BlueGreen: thanks for the points on airworthiness and certs.
I will also note that a lack of floats does not seem to have stopped the USN from operating Seahawks for about thirty years.
The idea is to operate from ships, not from the surface of the ocean.
As to fuel, from a few posts back:
Blackhawk has less fuel than Seahawk. (~2600 pounds versus ~4000 pounds, roughly). One of the numerous cases of the "not quite the same" roots of Seahawk as a "common airframe" to Blackhawk.
MRH-90 comparisons, in the maritime milieu, need to take that into account when discussing the matter of "legs" on a given model of S-70 or the other.
Then again, since the Block 1(B) Seahawk, as well as the F and H, provision for external tank is built in. Likewise for the R (Operational choice to use it or not).