I think it would be a really nice addition if ships could have a mast lock that the player could interact with (look at mast and hold "E") to raise and lower the masts of karves and longships. This would be a historically accurate feature, and would make bridge and boathouse building a bit more enjoyable. Currently, if the player wants to build a bridge that a longship can pass through, or a boathouse to store it in, they have to be ridiculously tall.