Prop size for a 16 foot pontoon?

1jimbeam

Recruit
Joined
Feb 18, 2009
Messages
3
What size prop should I try?

I finally got a tach working on the boat today.
The pontoon is a 16 footer.
The motor is a 1989, 40 hp mercury.
The current prop is alum. with a 13 pitch. here are the numbers stamped on the prop. 48 73136 A40L 13P
The wot rpm is 4100.
The speed checked with a GPS is 15 mph.


Thanks,
Jim
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: Prop size for a 16 foot pontoon?

It would appear you need about an 8" prop to approach about 5,100 rpm.
Your speed isn't bad but the motor needs to operate within its max rated rpm.
A 4 blade prop will resist venting better.
 

1jimbeam

Recruit
Joined
Feb 18, 2009
Messages
3
Re: Prop size for a 16 foot pontoon?

any one know what the numbers on the prop mean?


The L has me concerned.......standing behind the boat and looking at the prop it is turning clockwise.
Jim
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: Prop size for a 16 foot pontoon?

I didn't catch that.Clock wise(R) is normal and to the best of my knowledge I don't think there are any counter rotating 40s.I'm surprised they would use L for anything but counter rotation.Perhaps it is a poorlky placed,badly stamped R?
That is a Merc number maybe you can find it at the Merc prop site.I suppose it could be miss marked.
 
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