2B

Why did you think they had taken over the Mistress of the Seas?

I think they want to use it as a place to quarantine the infected patients so they can study the bacteria.

It was already there. It's a huge boat already filled with the equipment they need.

I agree with >2 EadieB: & >3 Olivermagnus: It was convenient.

I agree with the above

Initially, I had no idea why the pirates would want to capture the ship - I didn't even think of ransoming it, though that would have been a possibility.
It was only when we were told what was afoot that I became aware of the reason.