Mark when these boats were built in the 70's and early 80's fuel was cheap and they were designed to run at 10 or 11 knots burning about 8 to 10gph. Now few can afford to feed a boat that much fuel. So yes most trawlers only use the power of one engine most all the time. If one was to change the shape of the stern below the WL a bit so the hull becomes closer to a FD even less power would be required.
North Western Washington State USA