New to me motor

[Ats666]

Hi, I bought an old 2001 mercury 25hp 4 stroke Mercury Bigfoot with trim and electric start. Came with 2 props with some damage.
I have not mounted it yet but have cleaned the carb thoroughly so it runs perfect in a barrel and replaced the impeller, engine and lower unit oil change.
It's going to replace an early 80s 18hp 2s Merc that will be kept for a spare.

The boat is a old 80s 18 foot pontoon (smaller pontoons).
​It's a fishing barge that is almost always loaded to its maximum. ​​​​​

What is a good starting point?
I have a tach for testing.
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I've got a prop shop that will let me exchange as needed to get it right. ​​​​​​​

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Thanks
Allan

 

[Bondo]

Came with 2 props with some damage.
What is a good starting point?
I have a tach for testing.

Ayuh,...... Pick either of the two, 'n go from there,.......

 

[WesNewell]

This is where I'd start.
https://www.mercurymarine.com/en/us/propellers/selector/#!/step-one

 

[Sea Rider]

A good starting point is the one that the prop finder suggest as you'll be powering the toon with only a 25 HP motor while heavily loaded which is a rpm serial killer..

Happy Boating

 

[QBhoy]

Must admit, I’m not a pontoon boat source of info, but I don’t think you are going to see any real performance out your 18ft and especially if you say it’s always loaded up. That is, if that’s what you are after ?
otherwise, just get a try with the ones you have and try get it in the rpm range and get happy with the one that gives you best all round. I don’t think it’s going to plane though. As good as the big foot 25 is for punching above it’s weight...it ain’t that good.

 

[Sea Rider]

Tach current prop as max loaded, go for a wot run on flat calm water cond and report the max wot rpm the motor achieved to know if motor revs at least at its min wot rpm range.

Happy Boating