I did the same research as you, and I hate to slip your knots here, but I remain rather skeptical because I haven't found any references to matelotage as gay marriage that don't lead back to one particular book, Sodomy and the Pirate Tradition by Barry R. Burg. (Its reviews don't seem to indicate that it's a very well-documented bit of research itself - apparently the author tends to take leaps of faith without backing his assertions up with proof. The "if they don't specifically say they DON'T do it, then it must mean that they DO" sort of thing.) If you've found anything that gives printed research sources or primary sources that aren't that book, please, I beg of you, inform me!