There are a lot of discussions on TF about single vs twin. The points you'll hear are typically:
- (someone can correct me but I think) Twins burn around 50% more fuel (not usually 2X). Do the math...estimate your total running time hours (500?) for the trip, run the expected gph fuel consumption for single and twin, and see if the additional fuel cost is really an issue for you. There are plenty of big expenses besides fuel.
- More commercial boats, such as the ones on Deadliest Catch, run a single. But they have an engineer on board, major repair capability, etc.
- Two engines = 2X maintenance
- Single may give you more range assuming boat's total fuel capacity.
- Twin does offer a margin of safety but most debilitating engine problems are fuel related so unless you're running separate tanks they both are affected.
- Diesels, when well cared for, are very dependable.
Look up Richard on Dauntless.
https://dauntlessatsea.com
He's a TF member who's been back and forth across the Atlantic, all over Northern Europe, etc. in a Kadey Krogen. Single Ford Lehman diesel.
But in a GB 36 I'm not sure about the % of singles built. I believe far more were built as twins as it's a semi-displacement hull that is capable of some speed (at the price of high gph). So, you may not have many choices in a Single. Richard's KK is full displacement - and max hull speed is max hull speed for him.
- Twins offer better close quarters maneuvering although a thruster on a single could balance that out.
- single prop is usually more protected by the keel. Could be a significant consideration on that trip.
Nordhavn, Kadey Krogen, Selene and other fine trawlers are typically
Singles
Others here have more wisdom than I do... and also might take issue with my points. Or add more.