They will almost surely use the length listed on your
boat documentation. They have never come to inspect our boat, and when I have heard of times cruisers have had
customs at their boats, I've never heard of the length being scrutinized due to swim platforms,
dinghy davits, etc... (this can be common at
marinas for dockage fees, however). FYI,
Bimini has continued to charge at the old 35' cutoff...I can't guarantee that will continue, so boats over 30' should be prepared to pay the $300 cash.