I'm somewhat confused by the relative costs of some of the boarding upgrades; specifically Boarding Nets, Marines, Special Shot: Grapeshot and Grenades.
So far as I can tell, grenades are superior to marines; marines granting a +1 bonus and grenades granting a +D3 bonus (at least +1, probably higher). In the lists that can take marines, however, they are 15 points - compared to 10 points for grenades.
Similarly, Grapeshot is superior to Boarding Nets (+D3 vs +1) but in all the lists they cost the same amount (10 points each) for ships of the line. For frigates the boarding nets tend to be cheaper and the cost of grape goes up for frigates in many lists.
Can anyone supply any reasoning for these point costs? Is there some circumstance I'm missing in which marines are better than grenades, or boarding nets better than grapeshot? Some historical reason? In the Trafalgar scenario lots of ships have boarding nets and quite a few have marines, but there are no grenades or grape to be seen.