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Old 31 January 2016, 16:39   #1
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Bombard Aerotec - using a longshaft

Ok so, I need to raise my transom 2.5" or so to stop the splashing.

Is there any reason why I should not raise it 7.5" by bolting a thick plate to the outside of the transom?

Someone i spoke to mentioned twisting effect could be a problem.

What do people think?
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Old 31 January 2016, 17:23   #2
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I think that 'someone' is right. Sounds to me like it would put a lot of extra strain on the tube/transom joint, especially at the top. You're essentially adding a fairly significant lever and pulling the top of the transom back with a lot more force.

I'm sure some smart mathematician can do the sums, but I'm fairly sure the extra force will be enough to cause concern with a 25hp engine on the back.
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Old 01 February 2016, 03:20   #3
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see into shortening the leg neil if theres a kit for it.
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Old 01 February 2016, 03:27   #4
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I'm confused...are you using the correct short shaft for the 380 and concerned with the usual splashing? If so just a 30mm riser block under the engine clamp is all that is needed.

Or do you want to fit an incorrect longshaft engine to the 380. If so why? This is the wrong engine for that boat and adding a huge tall plate to the transom to accommodate it is wrong in many ways!
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Old 01 February 2016, 09:53   #5
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Max I think Neil already owned a 25hp longshaft prior to buying the Aerotec but so far has been using it with a shortshaft Tohatsu 9.8 so I guess he's wondering about adapting things for the 25 to save an outboard swap??

Back in my young days this sort of thing was often done to marry an existing longshaft to a displacement speed clinker harbour launch type craft. A wooden/steel/alloy type extension plate made up in the workshop and all sorted.

However the Aerotec is a very light SIB (albeit well made for it's designed intention) and I'd be worried adding an extra 7.5" to the transom height is a step too far with regard to loading on the transom/tube joints and from the perspective of raising the C of G well above the tubes.

Having said all that I guess it would be possible to make a temp plate for trial that bolted to the transom where the existing outer pad sits so there were minimal visible holes to fill if the idea was abandoned.
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Old 01 February 2016, 11:55   #6
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The extra 7.5" would stress the transom outside of engineered limits.

Catastrophic failure may result.
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Old 01 February 2016, 13:37   #7
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[QUOTE

Catastrophic failure may result.[/QUOTE]

And then it will sink or spontaneously blow up!
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Old 01 February 2016, 14:09   #8
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Quote:
Originally Posted by matt h View Post
[QUOTE

Catastrophic failure may result.
And then it will sink or spontaneously blow up![/QUOTE]

Transom might rip off, leading to your outboard becoming a "donation" to poseidon...also, flooding your boat.
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Old 01 February 2016, 18:28   #9
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Stig - thanks for your thoughts

Jeff - looking at a similar idea

Max - see Fenlanders statement. He is spot on in terms of what I am wondering. But... for the Tohatsu, a 30mm riser is not enough. A 65mm riser worked well. Need to try in between and see what works with a Yam 20 or 25 ss when I sort it, if that plan works.

Fenlander -a step too far is my thought too. Was just wondering what others thought. In some ways its no different to a jack plate on a speed boat.
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Old 02 February 2016, 16:32   #10
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Don't want to muddy the waters, but...

I've got the aerotec 420 and a long shaft motor. Obviously the 420 is designed for a long shaft. However, the only difference in the transoms is the cutaway on a 380 or no cutaway (420). Theré is no height difference in the transoms where they meet the tubes. Google 380 and 420 images and you'll see what I mean.

So, if the only difference is the cutaway, I don't see an issue.. but try at own risk!

Simon
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