Hi Dean,
It depends a LOT on the kind of usage you intend. Personally, I wouldn't put anything less than a 9.9hp four stroke on, although an 8hp four stroke would probably suffice.
In the Yamaha line the weights are as follows:
8hp 83lbs
9.9hp 99lbs
15hp 114lbs
I would suggest a long-shaft model, as the prop tends to come out of the water in heavy short seas.
To seal off the openings this is what I would do:
If possible seal the prop shaft so it can be used again in case an inboard is ever re-installed. A slightly tapered close-fitting softwood plug carefully driven into the tube, then a cap epoxied on the end should work. You could do this on both ends of the tube to be absolutely safe.
A threaded cap on the exhaust outlet, and the same on the engine intake seacock should work.
Peter
#1331 'Sin Tacha'
