RPM ? again

[MinUph]

Hello again,
I started asking about this and have more information to share while asking again. My toon is 18' 40hp Honda, Runs WOT at 4500 RPM. It should run at 55-60 according to the book. I have the engine running well, the prop that is on there is 12.1 x 9. I would like to pickup another prop and want to gain the 1000 rpm if possible. We run mainly with 2 people. 4 people changes the WOT rpm a little maybe 4000 max. But I want to work on 2 people as a standard load.
I have looked at some props and don't really know what way to go. I know dropping a pitch will help but what about the diameter? The props I've seen are no 12.1s.
I suppose I could go to a prop guy and have him help but you people are so much more fun and available in the evenings

 

[ranger 45]

Re: RPM ? again

Is that the right speed it is supposed to run? I think that speed is way to high. Mine is a 22 ft with a 115 and it goes 25. I think maybe you are expecting to much speed. I had a Lowe Roughneck 16ft with a 40 Yamaha that wouldn't go that fast.

 

[flycaster]

Re: RPM ? again

Is that the right speed it is supposed to run? I think that speed is way to high. Mine is a 22 ft with a 115 and it goes 25. I think maybe you are expecting to much speed. I had a Lowe Roughneck 16ft with a 40 Yamaha that wouldn't go that fast.

He is talking about RPM'S and not SPEED.

 

[EGlideRider]

Re: RPM ? again

I would try a 9 X 9

 

[MinUph]

Re: RPM ? again

I would try a 9 X 9

Thanks. I will see what I can find in a 9x9

 

[The Rooster]

Re: RPM ? again

"MinUph", I don't remember your first post on the subject, but, have you already checked the height of your engine, and/ or verified your tack is reading correctly ?

 

[MinUph]

Re: RPM ? again

Hey Rooster,
At what height should my motor be? And no I am figuring my tach is correct. Do I need to buy another to test mine?
Thanks.
Paul

 

[The Rooster]

Re: RPM ? again

Hey MinUph, just curious if your anti ventilation/ cavitation plate, just above your prop is riding about level with the water line while at normal cruising speeds, or if you see it well below the surface of the water? Normally should be close to the surface while cruising. As far as the tach, I ran into a similar situation years ago with a motor I had. I believe there was a button on the back of the tach I had to push or adjust so it would be calibrated to the correct hp motor I was running at the time. But having said that, other , more knowlegeable forum members need to chime in on this.

 

[EGlideRider]

Re: RPM ? again

The height of the motor will not cause the R's to be too low and it's very unusual to see a tach not accurate unless it is a new install. Go with the 9 pitch.

 

[Silvertip]

Re: RPM ? again

Pontoon engines run in very turbulent water so they should be mounted full down on the transom. Besides, this is a 40 HP motor. 12 inch diameter props on that engine is probably a planing hull prop (as for a "V" hull. That is to much diameter for pontoon use. As suggested, drop to a more useable prop which (without checking lower unit gear ratio) would be the 9x9 as suggested. Remember also -- that just because you increase RPM, you do not automatically increase speed. The reason for the increase in RPM is because the prop is taking a smaller bite on the water so it takes more RPM to maintain the same speed as before.

 

[MinUph]

Re: RPM ? again

I can't seem to find a 9x9 anyplace. Even at Honda.com.

 

[BatDaddy1887]

Re: RPM ? again

....try the outboard salvage yards sticky.....

http://forums.iboats.com/showthread.php?t=438822

 

[MinUph]

Re: RPM ? again

Well after figuring I would never find a 9 x 9 prop I wrote to Michigan Prop and they came up with this.

Propeller Dimensions: 11-1/2" x 8"
Propeller Series: Vortex
Propeller Blades: 4
Propeller Material: Aluminum

What do you guys think?

 

[crb478]

Re: RPM ? again

Well after figuring I would never find a 9 x 9 prop I wrote to Michigan Prop and they came up with this.

Propeller Dimensions: 11-1/2" x 8"
Propeller Series: Vortex
Propeller Blades: 4
Propeller Material: Aluminum

What do you guys think?

I would go for that one. You are trying to gain about 1000 rpm so that would be about right. Also I like the way four bladed props work on pontoons, especially when going in reverse.

 

[MinUph]

Re: RPM ? again

Just ordered one from here along with the hub for my motor. Will keep the group posted of the outcome. I'm excited to see the difference. I have experienced a properly propped boat before from one prop to the next and it can be amazing to difference in performance. I'm not looking for a speedboat here just a properly working boat motor setup.

Thanks for the help people.