WOT question.

Pirate Lady

Pirate Lady

Well-Known Member
Jun 2, 2020
7,533
Chesapeake Bay, Middle River
Boat Info
Sundancer 250 ‘91
Engines
7.4 Bravo 1
I see many threads about a boat won’t hit max rpm at WOT. I have never taken mine to max rpm, throttle pegged, to see what it hits or how fast it will go; same as I have never taken my car to speeds to see how fast it will go. I am satisfied at the performance 2800 - 3200rpm. It’s a cruiser.
Is that a bad thing? Is there a reason I don’t know about why i should be running at WOT?
 
It makes a difference if you're running gas engines vs diesels. Diesels should be run at WOT periodically, for short times, to get them to blow out the garbage that collects.

Beachcomber, at WOT, would run about 30kts. That's fun in a boat that size. You can just sit and enjoy the sound of diesel fuel as it screams through the plumbing between the tanks and the engines. :rolleyes:
 
WOT is the engine operating at its proper power band. The reason it's so important is that if you're unable to reach the recommended WOT your engine is working to hard at all rpms. So I take mine to WOT in the beginning of the season to make sure I can reach the top end of my specified WOT which is 4600-5000 rpms. I have spoken with Mercruiser reps and this is what they told me "they would rather have my engine propped so it hits the rev limiter 5150rpms vs. 4600 rpms". So my current boat could barely reach 4600 rpms when I bought it but to correct the problem I ended up changing props and now my WOT is 5000 rpms. The boat jumps on plane and seems to be quieter and more fuel efficient now.
 
Pirate Lady said:
Crossing Bay tomorrow, if it’s comfortably flat I will give it a goose. See what it does. I know my coupler is getting iffy so if it lets go I am blaming y’all.
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There is a good reason NOT to do it.
 
Pirate Lady said:
I see many threads about a boat won’t hit max rpm at WOT. I have never taken mine to max rpm, throttle pegged, to see what it hits or how fast it will go; same as I have never taken my car to speeds to see how fast it will go. I am satisfied at the performance 2800 - 3200rpm. It’s a cruiser.
Is that a bad thing? Is there a reason I don’t know about why i should be running at WOT?
Click to expand...


How fast the boat goes is sorta beside the point.

Engines are "rated" (technical term) at X horsepower and Y torque at Z RPM. Without over-heating, without excessive exhaust gas temps, etc etc etc

Given a fully loaded boat, clean bottom, and correctly tuned props, the WOT test is about confirming your engines are operating appropriately. And if not, why not? (Often its incorrectly tuned props, dirty bottom, or some combo...)

But it's a TEST. Not intended to imply engines should always or even often be run at WOT. (Diesels are usually run at 75% of WOT, 80% of WOT, 200 off the top, etc, depending on whose rule of thumb you buy into. And your fuel budget.)

And the speed you get when the engines make their rated WOT is sorta whatever you get. You might be able to make some slight changes by looking at load or tabs... but the boat speed itself is just an "interesting" number, not part of the engine health diagnostic.

-Chris
 
Spin mine up once a season just to make sure it can. Let's you know everything is clean and working properly.
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Mine sees the pin whenever I catch someone pulling my crab or prawn traps.. Hasn't let me down yet!
Have you calculated your mpg at 3400? You may be pleasantly surprised.
 
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I’ve got 1200 hrs on my 5.7L Mercruisers, I’d be cringing big time that right around the time I got to WOT there’d be a big BANG (or two), then I’d be dead in the water and @$&*)#)&)+/-/#(&)=;+:#’sc,fmvmc :eek: So I’m happy to stay a little bit shy of that mark………
 
Thornton69 said:
Mine sees the pin whenever I catch someone pulling my crab or prawn traps.. Hasn't let me down yet!
Have you calculated your mpg at 3400? You may be pleasantly surprised.
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I cruise at 3000rpm 24mph. Very satisfied with mpg. Filled tank on 6/4. Use it every weekend and still have 1/2 tank. Cant complain.
 
Being Satisfied is great for good life. Made me chuckle, many moons ago a bunch of us power plant mechanical maintenance crew guys were shooting the breeze, and our pickup truck gas mileage became the subject of discussion (and bickering….my truck gets blah, blah, blah). My closest friend shut the bickering down when asked how good his truck mileage was….his answer when my gas gauge gets below 1/4, I fill her up! End of discussion!:p:cool:
 
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