Brushless motors, generally the first two numbers are the can size e.g. B28-57-15L 28mm, the second two numbers are the can length 57mm and the KV is the revs per volt (1900kv = 21090rpm on 3S(11.1 volts) and 28120prm on 4S(14.8 volts).
My 3648-1450kv(1600 watts) on 4S=21460rpm over powers the old OS40 FSR(20,000rpm 1.6hp).
One hp= about 750watts.
This new brushless and Lipo battery stuff is so powerful it turned by ocean racer deep vee(geared 540 brush motor on Nicads(10 minutes run with the speed of a tug boat) into an insanely fast ocean racer in a bit of wave running on the prop in the water only.
Total hand full and a bit trying with over 1/2 hour running(5800mah battery).
Looking at the Snapper you may have to put the battery under the driver to get the balance point right.
I have had the original plans for the Sea Hornet, Swordsman and Sea Rover rescanned into PDF format, so I can get them reprinted to larger sizes e.g. Sea Rover 20% bigger to 35 and 1/4 inches and the Sea Hornet 25% bigger to 31 and 1/4 inches.
The Swordsman is 33 and 1/4 inches standard.
Also have all the frame drawings.
Checkout my boats atmodelboats.com forum site.
Any more questions we are all like helping out fellow modellers.