in the real world, do these work?

[not enuf toys]

props with the holes by the leading edge of the blade.

now i know the idea is for exhaust to come out there by the leading edge of the blade to allow the blade to spin faster (for just a split of a split second) before it bites the water.

but on engines that are not 1 million horse power, does the exhaust actually come out there? wouldnt air take the easiest route? through the large hole in the prop? lol

please let me know the truth behind this.

 

[H20Rat]

Re: in the real world, do these work?

yes it does work, and yes, most of the exhaust goes out the hub. One thing you have to remember is that it isn't exhaust pressure that is pushing gas out there, it is being sucked out. That is naturally a low pressure area, so there is no lack of gas...

And the effect can be fairly pronounced depending on the prop and boat. its more like a 2 speed transmission, and you can even tell sometimes when you get enough water speed to overcome the ventilation.

 

[not enuf toys]

Re: in the real world, do these work?

interesting

i would have thought the majority of the benefits would have been with whole shot not mid range...

does anyone know a good link that shows this in action?

 

[willamettejeff]

Re: in the real world, do these work?

My original 17p Turning Point prop did not come with the ventilation holes so I know how it performed prior to drilling the holes myself. Really improved the hole shot on my 14' boat and was especially noticeable with 4 people on board. Bought the second generation ones in aluminum in both the 15p and 17p. The 17p aluminum and later one in stainless both came the ventilation holes already there. Both perform beautifully with great hole-shot on my 14' Fiberform and now 16' Larson boats. Added the ventilation holes to my 15p one and again really improved the hole-shot on my 14' boat, but have found on my 16' heavier boat the vent holes are apparently too big. The motor wants to spin up to 5000 rpm just before the prop catches good enough to really get the boat moving along. RPMs will drop off greatly when this occurs with boat practically leaping onto plane. Overall hole-shot is still really good, but just a little disconcerting to have the rpms go up that much initially. Going to fill holes back in try some smaller ones. If your going to do it yourself, it is best to start out with smaller holes (~ 1/8" and work your way up). Mine, I think are 1/4".

-- Jeff

 

[not enuf toys]

Re: in the real world, do these work?

My current prop already has these so there won't be any self improvements made

Just wasn't sure

 

[craze1cars]

Re: in the real world, do these work?

I assume based on your photo and sig you're asking about your sterndrive? Realize that a torquey 4 stroke engine like yours....particularly if it is a V6 or V8, will see far less benefit from these holes than a high-winding low-torque 2 stroke outboard would (much like the gent probably has on his 14 foot boat who replied noticable gains). This is because a 6 or 8 cylinder 4 stroke develops substantially more torque at much lower RPMS than the 2/3/4 cylinder 2 stroke outboards do. At low RPMS a 2 stroke is essentially in a significant "bog" and it has a hard time coming out of it until RPMS come way up.

Allowing a few air bubbles to mix with water allows the prop to slip quite a bit, allowing the motor to spool up into a higher RPM range at a slower boat speed. Therefore the motor will be producing more power at that particular slower boat speed....and therefore the boat accellerates faster.

So don't forget many of the 2 stroke guys are spinning their motors at 6,500 rpms. And so when they take off at 1,500 or 2,000 they are producing very little power. Their peak power output is a far cry from your Rinker that is more likely making peak power down in the mid to high 4,000's and will almost never exceed 5,000....

4 stroke motors...ESPECIALLY sterndrives...make a LOT more peak torque very low, and therefore often don't benefit nearly as much from this "help." But that said, even a 4 stroke will show a little bit of benefit...it just won't be nearly as pronounced and obvious as the 2 stroke guys will experience.

 

[Tail_Gunner]

Re: in the real world, do these work?

I assume based on your photo and sig you're asking about your sterndrive? Realize that a torquey 4 stroke engine like yours....particularly if it is a V6 or V8, will see far less benefit from these holes than a high-winding low-torque 2 stroke outboard would (much like the gent probably has on his 14 foot boat who replied noticable gains). This is because a 6 or 8 cylinder 4 stroke develops substantially more torque at much lower RPMS than the 2/3/4 cylinder 2 stroke outboards do. At low RPMS a 2 stroke is essentially in a significant "bog" and it has a hard time coming out of it until RPMS come way up.

Allowing a few air bubbles to mix with water allows the prop to slip quite a bit, allowing the motor to spool up into a higher RPM range at a slower boat speed. Therefore the motor will be producing more power at that particular slower boat speed....and therefore the boat accellerates faster.

So don't forget many of the 2 stroke guys are spinning their motors at 6,500 rpms. And so when they take off at 1,500 or 2,000 they are producing very little power. Their peak power output is a far cry from your Rinker that is more likely making peak power down in the mid to high 4,000's and will almost never exceed 5,000....

4 stroke motors...ESPECIALLY sterndrives...make a LOT more peak torque very low, and therefore often don't benefit nearly as much from this "help." But that said, even a 4 stroke will show a little bit of benefit...it just won't be nearly as pronounced and obvious as the 2 stroke guys will experience.

Well said..but it still works