If you hook it up in series that's how you get 24 volts. A 12 volt motor is probably going to be fine for your little 12 foot boat but if you want more power you can get a 24 volt motor and really scoot! 8)
Congrats on the new boat. might want to check in to the little 3hp gas moters with the internal gas tank. They are awesome for boats that size. Light wieght, a tank of gas lasts for a day or two, and can usually mount it and an electric side by side. Also if you extend the length of your electric moter cables, you can stow the batteries up in the bow and they serve as a ballast. Good luck!
there is a guy in morrison selling a 8hp outboard for 500$, sounded good to me . if i wasnt going out of town tomorrow id be there. i do have a older five horse power 24 volt minkota that just kicks ass but id still rather have both gas and electric.remember all safety devices. i have been checked at four lakes last year.if youd like ill go out with you when i get back wich should be in two weeks. also no matter what others tell you its a good idea to regrease the trailer wheel bearings every spring. and just look over everything including wiring. everything is easier to fix in the driveway then out on the road.i also always try to check wind forecast before i go out. with a electric motor your not going to get out of trouble very easy.