...In possession of a Cat 30 MK1, circa 1984, with a A4 engine. It’s in pretty good shape but there are a couple of things: Should I get a better prop? This had been a fresh water lake boat and there is a stock prop on the shaft. We are moving to the Ocean. Better options available? Also: there is no GPS. The boat has new RayMarine speed and depth with Seatalk. What’s a good plotter? We are costal people (MA, NH, ME). Finally, now that we are floating in salt, heat exchanger for the engine?