outboards

[celtictemple]

Hi-I am looking to purchase an auxillary outboard for a motorcruiser appx 2 tonne weight. Would a 10hp outboard suffice or do I need 15hp? This is the first time I will have done this and as I am a novice to boating, help would be appreciated fom experienced boaters. Cheers

 

[AndieMac]

Hi-I am looking to purchase an auxillary outboard for a motorcruiser appx 2 tonne weight. Would a 10hp outboard suffice or do I need 15hp? This is the first time I will have done this and as I am a novice to boating, help would be appreciated fom experienced boaters. Cheers

Could you tell the forum what boat you intend to power, as no doubt some may have a similar arrangement already in place.

The weight of both engines (2 stroke) will be similar, and seeing as you are west coast Scotland, strong tidal flows will need to be factored in.
I would be thinking 15 hp (longshaft) on a good quality bracket, and sound fixture points and an internal backing plate. Keep checking the tension on the bracket nuts and bolts every season, to make sure they aren't working loose (nylock nuts?).

I know at least one type of 15, which has a 'Co-Pilot' lever (Merc. U.S.A. version) which slides across the front of the engine and locks it ahead. This enables the boat to be steered at the main helm by the outdrive or rudder, for a more comfortable, drier and better vision location.

Keep starting and running the aux. pretty reguarly, and get used to the process. Murphies law is going to say, when the main stops working conditions probably won't be favourable, its going to be no time to start the learning process.

Hope all goes well, and enjoy your boat.

 

[neale]

Hi-I am looking to purchase an auxillary outboard for a motorcruiser appx 2 tonne weight. Would a 10hp outboard suffice or do I need 15hp? This is the first time I will have done this and as I am a novice to boating, help would be appreciated fom experienced boaters. Cheers

An aux outboard is only going to push your boat along at its hull speed. I am guessing you are under 25ft based on the weight so your hull speed is going to be only around 5 knots. A 10hp will suffice although many 15's are based on the same engine so weigh exactly the same.

Things to think about are fuelling the aux. If it is 2 stroke and your main engine is diesel or 4 stroke you will need to carry a spare tank of fuel with enough capacity to make the aux usable. Then you have the problem of storing this extra fuel safely where the fumes can't collect in the bilge. If it is four stroke and your main engine is also 4 stroke, think about plumbing the aux into your main tank. This of course won't help if the reason for the main engine failure is dodgy fuel, so you may need to still carry a spare can of clean fuel just in case.

You will probably need a long shaft as a short shaft will probably not put the prop deep enough to keep it underwater as the boat bobs around at displacement speeds.

10 and 15hp engines are quite weighty, circa 40kgs, so you need a good strong bracket for it to be permanently mounted. You won't want to be trying to lift one of these onto a bracket out at sea. The best engine I think for this purpose is the Tohatsu 9.8 2 stroke. Same power as a 10hp engine but weighs just 27kg. Trouble is they are very hard to come by now.

Steering can be achieved either by locking the aux in the dead ahead and using the main boat steerage. Even if the boat is outboard or outdrive powered, this will act as a rudder. Or you could use the little outboard tiller to steer but you may need to consider a tiller extension.

Another thing to consider is that an aux outboard often sits on the transom unused and unloved and this is a recipe for it not to start just when you need it. If you get one, make a point of running it up regularly.

 

[Jim@sea]

Auxiliary outboard.

My 22ft (2 tonne) boat, semi planing hull, 72hp inboard diesel has a 9.9hp TWO STROKE outboard. Does 6knots. It is ideal as an auxiliary as being a 2 stroke it is not as heavy as a 4 stroke and as it is mounted on an outboard bracket which you have to raise and lower I can lift it with ease, but off the boat it probably weighs 60-70 kilos.
However if you change to a 4 stroke they are much heavier.
I believe in using one type of fuel and I am trying to buy a 4 hp. 2 stroke for my tender so that every can on the boat is the correct fuel mix. Because one day I will get it mixed up and use the wrong can.

 

[celtictemple]

Thanks, Guys for all your useful advice. Much appreciated. The boat is a Sealine 28 and has a petrol volvo penta engine, so good advice about using same fuel for aux. Much food for thought.