scale figures at the same scale?

I would make them to the same scale as the boat (or is that a ship) (how am I supposed to know, I'm a turret-head). Anyway, back to the scale question ... by making them the same scale you give the boat / ship a point of reference as to its size. If you scale the figs down then the ship would appear larger than it truly is.

I agree with Robert, you should use figures in the same scale as your main subject. From your write up, I'm not sure what scale you are refering to. 1" = 1' is 1/12 scale. As I know of no commercial figures in this scale you would be looking at scratchbuilding. Scale is a reference to 1 foot. For example, a six foot tall man (72 inches) would appear to be one inch tall if standing 72 feet away. A figure of this man would in turn be 1/72 of his height or 1 inch when held at one foot from you. I hope this helps.