the 550 size motor is the same size as the hammer's motor. the wave shark is bigger and heavier than the hammer. so the 550 wave shark is slower than the hammer. its not a hassle to use 2 batteries at a time. the blast is about the same speed as the hammer. the wave shark 550 and 775 dont have water cooling either but u wouldnt need it unless you are using 16 cells. i would just go with the 775 CEN boat. you will go about 20-22 mph stock as compared to your friends 15-16 mph stock. plus its very easy to upgrade to make it go 30+ mph

water cooling doesn't really effect top speed that much just your motors life etc. 20 runs 40 runs 60 runs. your motor just lasts longer with water cooling. plus for about 5 dollars you can buy what you need to easily install water cooling on any boat.

www.offshoreelectrics.com they have an article on how to install water cooling i think