Bombard Aerotec - using a longshaft

Neil Harvey · 31 January 2016, 20:39

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?

Stigomery · 31 January 2016, 21:23

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.

jeffstevens763@g · 01 February 2016, 07:20

see into shortening the leg neil if theres a kit for it.

Max... · 01 February 2016, 07:27

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!

Fenlander · 01 February 2016, 13:53

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.

office888 · 01 February 2016, 15:55

The extra 7.5" would stress the transom outside of engineered limits.

Catastrophic failure may result.

matt h · 01 February 2016, 17:37

[QUOTE

Catastrophic failure may result.[/QUOTE]

And then it will sink or spontaneously blow up!

office888 · 01 February 2016, 18:09

Quote:

Originally Posted by matt h

[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.

Neil Harvey · 01 February 2016, 22:28

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.

simonafloat · 02 February 2016, 20:32

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

Fenlander · 02 February 2016, 21:10

Simon muddy waters good if it helps sort the issue and don't doubt what you say but that's a bit weird re measurements. In the attached image I happen to have a level as a straight edge across my 380's transom and you can see that the standard cut down from straight across is close to the height of the level which is only 2.25" so you'd assume if things were as they seem from your understanding of the 420 then a longshaft on a 420 would be 2.75" deeper in the water than a shortshaft on a 380... and deeper in the water seems to be what Aerotecs dislike re spray.

And Neil mentions wanting to raise the height by 7.5" so I wonder if he has a "long" longshaft? If his older model 380 has an identical transom to mine... which I think it does... then the 7.5" lift would need a plate sticking 5" above the line of a level transom. All very odd??

Fenlander · 02 February 2016, 21:14

BTW while searching on Aerotec 420 transoms I came across an image showing a DIY spray deflector of a type I'd not seen before and it's so so simple!

http://img1.hyperinzerce.cz/x-cz/inz...su-30-hp-4.jpg

piotr · 03 February 2016, 06:40

Quote:

Originally Posted by Fenlander

BTW while searching on Aerotec 420 transoms I came across an image showing a DIY spray deflector of a type I'd not seen before and it's so so simple!

http://img1.hyperinzerce.cz/x-cz/inz...su-30-hp-4.jpg

Nice setup ! I wonder how he mounted the steeringconsole ?

jeffstevens763@g · 03 February 2016, 07:32

i agree with fenlander short 15in, long 20in extra long 25in so he should only need to lift 5in a false transom might be the answer if only talking 5in made from ss plate for strength.for me i would look at shortening the shaft especially if the boat is to be used to its full potential. OMO

cheers

jeffstevens763@g · 03 February 2016, 07:34

Quote:

Originally Posted by Fenlander

BTW while searching on Aerotec 420 transoms I came across an image showing a DIY spray deflector of a type I'd not seen before and it's so so simple!

http://img1.hyperinzerce.cz/x-cz/inz...su-30-hp-4.jpg

i ve seen that before on larger boats very simple good find david, i do like that A frame sets the boat off.

cheers

kaman · 03 February 2016, 10:04

That's a cracking looking Bombard.
Looks just the ticket.
You could transport a car on that trailer let alone an air floor sib

:thumbup:

Neil Harvey · 03 February 2016, 22:02

Ok, that transom mod won't help me as I have a waterfall under the ob handle!

Raising 65mm has fixed it. Less may work but I don't know.

LS ob is 20". 5" more than short but I need to raise by 2.5" potentially to remove the usual issue, hence 7.5" comment.

I also wondered if the 420 just did away with the cut out, hence my idea of raising transom maybe not being too much of an issue, because the stresses are in the same physical location on tube to transom fixes.

jeffstevens763@g · 04 February 2016, 07:01

not about the original problem but linked if anyone requires making the water deflector for the transom direct plastics in sheffield supply all kinds of sheet material 2-3mm HDPE would be ideal as its easy to cut and can be formed by a heat gun for right angles etc also thicker material for backing plates to secure to the transom just for info.you can cost it on the web site to see if within you budget they also offer a cutting service.

cheers

Neil Harvey · 06 February 2016, 14:21

Quote:

Originally Posted by Neil Harvey

Stig - thanks for your thoughts
Need to try in between and see what works with a Yam 20 or 25 ss when I sort it, if that plan works.

The Yam 20 ss plan is coming together. Collected a late 70's (roughly) Yam 20 ss in the week. It was described as "BEEN STOOD IN GARAGE FOR ABOUT 2 YEARS. WAS RUNNING WELL WHEN TAKEN OFF BOAT AND REPLACED WITH A BIGGER MOTOR. WILL PROBABLY NEED A SERVICE SO SOLD AS SPARES OR REPAIR"

Decided it was worth a punt for £200. After fixing some silly issues this morning, it is now up and running nicely. Needs the tiller arm sorting, a new thermostat, new impellor, spark pigs, and a bit of re-wiring. But should be a running order 20 short shaft for less than £300 I hope. Then time for a play.
It's 42kg, so a bit easier to man-handle than a 25 as well.

Fenlander · 08 February 2016, 08:32

Be really interesting to know if this 20hp changes your splashback issue. Going from 9.8 to 20hp will make a nippy outfit for sure though.