My GW42 has a 40-gallon main tank. That is a bit small, but it's worked out fine for me over the past 25 years.
The "50HP diesel" really isn't. It's likely to be a Perkins
4-108 which is really only about a 30HP diesel, despite the ratings of 40-50HP you see.
I carry 25 gallons of diesel in five 5-gallon jugs. Three of these fit very nicely beneath the lifting center helmsman's seat. Two others fit conveniently in the aft locker to starboard...way back under, leaving lots of room for spare oil
fluid, my autopilot
& tank, etc.
Thus there are no diesel jugs on deck
, but if I thought I needed more I could carry them.
The GW42 is one of the best production passagemakers around. She makes an honest 160nm per day....averaged over more than 20,000 miles. This amount of fuel was fine for my trips from DC to the Eastern Carribean and back (about 1,500 miles each way), from DC to Maine
and back a couple of times, down the ICW
to the Keys and back, etc., etc.
In 25 years I've only run out of fuel twice, both times within 25 miles of home and because I wasn't paying attention.
Yes, I'd like more fuel, but it's not a show stopper for me given the exceptional sailing capabilities of this boat.