I was unaware of how much of a problem bone callers were until today. We were having an hourglass duo fight and winning by a landslide. I am a level 400ish helm and my friend is a level 600 cannon so we are not exactly bad at the game. Both ships were mast down and we had a lot of cannon pressure on them. They decided to shoot 2 bone callers at us, one from each pirate, making us have 10 or so skeletons on our boat. The biggest problem was the body blocking, they would make it impossible to move around your boat because the would keep blocking the stairs, stopping us from bucketing, ladder guarding or cannoning, basically completely shutting us down. Even after killing them they shoot another 10 skeletons at us, managing to completely remove pressure from their boat as well as send a boarder who we were unable to guard.
This bring me to the second problem. Along with the insane damage that multiple skeletons do, we were unable to hit the boarder due to their continuous body blocks. Making it so that you can have more than 5 skeletons on one boat at a time is absurd not to mention the ability to spawn more immediately after they are defeated.
The other problem is that the sword is the only defence against this which forces you to play sword against people with many bone callers. Even then it is still very difficult to play against. With Rare adding so many different tools to the game I can't imagine they want a single item to be able to force you into a playstyle you don't enjoy.
Sunk twice to players significantly worse than us today and I felt that I needed to mention this. Call it coping if you like because it is. Please add some sort of cooldown before more skeletons can be spawned or at least make it so a ship can only have one bone callers worth of skeletons on at a time.