Hi peter, do you want a brass 3 blade prop for cosmetic reasons, if so they do look nice.
I did extensive testing with my 3 foot fireboat using brushed, then brushless motors, and then prop testing. I was using eagle tree data logging for watts, amps, gps speed etc.
The plastic two blade cheap as chips props actually produce similar readings to the more expensive brass 3 blades. Personally, as you are at the "guess work" stage, just use the plastic two blade ones, but use "x" pitch, standard wont give you the speed. Get a few sizes, 30, 35 40 mm and test. When you have the optimum set up you can then go to the expense of the brass prop. I sent Simon Higgins (ex prop shop) my readings and he made a specific prop for my boat, its a 35mm cleaver 3 blade. He has his own company now but I've forgotten what it is! He was at Blackpool last year so someone might have the list of traders. His props are balanced and one piece, very nice.
I also experimented with a belt driven gearbox. The set up I have at the minute is this motor

https://hobbyking.com/en_us/turnigy-t600-brushless-outrunner-for-600-heli-880kv.html

overkill really! but my 3 footer is an original very heavy aerokits boat.

Mark as you see for my 34" Crash Tender I reckon the 3542/1000 kv motor will be OK hence the 35mm dia prop proposal.
Just a thought on trimming the rudder assembly to fit under the deck - is this not going to mess up the top stuffing box/bearing on the rudder shaft/post assembly?
Cheers - Peter

Peter, Had a look at the Raboesch site, the prop i looked at was the Metric 162 - 17, 40mm dia. As you are looking at a 42mm motor, this should give more than enough grunt. What make of motor are you looking at??? my 46" Crash Tender has twin motors, with 45mm dia props, the motors are from Airtec, a Yorkshire model shop, might be worth a look at their site

Mark

Mark, thanks for the tip on being able to cut the post and tube on the medium rudder to fit under the deck......
I am planning to use a D 3542/1000 kv motor with max power of around 600W......not wanting to go for water cooled - I was trying to keep the heat down.......this was my reasoning for the 35 mm prop dia - 3 bladed brass for a higher efficiency. Did you have any idead what type ( A,C or D) of 3 bladed prop I should go for? Cheers - Peter

Hi Peter, I would use the medium rudder, the small is not going to give you enough steering, also with the medium assuming it fits the fitted rudder post you can cut the rudder post to fit under the deck. The prop depends on the motor you will be fitting, 35mm might be a bit small, 40mm would be better, again depending on the motor, no bigger than the case size, and go for something like 800kv for the extra torque.

Mark