1988 Force 125 HP outboard prop selection

[reswest101]

Hi there

I have a 1988 Bayliner Trophy 2110 Cuddy with a single Force 125 outboard on it. Boat is pretty heavy for its power and it will not plane. The best RPM we have seen is 4000 at WOT but it is often a few hundred RPM lower than and even with 2 people, minimal fuel weight, or gear it does not quite bring the bow down.

The manual calls for a 14 x 13 propellor for it.

I am assuming I need to go down to at least a 15 pitch and would prefer stainless if it is possible given my experience in the difference in getting boats on plane quicker.

I have a 15" stainless that was on my 1998 Merc Alpha one but it does not seem to fit the hub quite right. Splines are right but it is too big of a diameter to fit into the motor like the original prop did.

I assume I have the less desirable gear ratio on this one but how do I tell if it is single exhaust or a dual exhaust motor? I don't even know what exactly that means but I assume the exhaust come through the hub and elsewhere on the dual exhaust.

In ordering a prop for this boat what specifications would I be looking for in terms of size and what is inter-changeable with these older Force motors.

It is going to be used almost exclusively for fishing but it would be nice if we could get it onto plane and not have the motor working so hard pushing that boat through the water.

I would be more than happy with anything over 30 mph rather than the 15-20 mph it gets struggling through the water right now.

Thanks for your time

Gary

 

[brodmann]

The ideal operating range for that motor is 4500 - 5500 RPM's. To increase RPM's, you need to reduce the pitch. You haven't told us what prop you're actually using, so it's hard to tell you what you need to use. Pitch is the forward movement you should get out of one full revolution of the prop. If you are using a 17 pitch prop, you need to go to a 15 pitch prop to get your RPM's up. RPM's increase about 200 RPM's for every inch of decrease in prop pitch. So, unless you have some motor issues, you're trying to make your motor spin too much of a prop pitch. It's like starting out in 3rd gear. You can't reach plane, so you're never getting up on top of the water. You're wearing your motor out.

 

[jimmbo]

Before you start messing with Props, is the Engine firing on all 4 cylinders?
Do a compression test, post the numbers. Does it deliver a Spark that can jump a 3/8" gap at each cylinder?
Are the carbs opening fully when the Go Go Lever is at Full Throttle?

 

[QBhoy]

If you’re getting 4000 rpm and not planing…we need to have a good think about what’s going on perhaps.
The alpha prop won’t fit your gearbox on the force. The force has the smaller gearcase. Props for mercury 2 stroke outboards around the 75-125hp range (generally but not exclusively…) will be what you’re after.
But as said. I’d do a compression check on her. Double check the prop current details and the health of the hub/splines driving it.