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[Captain Flack]

How do you work out what size motor, battery, propshaft and prop(including blade numbers, you need for a specific hull?  For example, I have a wooden hull, fishing boat style, about 16ins long, and draws a couple of inches.  That's all the detail I have.  I have no idea who made it or when.
Is there a formula that you can apply? or is it just experience?

[pompebled]

Hi Captain,

Most is experience, a hull that small will be sufficiently powered by a 400 size, or a slow revving 540 size motor.
You'll have to take in account the propsize and pitch used and select the motor accordingly, for a fishing boat, about 4000 - 6000 rpm at the prop is sufficient, again, depending on propsize and pitch.

As always, pictures are 'mandatory'.

Regards, Jan.

[malcolmfrary]

A lot depends on the actual displacement of the hull, and its actual shape.  If it was a "sport fisher" type, the 400 would be appropriate.  If an "inshore fisher", the same motor on a lower voltage would work.  Possibly a Graupner multispeed, one of the smaller ones.  With that you get motor, gearbox, shaft and prop all in one go.
I have a trawler about that length, but it is a small scale model of a large trawler - that runs very well on a motor from a servo and a home made 1/2" two blade prop.

[bj]

How do you work out what size motor, battery, propshaft and prop(including blade numbers, you need for a specific hull? 

Here it is again......... take your pick on motor,  prop or engine.