Auxiliary Outboard for 32 ft trawler

I’ve donated an outboard motor bracket to my friends 32 foot trawler project. The motor bracket itself is rated for up to a 130 pound outboard and a 15 hp outboard should come in under that weight. Can anyone point me to a way to decide whether this outboard would be enough to move the boat?

I’m not expecting this outboard to conquer high winds or rough sea conditions but at least there would be some additional power in the event of a loss of function of the main motor, and the stern mounted outboard could also serve as a stern thruster.

 

A typical 15 hp outboard motor 'should' move a 32' trawler in very calm conditions - but it will be struggling as soon as you get a bit of a head wind or a slight sea.
What type of trawler project is this - eg a canoe stern type (like a Fales 32) or one with a broad transom?
And what is the main propulsion engine? Not so relevant, but still interesting to know.
Re justifying it's keep on board re use as a stern thruster - I would have thought that simply making best use of the 'natural prop walk' (either to port or starboard, depending on the rotation of the propeller) would have more effect?
If the boat is something like a Fales would it be possible to have a small motor sailer rig added?
I think that this would be more useful than having an O/B motor on the back - and the sails would also help to reduce rolling.

 

The choice of motor matters, to give the best chance of being useful, a "high thrust" variant would be required, typically an engine with a greater reduction ratio in the gearcase, takes a larger diameter propeller, and of course a pitch that allow the motor to rev out. Also, select XL shaft if possible. A "normal" outboard used to power a light alloy dinghy would not be worth trying.

 

Your friend should look into the high thrust outboards. They have lower gears and large area propellers.

 

glad to see you got an answer to your question.