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Old 30 October 2007, 09:51   #1
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Putting a long shaft engine on a short shaft transom

Hi,
i've just bought a Humber Assault (advertised as an Attaque!) and it turns out that the transom has been cut for a short shaft engine. The boat currently has a blown up "standard" shaft engine, which I am told is 18", on.

The seller tells me that Humber explained that the transom could easily be bulit higher by inserting a section of the same thickness of marine plywood and screwing it diagonally into the existing transom ? What do you think ? Would this be enough to support a 75hp 2-stroke Yamaha or 90hp Mercury ?
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Old 30 October 2007, 11:35   #2
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You might want to PM Nasher - I seem to remember that he had a similar experience
Or maybe wait a bit and he'll be along later
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Old 30 October 2007, 12:00   #3
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Depends on whether the the Engine mounting holes go though the new (extended) piece of transom or not, if they do then suitable reinforcement is required. This I would guess could be in the form of a stainless plate mounted on the outside of the transom and bridging original and new parts. Perhaps one on the inside too, this would provide a sandwich effect and would be a much stonger soloution.

There are other options, but none as simple and as strong as this one and certainly not easy for DIY.
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Old 30 October 2007, 15:52   #4
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Pablo

Hi, as ITB says I had a similar issue when I brought a cheap XL shaft Suzi to put on my Ocean that was cut for a Long shaft. I ended up doing the following.

I cut a large Alloy plate 15mm thick that bolts to the transom with 8 M12 bolts, and spreads the load out way past the original cut out. The engine then bolts through this into the original transom, and only the top engine mounting bolts are above the original transom height.

The actual transom is built up to the same height as the 15mm plate with a section of 2' x 4' Alloy box. This has tube inserts for the top two engine bolts to pass through. These stop the box section crushing.
Inside the whole lot is another Alloy plate 6mm thick.
Everything was finished off with white sealant.

I was told by a reputable boat builder that the 2' x 4' box etc was not needed as the 15mm plate would take all the engine could throw at it, but went with it for a neater finish.

The two images below show the inside and outside before the transom was painted and proper engine bolts used etc, so excuse the state it looks.

Nasher
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Old 30 October 2007, 18:52   #5
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Nice job Nasher - looks very good
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Old 31 October 2007, 04:15   #6
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Great

Looks very good indeed !

Thanks everybody for your help. I think Nasher has given me THE solution. I should be able to get some stainless steel to make the sandwich.
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Old 31 October 2007, 07:00   #7
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Pablo,

Would you be easier (& quicker?) to find a running version (any shaft length) of the one on there now, and swap the middle legs over? You'd be surprised how long some of these bits were carried across to "new" models - My 1993 Suz shares parts with the current DF30! You'd need a microfiche to suss out if it would fit or not.

This would then solve a lot of mucking around & adding weight to the hull.

Even easier - find a short shaft engine? (But I guess you have one lined up already - in which case could you find a siezed short shaft version & swap the bits?
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Old 31 October 2007, 09:18   #8
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As the boat is an Assault rather than the Attaque I was hoping for I think I want to set it up to use it one season and then sell it. The seller made a genuine mistake, he advertised it as an Attaque which I automatically / hopefully transfered into an Ocean Pro "Attaque Classic" 2m beam. As I got it at a bargain price and an Assault is still alot better than what I use at the moment then i'm at least going to give it a try.

It will sell better as a long shaft transom as most people here are fans of four stroke. Its almost impossible to find a short shaft 4 stroke with more than 50hp. I've got two engines lined up, a 90hp Mariner or a 75hp Yamaha, both old 2 strokes and dirt cheap. When I sell the boat I may have to sell it without the engine and so i'll put it on the Ocean Pro "Attaque Classic" or 5.4m SeaRider i'll get next year.

I'm only going on what i've read on this forum, I may even find the Assault will do me.
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Old 01 December 2007, 13:26   #9
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The story so far

I ended up doing it slightly differently. I've built up the transom with a piece of oak (at least 60 years old). It's going to be sikaflexed on and then a sheet of s/steel is going to be folded round.
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Old 01 December 2007, 13:30   #10
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Pablo, surely it would be stronger if it was held in with GRP or epoxy and then glassed over. Andy Hightower had this done on his South Coast Rib andGary did a really good job of it.

Pete
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