Best prop depth for outboard

What is the optimum prop depth for an outboard on a small 20ft Tri such as the TC601, just fitting it out and at this stage I have to mount the rudder and outboard. There shouldn't be too much of a problem of the mounting point out of the water by to much over the waves, as the boat is fairly short.

If the prop is too close to the rudder will you get prop wash onto the rudder blade, any experiances of distance between rudder and prop ?

 

Why do you need a rudder, if you have an outboard? Can you post photos?

 

Best look at the design on http://www.boatdesign.net/forums/multihulls/tc601-trimaran-design-tim-clissold-53157.html

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