Jay has the right idea
Jay is very very close to the truth. As a holder of a 100 ton license, and a graduate of the Maine Maritime Academy, I can tell you that displacement has nothing to do with rated tonnage. Rather, it is a reference to "cargo space". There is a formula for calculating your tonnage from standard measurements (i.e.: LOA, Draft, Beam) but it's at home in my notebooks and I am currently at work. I'll try to dig it up for you.I tend to agree with Jay in listing your tonnage as 6 tons, although it could concieveably be as much as 10 or 12.Also as Jay points out, the smallest license they issue is 25 ton, so in effect, your boat's tonnage is sort of a non-issue (for licensing purposes anyway).