i hate asking silly questions here....

[scoobert]

but here it goes.
can i take a fully built fiberglass cat, and modify the hulls extensively?
looking at a fiberglass cat with a planing hull. so i would want to change it to a trawler/sail hull. the inside is fully finished.

[Kettlewell]

You can do almost anything, but whether or not it is wise to do is another question. I have seen motorboats converted to sailboats and sailboats converted to motorboats, but almost without fail the result is a very poor vessel.

[scoobert]

it would remain power, just have no interest in twin 400HP engines pushing me at 35Kts.
and drag would be much less with a more canoe like hull.

[Teknav]

Unless you are a licensed marine architect with deep pockets, I would not try any conversions on my own. There are "tons" of calculations to be made, of forces that will be exerted on the hull. This will involve a complete redesign, testing and certification for "one of a kind". Take my free advice: Don't do it!

[RabidRabbit]

I would think if you pulled the 400 twins and sold them, then slap a pair of beta 38, 60, or 90s in, your fuel usage would drop dramaticly, as would your speed. Aim for 10kts max, 6 or 8kts cruise. New props are a must and I would pass on cutting into the hulls unless you have a real good plan. A repower for slow speeds seems doable.