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Old 22 July 2020, 06:58   #1
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Country: UK - England
Town: London
Boat name: 154
Make: Avon
Length: 3m +
Engine: Mercury 7.5 lightnin
Join Date: Jul 2020
Posts: 12
Incompatibility. The long and the short.

Hello all.
First timer here in lots of ways and glad to know Ribnet is out there for souls like me.
I am keen and hopeful to achieve my aim of mounting a long shaft safely on a short transom sib.
This is a restoration project without a time frame and also Importantly one with hardly any real budget Available, so on the cheap as the unit will only be used a few times a year when Iím allowed out by the wife and children. ( they will come along too in the future).

I seek all your wisdom and advice on the following set up;

The sib is a 40 year old Avon s400 ( All the tubes hold air but the hull skin needs 5 small patches here and there. Its a 15 - 16 inch transom depth In the middle then curves up about 1 1/2 inch either side to meet the tubes. It is 30 mm thick plywood. I have remade the ply deck sections so far and made a new screen.

I have yet to water proof the deck and will be seeking advice there too.

The whole set up will hopefully fold away into a small camping trailer neatly with all the kit In it for storage and then for my annual escapes).

The engine is a Merc 7.5 two stroke (circa 1981, currently non runner but turns free, engages into gears and worked 2 years ago Iím told, needs a big clean and service plus a few broken levels but mostly it is all there. Itís shaft from bracket to cav plate is 22 inch).

Iíve got another older model which is seized and battered for spares etc. (both engines cost me 100 quid).

Firstly Iím going to get the engine running ( by way of novice learning from U tube, manuals etc, If that all seems nice, then I would prefer to fabricate some sort of slot -on and then bolt down raised transom piece or if I have to, permanently make and fix the transom to the required height.

This is robust sibs and we once had a 35 hp on it for a season but my fears are that the extended 6 inches of transom and raised hieght of the engine block etc will make it a dangerous set up even thou Itís a 7.5.

I want to keep the prop as close to the surface as possible as I will be going on rivers, canals and estuaries and Sea.

Am I being paranoid about this? And should I just have an easier life and be more carefully with the extra depth of the long shaft in the water?

Obviously I want the optimum performance set up to be able to plane now and agian ( if that is possible with this heavyish boat and a 7.5 ?)

At the end of the day as I said my budget is tight but my dreams of good fun and adventure persist daily.

Any advice and tips much appreciated.

I live in Peckham London if someone knows who I may seek out to for advice in person.

Dai
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Old 22 July 2020, 14:12   #2
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Country: UK - England
Town: Retford
Boat name: Spy-sea-one
Make: Excel 435
Length: 4m +
Engine: Suzuki Outboard/25/4
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Hello and welcome nice project you have regarding the long and short with a 4 meter boat and 7.5 hp your not going to be bothered by shaft length because you will be at displacement speed I would guess even so you can cover good distances and see more at slower speeds IMO
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Old 22 July 2020, 16:41   #3
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Country: UK - England
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I'd be more worried about the electrics on one of those ancient mercs dying while I was using it than the transom giving up.

I certainly wouldn't feel massively safe anywhere I couldn't row ashore.
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Old 24 July 2020, 08:34   #4
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Country: UK - England
Town: London
Boat name: 154
Make: Avon
Length: 3m +
Engine: Mercury 7.5 lightnin
Join Date: Jul 2020
Posts: 12
Thanks all responders for the straight truth of the matter. I guess stupidity is often driven by a ruthless economic drive.

I have had great times on that old sib when my brother owned it and wish it to live on. I gather that they too have a safe life span of around 15 years plus which worries me now as this one is knocking on nearly 40.

The merc 7.5 engines were a cheap impulse buy in order to at least have some sort of basic set up. I have not read much in the way of praise for those dated engines and now wonder what I should be really trying to buy engine wise in order to achieve reliability, portability and planing power on the 4m sib?
The second non running older engine has a 17 inch shaft and looks exactly the same as the newer 22 inch one. Does anyone know if this is a pain or not to switch over and service providing the newer one actually shows some reliable life left in it once running? The engine block etc all look the same too.


If all that is a pointless economic pipe dream then I have read the rare gems to buy are Yams and Tohatsu 9.8/9 s. Hopfully these would push it up to plane also? or is the 4m Avon needing more grunt?

A 15 hp for all thier benefits seem to be a bit heavy to lug about for a solo weekender like me - any thoughts where to start again most welcome.
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Old 24 July 2020, 09:31   #5
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Country: UK - England
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Engine: Suzuki 8HP
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I would start by seeing if the long shaft one has a viable engine, get it running and if its ok think about swoping the power head over onto the other short shaft outboard.
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Old 24 July 2020, 14:26   #6
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Join Date: Oct 2011
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It's an old boat yes but with care and regular maintained it should be ok with low HP engines I would get the 7.5 running and go for it you will then have a starting point to work from IMO
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