I would look at the Perkins 6-354 or the Cummins 4's and 6's as they are very readily available, especially the Cummins, and very inexpensive, . The Perkins are easy to find here in the Caribbean because they are in a lot of sail boats, but I will probably go with the Cummins if I have to re-power. Actually, the 4-71 or 4-53 would be a better package in a trawler as they have much more torque, but harder to find service. These engines can be had for around $5000.00 rebuilt, or less if you know where to shop. My own boat, 50 tons full load, only uses 50 hp out of each of my existing 200 hp Volvo's. I use 4 gph at 1400 rpm, which is 8.2 knots, all I need to go. I understand from my mechanic the rule of thumb is 25 hp for each gallon of fuel used, at least in the older diesels. When I downsize, if ever I can reduce from about 1200 sq. ft. of space, 65 registered tonnes, and all house like room sizes, I will find find an old Hatteras 50 or 53 SF and put in the Cummins or Perkins. Nice living spaces with a back deck connected to the living room and kitchen, bedrooms down three steps. Great for older people as stairs are minimal. Steering station up top for visibility and out of the way in the living spaces. Easy to change ladder to flybridge to angled stairs when you don't plan on fighting fish in the cockpit. Enclose flybridge with AC and heat for year round comfort. It really doesn't take much to push a boat at displacement speed. Bob Phillips, Another Asylum, Tortola, BVI