80's Sea Ray Inboard to Outboard Conversion.

[dpb]

First off this is not a how to post, infact it may turn out to be a how not to post as the work is under way.
The work is being carried out on my project boat, subject of this thread:

My 80's Sea Ray 197 Monaco Project

The reason for the conversion is as a result of problems with the engine restore related on this thread:

Mercruiser 4.3 V6 rebuild fail.....so next step?

To fix the engine issues was going to cost me in the region of £2000 and I still had a seized up leg to sort out and the boat is unlikely to be worth such further expediture.
At first I considered a change to an outboard of equivalent power to the existing inboard but the cost of a decent engine and appropiatley engineered mounting arrangement would be equally if not more unviable.

Eventually an idea came together based on:
A slow boat, call it a river or lake launch , would be a useable boat.
The existing bathing platform is solidly built and can take at least three adults moving around on it with out moving. (say at least 250kg)
An outboard of 15 to 25hp should achieve 10knots.
Such an outboard weighs 40 to 75kg
A decent 4 stroke 15 to 25hp can be got for about £1500
Breaking and selling the existing engine is likely to achieve at least that amount.

Simply bolting the outboard to an L bracket fixed to the top of the bathing platform was not going to work as it would be too high, even for a long shaft.
The top of the outboard mounting had to be a few inches below the top of the platform.



The basic design then is to build a 'box' that hangs from under the bathing platform so that the mounting point for the outboard is in line with the rear of the platform.
The section of the platform that is aft of the existing cut out will be removed to accomodate the motor head.
Construction to be from 18mm ply and GRP.

The ply is screwed together using resin as a glue.
Wedge pieces smooth the corners and a filler made from resin with added granules fills any gaps before laying up the fiberglass



The bottom half of the box was glassed up first before fitting the base of the outboard well. The box overall depth is determined by the need to have something to fix the lower outboard fixing bolts to which is why there is going to be a hatch for access.



The ply is all 18mm that was recycled from some shelving that I made years ago.
double thickness for the outboard to be mounted to.
It is probably standard ply which should not matter if my glassing is done properly. Plus the boat will be trailer stored.
All faces and edges of wood have been 'painted' with resin before assembly.
The timber pieces are pressure treated.
I have placed a couple of off cuts of ply in a bucket of water to see what happens. (nothing yet after 2 weeks)

Thats it so far.
My intention is to probably paint the box with waterproof paint for good measure, mainly as I have no idea how to apply gel coat, plus I am not sure how waterproof the lay up is without a gel coat.
The existing hole in the transome will be blanked off with resined and painted 12mm marine ply, the idea being to be able to convert back if required in the future.
Any comments welcome!

 

[Seastoke]

First if you think you need marine ply for blocking the whole then you need it for your box , second, I don’t understand is the hole for the engine to go through. Also get a two stroke lighter and faster .

 

[jfm]

Seems fine to me. Bit heath rob but ok

Seastoke, the hole you can see is not for the engine to go through. It's for an access hatch to the lower mounting bolts for the outboard - all explained in post #1.

Gelcoat is easy so don't let it put you off. For a finished coat, mix in catalyst + styrene wax and it can be applied like a thick paint.

 

[dpb]

Seastoke, the intended use of marine ply on the transom is partly because I happen to have some, but also because I won't be sheathing it in GRP, though it will be either painted resined before bolting in place. If the whole thing works out then I may improve the arrangement at a later date.
The hole is as per JFM's comment.
Given that this will be a slow boat I dont think any speed advantage of the 2 stroke will be of much use and I think the quiteness of a 4 stroke will be a more pleasant experience at 8 to 10kn.

JFM, it is a bit heath rob, and is a development in progress which may need adapting or changing after trials. The two main questions for me are:
How will the boat be effected by loosing the 'ballast' of the existing engine? (Net loss of about 200kg)
I know the existing platform will take the engine but will be interesting to see how it handles the thrust of the engine.
I shall look further into the Gelcoat as always assumed it needed moulds etc....
Cheers

 

[Sticky Fingers]

Paint-on Gelcoat with the necessary additives is sold as ‘Flowcoat’.