Re: How long at WOT?
No highjacks have occurred. I am trying to answer the OP's question.
Is it more likely the OP meant 100% open throttle or 100% open throttle, running all out at the top speed the boat can offer? It's likely the latter. Unnecessary diversion has taken place. So, since we are talking about boats, my premise is more accurate: WOT = as fast as she is going to go, which is max engine RPM +/-
Diesels: Sorry you were caught trying to explain your claim that diesels don't have throttles. Modern diesels sometimes have throttles to control air intake, which is to manage combustion to another end in the interest of emissions control. Again, I'm not the one diverting attention with discussion of diesels throttles. The OP surely means all out top speed. The diesel diversion does not help here.
Most efficient operation = full throttle is yet another diversion. Full throttle in a gas operated boat engine in the real world does not equal maximum efficiency.
Carbed, two-stroke engines can run lean. I don''t know how the heck anyone lost the ability to understand that no matter what the settings are going in on any engine, the air/fuel mixture is subject to more dynamics than just 'it can't run lean, because fuel intake is a product of air intake.' In that case, how can any engine run lean or rich? For Pete's sake, the air temps and humidity levels and other factors (some will even say fuel temps) can change the air/fuel mix. An engine can run rich or lean in the same day and what the engine is doing at different times under different circumstances will even affect it. It's more dynamic that anyone is admitting. It's so dynamic that computer controls making thousands of adjustments per second are needed to manage it. On 2-stroke engines with carbs, the tune to slightly rich allows some room for error that invariably pops up during operation.
Full, all-out 100% speed from a wide-open throttle is worse than something less the 100% all out (Frank A and I explained a little of this). The margin of how much worse doesn't get too serious unless you can run, particularly a 4-stroke engine, at the absolute RPM limit it can operate at before bad, engine-damaging things occur (at this practical limit, the engine can experience moments of bad stuff).
If your engine is designed to run at 4800 RPM and wide open throttle finds you at 4600 RPM, you aren't running on the edge of disaster. If your running at 4800 RPM, it is more likely that you are occasionally dipping into the realm of where some bad things might happen to some engines.
