I like your thinking, Hoffalives. Damn the torpedos, keep at it. If not this one, another. Others are doing it, and making a good buck at it as well.
Look at the gadget that keeps you from having to take the whole damn water pump bolts out when you want to change the impeller. I know, modest in comparison to your proposed challenge, but innovative nonetheless. Or the refridgeration cooling loop that coils around the galley through-hole, using the up-and-down of the boat to circulate cool water around the coil as opposed to consuming power with an auxiliary raw water pump to do the same. I'm sure you've seen that in the back of CW or similar.
Now, some advice if you're willing to take it, explore the edges of your ideas. Step away from the raw-water circuit issue per se, and look at the solution - cold water all around you, moving, even when the boat's at rest, moving even faster when under way...what else could that do for you? I don't know the answer, but the approach is worth exploring - that is, ENGINEER IMAGINATION. Take the realities around you, benevolet or malevolent and exploit them.
Ok, it's late, enough L. Ron Hubbard impersonation for today.