This 1984 board game published by MB (Milton Bradley) was part of their Gamemaster series. It was the 3rd in the series which were all designed by Larry Harris.
Broadsides and Boarding Parties is a duel between a Spanish galleon and a pirate ship and it's the only one made for two players while the others are for two or more.
Each player take turns moving their ship and firing at the other enemy ship to sink her. If the ships collide then players may take boarding parties onto the other ship to try to win.
The 1982 original version of this game (published by The Citadel), used a paper map and cardboard pieces and did not have the plastic ships, cannons, and other pieces. When Hasbro got the publishing rights, they added these components to bring the physical components in line with all games in the series.
However, many players found that the large ship models were hard to disassemble, making the storage of this game difficult.
A more serious problem was that the gameplay was not considered up to the level of the other games in the series. There was relatively little strategy and more luck involved than the other games. As part of a series, Broadsides and Boarding Parties was unfavorably compared to the other games and was less popular.
Broadsides and Boarding Parties was discontinued several years after its introduction.
What's it worth? Take a look at this Broadsides Boarding Parties price guide: sold listings for a value indication.