New prop for 15hp 2 stroke mariner

[Duluxdoggy]

After a test run on our new motor. I think I need to replace this prop as it is bent and chipped. Also 2 up the boat doesn't get over 8mph. Managed to get it to plane at 20mph solo. But not enough pull with us both on board.

Have had a look but can't see any info on the prop. Anyone have any advice?

Edit: just read that this prop gaurd could be sapping power. can't test until next weekend tho.

[Fenlander]

Sorry when we all said buy that engine I don't think any of us thought to say prop guards are not needed in normal leisure use and they spoil performance so yep take it off and you should gain a great improvement.

That prop does look well past it so yes I'd get a replacement or have it repaired. It's not just it's effect on performance but an out of balance prop will over time cause gearbox bearing/seal issues.

It can be made like new by people such as Steel Developments...

9.1/8" to 11" diameter Aluminium Propeller Blade Repair Service 2, 3, or 4 blade

and it will be about £58 inc them sending back to you so add in your cost posting to them it will be almost £70. Having it repaired with two lots of post plus their workshop time will likely mean you'll not have it for next weekend.

They would sell you a new one for £96 inc post.

So your best bet may be Ebay where as an example this excellent looking used one is £57 inc post but he is accepting offers so perhaps £50 inc post and you'd have it for the weekend.

http://www.ebay.co.uk/itm/MERCURY-MA...MAAOSwnHZYgKEY

When you are ordering a new or used prop you must take off the old one and measure the gearcase (the dia the back of the prop sits against which is probably 2.5"), count the splines which are 14 on later motors but I think 8 on yours, the overall diameter of the old prop and finally you need to know the pitch you want. The standard for a 15" is a 9" and I've never known this not suit a whole range of uses. However don't go over this or it will be like trying to pull too high a gear in a car.

Give all this info to the seller so you are sure of getting the correct one..

Hope that helps.

[Max...]

Kind of bolting the stable door after the horse has gone with whoever fitted that prop/guard - it looks properly fooked despite the guard!

[uncle al]

don't forget, your propeller is the governor for your OBM. Too small a pitch, you can over rev the engine and stress it. Too large a pitch it will be like driving away in your car in third gear, again stressing the engine. there is usually a pitch number stamped on the back of the prop, its on the face that sits against the thrust hub.IE P13 That is a 13 inch pitch.

[Duluxdoggy]

Ok. So removed the prop and gaurd. 9 1/4 x 10 1/2-j
With 8 spline.

[Duluxdoggy]

That ebay prop is 9 inch pitch. Would that effectively give us a little more torque?

[Fenlander]

OK so you need 8 spline, 2.5" gearcase, 9.25" dia and...

Last figure the pitch.... now that 10.5" is not a standard I'd expect to see on a 15hp and given you've said you load is robust and you go on rivers I'd say go for the standard 9" pitch.

Removing that prop guard and getting rid of that over pitched damaged prop should make the outfit feel so much better.

[Fenlander]

>>> ebay prop is 9 inch pitch. Would that effectively give us a little more torque?

For any given speed it will allow the engine to be at more favourable revs and together with scrapping the guard should lose the issue of not getting on the plane 2 up.

If you were only ever going on the river a 8" or perhaps even 7" pitch would suit but at this stage of your early days fact finding I'd not do that.

Note: The Ebay guy (Bill Higham) has a prop the same £5 cheaper... don't buy that as it looks to have been filed in the past to get rid of damage.

[Duluxdoggy]

ok, I have just made an offer on the one you linked. if it comes to it would paying the full asking price be such a bad deal?

just noticed that the same seller has 2 of these listed £5 apart...
Thank you for your help.

[Fenlander]

I'd always try a near offer but yes it would be OK to pay full price really as it will get you back on the water far quicker and at less cost than a refurb.

[Duluxdoggy]

what about
Propeller for Yamaha outboard 9 1/4 x 8 J 9.9 15 20 hp 8 splines pitch 8 | eBay

EDIT: just noticed pitch is 8"

[Fenlander]

I see no advantage in the white one and despite the fact I "think" your age of Mariner is a Yamaha design no point in risking it not fitting when the Bill Higham one is a genuine Mercury/Mariner one so sure to fit.

[Duluxdoggy]

have just phoned Bill Higham store after searching for mariner dealers..

gave them the engine serial and they said the prop wont fit as it is for the american model. however they do have one that will fit, 9" pitch. £45 plus postage. so have ordered that 1. should be here before weekend.

[uncle al]

Be careful using the 9 inch pitch, as you will increase the Wide open Throttle by about two hundred RPM or more.If you had a rev counter fitted it would be easy not to over rev your OBM.

[beamishken]

That engine is a yamaha badged as a mariner, when looking for bits you'll have more luck searching for yam 15hp parts which is what it is.
The smaller pitch prop should be fine for your purpose as your in a river so won't be sitting at wot until you venture further a field.
In any case you are doing the engine less harm by being under pitched and allowing it to rev freer than you are by being over pitched and overloading the engine

[Duluxdoggy]

Originally Posted by uncle al

Be careful using the 9 inch pitch, as you will increase the Wide open Throttle by about two hundred RPM or more.If you had a rev counter fitted it would be easy not to over rev your OBM.

I have ordered a cheap tach. Will be interesting to monitor the situation.

But for our use won't be at WOT all the time anyway. Just nice to have a bit more poke from time to time.
The river limit is 6mph anyway!

If what fen says is correct tho. It should of had a 9" pitch anyway. So we are returning it to stock.