Prop drilling, do I understand this?

[kxracedad]

Been reading a lot about this, the picture I have seen in several places doesnt make a lot of sense to me.

From what I have read, it looks like you drill a 3/16" hole about half an inch in front of the leading edge of the prop at the base of the blade on the exhaust side. Is this correct?

motor is a 115 mercury, about 1984

 

[Bifflefan]

Re: Prop drilling, do I understand this?

Where are you reading this?

 

[will941s]

Re: Prop drilling, do I understand this?

I've seen "turbo" props with the hole cast into it to let exhaust escape until the bulk comes through. Allows for faster gains in rpm's and they say when the prop catches you kind of blast out of the hole. Due to the prop grabbing at higher rpm's. I guess you could drill a hole in your prop and get the same effect, I don't know what HP range it's more effective with though. I've only seen the props on larger OB's. The hole is usually infront of the blades though, between the blade and the lower unit. I would think the exhaust tunnel around the hub would be changed on those props somehow though. Probably not the same design as a regular prop. Maybe someone who owns one of the props will chime in and give the basics about it and how it works.

 

[CharlieB]

Re: Prop drilling, do I understand this?

Many props are 'vented' to allow a measured amount of cavitation, the blades cannot get a full 'bite' on the water and allow the motor to quickly speed up into their horsepower range.

As the boat begins to climb up onto a plane and boat speed begins to rise the water flow over the hub 'seals' off the holes, allowing the blades to get grip. Engine speed drops almost like shifting into 2d gear, the motor accelerates the boat on up to WOT speed.

Mine works GREAT.

Search the prop forum for better instructions, check out the props at your local prop shop. You want to be CERTAIN of position and size before you start poking holes in your prop.

 

[Rscardina]

Re: Prop drilling, do I understand this?

thats sounds pretty cool... anyone know what kind of pressure get exerted on the transom??? any more or less that no holes..

i'm asking becasue it seems the engine can get higher rpms beofre tghe hole shot so i would think its a good kick when she catches...

 

[emckelvy]

Re: Prop drilling, do I understand this?

We drilled ventilation holes in our props years ago, works like a champ to get the smaller motors up in their powerband quicker. Especially with skiers, etc where you've got a real heavy load at takeoff.

Just be careful not to drill the holes too big. I did some 3/8" holes on an old 100hp and it slipped like crazy! 3/16"-1/4" is usually big enough to get the effect.

I've attached some info that should help.

Have Fun.........ed

 

[kxracedad]

Re: Prop drilling, do I understand this?

thanks for the info

do you have that attachment in a larger version or pdf?