks for the advice. Definitely trying 7/32" or 1/4" holes this weekend... <br /><br />Cobra - Yeah when I got the boat it had a 13X15 on it. Serious holeshot but it was over 5500RPM WOT so I went to a 14X17, got it to about 4800RPM with still a very good holeshot. Went to the 19, hit 4400Rpm wide open and picked up a few MPH, but the holeshot went down the toilet. If I can get the 17P holeshot with the 19P top speed I'll be a happy person.

 

[TwoBallScrewBall]

Re: i drilled holes in my prop, guess what happened?

Can someone explain to me why the hole is behind the blade instead of in front of it? It would seem that if you put the bubbles in front of the blade it would help more. I am not saying that is the better way because I'm not an engineer, it just makes more sense to me. I'll be following the diagram, just wanted to know the "why" behind it.

 

[phatmanmike]

Re: i drilled holes in my prop, guess what happened?

i put my holes equally between the two blades(x3) and about a 1/2 inche from the edge of the prop, by the gearcase...day and night difference. boy do i love this forum!

 

[TwoBallScrewBall]

Re: i drilled holes in my prop, guess what happened?

So it does not really matter where they are as long as they're spaced evenly? I did it last night, followed the diagram exactly so they're about 5/8" behind the front leading edge of the blade on the hub, 5/8" in from the edge. Going to dump the boat in after work today for some fluke fishing so I'll see what difference it made.

 

[stsmith]

Re: i drilled holes in my prop, guess what happened?

This sounds like a good answer to my problem. However it does not state how deep to drill the holes. Any suggestions?<br /><br />Smitty

 

[TwoBallScrewBall]

Re: i drilled holes in my prop, guess what happened?

The holes go clear through the hub. <br /><br />I started off with 1/4" holes yesterday. Like Mike said, night and day difference. My 19 footer is now planing faster with 3 people in it than it did with just me alone. I'm happy! <br /><br />I highly recommend this to anyone who needs holeshot help. Saved me from buying another prop!

 

[phatmanmike]

Re: i drilled holes in my prop, guess what happened?

I highly recommend this to anyone who needs holeshot help. Saved me from buying another prop!

... i love a story with a happy endin' !!!!!!!

 

[TwoBallScrewBall]

Re: i drilled holes in my prop, guess what happened?

Update, I upped the hole size from 1/4" to 5/16" and tested it out yesterday. Getting even better, really pushes me back in the seat now when I get on the gas. And I keep my good 19" pitch top end speed and WOT. Pretty much like a poor-mans torque shift, the out of the hole that my 14X15 had with the WOT and cruise of the 14X19. From 'no wake' speed, it takes 3.5 seconds to plane out completely and not much more than that to be at full speed, whereas before the vent holes were there it would really really drag out of the hole with this prop. Going to stick with the 5/16" holes unless I get another spare prop to experiment on. Want to avoid what happened to JD...

 

[Snowdrggn]

Re: i drilled holes in my prop, guess what happened?

Steve Huminski: <br /> The holes are drilled behind the blade because that is an area of negative pressure when the prop is spinning, thus "pulling" the exhaust gasses out through the holes. If the holes are drilled too close to the front face of the blade, the pressure is high enough to restrict the exit of the gasses, thus defeating the purpose of drilling the holes.....<br /><br />This modification works very well on small engines as well. I used it on the prop on my 15hp Rude on my 10 ft Zodiac inflatable. ( 32mph GPS, empty boat, full underwear!)

 

[Snowdrggn]

Re: i drilled holes in my prop, guess what happened?

Should have mentioned that the boat, motor, and fuel only weigh 155lbs!

 

[Scaaty]

Re: i drilled holes in my prop, guess what happened?

Originally posted by Steve Huminski:<br />[QB] Isn't this dangerous from a balancing perspective?<br /><br />No. We did this on race boats back in the 70's

 

[Scaaty]

Re: i drilled holes in my prop, guess what happened?

I remember back then (1974 Switzercraft, 150XS Merc shortshaft, surface prop) running a 28 inch pitch Stainless 2 blade with no "Thru-hub" at all. Fun boat that really got the girls with a rooster tail better than a jet pump, only REAL!

 

[Dave Abrahamson]

Re: i drilled holes in my prop, guess what happened?

If I decide to try this,(1983 Johnny 90 hp 1975 16.5 Wellcraft Airslot),can the procedure be reversed? I don't have a welder to reseal the holes, so what would be another option to plug them up? Also, does this raise the wot rpm's?<br /><br />Dave

 

[DJ]

Re: i drilled holes in my prop, guess what happened?

Dave,<br /><br />

Worse case scenario, if you overdo it by making the holes too large take your prop to a machine shop and have it prepped for the Mercury PVS plugs.<br />

Should not effecrt top speed, at all.