prop ventilation holes

[rudeafrican]

I have just read an article on prop ventilation where they recommend drilling holes in the prop hub at the base of each blade to allow exhaust gasses to swing the prop. According to the article, this increases hole shot. <br />Here in South Africa we launch our boats off the beach through some serious breakers where holeshot is of utmost importance. Has any body tried this method and does it improve holeshot noticably?<br /><br />Thanks guys

 

[Bear]

Re: prop ventilation holes

Check these:<br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=17&t=002637 <br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=17;t=000740

 

[rudeafrican]

Re: prop ventilation holes

Thanks Bear. I'm gonna give it a bash and see how she runs.

 

[MGuckin]

Re: prop ventilation holes

Prop Venting

 

[Kenny Bush]

Re: prop ventilation holes

Yeah Rude Afro, It does help on my 23 footer. Basically this method lets the prop spin more easily at start and slow speeds. As the boat gains speed, the holes blow less and less air bubbles in front of the prop, thus allowing the prop to get more bite with the engine rev'd up. Good luck.......BushCat

 

[ob]

Re: prop ventilation holes

rudeafrican, If you drill it insure that you drill the holes right at the leading edge of the blades on prop barrel.

 

[rudeafrican]

Re: prop ventilation holes

Thanks bushcat and ob.<br /><br />I've marked the spots for the holes (in line & +- 5/8 " down from the leading edge)and will drill tomorrow after work. Started raining here so I had to push the boat back into garage. Will go and play and try it out this weekend.

 

[Hooty]

Re: prop ventilation holes

When you drill, start small and work up. I also might start with just one hole. Some venting props have different size bushings that go in the hole to make them smaller. <br /><br />c/6<br /><br />Hooty

 

[rudeafrican]

Re: prop ventilation holes

Hi Hooty,<br /><br />By small do you mean 1/4"? I intended to work my way up from 1/4" to absolute max of 1/2", if that much. 1 hole I take as 1 hole on the whole hub or is it 1 hole per blade?

 

[Hooty]

Re: prop ventilation holes

One 1/4" hole per blade is a good starting place. Did you take a look at the "Prop Venting" link? Some good intel there.<br /><br />c/6<br /><br />Hooty

 

[ob]

Re: prop ventilation holes

rudeafrican, 1/2 inch is too big.I would start pilot hole with 1/8 inch and incerase up to 3/16 to 1/4 depending on the size prop we are taliking about.

 

[rudeafrican]

Re: prop ventilation holes

Yeah I did, that's what convinced me to take the plunge and drill the holes. Can always be welded up if it's a screw-up and on the other hand, if it works, something for FREE! I wonder why all props are not made as a standard with the ventilation holes? <br /><br />As I said in my original post, we here require top class hole shot and are not too worried about top end. If I see a 12 foot breaker developing in front of me, I need to run and run fast, considering it's only a 16 foot deep V!

 

[rudeafrican]

Re: prop ventilation holes

Hi ob,<br /><br />prop size = 11 3/4" x 17 pitch on a 40 hp 'rude. I run twin motors on a 16' deep v hull. I also think 1/2" might be too big that's why I will increment in small steps

 

[DJ]

Re: prop ventilation holes

rudeafrican,<br /><br />A 17" pitch prop. seems like an awful lot for a 40. You must have a real light boat.<br /><br />Do you have any idea how many rpm's you are turning?<br /><br />Just checking.<br /><br />Let us know how your "ventilation" project works out.

 

[Dhadley]

Re: prop ventilation holes

Make sure its on the back (low pressure) side of the blade. Holes in front (high pressure) of the blade are for something else. Just follow the pics the guys gave you the links for.<br /><br />Good luck!

 

[radsrh]

Re: prop ventilation holes

Do you have a Mercury dealer near by, if you do they sell a line of vented props that take different sized plugs. They range from a solid plug to .280/7mm small .350/9mm medium and .470/12mm large if you would drill the hole size to match there plug size you would be able to try a varity of different vent holes for the price of the rubber plugs and if you do not get any improvment you could just push in the sold plugs the part numbers are solid 19-856622 <br />small 19-856622 28 medium 19-856622 35 large 19-856622 47

 

[rudeafrican]

Re: prop ventilation holes

djohns, the prop is only 11 3/4". The pitch is 17.<br />Dhadley, now you are confusing me bud, as far as I can tell from all the drawings shown on the linked sites, the holes are on the leading edge? <br /><br />Rad, those Merc props with the holes and different size plugs would set me back $500 each here in South Africa, unfortunately not an option for me at this stage. I'll have a look see if they'll let me have just the plugs, good idea there rad.<br /><br />Thanks guys

 

[DJ]

Re: prop ventilation holes

Rudeafrican,<br /><br />Sorry, I think you misunderstood what I meant. I meant 17" pitch. Still seems like a lot.<br /><br />Listen to DHadley. He knows a great deal about these things.<br /><br />Still curious about your top rpm and your application/results.

 

[rudeafrican]

Re: prop ventilation holes

Djohns,<br /><br />the 17 pitch was sold as a standard on that motor. I have thought about changing to a 15. My rpm's are 5500. I had another look at those drawings and I am eternally greatfull to dhadley for pointing out it is on the rear end of the blade. Amazing how you can look at a pic and see only what the mind wants to see. I am also very glad it started raining last night, preventing me drilling the holes in the wrong spot!

 

[DJ]

Re: prop ventilation holes

rudeafrican,<br /><br />Sounds like the rpm's are OK. Going to 15" won't hurt (I believe) those engines, they can easily stand a few more. Just because you have them, doesn't mean you have to use them. I would DEFINETELY try the "venting" before spending the $$$ for new props.<br /><br />You're right, DHadley knows about these things.<br /><br />Glad you caught it before you went to mining with your drill. <br /><br />Let us know what happens.