1989 24' suncruiser pontoon 1999 35 hp Johnson prop question

[Blujay96]

I have a 3 blade prop that is slipping. Wondering about going with a 4 blade prop. My current prop is 10" with a 13" pitch 3 blade. It is running at 5500 rpm wot. Which is right within where it should be. Wondering what would be the correct pitch in a 4 blade. Also what would I lose in speed. I hit a top speed of 16 mph right now. I don't want to lose much speed

 

[steelespike]

Re: 1989 24' suncruiser pontoon 1999 35 hp Johnson prop question

delete

 

[steelespike]

Re: 1989 24' suncruiser pontoon 1999 35 hp Johnson prop question

A 12" 4 blade should maintain rpm and may hold speed or improve speed with a slight decrease in slip.
I think your having "ventilation", prop fouled with air. Slip usually refers to the prop hub slipping in the prop.
Have you tried lowering the motor?

 

[Blujay96]

Re: 1989 24' suncruiser pontoon 1999 35 hp Johnson prop question

Steelespike why delete did I do something wrong??? Thanks for the information. I marked the hub and prop and went out. The hub is slipping. I have not tried lowering the motor. The cavitation plate(?) is level with the bottom of the transom tub. I have lost traction on the water going over a wave once so maybe might be a combination.

 

[steelespike]

Re: 1989 24' suncruiser pontoon 1999 35 hp Johnson prop question

Delete is just a duplicate of my post that either my computer or the iboats system causes if I don't double check which post I'm operating in.

 

[Blujay96]

Re: 1989 24' suncruiser pontoon 1999 35 hp Johnson prop question

Ok thanks

 

[jestor68]

Re: 1989 24' suncruiser pontoon 1999 35 hp Johnson prop question

Since the typical 4 blade prop(same material) runs about a hundred rpm lower than the same pitch 3 blade, I agree that a 12 pitch 4 blade should not lose any rpm.

The extra blade area will produce more thrust per revolution and likely not lose any speed. It might actually go faster.

One of the 4 blade prop's attributes is resistance to ventilation. Maybe that's why Mercury bills their Spitfire 4 blade prop as their "best pontoon prop".

Running your motor at less than max rpm (5200-5800) will help it last longer and use less gas.

 

[Blujay96]

Re: 1989 24' suncruiser pontoon 1999 35 hp Johnson prop question

Ok I ordered up the 4 blade 12 pitch. Should be here tomorrow. Hope to try it out this weekend.

 

[Blujay96]

Re: 1989 24' suncruiser pontoon 1999 35 hp Johnson prop question

Well went out today. 5400-5600 rpm wot. 15 mph. So not bad there. I lost traction on the water once. Here is a picture of the height of the motor.

 

[steelespike]

Re: 1989 24' suncruiser pontoon 1999 35 hp Johnson prop question

Occasional venting on a pontoon is not unusual if its a pain you could try lowering the motor.
If it solves the venting it might also reduce your slip numbers enough to maintain speed easier.
A slight tweak of the trim up or down may reduce the venting as well.