Propeller splines on '09 20 HP

Does any one know what the spline count is on this engine? I am going to use two of them on a 32 foot sailing catamaran and suspect I will have to repitch the prop since this is such an unusual application.

I have not yet received the engines but would like to start researching the project.

Elrod

[boats.net]

Don't know spline count but it uses same prop as 9.9 and 15hp.