Is my prop likely to be the OEM fitment?

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Froglet England
Newish Member, But I Like It Here
Posts: 15
Joined: 15 Apr 2018, 13:32
Boat Make: Honwave T38 ie1
Outboard: Mariner Marathon 25hp
MMSI Number: 10
Location: South Bucks
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Is my prop likely to be the OEM fitment?

Post by Froglet » 30 Oct 2018, 22:01

When I bought my 2nd hand T38 it came with a Mariner Marathon 25hp 2smoke. The prop had already suffered a little scuffing to the leading edges of the blades, but it was mostly paint removed and the aluminium wasn’t too marked so I just went with it.

Then while exploring lesser travelled sections of the Thames I dinged it further by finding an unexpectedly shallow and pebbly section of river. Live and learn. :oops:

It’s not wrecked, but the blades are all roughed up, so after looking at repair options and reading posts on here I’ve packed it off to Steel Developments to get rejuvenated. Meanwhile I’m looking at replacements to have as a main/spare prop.

The engine plate identifies the outboard as a 2005 MA 25 M, Mercury Marine, Brunswick Corp, made in Japan. The incumbent prop is a 9.9x13 with a 10 tooth spline.

Is this likely to be the original prop? Looking at propellershop.co.uk the props listed with those dimensions are Tohatsu/Nissan, Honda or Yamaha. Although the part number for the Yamaha is different. Plus they are mostly listed as suitable for 4 strokes, although I can’t see how that matters… much confused.

This also leads onto questions of performance. The Thames has a 5mph speed limit so getting on the plane isn’t really on the menu, but on other stretches of water I’ve found slightly odd behaviour. With 25 horses to play with the T38 sits up on the plane quite briskly and once up to about 12mph will skip along very comfortably with minimal wake and splashing. However as you start to speed up the bow begins to push in a bit, the steering gets heavier and I get the much-talked-about floor bulging. So I thought I could trim the outboard up a notch to see if that lifted the bow, but not only did it still dig in, but the motor would suddenly ventilate with the revs rising, but speed falling. BUT….. this is all with the abused prop. I’ve only just read up on how much of an effect that could be having, hence repairs and replacements.

Any thoughts? Does that sound like a suitable prop for a 25hp? Is it worth me waiting for the return of the repaired prop and testing handling and speed with that before looking at what to buy as a spare/alternative prop?

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PeterM
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Re: Is my prop likely to be the OEM fitment?

Post by PeterM » 30 Oct 2018, 22:31

It sounds like the one you have works...maybe ask if steel developments can send you 2 back? I mean that seriously as they may well be able to sell you another the same?

I suspect when fixed the current prop will be exactly like it was. At the lower hp sizes you don't gain or lose much in a minor prop dings. To be fair the prop guys are best to explain it all.

Props do have different fittings between manufacturer. So yam props won't fit mercury etc although there is some compatibility between some makes.. prop guys can explain all...

Your boat issue sounds much like lots of sibs and due to boat set up not the prop. Airfloor not up to pressure is a common cause if this.

Froglet England
Newish Member, But I Like It Here
Posts: 15
Joined: 15 Apr 2018, 13:32
Boat Make: Honwave T38 ie1
Outboard: Mariner Marathon 25hp
MMSI Number: 10
Location: South Bucks
Has thanked: 2 times
Been thanked: 3 times

Re: Is my prop likely to be the OEM fitment?

Post by Froglet » 25 Nov 2018, 12:07

Prop came back from Steel Developments last week looking a fair bit better. Blades all welded and ground back, although if I'm nitpicking there is a bit of a run in the paint on one blade. With postage etc this isn't perhaps the most economical way to deal with a damaged prop. On an engine of this size the props are cheap enough to almost be considered a consumable item. However I feel better about recycling the original rather than binning it.

When I removed the prop I found the nut was loose and only held on with the split pin. Never had an engine like this before so thought nothing of it. When I consulted the manual to refit the prop I found to my surprise that it wanted to be torqued up to 75Nm or 55ftlb! :o That's like motorcycle axle levels of torque! So all cleaned, grease re-applied and nipped up to spec with a fresh split pin fitted.

Don't know if that will make any difference, but I'm about to find out. All packed up ready to head to the river. Was planning on going on Friday, but the weather was decidedly vile. Much nicer today.

Will also test the tube and floor pressures after a bit on the water, but I suspect that air and water temps are closer at this time of year than in the summer.

let the "sea" trials commence!

:thumbsup
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