How Sharp Should You Make Your Prop?

[Deep_Blue]

My neighbor insists that a prop isn’t a prop unless it’s sharp. He takes his prop off his boat every few weeks and sharpens it with some kind of wheel for sharpening knifes. The way he keeps it, it almost feels like you could cut carpet with its edge! Does a sharp prop really make a difference? He laughs at how dull my prop is, saying "looks like you sharpened that thing with a sand blaster" yet my boats faster then his, lol!

 

[JB]

Re: How Sharp Should You Make Your Prop?

"yet my boats faster then his"

Answer your question?

Modifying the leading edge of the blade can seriously affect it's hydrodynamic performance. Unless the hydrodynamic profile is preserved performance will suffer.

Consider what the moving leading edge of the wing on some fast aircraft is used to slow them down.

 

[imported_Curmudgeon]

Re: How Sharp Should You Make Your Prop?

Props with "sharp" edges are ripe for damage from the least impact, not to mention the damages of edge flex when the blade gets too thin. You buddy could have to remove his lower unit for repair if he takes enough off the edges to unbalance the blades. Each to his own, I guess ... :/

 

[Dhadley]

Re: How Sharp Should You Make Your Prop?

I want that guy to be the set up guy on the next boat we race against.............

 

[jtexas]

Re: How Sharp Should You Make Your Prop?

oem manual includes the notation that the leading edge should be rounded the trailing edge sharp. Mercury warns that sharp leading edges cause cavitation.

wonder why he has to resharpen it so often? what's he cutting with it besides water?

 

[steelespike]

Re: How Sharp Should You Make Your Prop?

Did you ever see an old knife that had been sharpened
many times.Same thing is happening to his prop.
Not to mention the hydrodynamic performance problems he is creating.A light dressing of the edge to clean up minor nicks.No more.Anything requiring more
should be addressed by a prop shop.

 

[Vlad D Impeller]

Re: How Sharp Should You Make Your Prop?

I'll bet you that his prop doubles as a salad maker. d

 

[VADER8674]

Re: How Sharp Should You Make Your Prop?

sea weed salad sounds good to me

 

[Texasmark]

Re: How Sharp Should You Make Your Prop?

Well, My Ballistic HP features the fact that the leading edge of the blades are thin (sharp???) and the trailing edge is cupped and ground off square so that it is thicker at the rear.

I have mentioned many times on here what that prop has done for my boat so there is some confusing info here as to what's what.

Course you have to factor in the variables. Boats come in all sizes and shapes and with engine variables and all it depends on the installation what prop works best.

Mark

 

[Texasmark]

Re: How Sharp Should You Make Your Prop?

One more comment on this subject. I bought an alum prop with one inch LESS pitch and was a Hustler brand, advertised to be high rake, high perf and was cupped. The thing I did notice was that the forward side (leading edge) of the blade was much thicker than the Ballistic.

This prop cost me 6 mph and 600 rpm's over the Ballistic, even with less pitch where you'd think the rpm's would be higher. Don't know what to blame it on other than that thick leading edge.

So it must be liken to trying to swing a baseball bat through the water vs a kitchen knife. Much less resistance, hence more speed.

I do realize that a sharp leading edge could leave you at risk if you strike something, but if it's not a rock it may just slice right through it.

Just some thoughts.

Mark

 

[deejaycee_2000]

Re: How Sharp Should You Make Your Prop?

my racing boats all have really sharp SS props, we get them custom made here in SA from specialised SS engineers, and the are much faster than branded racing props that i have tried .... some racers say they are made sharper to cut through the sand as we race up all the way on the beach ... and almost on the sand in the surf, some beaches have a bit of kelp (sea bamboo) and apparently it helps to cut through them aswell .... that is what I have heard, my props are sharp but never really had issues ....

 

[Mark42]

Re: How Sharp Should You Make Your Prop?

Mark,

The cup on the prop will make a big drop in RPM over a non-cupped prop.

 

[walleyehed]

Re: How Sharp Should You Make Your Prop?

Big difference between sharpening the leading edge and having a thin blade with a "thinner" edge.
Truth be known, he's messing with the wrong side of the blade.......

 

[Texasmark]

Re: How Sharp Should You Make Your Prop?

Hey Mark, my man, I'm still 100 rpm's over my WOT MFGR # and am running the highest pitched prop I can buy.......other than a custom.

Mark

 

[Texasmark]

Re: How Sharp Should You Make Your Prop?

When I get to it, I will get my wife's digital camera and take some pics of this tin lizzie thing. For what it's worth, when I am hooked up and buzzing along, the spray from the hull touching the water comes out at the corners of the transom, not before.

Think about that. When's the last time you had, saw, or rode in a stock, production boat, with no fancy amenities (trim tabs, jack plates, or whatever) that could run 50+ mph in July at 900ft altitude, 17' boat, 90 hp stock engine, and the spray was at the corners of the transom, not ahead of it......with a piece of crap Ballistic prop doing the propulsion.

Mark

 

[dakotashooter2]

Re: How Sharp Should You Make Your Prop?

I'm more concerned that my prop has a fairly "smooth" edge with no major dings. If he is running in a manner or places that require him to "sharpen" his prop every couple of weeks I'd say the prop is going to be the least of his problems.
FWIW I doubt that he would probably even notice the difference.

 

[Texasmark]

Re: How Sharp Should You Make Your Prop?

Bumping it up. Waiting for takers on my piece of crap tinlizzie and Ballistic. 8)

Mark

 

[JoeMan]

Re: How Sharp Should You Make Your Prop?

wonder why he has to resharpen it so often? what's he cutting with it besides water?

Did you ever see the Seinfeld episode where Kramer loans his lunchmeat slicer to Elaine and she trims the heels on her shoes? Maybe something like that.

 

[Texasmark]

Re: How Sharp Should You Make Your Prop?

How about this. Take a baseball bat and a michette. Drive both through the water with your bare arm's muscle. Which one goes through the easiest?

Rest my case.

Mark

 

[jtexas]

Re: How Sharp Should You Make Your Prop?

When you drove the machette through the water, did you hold it so that the blade was aligned with the direction of travel?

If so, then you have proven that a prop with 0" pitch should be as sharp as possible.

Try paddling your boat with the machette and the baseball bat.