Make sure you are not using a fuel canister from any mod like the large ones from FUEL API. Only vanilla canisters

I can't even do it on land.
No matter where I go, the "Add Gasoline" function is either red, with no indication of what's why or not showing up at all.

I am hosting a server for me and my friend. We are using a rather large modpack, but I don't see, how they would get in the way of only this feature.

P.S.
Now that I think about it... The movement is pretty messed up and sailing yachts don't sail
Maybe it is a modding issue.

Just as an FYI, I had this issue with a speed boat, but then figured out you needed to be in a specific seat to refuel on the boat.