The major issue I see with a long range cruising power tri is the weight. Not the hull
weight but the fuel
weight. To cross an ocean, even with a very efficient diesel, on a 40' trimaran
would probably require 500-1,000 gallons of fuel. That's a huge percentage of a 40' trimarans load carrying capability. Sure you save some weight by removing the sailing hardware
, but some of the savings is going to have to be in a larger engine
It's probably doable and retain some living space, but I doubt the numbers would work out in your favor.