I met Capt. Rob Modys, a Bass Pro guide, in Fort Myers Beach, Florida, and I immediately regretted not having my travel rod when several tarpon rolled as we idled into the Gulf. But duty called, and we proceeded with the test. Modys’ boat carried the economical Mercury 150 four-stroke, and it proved to be a sensible match. At wide-open throttle with a 17-pitch propeller, the GPS registered 39.9 mph. Dialing back to 4,500 rpm, we made 33.1 mph. The same boat model, rigged with a Mercury 150 hp Optimax direct-injection engine, produced a top speed of 43.5 mph during factory tests, with a fuel rate of 14 gph.