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Old 06 September 2006, 16:14   #1
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Country: UK - England
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advice on small backup outbaord

i have a searider 4m with 50 merc and want to put a small motor on the back for safety what size would i need to get me out of trouble also what length shaft would i require as its positioned to one side !?
also would the extra weight be an issue?
thanx
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Old 06 September 2006, 16:33   #2
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Cant be sure on power but I have 6hp on my 5.8m Humber so you shouldn't need that much, maybe a 4hp or something? The rule of thumb quoted to me was 1hp per metre of boat.

What I did on mine was to decide where I wanted the aux on the transom and measure the transom height at that point to make sure the prop would be below the hull in a clear flow of water, I ended up needing a long shaft, and having had it out for the first run on the weekend, it is just right
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Old 06 September 2006, 16:57   #3
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Depends on the setup as to what'll even fit on an sr4 dino-you might find you'll need a bracket to mount it on too. The only one I've found so far that'll go straight on is the 2hp evinrude/johnsons from the 80's that only have a single transom clamp screw. Even that is tight. I managed to get an old 4hp Evinrude (the old one with no neutral selector) on with a bit of clamp trimming and so on but that was with a Blueband 50 as the main engine and they are quite a bit slimmer than the later motors.
4hp was ideal though.
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Old 06 September 2006, 17:22   #4
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did the 2hp manage to move it well enough? i know where there is just such an engine in need of some tlc that i have been consiering for a similar sized boat... because i think it might just fit.
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Old 06 September 2006, 17:37   #5
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Quote:
Originally Posted by Polwart
did the 2hp manage to move it well enough? i know where there is just such an engine in need of some tlc that i have been consiering for a similar sized boat... because i think it might just fit.
Dunno-I bought the 2hp and the 4hp as a job lot and tried them both to see if they'd fit but decided more was better and used the 4hp. It was a fairly easy (20 minutes with a bit of fancy angle grinder work) job to make the 4hp fit.

Ollyit might know-I think he's got a 2hp evinrude he uses as an auxiliary.
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Old 06 September 2006, 17:56   #6
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Quote:
Originally Posted by Dino89
i have a searider 4m with 50 merc and want to put a small motor on the back for safety what size would i need to get me out of trouble also what length shaft would i require as its positioned to one side !?
also would the extra weight be an issue?
thanx
Hi there, my last rib was a 4mtr with a 40hp mariner. Our spare outboard was a 2.5 mariner which clamped straight on to the transom with no problems apart from limited steering due to being close to the other one.therfore using the main engine to steer worked very well. we managed to gain a speed of 4mph with 3 up. thats quite slow i know, but far better than paddling away!
regards
pete
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Old 07 September 2006, 14:09   #7
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Auxillary

Hi, I have a 5m RIB with a 65hp and a 3.5 Tohatsu.

I tested the 3.5 Tohatsu out last weekend in the fairly strong wind and it powered me back inshore after my 65hp struggled/failed to start and I drifted out.

The Tohatsu's have a grab handle at the front which you can steer with if the tiller is obstructed.

Thinking of modifying this grab handle into a centre tiller.

Pics of my RIB and donkeys here: Auxiliary thoughts
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Old 07 September 2006, 15:00   #8
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thanx for help seems space is limited and the 3.5 tohatsu doesnt sound a bad place to start looked at brand new 3.5 2 stroke for 350.00 any one know of cheaper?
has anyone got pictures of there aux and how they fit for space
thanx
Nos do you have long or short shaft aux?
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Old 07 September 2006, 17:41   #9
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I used a shortshaft-the prop was mostly below the level of the hull due to being offset on the transom and it's not like a 4 will get it to planing speeds. It didn't cavitate. BTW the 4hp and 2hp 80's evinrudes use the same prop hub so props are interchangeable if you want a bit more torque. .
An SR4 is fairly stern-heavy with a 50hp on and the flooding hull full anyway so no real danger of the prop coming out of the water.
It's a lot easier to get a cheap shortshaft too!
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Old 07 September 2006, 17:53   #10
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I've got SR4 with 50 and have used both a 4hp merc Aux and a 3.5 Tohatsu. Both worked well. Tohatsu gets just a little over 4 knots (2up) and steering with main engine works well.

No problems with mounting it either since it's so slim and there is enough room for some steerage without it hitting the sponson. Only think I noticed on my old engine with hydrofoils was that it was possible for the Aux prop to hit them if both engines were turned towards each other.

One tip - tie the engine up so it can't bounce on the lift pin when underway with main engine or pin will eventually bend!
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