Boat will not plane at wot

[firehog6305]

Hey guys I need some advice. I just purchased a 1979 25ft Apollo Cruiser that had been sitting for 2yrs. After a few week of making sure everything was water ready, including changing gas, oil, filters, tune up and rebuilding the carb. I finally took out for a test drive. It runs great but will not get up on plane. After looking into the prop I noticed that it has a 14.5 dia 19pitch on 3 blades on it. (By the way its a 350 OMC stringer 800) This prop does not seem to be the original one, because the previous owner had to remove the trim tab off of the outdrive because this prop would not fit otherwise. I know the lower the pitch and smaller prop would give it a better hole shot to get up on plane, but how can I find out what prop size I should go with, or what came on the boat from the manufacturer? I did a prop search on some websites and it said 14 to 14.5 and 17 to 19 pitch, but if I did that there is no way that the trim tab would be able to be on the outdrive. What are you're thoughts?

 

[alldodge]

There are many reasons why a boat will not reach WOT, but with your not reaching planning speed with a 350., i would look at the motor

Do a compression test (150 psi)

 

[jimmbo]

When you say OMC 350, I am going to assume you mean an OMC 260hp I/O. It had a 1.4:1 gear ratio from the factory. On a 25 ft boat the OMC 1981 Propeller chart recommends a 14" Double Cupped SS, or a 15" Al. Back then AL props were rarely cupped. So I would recommend a 14" 3 blade, or a 12" 4 blade as a starting point

What RPM did the engine attain with the 19"?

 

[Sea Rider]

Factory delivered props with engines are usually highly over pitched as manufacturer wants to play safe for engine not to over rev it as won't know which water craft will be powering it. Once break end period has ended or when buying second hand boats must perform a prop maximization for the given load you'll be boating with to get the max out of the engine.

Prop right your engine to rev middle to max wot rpm range as factory stated. Max revs if wanting best hole shot with slight less top end decrease or medium rpm range if wanting to increase top end speed with less hole shot added penalty, you decide.

Happy Boating

 

[Retired Mechanic]

A boat that size would probably run a 17 or 15 pitch prop. But more information is needed and more importantly a picture of how your current prop is installed. If the trim tab was removed to install the prop it is the wrong prop or incorrectly installed.

Also, what is your RPM at WOT. Are you positive the engine is operating at full power. Did you use an automotive or marine rebuild kit for the carb? What tune-up specs did you use. We had a lot of issues with the carbs on those when they were new. If the spring tension for the secondaries wasn't adjusted just right you encountered all kinds of runnability problems.

Paul

 

[wahlejim]

Get the boat weighed at a truck scale. Figure out how much it should weigh and do the math. You have a 40 year old boat that sat for 2 years. I personally wouldn't spend a dime on a new prop unless I was sure it wasn't water logged. That would be my first step.