overloading

[Serenity]

I installed a new prop on my 28TE w/315 YANMAR. I was only able to aceive 3650 (photo tach) on the engine. I brought the prop back and it was repitched. Now I achieve 3800, which is still short a 100 rpms I believe. The question I have, as per my Yanamr manual, the Full Load Speed should be 3800 and the Propleller Matching Speed should be 3900+. What is the difference? Boating is such a simple sport.

[N4QC]

My book for Yanmar engines shows 3800 rpms as “Maximum output at crankshaft” for an 6LPA-STP 315HP engine. Continuous output rating at the crankshaft is 3600…

If you have a different engine configuration then these numbers don’t fit. This doesn't answer your specific question, but I hope it helps…

[RobS]

This one should be clear

[efishnsea]

They said at Mack Boring that the boat should be propped so the 6LP engine could acheive 150 rpm over WOT so that the govener will better control engine speed. Over propping will cause the engine to smoke.

[N4QC]

In as much as the 3950 rpm is not being reached (wide open throttle in neutral), you may want to test the rpm max with the engine hatch open. This, along with a clean turbo air filter, should help determine if air is a possible problem. Verification of the fuel supply system would also be on my check list.

The amount of air being supplied to an engine compartment is often overlooked…

Have fun,

[Serenity]

This one should be clear

Rob. I have the same chart. The question still remains, what is the difference between "MAX output RPM" and WOT RPM for propeller matching calc? When I ran her the other day there was no black smoke. Could fuel siting there all winter, stablized, lose some of its cetane rating? Our best to Erica on Happy Mommas Day.

[Serenity]

In as much as the 3950 rpm is not being reached (wide open throttle in neutral), you may want to test the rpm max with the engine hatch open. This, along with a clean turbo air filter, should help determine if air is a possible problem. Verification of the fuel supply system would also be on my check list.

The amount of air being supplied to an engine compartment is often overlooked…

Have fun,

I can hit WOT, 4250. at the dock It sounded like a Tom Cat spooling up the turbines before lift off. The engine only has 125 hours on it, but the prop had 14 years. These possibilities are starting to sound like Tin Cup, put your hat on backwards, take the change out of one pocket and put it another, etc.. I will open up the hatch. I just love the sound of a turbo screaming at 2 in the afternoon.
Thanks

[RobS]

The question still remains, what is the difference between "MAX output RPM" and WOT RPM for propeller matching calc?

Max output rpm is the max "usable" rpm.

Max WOT rpm for prop matching is just a “tool” to gauge that she is loaded to an amount that allows the engine to perform within specs.
By specs I mean: "x" horsepower at “x” fuel burn rate to turn "x" rpm.

Too much load and she is gonna keeping trying to make more hp to turn the rpm by pulling in excessive fuel, hence the black smoke. And then you can say good-bye to the factory fuel burn chart.

(BTW, Max, I saw your post on my droid yesterday and passed your message on to Erika, thanks!)

[JeffM]

WOT is what you are interested in. With your boat loaded while underway, this is the RPM you should be able to reach. If you look at the Chart attached above, your WOT should be 3950 to 4050. If it is much below this, you have an issue or boat is overpropped. Running a diesel like a 6LP in an overpropped condition is not good for it. It will affect the life of the engine. Max RPM in nuetral is the No-Load test. Not what you want to do to assess a prop configuration.

[jleonard]

WOT is what you are interested in. With your boat loaded while underway, this is the RPM you should be able to reach. If you look at the Chart attached above, your WOT should be 3950 to 4050. If it is much below this, you have an issue or boat is overpropped. Running a diesel like a 6LP in an overpropped condition is not good for it. It will affect the life of the engine. Max RPM in nuetral is the No-Load test. Not what you want to do to assess a prop configuration.

Yes but you need to know first if the engine can reach the corec t rpm in neutral. That tells you the linkage and pump stop is correct.
And you also must know that your tach is reading correctly by calibrating it with a hand held "photo tach". If the tach is not accurate, all bets are off.

[RobS]

Right on Jay.
1st check tach accuracy with strobe
2nd check no load WOT
Only know can you move on to WOT under load

[JeffM]

I apologize if I provided incorrect information. But in this case, he already indicated he was using a photo tach and that his no load was 4250. I was only trying to help. I'll let Rob and Jay handle all this stuff in the future. Good luck with your prop,

[DougSea]

I apologize if I provided incorrect information. But in this case, he already indicated he was using a photo tach and that his no load was 4250. I was only trying to help. I'll let Rob and Jay handle all this stuff in the future. Good luck with your prop,

Hey Jeff,

I don't think the guys were trying to say your information was incorrect, and I suspect they missed the photo tach reference above that you picked up on. In my view, this post, like many on this board, is made more valuable by everyone's comments and collective wisdom.

So please, don't hesitate to post!

[RobS]

I apologize if I provided incorrect information. But in this case, he already indicated he was using a photo tach and that his no load was 4250. I was only trying to help. I'll let Rob and Jay handle all this stuff in the future. Good luck with your prop,

Jeff, specific to Max's stage in the game your post was accurate but I read it as a general comment and do not want a future reader to overlook the importance of the first two items to check before focusing on the prop. Everyones comments are always valued please keep them coming...

[jleonard]

I apologize if I provided incorrect information. But in this case, he already indicated he was using a photo tach and that his no load was 4250. I was only trying to help. I'll let Rob and Jay handle all this stuff in the future. Good luck with your prop,

Jeff, specific to Max's stage in the game your post was accurate but I read it as a general comment and do not want a future reader to overlook the importance of the first to items to check before focusing on the prop. Everyones comments are always valued please keep them coming...

Exactly. The ONLY reason I mentioned it again is based on my experience....at Mainship raftups I checked several new boats, many with Yanmar engines, and I never found one to be close, except for one and that was a twin engine boat with only one tach correct. LOL And if you read the boat borads, almost 100% of the time this step is eother overlooked or treated lightly.