Outboard on heavy wooden boat

[Mollyfish]

Hi everybody, can anyone help me? We've got a 1950's 30ft wooden boat, think it weighs 10 tons. I'd like to fit two outboard engines. I believe the original diesal inboard was about 40 horsepower, does this sound about right for this size of boat? Also, will any standard propeller size/torque ratio be ok, or do I have to get a specific set-up?
Any help greatly appreciated!


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[Peterduck]

Two ponies do not equal one Clydesdale. Even diesel outboards would have their work cut out propelling a ten-ton boat. Ordinary two-stroke petrol outboards also go through a lake of fuel compared to a diesel, and then there is the matter of simply having petrol on board a boat. My own boat is also about 10 tons and has a 40hp diesel, which seems to be about the right size for it. 10 tons of boat wants some real grunt to move it, and when everything turns pear-shaped, as occasionally happens at sea, you are going to want all the grunt that you can get.
Peter.

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[Sniper]

I guess it depends what you want the engine to do. If you are looking for the sort of performance that a high power inboard diesel will give (i.e. motoring ability over a prolonged period in all conditions) then you will probably be disappointed by outboard power. If, on the other hand, you only want auxiliary power to move the boat gently in reasonable conditions then a smallish outboard should do fine. There's a sailing barge, 'Betula' which uses a 40hp outboard attached to the rudder as auxiliary propulsion and this seems sufficient to move her along when necessary. Other similarly sized craft have used the same solution.

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[trouville]

you cant think of an out board on a 10 tonner its easier than a sweep but only for moving in light conditions . I moved my 12 ton sail boat while charging my engin starting battery, with a johnson 6 hp i made slow progres with almost no tide and almost no wind and both with, but even with a very light wind as it turned it gradualy became hopeless and expensive! I enjoyed trying charging my batterie using an inverter + 2 60 watt solar panels and my services battery to charge the engin battery.

It was a wonderful day the wind had droped to nothing after a good sail it was 3.00pm 1 hour was enough to try both using my outboard and to charge my engin batterie.
i now know how the out board moves my boat im glad i tried so i wont waist time setting it up again but in need get the anchor ready!

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[mikesharp]

I think you have the right approach there. I depends what the motor is for.
Our 25 ton yacht when suffering engine failure in NW Spain was driven against a fairly stiff wind by our rubber dinghy with 5 horses in order to lift the fairly heavy ground tackle. We thought it would just share the load with the chain pullers (no capstan) but in fact had to be throttled back to avoid over shooting. It could be though that the dinghy gets a better transfer of power from the outboard than we would get from a boat mounted bracket (hull shape and all that)

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[trouville]

pushing to help get in the anchors one thing but pushing to go somewheres another.If you have no choise get the dingy out and push you will get on at least, but an out board as anything other than an emergency or help out is silly if its transom mounted a following sea will constanlly swamp it and the dingy a better choise will be push off from time to time ,my jhonson 6hp is bullet proof but after an hour or so heats a bit
Having recently been sailing a 20foot platic racer with a 2 hp as main engin i found we got up the river without any problem we even moterd the 4miles to the start (no wind in the bay) but when we went in to a lunch port i dicoverd reverse to be a joke and no breaks!! Stand by the fend the key off crunch!!!well now i know, on my heavy dingy 200kgs i can zoom in (when alowed) come along side and just touch revers to stop i can also reverse without difficltie but not with a light weight sail boat to back up i had to throw i line and warp me in

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