ORIGINAL: TERBObob
Are you inverting the Zen ? If not , then you should go with the size of the prop , and then half more added , for a correct side to side width .
( example - say your running a 16 inch prop ... the width of the boat should be at aprox 24 inches )
exept for nitro's where teh ull is only 2" wider than the prop.
shaun