Question: how to calculate the gross tonnage of a vessel?
Answer: For a boat with a simple sailing hull: Gross Tonnage = (. 5 x L x B x D) divided by 100.
For a sailing boat with keel: Gross Tonnage = (. 375 x L x B x D) divided by 100.
For power boats: Gross Tonnage = (. 67 x L x B x D) divided by 100.