I’m a retired marine engineer too. I won’t touch gas pipes and their connections but anything to do with water and oil I will definitely do, also all small conductor electricity jobs if I have the time, but I don’t possess the tools for the larger stuff.
I once had a BG “boiler engineer” tell me my boiler had to be repositioned due to the proximity of a window to the flue. I checked the regs and he was wrong, I’m convinced that BG fitters were incentivised to find (create) work at one time.
Another retired Marine Engineer here, we seem well represented on the forum.
I wonder what your BG engineer would make of a ships boiler.