how to plug exhaust relief holes in SS prop?

BF

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One of the spare props I have lying around is a rapture (I think?) 3 blade SS that has 3 exhaust relief holes drilled thru the hub about 1/3 of the way back from the front edge. Looks like it was factory done. I bought this used years ago, and have tried it on a V150 I have but it didn't have enough pitch for that rig. I'm thinking it might make a good water sports prop for my 3.0 mercruiser. Aside from not having enough pitch for the other rig, it seemed to get no bite out of the hole (mega ventilation). How would one plug those relief exhaust holes? I'm sure they must make nice little rubber or plastic plugs for those, but I can't seem to find them. Maybe a blob of silicone gasket maker would do the trick... or a pop rivet.... but anyone know of a more refined solution?
 

WIMUSKY

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I'm not positive, but I don't think Rapture's came from the factory vented. And by your description the venting may be in the wrong locations. Below is where the vents should be.......

 

Chris1956

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Rapture props are vented from the factory. I used one on my MerCruiser 4.3LX. I plugged the holes with a small stainless oval head screw and nut. The oval head fit the vent hole just about flush. The nut was on the inside of the hub. Start the nut onto the screw, and then cut the screw to length.
 

BF

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OK... screws/nuts sound like a good option... do you know if rapture made plugs for those? Or tube inserts that would allow you to make the size of the holes smaller? I seem to recall reading literature about some prop having that... BTW, I might be wrong about them being 1/3 the way from the front... working from memory. But they are towards the forward side of the prop.

thx for the replies
 

midcarolina

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Follow this link below............. Iboats probably sells them too, but I didnt take the time to drill down thru the search.
 

Chris1956

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Rapture made plastic plugs for the vents. I never saw a way to reduce the size of the holes though.
 

Texasmark

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Curious as to why you want to plug them?

Their purpose is to unload the engine so that it can rev up faster under the stresses of the "hole shot"....getting the boat on plane. This allows you to have a prop with 2 pitches essentially. With the prop unloaded somewhat in the shot, it acts like a prop with somewhat less pitch...amount depends upon the size of the holes. lets the engine rev faster, gets you out of the hole faster (especially with high transom loads like I/Os and jump seats full of occupants) and on your way. Then once on plane, at some point the water pressure will seal them off, the engine will take on the load (you can hear/feel the revs drop) the boat picks up speed at the same throttle setting and you are running on the actual pitch.

On changing the size of the holes, I know plugs are out there with different hole sizes and no hole if you want to block them off entirely.

Mark
 

Chris1956

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Mark, I blocked them off when I used theRapture on my I/O. I thought the low end power of the MerCruiser 4.3LX was sufficient, and didn't want any slip. I unplugged the holes, when I put the same prop on my Merc OB. I thought the vents would allow faster rev up, and get into the power band sooner.

Just my reasoning. I am interested in the reasons the OP has.
 

BF

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Thx for the responses... I had typed and thought I had posted a thx to midcarolina for posting the link... but it must've vaporized... Now that I know the right name for them, I should be able to source them... Obviously my google search terms were not up to snuff...

As for Texasmark.... Chris basically has it...Here's the story.. I originally bought the prop to try on my 16' glastron CVX with V150 merc... I didn't like it on there. With the holes, it has massive slip out of the hole. The boat normally jumps on plane, so that wasn't a problem I was trying to fix. But I didn't bother plugging the holes then, b/c the prop didn't have enough overall pitch for that rig anyway... Oh well, I decided to put it on a shelf rather than sell... I've since bought a 17' I/O with 3.0 mercruiser... Has been great. Now the kids are bigger and doing more watersports, so I thought the 3.0 might do a bit better towing out of the hole by dropping some pitch. I haven't tried it yet, but I expect that the pitch of this might be good for this application, but I don't want it to blow out / ventilate like it did on my OB. I don't want to rev my 3.0 anything like my V6 2 stroke (which I often spin like a weed whacker :) )... so I'll start with the holes plugged first.... That's the rationale (and is pretty much what Chris figured)
 

Texasmark

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You are on the right track. The hole size is to be varied to suit your rig. You want (my opinion/experience) around 500-1000 rpm increase due to slip when you firewall it in the hole. Too much rpm increase, holes are too large and wasting thrust making for a slow hole shot with the engine on the other end of the power spectrum....in the over rev mode vs the lugging mode. Not enough increase and they aren't doing you much good.

If you keep it firewalled through the whole plane out process they should seal off shortly after your bow comes back down. In rough water conditions they CAN add to unnecessary ventilation but tucking the trim somewhat usually corrects that.

On vent holes vs a shallower pitched prop with water toys it's a toss in my opinion. What difference does it make if the engine has increased revs due to porting or a shallower pitched prop. However with porting you can play with your toys and when it's time to load them up and go home, you have the higher pitch to get you home faster and cheaper.

Mark
 
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