Whether or not you'd have an issue would be related to the actual pressure on the suction side of the pump in the heat exchanger itself.
And you'd need to have an idea of the actual raw water temperature there as well to know if you were at risk of dropping below the vapour pressure temp, which could cause flashing and pump cavitation. Few systems actually monitor the RWC temperature....
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"