Can anyone point me in the right direction to size a prop for an electric boat?

I want to size a prop for a Speed Gem 9TD Cryptonite motor (I figure it puts out about 150-200 watts).
I need high torque, low speed for the boat to pull a payload at only 2-3MPH.

Can anyone suggest what size prop I should begin with or how to analyze this requirement?

Thanks

if you are going to be going that slow then you may want to consider a pump for the water cooling. try graupners web site i think they may have 4 or even 5 blade props that are made for tugging, as far as size goes i cant help you there because everyone says im over propped on my set up