Spare Prop for 15HP Mariner 2 Stroke

[mm289]

Hiya, thinking about getting a spare prop prior to our trip to Scotland. Never purchased a prop before so whats the process, where to buy, what do I need to know?


Cheers,


Paul.

[Fenlander]

First find out your existing prop size pitch and diameter.

Are you happy with this or would you like a spare that also gives you an alternative for heavier or lighter loads?

Do you have a cheap tach to know if the OB is getting to the correct revs at the moment because perhaps with that you'd find the existing wasn't the best so you could get a new pitch and keep existing as the spare?

Having said that my gut feeling added to experience is that most SIBs perform well with the 9" on the Mercury/Mariner 15 2-stroke that is the usual standard prop on your OB... but of course you may have different to standard at the moment.... and wait a moment... don't you have an Frib?

If Frib that may change things as their hulls are so efficient you may already be in over-rev territory if using a 9" pitch.

If you don't have one yet a small £6-£20 tach is the starting point for this prop choice.

When looking at your existing prop it would be useful to know if there are markings or a part number that tells you if OE or another brand to get a known starting point. On a 3.6m SIB I bought a 9" pitch Solas as a spare for the Mariner 15 and trying it the performance was ruined so I swapped it for a new Mercury/Mariner OE prop which was perfect.

New OE prop about £90... new aftermarket nearer £50.

So yep... I reckon rev counter first... or give us some readings if you already have one.

[mm289]

Cheers Fenlander. I did put a tach on it but it failed after the second outing , won't have time to run it again before we go to Scotland unfortunately.


Dumb question alert, is the pitch measurement the depth of the cup on the blade i.e. distance from leading edge to trailing edge?

I will go and inspect the current prop tomorrow for markings. On the Frib 330 it tops out as 19-20kn solo which is pretty much the most anyone seems to get out of one of these so I am guessing the prop ratio isn't far off. It can take a bit of effort to get on the plane 3 up but it does get their and holds it with no problem.


If anything my problem is how "bow up" it goes when getting on the plane but I think that is more about weight distribution


Cheers,


Paul.

[Fenlander]

Pitch will usually be printed on the prop or can be looked up if it has a part no. but no pitch.

Measuring the pitch of a prop isn't that simple... for example the measurement you mention is about 2.5" on a 9" pitch I have in front of me so no help.

This guy explains how to do it and I'd lost the will to live before halfway through the video never mind trying it in practice.

https://www.youtube.com/watch?v=Uzv_m_Gm1es

Trust me 90% of props have markings you can decipher.

From your comments 3-up it sounds like you certainly don't want to pitch up.

Getting a tach (that lasts more than one day) would still be useful given the low cost. It's always worthwhile to know if you are pushing you luck at max revs all the while... or on the flipside if you are over-pitched with you normal load such that dropping an inch would help overall.

[Fenlander]

>>>On the Frib 330 it tops out as 19-20kn solo which is pretty much the most anyone seems to get out of one of these

I guess that's about right unless a tach showed you were maxing out on revs and could go up a pitch... but of course only when 1-up.

As a matter of interest 19.9kts was the max I saw with a Mariner 15hp 2-stroke (OE 9" pitch prop) on a Zodiac 360 Acti-V air floor with just me. That was a light SIB with a modest V so quite a skimmy shape and equates well to your speed. I didn't have a tach back then to know the revs though.

[mm289]

Thanks Fenlander, will go ivestigate the current prop in the morning
Cheers
Paul

[jeffstevens763@g]

I would consider coming down one pitch just so you have a crisper response when carrying weight IMO you won't loose too much top end speed that way you have a spare prop and more scope for different scenarios

[mm289]

Just had a look, the markings on the side are A12 9P so presumably 12" diameter and 9" pitch? or 12 spline and 9" pitch?


Cheers,


Paul.

[mm289]

So just popper the prop off. It is 8 spline and 9" pitch and as far as I can tell 9" diameter which is the standard prop listed for a 15HP Mariner so thats cool.


Glad I took it off, as mine has a nyloc nut rather than a castle nut with cotter pin. Whilst it is a M10 thread the nut fitted was a very odd socket size, possiblly 15mm, ended up using a 19/32 AF which was a perfect fit. If I had had to swap whilst on the boat I doubt any of my standard toolkit would have fitted!


Cheers,


Paul.

[Fenlander]

A12 is an abbreviated bit of the part number which is likely to be 828156A12.

That is for the standard 9" dia x 9" pitch OE prop I've had on all three OBs of this type I've used. I think it should be 8 spline.

Like this one here.

https://seamarknunn.com/acatalog/Mar...SABEgKGOPD_BwE

Actually if you were keeping the same pitch this looks what you need and a bargain price too...

https://www.ebay.co.uk/itm/mercury-m...oAAOSwXFldUFAE

Remember to buy a spare nut or two!

In my boat toolkit I always carry an offset ring spanner to fit the prop nut... it's of a length where tightened to the maximum comfortable amount the torque is about right. Also a small wood block that goes between one blade and the AV plate to stop the prop turning.

[Fenlander]

Here is the official service manual for your outboard and on page 1A-7 there is a table of prop choices for the 15hp with part numbers.

http://www.baads.org/wp-cms/wp-conte...nual_PART1.pdf

[mm289]

Awesome, thanks Fenlander


Cheers,
Paul.