A lot of the research
in PV is around cooling the panels and/or increasing the efficiency at higher temperatures. Liquid cooling has been approached many times, but has generally proven to be not cost effective.
However, in the special situation of a boat installation
it might be worth the effort/cost. The normal operating cell temperature (NOCT) of most silicon cells is around 45C (at 20C ambient temperature) and the typical power derating is around 0.4%/C. So, if you can run the panels 15C lower in temperature you should see about 6% more output. The greater the temperature difference the more you gain. Is that enough to pay for the energy and capital costs?
I like the idea in theory, not so sure about in the real world for most applications. One place it really makes sense (and have seen it in actual use) is for a heated swimming pool. Water at 25-30C is great for pool heating, and the filtration/circulation pumps for pools are energy hogs. Getting both out of the same installation