Will I damage my engines

Irish Rover

Irish Rover

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2 x 75HP Yanmar 4JH3TE turbo with 2,900 hours each. I want to use my boat for fishing - trolling at around 3 knots. I'd be using one engine at a time running at around 8/900 revs. My plan would be to ensure I get the engine up to temp before reducing the revs and give it a good blow out at higher revs at the end of the day. Will I damage the engines or is there anything else I can do to minimise damage. All advice appreciated.
 
Shorten the lifespan .
Here’s by reasoning .......

Agglomerated soot clusters are commonly called sludge. Second, only to high temperatures, sludge does more damage to a diesel engine than anything else.

We all realise without oil, a diesel engine runs steel on steel. Pistons rub on cylinders and valve hinges grind. In a matter of minutes, the engine will overheat and seize up. You can see that happen so it needs no further explanations.

But, sludge literally, sands down the interior components of a diesel engine. The engine will not typically overheat or seize up immediately. But, the damage created by sludge can be far worse.
This sludge or correct term “ agglomeration “ form with low Exhaust Gas Temperature ( EGT ) .
Ideally under normal load we are looking at a range of 550-north of 600 ish .
Degrees .
As soon as you back off the sticks the EGT ,s instantaneously drop .
Sure the water jacket temps hardly move ,buts it’s the cylinder temps / pressures that drop .So water jacket temp is meaningless.

They say a final end of day blast home helps blow out any agglomerations,but remember you been sanding down the cylinder bores and anything else the new added abrasives in the oil have been in contact with for how ever many hours @ 3 knots before the run home .
A fast run home at the end of the day only “ cleans “ the sludge from the cylinders it does not remove the extra added abrasives from the oil .

Mitigation the 2nd part of your post ?

Don,t run below design boat speed .

If you find you are doing a lot of D speed in a designed P speed boat think about more oil/ filter changes to remove the extra build up of abrasive particles.

Change boats to a petrol or designed D speeder diesel ,the latter will have an engine that manages to load up and keep the EGT,s in the least harmful range .
 
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As far as I know there are 2 issues.

1 this tends to be a pita in practical terms. The boat does not track straight and things like power steering pump will be on one engine and not the other.

2. The gearbox is not designed to turn for long periods without oil pressure.

Re 2 people will probably have different views of how long you can do this for before it becomes an issue.
 
Tend to agree with Jrudge re gearbox .
Gearbox low pressure issue .
Maybe ?
I think it depends on which type .
Twin disc I thought are fine at low rpm the P is 5 bar at 1st click which equates to 600 rpm and 7+ knots .
Running at design speed the P rises to 17/18 bar say at 1750 rpm 27 knots .
The only proviso in the Twin Disc manual is windmilling .
This is when ( Op suggest turning one engine off ) the off engine in N , the prop spins in the wake and turns its 1/2 of the gearbox ,presume the other disc attaches to the engine is not spinning so the book says ok for short periods but prolonged it recommends and outlines a method of locking the disc / prop that’s spinning otherwise as you say permanent damage .
Of course the Op needs to read his own GBox manual
 
Thanks for the replies. As some of you will realise from past posts I'm not very technically gifted so I have no hesitation in saying I didn't full understand some of what has been said. I only ever use 2 engines when I'm in the marina or other confined area and when anchoring. All my other use is with one engine generally running @ 2,200 rpm and making around 7Kns. Previous owner had the boat for 10 years and he used it in exactly the same way. The boat is slightly skewed on one engine - AP shows it at about 4 degrees. As far as I know the 2 units are completely independent of each other and each has it's own gear box - a Kanzaki-Carl Hurth KBW21 with a mechanical wet multiple disk clutch [whatever that is].
@Portofino - thanks for your posts. I understood the first part of your #2 but I have no idea what D speed and P speed mean never mind knowing what they are for my boat. Can you help a poor numpty.
 
Irish Rover said:
Thanks for the replies. As some of you will realise from past posts I'm not very technically gifted so I have no hesitation in saying I didn't full understand some of what has been said. I only ever use 2 engines when I'm in the marina or other confined area and when anchoring. All my other use is with one engine generally running @ 2,200 rpm and making around 7Kns. Previous owner had the boat for 10 years and he used it in exactly the same way. The boat is slightly skewed on one engine - AP shows it at about 4 degrees. As far as I know the 2 units are completely independent of each other and each has it's own gear box - a Kanzaki-Carl Hurth KBW21 with a mechanical wet multiple disk clutch [whatever that is].
@Portofino - thanks for your posts. I understood the first part of your #2 but I have no idea what D speed and P speed mean never mind knowing what they are for my boat. Can you help a poor numpty.
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Most of the above you can ignore because they are talking about big, high powered engines whereas yours are simple, low specific output engines with semple mechanical gearboxes.

The only real downside of running at those low revs is that the engine is not fully loaded and may suffer from long term bore glazing. However this normally occurs in low hours engines that are not well run in. There may also be an issue with deposits building up in the turbos and exhaust manifolds. On the other hand doubt your ratio of low running to normal will not be high so the good blast you suggest will clear the deposits and regular oil changes will keep the oily bits clean.

BTW D and P are short hand for Displacement and Planing speeds - again not directly relevant to your situation.
 
I can remember a conversation with a Caterpillar engineer some years ago who said turbo charged engines shouldn't be run at idleing speeds for prolonged periods as A, it soots the turbo up and B, as Portofino says it degrades the oil.
 
Tranona said:
Most of the above you can ignore because they are talking about big, high powered engines whereas yours are simple, low specific output engines with semple mechanical gearboxes.

The only real downside of running at those low revs is that the engine is not fully loaded and may suffer from long term bore glazing. However this normally occurs in low hours engines that are not well run in. There may also be an issue with deposits building up in the turbos and exhaust manifolds. On the other hand doubt your ratio of low running to normal will not be high so the good blast you suggest will clear the deposits and regular oil changes will keep the oily bits clean.

BTW D and P are short hand for Displacement and Planing speeds - again not directly relevant to your situation.
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Thank you - the only better news I could get is that red wine and Turkish beer won’t damage my health.
 
Sorry for the abbreviations
D means displacement speed for me up the bow wave .
P planing speed .
Permit me to use my boat to illustrate.
Using the load guages and fuel consumption L/ h I suspect D for me (14 M ) is about 9 knots .Say 825 rpm
Any further rpm both the load and L/h rises as the boat starts to push a bow wave ,but does not lift enough to get up on top .
Planning is about north of 18 maybe higher in a big sea around 20 knots . Sort of 1400 rpm ish when the turbos start to spool .Its this point that the EGT,s rise from 250 through 350 to around 400
Planing is when ( in my book but arguably other will disagree) is the point at which when any further advance of speed is followed by a reduction in the angle of attack, in simple terms =trim angle decreases with further speed .
At around 1600 rpm onwards the EGTs rise north of 500 degrees thus theoretically reducing agglomeration to a minimum.

It might be helpful to indicate which boat you are runing .
Also where your 2200 rpm is relation to the engines normal designed running rpm .
In the abscence of EGT or load guages your fuel burn can be roughly used to see if the engines are operating outside the agglomeration zone .
So for me tick over 7 ‘knots 12 L / h , 9 knots 18 L /h , 27 knots 90 L/h all per side .
Running about more than I have to @7 or 9 knots puts me into the super agglomeration zone .
 
Tranona said:
Most of the above you can ignore because they are talking about big, high powered engines whereas yours are simple, low specific output engines with semple mechanical gearboxes.

.
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Diesel fuel needs to burn between 500/650 degree to minimise agglomeration.
Doesn’t matter in what !
The actual diesel molecules and inlet air molecules that are trying to combine efficiently are the same in 20 ft yacht with a Yanmar 1GM as a “ high powered “ planning craft like mine .
The agglomerations arn,t picky :cool:
 
Pinnacle said:
Porto

OP has a power cat with 2 x 75hp Yanmars. See #1 . Planing speed is thus not relevant to him.
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Never said it was just answering his Q re “ D and P “
The design operating speed is relevant that’s what I,am trying to determine.
Does 2200 rpm achieve somewhere between 500 / 650 EGT ? Or sufficient cylinder temp to minimise agglomeration ? That’s the killer ( scuse the pun ) question .

800/900 rpm feels waaay too low .

Fuel burn as I said is his only way to start to understand how far off if any he is .

You either believe in agglomeration or not .Go and google it .

Hey matters not one bit to me if he gets another 2900 hrs or another 290 ( because the previous owners trashed them ) or 3x 2900 hrs before a strip down and rebuild .
 
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Irish Rover said:
I’m a bit lost again but if it helps I burn 3.5 LPH @ 2,200 rpm making around 7 knots.
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Lol don't worry your not the only one that gets lost. All very complicated to me as well. I have a yanmar engine as well all be it much bigger. I often travel at low revs and enjoy the journey and save a fortune on fuel at the same time but I do also open it up and as has been said I burn the soot off. Personally I just use it how I want too but I service it every year and as I said I put the engine under load regularly. I do understand that marine diesels like to be worked and try and do that when I can
 
All i can say is that I don’t have any problems trolling with my trolling valve at 1.8 knots at 850 rpm with my nanni Diesel 200 hp turbo charged toyota engine, I still hit recommended max Rpm and WOT speeds like originally stated in the engine manual so I do not think that my many hrs of trolling have damaged anything. No excessive smoke...nothing unusual.
Just as in your case, I was worried when I changed boats from a petrol to diesel powered but I was reassured by numerous members of my fishing club with Viknes boats , these boats usually come with Volvo or Yanmar motors , some of these boats are equipped with manual trolling valves from the factory itself ,( one or 2 have the electronic versions )and many of these boats have run for more than 10 yrs without problems trolling.

The other club members do not even use any additive, I use Belladd diesel additiv always as they claim it makes a cleaner diesel burn.
 
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Irish Rover said:
I’m a bit lost again but if it helps I burn 3.5 LPH @ 2,200 rpm making around 7 knots.
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Looking at this indicative link
https://www.tradeboats.com.au/tradeaboat-reviews/engines/1505/yanmar-4jh4-te-boat-engine-review

It’s clear at 3.5 L/h it’s under performing .
I,am looking at the 10 L/h at 2800 and crucially the axterix under the graph *
It says “ min and max “ rpm .
I can’t see @ 800/900 rpm your original Q btw ,that you will get anywhere near optimal cylinder temp for the least agglomerations forming .
So I stand by what I said “ shortening the life’s span “ in my 1 st reply .
Which I guess is an inverted yes to causing damage .

Reminds me of smokers and that debate .
“ been smoking for 40 years and still alive “
“ know a chap who’s 85 smoked all his life “
Thing is you live longer if you don’t smoke and it shortens your life and is harmful to the body .Most people accept that .

But with marine diesels regarding EGT,s / cylinder temps and minimising agglomeration the same scientific logic does not seem to work .

Each to there own I guess .
 
Portofino said:
Looking at this indicative link
https://www.tradeboats.com.au/tradeaboat-reviews/engines/1505/yanmar-4jh4-te-boat-engine-review

It’s clear at 3.5 L/h it’s under performing .
I,am looking at the 10 L/h at 2800 and crucially the axterix under the graph *
It says “ min and max “ rpm .
I can’t see @ 800/900 rpm your original Q btw ,that you will get anywhere near optimal cylinder temp for the least agglomerations forming .
So I stand by what I said “ shortening the life’s span “ in my 1 st reply .
Which I guess is an inverted yes to causing damage .

Reminds me of smokers and that debate .
“ been smoking for 40 years and still alive “
“ know a chap who’s 85 smoked all his life “
Thing is you live longer if you don’t smoke and it shortens your life and is harmful to the body .Most people accept that .

But with marine diesels regarding EGT,s / cylinder temps and minimising agglomeration the same scientific logic does not seem to work .

Each to there own I guess .
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You are misleading the OP. Please read his original post where he clearly states he intends running at 8/900 rpm.

2200 rpm is the normal cruising speed (perhaps a little low) for this 75 hp engine which peaks at 3700 rpm and the fuel consumption he is achieving is correct. It is 2l capacity so very lightly stressed. (My 2l Ford car of similar age produces 140hp at 4000rpm!) This is a displacement boat with a maximum speed of around 10 knots and a cruise of 7 when it will be using around 40 BHP from one engine.

All very different from the sort of engines and boats you are talking about. So, while running continuously at low rpm is not a good idea the type of usage he suggests will do do any harm provided he runs it hard from time to time and follows the service schedule for oil and filter changes.
 
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