New Motor on Pontoon - need to get the prop figured out!

[brownb01]

Hello ? I?m looking for some help getting my pontoon setup with the right propeller. It?s an 18? Bass Buggy with a new Suzuki 90Hp. The place that installed the motor put a 13.75 X 15 4 blade on it. The problem with this propeller is my RPM?s are limited to about 5600 and with weight on the boat the prop is either ventilating, cavitating or bouncing out of the water ? I?m not sure which. With only me on the boat it seems to do fine other than the limited rpm?s. (should be able to get to 6300)

I happened to have a Black Max 14 X 15 3 Blade that I tried. With this one I get too much RPM?s and the ventilating or cavitating is worse and happens with the throttle instead of when it?s bouncing around on the water. I can slowing ease into the throttle on this one and it seems to do ok ? other than the RPM?s would get too high.

A few things I was thinking about trying ? going back to a 4 blade and going to a 14 X 14. I was thinking a larger diameter to prop to fix the coming out of the water feeling (seemed better with the 14? that I tried), and dropping in pitch to get the rpms?s up. However, is going up in diameter going to counter the drop in pitch? If I go to a 14? should I drop the pitch more than 1 degree? Maybe a 14 x 12?

I?m open to any suggestions ? also thinking maybe the motor needs to drop down some.

Appreciate the opinions ? thank you!

 

[ondarvr]

Pontoon boats can have odd issues with ventilation, so it may take a little work to dial it in. Normally lowering the motor a hole or two will make a big difference, then possibly going with a lower pitch 4 blade prop. Diameter will make a difference, but not a huge difference.

 

[Scott Danforth]

you will need to raise and lower the motor as indicated to dial in the height prior to worrying about the prop. also, if you are testing alone, the motor will run different with more people on board. you will want to test with various people on board as well. too high and you ventilate, to low and you plow and dog the motor.

 

[ahicks]

My first move, from what you've written, would be to drop the engine. So we're agreed there. Whatever it takes to stop the venting in rough water. Try one hole, and go to 2 if that doesn't work.

Regarding the prop, that's going to depend. If you're just cruising, with no plans to pull a tube or anything, the 4 blade you have will keep the rpms down, for less noise, better mileage, and possible longer engine life. However, if looking for max performance (who would put a 90 on an 18' boat if they were NOT looking for performance?), I agree with your thoughts there as well. Get the engine turning right at max when lightly loaded (1-3 people).

That Black Max prop could likely be re-pitched by a good repair shop that understood what your existing and target rpms were.....

 

[Sea Rider]

OB sits way high on transom. Drop 2 holes down, load must be well balanced on deck, set trim to neutral (90?) test on flat calm water cond till prop stops ventilating, if keeps ventilation drop one more hole down and so on..

Happy Boating

 

[brownb01]

Alright - I'll drop a hole this weekend and test. I keep this boat on a lift - is there an easy way to lower it? Or do I need to pull it the boat on a trailer and use a jack of some sort to lower it down a hole?

 

[Sea Rider]

You can do that while boat sits on a trailer, will need a small crane or many hands to hold OB in place while loweing it down. If upper swivel bracket is already resting even on transom will need to chop transom down say 1" or install a jack plate. How many holes are there left to lower OB down ?

Happy Boating

 

[ahicks]

Is the lift in shallow water? If so, and you can find (draft/bribe) a couple big friends to give you a hand for a few minutes, you could block up the engine and use the lift to raise/lower the boat while your buddies are carefully balancing that nearly 400 lb engine......

Trailer method is similar, using the tongue jack to raise and lower the back of the boat.

OR, play it safe and run it to a marina or somebody you know with a fork lift or front end loader.....

 

[brownb01]

Thanks for the feedback. I'll go the trailer route. I've got some jacks that will work and the bottom two holes on the motor are slots....so shouldn't have to balance much.

 

[ahicks]

Perfect!