In the current beta naval battles are handled like land combat. In the next beta naval battles is different but you would have STR 2 in the next beta.
We are going by Warlords 2 DLX and there land units don't get STR 4, but units with more than STR 4 only have STR 4. Also the pegasi +1 stack will not apply to land units on water. Land units simply suck on water .