Prop question for DHadley

[mjash]

DHadley,<br /><br />How much slip should I expect out of a michigan ss cupped prop. 13 1/4 x 17<br /><br />Thanks

 

[Dhadley]

Re: Prop question for DHadley

Depends on the given hull & set up but we look for something around 12% or so on a recreational rig.

 

[misterguru]

Re: Prop question for DHadley

Hi DH, I don't want to invade this guy's thread, but I have a prop question for you.<br /><br />I have a 40hp Mercury 1977 402(I know its the wrong engine type for the forum, but you sure helped me fix my buddy's Evinrude carbs! Thanks again!). My 40hp is on a VERY heavy little fishing boat... lots of plywood, carpet and my fat butt.<br /><br />It has a factory 13p x 10.75" 3 blade prop (part 48-56236A1 13R) and only runs 19 mph at WOT at 4200 RPM and drops to 3900 RPM with my wife and daughter added.<br /><br />A month ago I thought I had researched this enough and bought a 4 blade Michigan Vortex 10p x 12 from iboats.com Well I dropped 100 RPM, just the opposite of what I thought would happen. I thought 13p to 10p = 600 RPM increase? But 4 blades... design? I dunno!<br /><br />I assume I need to go with the lowest pitch available... it's probably too much weight for the motor, but I am thinking the closer I can get the engine to the 5000-5500 rpm range it will be stronger, more efficient, etc.<br /><br />I see the Hustler 8p x 12.5 is just $70 on sale.<br /><br />Thanks in advance!

 

[martinphantom]

Re: Prop question for DHadley

But you increased the size from 10.75 to 12-this takes more power to turn. Keeping the same diameter would have been better. Also changing from a 3 blade to a 4 blade was a wrong choice-takes more ummph to turn. Just my opinion.

 

[Dhadley]

Re: Prop question for DHadley

A 4 blade will, generally, rquire more height (X dimension). Where is the AV (cavitation) plate now in relation to the bottom of the hull?

 

[misterguru]

Re: Prop question for DHadley

Ahhh... well I have a Tiger Shark hydrofoil on there too... that may have affected the 10p 4 blade performance.<br /><br />I should have mentioned that DETAIL, eh? <br /><br />A friend just loaned me a 12p factory prop with a couple of gravel scars on it... the belt sander says, "Hello."<br /><br />I will try it.... anyone have a 10p 2 blade around?<br /><br />Thanks.

 

[Dhadley]

Re: Prop question for DHadley

Any kind of a tail will hurt if the motor is too low. <br /><br />Wheres the AV plate????

 

[misterguru]

Re: Prop question for DHadley

I can't answer DH: I will take a measurement this weekend.<br /><br />I do know it pitches a small rooster tail up about 12-18" I will take the hydrofoil off and see if the performance is better.

 

[Dhadley]

Re: Prop question for DHadley

Everything youve mentioned indicates the motor is too low. Consider raising it. That will reduce drag and allow for better efficiency.

 

[misterguru]

Re: Prop question for DHadley

OK DH!<br /><br />I suppose I will try 1" increments? I can probably go up to 3" without getting "out of bounds"