LOL, Mike's your man!! :)
In all fairness, once you figure out how to read the different prop numbers, it's a bit simpler...
The site I quoted above, has that part down pat!
Understanding diameter of the prop and pitch (which is the distance the prop travels forward on 1 revolution, theoretically) and shape is pretty much all there was to it...
To get the top speed, I believe Mike did the following calculation
33mm diameter at 1.6 pitch (calculated pitch x diameter = distance travelled by one revolution) would yield
33 x 1.6 = 52.8mm/ revolution
2500KV motor @ 11.1 volt = 27750rpm at full throttle
27750rpm x 52.8mm = 1465200 mm/minute
Converting this to a bit easier figure = 87.912 km/h THEORETICALLY
However, in reality, the prop slips in the water, and so you loose anywhere between 15% - 30%, so 67.6 km/h is possible...
The shape of the prop, determines it's efficiency to a large degree
Other factors play in at these speeds as well, coz now you have tremendous drag from the hull to think of, plus that massive fin, total weight, water conditions etc
I'd really like to figure out what the heck the different diameter has an effect, I think it pushes more water, so you'd think higher speed. I think it comes at the cost of engine heat... anyone care to clarify? :)
PS. I'll bring my boat down to Brissy when I've built it, can show it all to you then ;) I'm sure I've got a fair bit to learn yet :p