Mercruiser Prop Question

I have a 1988 Monterey 23' Cuddy Cabin with a 5.7 Mercruiser and an Alpha1 outdrive. I just purchased the boat and dont have much in the way of manuals and specs. Currently the boat will cruise about 35 MPH acording to the GPS at about 4000 Rpm. Im thinking that it should be getting a little more speed based on what I have been reading. If I were to change the prop what would be my best bet in a SS replacement for better top end primarily.

Re: Mercruiser Prop Question

We need your present prop size, max rpm and speed.Also the max recommended rpm perhaps on a label on the motor.Prop size is usually on the barrel or under the prop nut.

Re: Mercruiser Prop Question

You also need to confirm that the tachometer is correct and that you are trimming the boat properly. Also you need to let us know what type of load you typically have and what you will be using the boat for. Unfortunately there is not a miracle prop that will give you rocket-like acceleration and the highest top speed. Okay, there are some "shifting" props out there used, but parts are scare and prices are sky high.
The WOT RPM range on that boat should be something like 4200-4600 rpm. (or 4400 to 4800) Whatever prop you have needs to be in that range at WOT with your typical load on board.

Re: Mercruiser Prop Question

About 35mph, at about 4000RPM with about a 17" prop and about a 1.5:1 gear ratio gives you about a 20% slip which is about right.

Re-test at WOT witha "normal" load and post the results. Otherwise, it is all just guessing/ish.

Re: Mercruiser Prop Question

Ayuh,...

And,..
A 1988 is About old enough to be About waterlogged...
The floatation foam could be About Soaked....

Re: Mercruiser Prop Question

jmerc57 said:

I have a 1988 Monterey 23' Cuddy Cabin with a 5.7 Mercruiser and an Alpha1 outdrive. I just purchased the boat and dont have much in the way of manuals and specs. Currently the boat will cruise about 35 MPH acording to the GPS at about 4000 Rpm. Im thinking that it should be getting a little more speed based on what I have been reading. If I were to change the prop what would be my best bet in a SS replacement for better top end primarily.

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First you have to make sure your engine is putting out it's full power. Otherwise a SS prop won't help, it takes more power to spin that, but it will push more water, and give you a higher top end. This is big investment, so make sure all else is good first, so you can choose the right pitch SS prop.

I had a 79'- 24' SeaRay Cuddy with a 350/260 Merc. type 1 drive, that would do 40mph at 4600rpm fully trimmed out, using a 17" pitch alum prop.

I don't know if your boat is lighter, or heavier, but it should run about there.

Trimming: The trick is, get it up to WOT, then power trim the drive up, till your prop starts to slip (you can usually hear, and feel it slip) then trim down just a bit till it grabs, and you should gain a few mph. Don't forget to trim the drive in all the way when you come off plane, or it will struggle when getting back on plane.

Re: Mercruiser Prop Question

Thanks for all the help folks. Ill try to see if I can find the prop info tomorrow but if I cant see anything it will have to wait till I pull the boat out of the water in 2 weeks. I dont have any manuals or specs on the boat so Im not sure of anything I do. Unfortunately the previous owner isnt very helpfull as far as info goes but he still insists the boat did mid to high 40s acording to his GPS. Tommorow Ill run it at 4600 RPM's and trim it properly and get another speed reading as well. Thanks again guys and hopefully Ill have some more detailed info to post here tomorrrow.

Re: Mercruiser Prop Question

I concur with 180shabah on his figures. Chances are, it's a 17" pitch prop for that size boat, & power pkge. Don't just run it to 4600rpm, Run it to Wide Open Throttle (WOT) and see what rpm she'll do, this way you'll see if the previous owner is right, or not. then get back to us. good luck, Mike