one more time

[cuzzx]

and this is it, I'm tired of this.

Ok, I have a older 20ft pontoon with a older Mariner 75hp running a 13 3/4 x 15 aluminum prop. This is what the toon/motor did today.

Toon weights about 1200lbs, motor is 280lbs. two men at 375lbs. gas 10gals. and gear around 50lbs.

motor at WOT 4200rpm/15mph

3300rpm/11mph

2600rpm/7 mph

2200rpm/4 mph

setting in the water the motor's cavitation plate is about 4inches below the water line, with the motor running at WOT you can see the bolt that holds the trim tab at water level.

What do you think needs to be done to get R's up and speed right?

 

[cuzzx]

Re: one more time

thanks all

 

[Silvertip]

Re: one more time

1) Verify the tach accuracy
2) Verify the engine is making full power (compression check)
3) Verify that the throttle is opening fully (butterflies perfectly horizontal in the carburetor bores).
4) Lose the 15P prop -- try a 13P or even an 11P (This is a pontoon not a "V" hull).
5) How old is your engine (4 cylinder or 3). Gear ratio will unltimately determine what prop is best. 3 cylinder is 2.33:1 gears so a 13 should be fine. Don't know what the ratio is on the 4 cylinder mercs.

 

[mthieme]

Re: one more time

You need a flatter prop.
You can get your current one set to 13 cheaper than you can buy a new one.

 

[cuzzx]

Re: one more time

engine is a 3 cyc , 1995 in real good shape, low usage for that year.

 

[cmchesse]

1985 70hp Johnson

1985 70hp Johnson

I looked over the prop and the only number I can find is CG7936? Not sure of the last number. My problem is that I put that in google and found nothing. I looked at the props listed on I boats and the number is not even close. How do I tell what prop this is. I do not have a spare and would like to get one.

by the way, this number was imprinted between the blades.

 

[Silvertip]

Re: one more time

In your original post you said you had a 13-1/4 x 15P prop. That's all you need to know. You know the engine year and model, and you know what diameter and pitch prop you have. (By the way -- how did you determine that was a 15P prop?) As for the number you found, every prop manufacturer has their own part numbering scheme so naturally you would not find it on iBoats unless that particular manufacturer was carried by iBoats. To buy a prop, click on the MARINE STORE button at the top of this page right under the iBoats logo. Scroll down and click on propellers. Enter the year make and HP of your engine and then search. You will be shown a list of various props. If you want a 13P, click on that and you will be shown a list of brands iBoats carries. Pick one you like in aluminim, stainless, three blade, or four blade.