How long is it safe to run Wide Open Throttle?

I have twin Yanmar 110 hp 4jhj4lte motors. Rated max RPM is 3200 and that's what it will make. Someone ran my boat for 90 minutes at WOT yesterday. Is that a dangerous thing to do? My instinct was certainly not to like learning they did that.


David Hughes
2009 Leopard 37 Powercat

If engines are healthy, it will do no harm. If engines are weak in any way, that is when you will find the weakness!!

If you are going to charter the boat, consider turning down the throttle stop screws so even if "on the pins", the throttle will not be full.

If you can dig up the spec sheet for the engine it should tell you. I don't think 90min is a big deal, even for the most moderately rated engines. Each manufacturer calls it different things, but Deere rates them M1, M2, M3 etc. Ours is M2 which means 16/24hrs at WOT, and the remaining 8/24hr at either 100 or 200 RPM below rated max RPM. M1 is continuous duty, WOT.

You can run a diesel engine wide open under load for ever and not hurt it. Every diesel engine has a governor which limits the maximum RPM to the safe level determined by the engine manufacturor. The second worst thing you can do to a diesel is lug it around at low rpm and light loads. The worst thing you can do is use it for short periods of time and never give it a chance to properly warm up before shutting it down.

Thanks, everyone. I appreciate it!


David Hughes
2009 Leopard 37 Powercat

Diesel engines vary on the length of time it's prudent to operate at maximum capacity. Check with the diesel engine's maker regarding your particular engine.

David,
If you are located in Cape Coral, I would call Mastry in St. Petersburg, they are the Florida Yanmar dealers. My guess is not to worry about it. You didn't mention if there were any issues - high temp, smoke, etc. If the engines can't handle WOT for 90 minutes, then I would be worried more about them being the proper engines.
Good luck

My poor engine only sees two speeds, idle + 100 in no wake zones and WOT everywhere else. It hasn't complained yet.

stanfromhell said:

You can run a diesel engine wide open under load for ever and not hurt it. .

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A term called duty cycle enters it. Also correct sized props to allow engine to comfortably reach rated RPM plus about 50 RPM. I'd not bless full throttle longer runs without knowing these two things.

stanfromhell said:

You can run a diesel engine wide open under load for ever and not hurt it. Every diesel engine has a governor which limits the maximum RPM to the safe level determined by the engine manufacturor.

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This is untrue and a dangerous statement. Read Ski's reply above. The governor is a much more complicated mechanism than just limiting max RPM. And if your props are not pitched properly, you can do significant damage operating at WOT.

Most manufacturers publish a Max continuous power(MCP) rating. Cummins is usually 200rpm below WOT. And if I remember correctly, they do not recommend running WOT for more than an hour. Yanmar is similar. Will 90 minutes hurt it???? Ski's answer is the answer. Probably not... as long as all supporting systems are up to snuff.

My question is why did you let someone else run your boat?

kyle911 said:

My question is why did you let someone else run your boat?

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Thinking the same like lending your chainsaw,trimmer,pressure washer ,wife.

They all come back rooted

kyle911 said:

My question is why did you let someone else run your boat?

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Charter, me-thinks.

Just to reiterate as said above, there is no standard that is good for all diesel engines. I'd guess yours are rated for heavy duty, but I don't know. This is something you need to learn about your engines, their specific ratings and the manufacturers recommendations. We have some engines that are set up for fast vessels with low load factor and you run those a minimal amount of time at WOT, normally running at 80% load. On the other hand the same basic engine comes with medium and high load factor ratings and with a continuous use rating.

It's doubtful the 90 minutes did any damage, but none of us know what temperatures were reached or any other aspects of that run.

While I agree that 90 minutes at wot did no harm, I do believe that extended operation at wot is bad.


That engine is 2 liters, so 110 hp is 55 hp per liter, not an insignificant amount of load, even for a diesel. Marine diesels fail much more frequently because one of the marine systems lets go and a severe overheat occurs with catastrophic results which is what Ski implied above. These events are the product of lack of maintenance and marine corrosion.


But assuming something like that doesn't happen, the more you load your engine the fewer hours it will last until significant blowby occurs, low compression makes it difficult to start, etc.


The following is mostly speculation, assuming no catastrophic event:


10 hp per liter, 20,000 hours
30 hp per liter, 10,000 hours
50 hp per liter, 5,000 hours
70 hp per liter, 2,000 hours


I base the above partially on the fact that the 370 hp Cummins 6BTA (63 hp per liter) was one of the few high performance recreational diesels to pass the Navy's 1,000 hour endurance test, much of which is at full load.


David

MurrayM said:

Charter, me-thinks.

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Yes. It is under a three week charter right now. I only know it was run hard because I have a LandAirSea GPS tracker and it showed 14-15 knots from the Miserable Mile up to Tween Waters Marina on Captiva. I looked up the manual and it is approved for continuous output at 3110 RPM of its 3200 Max Rated Output, so it seems to be pretty good with extended high RPM as long as all the supporting systems remain working properly....


David Hughes
2009 Leopard 37 Powercat

I like the idea posed earlier since you are chartering the boat - turn down the throttle stop so it won't go over about 3000 rpm. Seems like cheap and effective insurance.

twistedtree said:

I like the idea posed earlier since you are chartering the boat - turn down the throttle stop so it won't go over about 3000 rpm. Seems like cheap and effective insurance.

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Yes. I would do this yesterday.

Why are they running so fast in the ICW anyway???

EVEN Marine engines that are converted from industrial or heavy duty truck engines will come with 4 ratings.

From light duty to 24/&

ONLY the 24/7 rating can be held for "ever" the rest have duty cycle RPM and time limits.

IF there is no set of graphs for the engine you have I would take a look at real marine engines and reduce the power available to the charter party.

A simple rule of thumb is 80% max power at 90% rated RPM.for industrial diesels.

You may need to swop props to limit the un knowledgible renters abuse..

FF said:

You may need to swop props to limit the un knowledgible renters abuse..

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I think I'll try the throttle stop at 3000 and consider dumbing down the props as last resort. Thanks again everyone. And yes I suppose the guy was going 15 in the ICW just because he could. LOL. And there are many boats going much fatter than that there, trust me.



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IMHO - in addition to ensuring the boat is correctly propped for load I would always run pyro and boost gages on these types of turbo engines. Once you are above a level where you will be utilizing 30 hp per liter having real time knowledge of EGT and boost is an easy and quick way to know if you are nearing trouble. Adding both pyro and boost to twin engines cost less than $500 if you are handy and could easily save yourself a lot of grief. Too many boats begin life correctly loaded but then changes to their weight, hull, running gear, or the weather put them in an operating zone which could cause real issues.

cardude01 said:

Yes. I would do this yesterday.

Why are they running so fast in the ICW anyway???

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Why wouldn't you?

Because I can't I guess. ?

Actually, I like going slow so I can take in the scenery. I can't imagine going that fast through most of the WC Florida ICW. That would be nerve wracking.

In open water fast would be nice however.

A fatter boat might be going slower.

Hopefully you have figured shorter engine life into your charter fees.

the running gear guys love people going fast in the shallow ,twisting often changing Gulf coast ICW

Read your engine manual.

cardude01 said:

Yes. I would do this yesterday.

Why are they running so fast in the ICW anyway???

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Wifey B: Ummm.... To some of us 15 knots is slow.

Yesterday, east of Fort Myers. He was probably doing 50 and I doubt he was at WOT. We heard him before we saw him.

BandB said:

Wifey B: Ummm.... To some of us 15 knots is slow.

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You young folks are always in such a hurry!

When I want to go fast I get in my dinghy with my big Johnson. ?