Need prop specifics

[Brian Shepherd]

Hi

I have a 1991 Sea Ray Serranto 24' Cuddy with a 5.7 alpha one drive. The WOT is only 3800 RPM and I have a top speed of 37 Mile per hour.
I have read that my prop is most likely incorrect and it does not have any markings on it, I can say it is a 3 blade stainless prop.
Any suggestions? Should I get another prop and what is the correct size?
I would prefer stainless and want a higher top end speed.

 

[Lazy Daze]

Check the prop again, first. Between the blades... around the hub from the topside of the prop... around the hub from the backside (remove).

Your speed doesn't seem to match the RPM. Meaning, your RPM's might be off. Try exercising the selector switch on the backside and make sure it is on "8".

Is the speed GPS-based? That needs to done for accuracy.

Are you trimming the engine properly and fully?

Is the boat hull perfectly clean and the prop in perfect shape?

What kind of weight was in the boat?

All of these questions need to be answered for the best help.

Also, always feel free to search on this forum for these basic topics. There are many, many threads about this and you can read up on it.

 

[Brian Shepherd]

Hi
The speed is GPS based, what selector switch are you talking about when setting on 8?
The boat is clean with 2 people and trimming actually did not make any difference.
I will do another run this weekend for verification.

 

[Lazy Daze]

On the backside of the tach.

Trimming should absolutely make a difference. Either you didn't trim enough or it is inop.

 

[Thornton69]

Agree with Dennis that one of your numbers are out. Our older 24' cuddy is more than likely a bit heavier than yours unless you have the command bridge. We top out close to your speed but at 4450 rpm. If you have confirmed what ratio your drive has, have found the Merc prop calculator to be pretty much bang on for our boat.

 

[Brian Shepherd]

I did get the trim to work and managed to get a WOT of 4400 rpm but my speed on GPS was still only 39 miles an hour. I expected with a 5.7 it would be a lot faster.

 

[Lazy Daze]

How many people in the boat this time? How far did you trim it up - explain your trimming procedure to get that 4400. There were questions asked that still weren't answered - we won't be able to help, otherwise.

At nearly 30 years old, the other possibility is that the engine just isn't making the power it used to or needs a tune-up. But I wouldn't expect a whole lot more speed. Google around and find the MAX RPM range for your year engine, as well. I'm not sure if in '91 it was rated for 44-48 like it is in later years.