BOAT-COMPARATOR Guide
B7, GTL or HVO: which diesel fuel for a rental boat?
More and more marina pumps now offer a synthetic diesel alongside regular B7. What GTL and HVO actually are, and what they change for a pleasure-boat diesel engine.
On a rental sailboat or catamaran fitted with a diesel engine, fuel is no longer just the familiar B7 diesel. More and more Mediterranean and Atlantic marinas now offer a separate pump labelled GTL or HVO — two synthetic fuels that replace ordinary diesel without any engine modification.
B7 diesel, still the majority standard
"B7" refers to diesel containing up to 7% biodiesel (fatty acid methyl ester from vegetable oil) blended with fossil diesel. It's the standard fuel at French marina pumps, perfectly tolerated by virtually all marine engines in service.
GTL: natural gas turned into synthetic diesel
Labelled GTL (Gas-to-Liquids), this is a paraffinic fuel synthesised from natural gas, with no biocomponent. Cleaner burning (less sulphur, fewer particulates), it substitutes directly for regular diesel with no engine adaptation.
HVO: hydrotreated vegetable oil
HVO (Hydrotreated Vegetable Oil) is produced from vegetable oils or recycled fats treated with hydrogen, which makes it chemically very close to fossil diesel — unlike ordinary biodiesel, it doesn't degrade in storage and stays usable blended in any proportion, or even pure, in an existing diesel engine. A study by Ushakov and Lefebvre published in 2019 in the SAE International Journal of Fuels and Lubricants, run specifically on a marine diesel engine, measured a 10-15% reduction in nitrogen oxides and a 50-55% reduction in unburned hydrocarbons with HVO compared with standard marine gas oil (see the study on Google Scholar).
What it actually changes for a renter
Nothing to adjust in how you sail: a rental boat's diesel engine runs with no special settings on GTL or HVO, and both blend freely with any B7 already in the tank. The difference shows up in the smell (noticeably milder at the pump) and in exhaust emissions, not in power or fuel consumption, which stay comparable.
Where and why these fuels are spreading
Some marinas, particularly in Scandinavia and increasingly around the Mediterranean, now offer these fuels as an alternative to cut the footprint of berthed fleets. If they aren't available at your stopover, regular B7 remains the default with no loss of performance. Our guide to E10 and 98-octane petrol covers the equivalent topic for petrol engines, and our fuel budget guide helps estimate a fill-up regardless of which diesel is available at the pump.
Free checklist
Rent a boat with no nasty surprises
Deposit, insurance, check-in inspection, fuel, navigation areas, weather: our checklist covers everything to verify before booking and on departure day. Sign up to access it and receive our tips by email.
Thank you! Your checklist is ready: Rent a boat with no nasty surprises →