Running a diesel at high revs?

[ash2020]

We are now the proud owners of a Varne 27 with an almost new Beta 14 diesel.
I've always been a bit nervous about running diesels at higher revs but the other day we were stonking along at 6 knots, with the engine at 3,000 rpm and it made such a difference getting home when we were tired and just wanted a beer and a hot bath.
I actually phoned the tech dept. at Beta Marine the next day and asked whether they were OK with their engines running for hours at near max revs. They said yes, no problem, obviously they use quite a bit more fuel, but then they are so miserly anyway. They are tested at max and designed to do it.
Any thoughts/advice?

 

[jdc]

I can see no reason from the perspective of basic engine not to drive your engine quite hard: most marine engines fail through ancillary items rather than the basic engine, and every diesel engine should be able to do something in the region of 1 - 3 billion revs in its life (coincidentally so does the human heart). 10,000 hrs at 3000 rpm = 1.8 billion turns (and 80 years at 60 beats / min = 2.5 billion beats).

I don't suppose you'll do 10,000 hrs over the time you have the boat (10,000 / 250 hrs/year = 40 years).

However,
1. it's much worse for fuel consumption per mile, let alone per hour: like 4x worse than 1500 rpm would be
2. it's ok assuming that the cooling system is in perfect shape; high revs demand perfect water flow and impellers etc, so it's more likely to overheat before you notice and take corrective action
3. it puts an equally high demand on oil: one should change oil probably as a function of revolutions turned rather than mere time running.

 

[theoldsalt]

Simply put - diesels thrive on hard work. You do far more harm idling around for hours.

 

[Topcat47]

Simply put - diesels thrive on hard work. You do far more harm idling around for hours.

+1. You'll probably find the "sweet spot" is around 2700 anyway. I don't know about the Beta but my 1GM10 barely produces any "shaft HP" at 1500 rpm. The Yanmar curves show just under 1kw shaft HP at 1600 rpm, not a lot to drive a 4.5tonne boat.

 

[Lon nan Gruagach]

Max revs is determined to be OK, even has a bit of a margin built in. "Near max revs" is well within what it can handle happily.

 

[Twister_Ken]

Yanmar suggests running its engines at full chat from time to time...

"Periodically operate the engine near maximum speed while underway. This will generate higher exhaust temperatures which will help clean out hard carbon deposits, maintain engine performance and prolong the life of the engine."

It also says, about stopping the engine...

"1. Reduce engine speed to low idle and put remote control handle in neutral.

2. Accelerate from low speed to high speed and repeat five times. This will clean out carbon from cylinders and the injection nozzles.

3. Allow the engine to run at low speed (approximately 1000 rpm) without load for five minutes."

 

[skyflyer]

I seem to recall that the manual quotes a max continuous RPM and a slightly higher maximum to be used for 30(?) minutes only.

Presumably the max continuous is exactly that! Around 3400 rpm for my 3GM30F Yanmar IIRC

 

[Tranona]

You should be able to achieve close to the maximum of 3600 rpm if the prop is sized correctly and cruise in flat water at around 2500. Your 3000 will allow you to make better progress against wind and waves. The same engine is also used in the 10hp and governed to a maximum of 3000, so your engine is working well within its limits.

 

[bitbaltic]

1. it's much worse for fuel consumption per mile, let alone per hour: like 4x worse than 1500 rpm would be.

I was expecting something like that the other day when I filled up after motoring for c 8 hrs at 2800 to 3000 rpm. Normally if I run the engine for short distances at 1500 rpm I budget a bit less than 1 l/hr which seems about right averaged out. I was expecting the 8 hours of high chat motoring to have drunk fuel but only filled up 14L, less than 2/l hr. So not bad.

Engine is penta 2020

I did not ring Volvo as a precaution afterwards....

 

[Koeketiene]

Yanmar suggests running its engines at full chat from time to time...

"Periodically operate the engine near maximum speed while underway. This will generate higher exhaust temperatures which will help clean out hard carbon deposits, maintain engine performance and prolong the life of the engine."

It also says, about stopping the engine...

"1. Reduce engine speed to low idle and put remote control handle in neutral.

2. Accelerate from low speed to high speed and repeat five times. This will clean out carbon from cylinders and the injection nozzles.

3. Allow the engine to run at low speed (approximately 1000 rpm) without load for five minutes."

We never, ever run the engine at (near) max revs. Hardly ever more than 2000rpm.
The reason for this is the following: the prop is quite close to the (skeg hung) rudder - maybe 1' away.
Once the engine revs exceed 2000-2200rpm the wash from the prop over the rudder becomes so strong that it becomes hard to steer in anything but a straight line.

Whilst replacing the corroded exhaust elbow (due to a badly set up exhaust system) engineers found that the turbo waste gate had seized due to large deposits of hard carbon.
Was also told that this was due to the fact that we never run the engine at (near) max revs.
The seized turbo wast gate is still in there. Engineers were unable to free it. Plan to address the issue when laid up for winter.

Does the panel think that running the engine at max revs for some time may free the seized turbo waste gate?
Or is running the engine at max revs with a seized turbo waste gate a strict no-no?

 

[William_H]

Seized turbo waste gate. Presumably seized in the open or partially open position. This should not pose any real problem except the inability to get max power. No I doubt high revs would free the waste gate although occasional high revs might have averted the seizure in the first place. good luck olewill

 

[ex-Gladys]

In the modern car world with things like Diesel Particulate Filters, applying what's described here (also known as an Italian tune-up) will burn off the particulates. On a Skoda Octavia I had several years ago, I was also advised by my one man band mechanic to do a full revs run in third on a dual carriageway to give the vehicle a better chance of passing the emissions part of the MOT... I think the only difference is that when you run a marine engine at WOT you are reaching a load limit, and actually you may be running with the engine over fuelling because it can't reach the revs for the throttle position

 

[pmagowan]

I run my Beta20hp as hard as I like depending on the circumstances and it doesn't seem to affect it. I can't see that there is that much to go wrong other than overheating which I suspect I would notice. Modern cars are different as they have all kinds of gubbins. My Honda accord gave me a warning light a couple of times when I had been driving very economically on purpose. It asked me to drive a bit harder to burn off particulates in the DPF.

 

[Tranona]

We never, ever run the engine at (near) max revs. Hardly ever more than 2000rpm.
The reason for this is the following: the prop is quite close to the (skeg hung) rudder - maybe 1' away.
Once the engine revs exceed 2000-2200rpm the wash from the prop over the rudder becomes so strong that it becomes hard to steer in anything but a straight line.

Whilst replacing the corroded exhaust elbow (due to a badly set up exhaust system) engineers found that the turbo waste gate had seized due to large deposits of hard carbon.
Was also told that this was due to the fact that we never run the engine at (near) max revs.
The seized turbo wast gate is still in there. Engineers were unable to free it. Plan to address the issue when laid up for winter.

Does the panel think that running the engine at max revs for some time may free the seized turbo waste gate?
Or is running the engine at max revs with a seized turbo waste gate a strict no-no?

Can't comment on the turbo issue, but long term suggest you reduce the pitch of the prop to increase the revs for a given boat speed. Running as you are is not good for the engine, and actually you may find the turbo is never working, or right on the edge of cutting in and out. Turbos never were a good idea for yacht auxiliaries in the lower hp range. Better to go up in capacity to get the extra power and run the engine in its working rev range of around 70% maximum power and prop it so that you achieve hull speed at close to rated maximum.

 

[Koeketiene]

Can't comment on the turbo issue, but long term suggest you reduce the pitch of the prop to increase the revs for a given boat speed.

Can one change the pitch of a feathering prop?

Running as you are is not good for the engine, and actually you may find the turbo is never working, or right on the edge of cutting in and out. Turbos never were a good idea for yacht auxiliaries in the lower hp range.

It's 60hp engine. (Nanni N4.60)

Better to go up in capacity to get the extra power and run the engine in its working rev range of around 70% maximum power and prop it so that you achieve hull speed at close to rated maximum.

According to this http://www.peachment.co.uk/nanni-diesel-n4-60-marine-engines/ max rpm is 2800.
When motoring we usually make 2000-2200 rpm - well in excess of 70% of max rpm

 

[sailorman]

Can one change the pitch of a feathering prop?



It's 60hp engine. (Nanni N4.60)

What make prop
my MaxProp is full adjustable for pitch & handing. why wasnt this sorted on engine commissioning & hand over.
Running @ 2k rpm what hp are you using , at a guess 30hp

 

[Koeketiene]

What make prop

Darglow Featherstream

my MaxProp is full adjustable for pitch & handing. why wasnt this sorted on engine commissioning & hand over.

Good question.
I am starting to ask a lot of questions about the installation and commissioning of the engine.
Starting with the incorrectly configured exhaust system and now this.

 

[sailorman]

Darglow Featherstream



Good question.
I am starting to ask a lot of questions about the installation and commissioning of the engine.
Starting with the incorrectly configured exhaust system and now this.

i get hull spd @ 100 rpm under engine rated max
cruise @ 2k & wot @ 2900

 

[Tranona]

Can one change the pitch of a feathering prop?



It's 60hp engine. (Nanni N4.60)



According to this http://www.peachment.co.uk/nanni-diesel-n4-60-marine-engines/ max rpm is 2800.
When motoring we usually make 2000-2200 rpm - well in excess of 70% of max rpm

You should be able to achieve 2800 and cruise at 2000+. If you are achieving hull speed at 2200 you are overpropped (and probably overpowered). Depending on the make of prop you might be able to adjust the pitch - certainly on a Maxprop as sailorman says. What prop do you have?

 

[Koeketiene]

You should be able to achieve 2800 and cruise at 2000+. If you are achieving hull speed at 2200 you are overpropped (and probably overpowered).

We motor at a sedate 6kts (2000-2200 rpm) - never said anything about hull speed (which is approx a bit over 8kts)

Depending on the make of prop you might be able to adjust the pitch - certainly on a Maxprop as sailorman says. What prop do you have?

Darglow Featherstream (see #17)