Robs
What the man says!
No calculation involved - just fit capacitors
<<9.6v, 21000rpm and BRS-540S6528>> You have most of the information you need right there!
It is wound for endless life at 9.6V (is there Really an 8-cell vacuum cleaner?) so it will have an interesting life at 12V and will run at much more for as long as you need in a boat
The frame is a 540, which means it is 54mm rotor armature length (equivalent to a speed 500 in size)
S6528 is the makers code for the way it is wound, what wire etc. If it is from a vacuum this is a very low torque, high speed application so it will be 3-pole and probably quite a beefy wire and few turns (to give the high speed)
The case will also say a makers name or logo, Mabuchi,, Johnson or similar - you might be able to find the exact model on their website - especially if it is Mabuchi
Useful motor if you want to run it on 7.2 to 12V, possibly more - what are you aiming to power with it? Would probably be good with gears
hope this helps
andrew