Mariner 20e Propeller advice

[shetland_refurb]

Hi there,

Hopefully someone can help! New to boating here, so have limited knowledge, please bear with me on any of the following terminology!

I’m in the process of refurbishing a Shetland 535 (fun project with a friend!)

The boat wasn’t purchased with a motor, but we have recently managed to pick up a Mariner 20hp outboard, which is by no means new, however for its age seems in great condition (looked practically brand new under the hood and hardly ever used!). The propeller however was basically disintegrating and badly worn. Which leads me to the question, what is the best replacement?!?

Information I have -

Motor is a Mariner 20e, serial number 6a9L 550502.

I can just about make out on the existing propeller a stamp that says - 9 7/8 x 9F.

A question I have is does it NEED to be an exact like for like replacement? Or is there any kind of leeway with the pitch?? I’m asking as when I search for the above they seem to be few and far between options that match!

Also, any watch-outs/must dos when fitting a new prop, and running a motor that’s not been used for a few decades

Very grateful for any help or info that can be given!!

[boats.net]

Best performance out of that motor is within 4500-5500 Rpm's so for the best performance you can connect a tachometer to it and change props until you get within the that rpm range. Generally the low side of rpm range will give best speed but the high end of range will give the best hole shot and best fuel economy. If that prop is ok enough to run it and see how it performs on your boat you might be able to get a good idea of which way you need to go, If the boat is hard to plain off then choose a lower pitch prop( 8 pitch is lowest prop available) if rpm's seem to be racing at wot open throttle then choose a higher pitch prop.

[shetland_refurb]

***, great fast reply! Thanks!!

Perhaps I should have mentioned the plan for the boat is literally just to take it on the local rivers as a day boat with the kids, so not open sea at full throttle!

I unfortunately don’t have the option of a tacho, or to be able to change out the props to find the best match (however awesome that sounds!).

It is literally just a case of finding a good enough match, on a budget from an online website etc. Good enough to push the boat along at 4/5 knots. So I guess I’m just trying to understand if that is all that is needed, is the pitch of the prop THAT important?

Thanks again for the reply!

[boats.net]

You can search the internet for "Propeller Calculator" but you don't have enough information to come with a accurate match, probably will have to stay with the 9" pitch and load boat down like would for a normal run and see how it does.