Mariner 20e Outboard Propeller question

[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 559502.

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!!

 

[CLB]

That size boat with 20hp is only going to be a plodder, so I would have thought an exact match is not too important. A similar pitch will do the job.

 

[Shetland_refurb]

Thanks for the reply CLB, the idea is exactly that, just a little plod down the Thames, not planning on taking her out to sea!

Therefore, can I ask, as long at the diameter 9 7/8 is a match, and the prop is a 10 toothed spline, then would say something up to 10-12 inch pitch still be ok?

Sorry if it sounds like a daft question, just trying to find the easiest option to get the boat on the water!

Thanks again.

 

[QBhoy]

Hi there.

My honest advice is to sell the mariner 20 and replace with a good late model 50/60hp 2 stroke. There isn’t much difference in financial terms and will make the boat do what it was designed to do.

As for the prop...it might suggest it’s a 9” pitch, but I’d find that either unlikely or entirely not suitable for the set up mentioned. To throw a comparison, a 4hp would come standard with a 7” or 7.5” pitch prop usually.

A 20hp on that great wee boat, would perhaps only just get on plane with one or lightly loaded situation. But would be working really hard at it. You’d be as well with a 10hp really.

These great wee boats were known for planing well and stability whilst at it. Max hp is likely around 60hp but 2 stroke weight. They’ll perform ideally with anything from 40-60hp 2 stroke. She deserves a decent engine !

All the best

 

[Fishtigua]

Looks like they've stopped making many of the props for the old 20.

https://www.marineengine.com/parts/mariner-outboard-parts/20c-thru-prop-exhaust/6a9550694-and-up-el/prop-chart

 

[CLB]

While the Mariner 20 is not the best engine in terms of size, too small to give fast speeds, and bigger than needed to go slow, it is the engine you have and will be perfectly acceptable for a slow plod up and down the river. I have a similar setup on a 4.8m boat. It is rated to 40hp and I have an old 2stroke 20hp on the back. It won't plane, but it goes nicely at displacement speed, with power in reserve if needed. It has an 11inch pitch prop (albeit 10.5inch dia), so I suspect something similar on your mariner will be fine.

 

[rosssavage]

Just don’t stick a 50hp 2 stroke on it for the Thames!!!

Noisy, only be used at low revs so will get gummy etc etc..

The mariner 20 is more than adequate. I’m guessing it’s a twin cylinder 4 stroke, so will be quiet and smooth for your application, whilst sipping petrol.

Prop pitch isn’t a game changer in your use, but he closer match the better.

You could talk to Norris Marine to see if they have one for you - they have an alladins cave of second hand bits. If he doesn’t, he’s also a master prop repairer and finisher, so he may be able to tweak whatever prop you have to get the pitch closer.
https://shop.tnorrismarine.co.uk

 

[Fishtigua]

Just don’t stick a 50hp 2 stroke on it for the Thames!!!

Noisy, only be used at low revs so will get gummy etc etc..

The mariner 20 is more than adequate. I’m guessing it’s a twin cylinder 4 stroke, so will be quiet and smooth for your application, whilst sipping petrol.

It's an old 6A9 2-smoke, pretty unbreakable even for an oiler.

 

[rosssavage]

It's an old 6A9 2-smoke, pretty unbreakable even for an oiler.

Sorry, my mistake.. I’m not an expert on serial numbers!

I assumed 4s as I have a mariner 20 on the back of my rib, and that is a 4s. Obvs much newer than the OP’s I guess.

 

[Shetland_refurb]

Thanks for the feedback! I’ll try to hunt out a Prop between the 9 7/8 x 9” to 9 7/8 x 12” range, seems the most appropriate given what you’ve said. I’ve also just emailed Tnorris Marine as suggested, they’re actually fairly local to me so perhaps there’s an option there ?

It will be a big day when we finally launch, it’s been a long project, the boat was in a right state & practically stripped back to the shell and the Prop/motor is one of the final pieces of the puzzle!

 

[Shetland_refurb]

Sorry, one other quick question...

I have heard that these Mariner 20e’s are basically Yamahas rebranded, therefore if looking for a propeller online, is it ok to look for Mariner & Yamaha compatible props?

Or is it just a case that any Propeller with the correct diameter & pitch that is a 10 toothed spline is ok?

Again sorry if the answer to this is obvious and it’s a complete newbie question!

 

[gordmac]

Sizing props correctly is not easy but I suspect as you will only be doing hull speed, 4 or 5 kn, pretty well anything that fits will do at least to get you on the water.

 

[CLB]

Sorry, one other quick question...

I have heard that these Mariner 20e’s are basically Yamahas rebranded, therefore if looking for a propeller online, is it ok to look for Mariner & Yamaha compatible props?

Or is it just a case that any Propeller with the correct diameter & pitch that is a 10 toothed spline is ok?

Again sorry if the answer to this is obvious and it’s a complete newbie question!

The 10 spline tooth needs to be the right shaft diameter. I don't know if there are other outboard prop shafts with 10 splines that are bigger or smaller, but it is possible.

 

[silverdee]

steel developments will get you a prop no problem