Marines are fine. They can't help with anything. If they were helping, then the wouldn't have prep bonus, would they? Nay!
They also pay a heavy penalty on crewing, larger than their boarding bonus. I says, its a LTP issue with boarding, as most of the captains I do battle with have a very poor understanding of how boarding works. When ye face a good boarder, ye know it! And when ye face a poor boarder…. ye know it right away that this poor sap has no clue.
Leave 'em the way they are, Pagan Pete says! +3