Hi Jo, that’s an interesting paper with some useful concepts not often published. Thanks for posting it. I have enjoyed reading it.
Robert, that paper will give you some idea of what is involved in designing a propellor from scratch. For an easier answer to your question, I suggest that you refer to your signature panel, and visit your local hobby store, or favourite on line outlet, and buy a few ready made model boat propellors, and see which one works best. Then you can make a similar propellor from your preferred materials, knowing that it is based on tried and true model size propellor designs. You will also see the blade profiles and outline shapes selected by the model propellor manufacturers.
Select the largest diameter that will fit your model while still leaving a sensible clearance between the propellor blade tips and the hull. About 10% of the diameter is usually suggested for full size sail boats, but a little less will still be ok on a model where the hull stiffness is usually relatively higher than a full size hull. As Jo’s paper states, the larger diameter is normally more efficient, meaning more thrust for a given engine power. For your specific model, I would expect a four blade propellor might be a better choice than two blades, but if not too expensive all the available options are worth a try. Once you have a good selection, you might even consider one of the commercial brass propellors which will look more in keeping with your model than the usual red plastic ones, but more expensive so better to work out a suitable size and pitch first. This leaves only engine rpm to experiment with.
I have enjoyed following your build almost since the start, exciting to see it ready for a propellor.
MJM460