Note two things ... I might be wrong on the 2 clamps on vent lines being required or not (old memory?), but fuel can and does go up and down a vent line, so at least the lower connection should have 2 clamps by good practice anyway. Second, the ABYC guidelines (some call them standards) do indeed differ from the US Coast Guard (the included stuff above). In particular, the ABYC and USCG differ on things such as square inches of scupper, how high scuppers must be above the waterline etc, time to drain water out of a boat, ventilation, and fuel system requirements. This is why the plans do NOT specify these details but DO state that the builder must research local regs and comply on their own (their responsibility). Someone has to be the tie breaker on which regs to follow, noting that while the USCG publishes Standard (must-comply), that they are for commercial manufacturers. The ABYC publishes Guidelines, not Standards, that are optionally followed ... but God help you if you want to manufacture and sell boats that violate the ABYC guidelines! They may as well be standards.
With homebuilt boats, it's up to you to follow what rules you choose - but the recommendation is to follow them all as closely as you can - they were written based on real-life situations where safety turned out to be lacking. When the USCG and ABYC standards contradict, it's up to you to make a wise and considered decision on which to follow, or neither. IF you are going to build an 'inspected' boat, e.g. you want a 30-foot Kodiak and a 6-pack captain's license so you can run a charter, then you will fail your commercial boat inspection if you don't follow the standards (you can decide on the contradictory ones and which to do - take your own chance with that). From what I can see, inspections are more focused on safety items aboard than exact details on boat size versus scuppers, ventilation, or fuel systems - but you never know.
Brian
