Continuous output rating
The continuous output rating is exactly what it sounds like, the amount of power that the engine can produce continuously. Unfortunately, manufacturers ratings are in laboratory conditions: at "standard temperature and pressure" (sea level and 58 degree air), the engine is turning a dynamometer (not a "closest fit" propeller), with an ideal exhaust system, unlimited cool water for cooling, no alternator, and not enclosed in a tight engine box. Especially you should note that the rated output is *16 horsepower* (which happens to be at 3400 rpm), not 3400 rpm and however much throttle it takes to achieve that. For example, say you have 0.4 inch more pitch on your prop than "ideal" (the prop installed was rounded to the nearest whole inch). In this case you may have to output 17 horsepower to get 3400 rpm. That means when you spin up to 3400, you are over the continuous rating. My point is that when you are spinning 3400 rpm, you have no idea if you are putting out 10 hp or 20 hp. And again, unlike in the lab, you probably have restrictions in your exhaust system, restrictions getting intake air, the air surrounding and going into the engine is warmer than 58 degrees, and so is the cooling water. So yeah, it's gonna overheat. The basic rule of thumb is put on a prop that gives you the closest rpm to the engine's maximum, then for "normal" powering run your engine at 75%-80% of the max rpm. If this is rpm puts you well below hull speed, your engine is too small. On the other hand if hull speed is achieved at very much below that rpm then you are probably overpowered. A little overpowered is fine because wind and waves will sometimes be working against you, and because you will have other power drains -- a 100 amp alternator going full out charging low batteries will take 5 hp or more. Whew! Got all that?
