High thrust propellers

[Mikem]

Is there any advantage in swapping out the existing three blade prop on our Mariner 9.9 hp two stroke for a "hight thrust" four blade prop. This 9.9 moves the C-25 at six knots as is. Would the high thrust move it any better? Any idea what the price might be?

Also, there is a an alternator/battery charging kit available. This is a 1998 motor that runs like a top. Is that worth the effort as well...maybe $500 if I had it done.

thanks

 

[jimg]

High Thrust Prop

A "high thrust" prop simply has less pitch, and (maybe) larger diameter. There is not much room on that motor for a much bigger prop. What less pitch does is essentially "slip" more, allowing the engine to rev higher and reach the engine's rated power more easily. It will also make more noise and use more gas. I had one for a while and went back to a stock prop. 6 knots is pretty good for a C25, and I would bet that is not even at full throttle.

Also, I don't think you are going to find a 4 blade prop for that outboard.

 

[Squidd]

Before you spend $500 on a "kit"...??

Get a voltmeter out and check the wires coming out from under the flywheel (near the front) probably 4-5 wires.... Check the "red" one (+) against the block as ground (-) Looking for 12.5 to 14 vDC (it will vary with motor speed)

More than likely you already have a low amp charging system on the motor (6 amp or so) and the "Kit" will only get you up to 10 amp or so...

But that would be at 3/4 to full throtle, so the low pitch prop may yet be an asset...

 

[Merlin Clark]

I went with the high thrust prop (3 blade) for my Tohatsu 6hp.
The trade off is better manuverability, starting and stopping my boats 5k lbs; and the downside is as Jim stated, more noise and fuel because of higher RPMs. Old 7.8" (dia) x 8" (pitch) and new 8.375" (dia) x 6" (pitch). I think a 8" x 7" would be a happy medium. I may take my old prop and see if it can be re-pitched to 7".

 

[Mikem]

Thanks to all. I will check the wires coming out from under the flywheel and go from there. I should be content with the 6 knots.