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Author Topic:   Ideas for plugging vent holes
Perry posted 02-18-2003 12:54 PM ET (US)   Profile for Perry   Send Email to Perry  
A bought a scond hand Rapture prop and it appears the previous owner drilled the vent holes larger than original size. With current pitch (15") I dont need the extra slippage and want to plug the holes. Any ideas on how to do this? Epoxy?
where2 posted 02-18-2003 10:43 PM ET (US)     Profile for where2  Send Email to where2     
Drill them out until they are the size of Mercury's variable vent system, then get a set of snap in plugs. With the snap in plugs, you can tune to your liking.

Or, I've always wondered whether a properly sized rubber grommet would stay in the holes...

There's always MarineTex or JB-Weld if you want to fill them totally.

captbone posted 02-18-2003 11:21 PM ET (US)     Profile for captbone  Send Email to captbone     
The merc vent idea sounds like a darn good solution.
Perry posted 02-19-2003 02:35 AM ET (US)     Profile for Perry  Send Email to Perry     
Hey where2, that is a good idea. I think I will visit the Mercury dealer and buy a set of snap in plugs.
Bigshot posted 02-19-2003 08:47 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
take the prop with you.
hooter posted 02-19-2003 09:19 AM ET (US)     Profile for hooter    
Couldn't you just ask the guy that "turns" (repairs edges with new weld-on stainless, re-cups and buffs out) your prop to fill in the holes next time you bring it to him? Doubt he'd charge extra.
where2 posted 02-19-2003 12:20 PM ET (US)     Profile for where2  Send Email to where2     
One of these days, I'm going to haul my 14.4v cordless drill with me and continue my prop vent tuning. I always figured if I got "too big", I would try rubber gromets, or merc's vent plugs. The holes merc uses are probably 1/2" or 5/8"... Definitely, buy the plugs before you drill the holes larger.

I noticed the Yamaha 225/250hp engines at the show in Miami had rectangular notches rather than round vent holes. The notches were roughly 1/2" wide, and stuck 3/8" back from the gearcase. Obviously, larger vents do something...

lhg posted 02-19-2003 05:00 PM ET (US)     Profile for lhg    
Michigan Wheel's Rapture props do not come with vent holes, from what I have seen. Drilling holes in one of those large enough to accomodate the Mercury vent fillers is not going to be easy! I think 5/8 is required.

Mercury's first generation of vented props had the rectangular holes. There is a solid rubber filler available for those, if needed.

Perry posted 02-19-2003 06:10 PM ET (US)     Profile for Perry  Send Email to Perry     
According to the Michigan Wheel web site, the Rapture does come with vent holes. The 1/4" holes on the prop I have were drilled to 5/16". 5/8" may be kinda big to drill out to fit snap in plugs. I'll think it over first.
Seabrook posted 02-20-2003 01:20 AM ET (US)     Profile for Seabrook  Send Email to Seabrook     
Do not worry about the size of the vent holes unless your prop aerates too much when you first take off. Once you get going, the size of the vents, or whether or not you even have vents, will not affect your RPMs. The vents only are only effective in the first second or two during take off as the holes vent the exhaust air so that the prop can slip to get the RPMs up to get you on plane faster. Once you get much forward momentum, the exhaust leaves via the rear of the prop just as if you had no vents.

If you problem is on the initial take off, then I would have a prop shot cap the holes for you. I am not sure that Marine Tex or the like would work to cover large holes.

Perry posted 02-20-2003 12:25 PM ET (US)     Profile for Perry  Send Email to Perry     
I was told by a number of people that the vent holes cause slippage up to 25 mph. Beyond that speed, water going over the hub seals the holes. This would cause the boat from keeping on a plane at lower rpm's. I'll try the prop and compare the difference between my non-vented 15" pitch Solas and the 15" pitch Rapture before I make any modifications.
Seabrook posted 02-20-2003 12:43 PM ET (US)     Profile for Seabrook  Send Email to Seabrook     
I am interested to see how your test turns out.

I do not think it is the water going over the hub sealing the vent holes that stops the exhaust gasses from exiting the holes and causing aeration (slippage). I think it is that the exhuast gas will find the easiest path to exit. At rest, a portion will go up and out the vent holes. Once you start moving, the momentum of the boat (and it does not take much) will push the prop past the exhaust and the easiest path out is through the hub. This is my opionion anyway. Let me know how your test goes.

lhg posted 02-20-2003 01:33 PM ET (US)     Profile for lhg    
It has been my experience with Mercury's vented props that design and size of the vents is important. On my 25 Outrage, I have the older style (circa 1990) large, square, non-adjustable vents in my Laser II props. These do give slippage up to about 25 mph. But these are the old design. Mercury has since improved this design with their new adjustable vent design, and they greatly reduce slippage at planing speeds, where it clearly is not needed. I have this style on my 18 Outrage, and they are superior. The current style of round holes, about 3/8" in diameter, now used by most manufacturers, does not allow much slippage once plane is achieved.

Merc's performance props cost a little more, but you get what you pay for, and one of these features is their patented, adjustable vent system.

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