10% rule

[flyboyjack]

Anyone familiar with this rule? Yesterday during our sea trial, it was explained that if you run at less than best cruise RPM,... you should/can run the Cummins at max RPM for 10% of the time it was not at best cruise RPM. So, I think, if I run at 8-12 knots for an hour and a half, then I should run her at max RPM for 9 minutes? I know I should work the motor periodically/hourly. But just wondering...........

Flyboyjack

[eseyoung]

didn't know about that one. Are you sure that they didn't mean that during the trial they ran it 10% below 80% at optimal and 10% above. that kinda makes scene to me so you have time at all operating ranges.

As far as i know there is no reason to run at the max other than once or twice a year just to make sure everything is OK. I have heard of the 80% rule. It says that 80% of wear and failures happen with in the last 20% of a duty cycle. Try to run my diesel engines (land and sea) at no more than 80% of max. That and regular maintenance, i feel is the key.

[Yearwood]

The 80 percent rule has been around ever since I studied diesel engineering. I would not replace it unless the engine manufacturer had a clear statement to the contrary. Furthermore, the alleged 10 percent rule as stated makes little sense in my opinion. Wear patterns develop in engines and subjecting them to additional stress as they age does not seem logical.

[jleonard]

They are talking about duty cycle and it sounds like the explainer was a mixed up. There is no "rule" saying you need to run at max RPM for x amount of time. That is urban legend.
You should check out www.boatdiesel.com and read for a while (maybe even join, it will be the best $25 you spent) and you'll get the real truth.

[seasalt]

I take a couple of 3 hour one way trips a month. I run most of the time at 1500 rpms. That is about 8.5 kts. The temps look to up to where they should be.

But, and you will know where I am talking about, when I get about 5 milses south of Ponce Inlet I put the tabs down and bring both up to WOT for just a few seconds (to see if they will still do it) then drop down to about 2400 rpms for a 18.5 kt cruise in.

I have had Detroits and Cummins and I have never heard of the 10% rule as you state it. I have heard that Detroits like to be run at 10% off WOT but that is the only 10% I have heard of.

[whwells]

These comments from a Certifed Yanmar Man who maintains my boat. Craig has been kind enough to come speak at our NW Rendezvous the past two years.
In addition to maintaining many boats around Anacortes he services mine and another 31 Albin twin at our marina who's owner's are also active members in AOG. Craig feels I should in the last 10 minutes of the return to Port run it near flat out. Frankly, I can't bring myself to push the engines that hard. I will and do bring them to about 90%.
Craig feels this is the best way to clean out the exhaust system and the risers. Down side is it sucks the fuel. Still unless someone says this should not be done it seems to be working.
It does not satisfy the 10% discussed here.
whwells "Howard"
2006 35te SportfisherFlybridge
2004 Osprey Pilothouse 22

[Pitou]

Flyboy -
In case you're still watching this thread ... My 6BTA manual said "do not run at WOT more than 10% of the running time" / 6 minutes for every hour of running. I used to run mine at 73% to 80% for cruise and rarely at 100% and only to occassionally blow out the crud or catch a bridge opening.

As Jay said check out boat diesel .. a membership to boat diesel is a must in my book for all marine diesel owners.

[jleonard]

Manufacturers sure are funny the way they write this in manuals, IF they address it at all.
For example my old Perkins spelled it out so there was little chance of misunderstanding. It said something to the effect of "run at WOT (2400 rpm) for no more than one hour, then reduce rpm to 2250 for 10 minutes, then repeat. (16% rule?)
My Ford Lehman only has a arrow on the power chart with a notation saying "max continuous" showing the range from 1600 to rated WOT (2500). That's pretty vague. Maybe the 0% rule?
My Cummins 6BTA (circa 1999) said one hour out of 8 at WOT. (would that be the 12.5% rule? LOL) I gather it didn't matter how that was accomplished?

The Cummins tech that certified my repower told me also to run at WOT on my way back to homeport. Why? Not to "burn out the carbon" but only to insure everything was up to snuff. He said run for a minute or two, make sure you can hit the correct rpm, make sure the coolant temp is right, etc. If anything goes wrong, your home and it's a short tow.
Made sense to me.

So what does all this mean to me? From being a boatdiesel member for almost 15 years, reading other forums, talking to mechanics, etc., I know that correct engineloading is extremely important, as is exhaust system design. I know that if you run your engine too hard you'll kill it for certain. I know that a sea water cooled intercooler will build up condensation and crud up the intake path, especially if you run at a low rpm. I know that when you cruise a long time at low rpm you need to have the engine temp in a good range (you must have some load on the engine).
There's more but I'll stop after saying I don't care what you use for additives, what oil brand or viscosity, or how often you change it.
Happy New Year!

[mike66]

Happy New Year to you and all on the forum. Thanks to all for your valuable input and interesting discussions about all things Albin.

I always cringe when I push that throttle forward on the way in, crossing my fingers that the temp gauge doesn't follow the tach up the scale......on the other hand, what you don't know can kill you........