Yanmar 3YM30AE engine - what revs do you cruise at?

[wonkywinch]

Reading the small print in my Yanmar 3YM30AE engine, it has a "fuel stop" at 3,200rpm and states "continuous operation" at 3,100rpm. I was always taught to run these 3 cyl diesels at around 2,500rpm (needle straight up on rev counter, easy to set). I know these engines are designed for long periods running at a single speed (their predecessors were used as paddy field pumps in Asia running for years at a time).

Curious what normal motoring revs you set if you have the same/similar engine? Do you do the carbon clearing procedure after a day out (clutch in, 5x short bursts of full power)?

 

[Tranona]

The difference between running engines at constant speed on things like pumps is that the engine is fully loaded at all revs whereas a boat engine is only fully loaded at the maximum permitted by the propeller. So your propeller will be sized to fully load the engine at somewhere around 3200rpm as can be seen in the power curve yanmar.com/marine/product/engines/3ym30ae/ This normally allows a typical cruising speed of, say 5.5 knots at half potential power output, so +/- 2400ropm. On my Volvo D1 30 which has a similar power curve I cruised at 2200rpm and 5,5 knots and maximum 3100rpm. Your 2500rpm is on the high side but much depends on the specific prop and boat, particularly displacement and windage.

The advice of periodic short runs at close to maximum under load is wise to reduce build up of unburned deposits particularly in the exhaust valves and outlet.

 

[Stingo]

Yep, what Tranona says.

I found on my boat that 2200 rpm gave best economy and speed. Every hour, I'd go 3200 rpm for two minutes to clear the muck.

 

[Lightwave395]

Yep, what Tranona says.

I found on my boat that 2200 rpm gave best economy and speed. Every hour, I'd go 3200 rpm for two minutes to clear the muck.

My 3YM30 (currently around 700 hours) is much the same, we cruise around 2200 rpm if we're not in a hurry with the added benefit of running on fumes and 2400 to 2500 if we are. Occassional burst of up to 2800 or so but probably not often enough... with a clean bottom 2400 is about 6 knots on a 7500 kg 12M boat

 

[jwilson]

My very early 3YM30 (slightly smaller capacity engine than the new 3YM30AE version) has been used for charter as well as by myself. Now at engine hours approaching 6,000 I run it at 2400 to 2800 as "cruising speeds", also giving it an occasional few minutes at full throttle, which gives 7.9 knots when launched with clean bottom and prop. 35 ft 12,000 lb sailing yacht. Engine still starts instantly, no smoke and very low oil consumption. I think it is now on it's fourth starter motor and third water pump though, plus three exhaust elbows. Apart from that it has been regularly maintained.

I believe diesels like hard work, and when I meet a smoky diesel that is giving problems starting it usually has an owner who says "I only ever use low revs", or "...just to get on and off the mooring".

 

[Koeketiene]

Our 3YM30 was installed in 2001.
It had 965hrs on the clock when I bought her.
The hour meter stopped working a while back, but I 'do' roughly 100hrs/pa.
Cruising throttle is about 2.4-2.5K rpm.
This gives me about 5kts and 2.3-2.5 ltr/hr.
Boat's 36' and weighs in at just under 8T.

 

[jwilson]

Our 3YM30 was installed in 2001.
It had 965hrs on the clock when I bought her.
The hour meter stopped working a while back, but I 'do' roughly 100hrs/pa.
Cruising throttle is about 2.4-2.5K rpm.
This gives me about 5kts and 2.3-2.5 ltr/hr.
Boat's 36' and weighs in at just under 8T.

Re you sure it's a 3YM if installed 2001? I thought mine at 2004/5 was one of the very first. It certainly had the common overheating problem suffered by the first 5,000-odd of these engines, addressed by a better heat exchanger being fitted under warranty.

Yanmar/Barrus of course did not publicise this or contact owners, so those who never ran their engines hard may never have found the problem and had it fixed free.

 

[Koeketiene]

Re you sure it's a 3YM if installed 2001? I though mine at 2004/5 was one of the very first. It certainly had the common overheating problem suffered by the first 5,000-odd of these engines, addressed by a better heat exchanger being fitted under warranty.

Yanmar/Barrus of course did not publicise this or contact owners, so those who never ran their engines hard may never have found the problem and had it fixed free.

Boat had a major refit in 2001-2003 (by second owner) in Holland. Carried out by the yard that built her.
She was re-engined at that time - I have the invoice.

Re: heat exchanger.
Had to replace the heat exchanger replaced this winter (cracked).
The mechanic who installed the new heat exchanger told be he believed it to be the original one.

 

[Refueler]

Really on small diesels as we use in boats ... what brand it is doesn't really make much difference in regard to this.

Load ... mmmm that's an interesting subject ... real load is when boat is being pushed to accelerate .. once it reaches the rpm / speed load reduces until boat slows due to waves or other influence and needs to maintain speed... you can hear this ... engine is 'growling as speed increases ... then quietens as speed is reached. Max throttle or not - it happens.

The trick to clear engine - is actually not just open throttle wide and let it sit like that for xx minutes or so - you can in fact increase the carbon and shite in the engine if not propped right. The trick is to vary the engine from wide open to slowish in repeated steps - get it loaded and actually burning ALL fuel that gets squirted in ...

I work to the idea of engine running at sweet least vibration level ... when all is as smooth as possible .. that would usually be about the 2000 - 2300rpm on my 2GM and also on the Perkins 4-107 ... vasty different engines - but illustrates my point about brand not really matter.
Every so often I give then a 'thrash' at full and varied throttle ... making the engine load as it accelerates the boat ..

If you see black exhaust as my Perkins does at anything over 80% - that's pumping in too much fuel ... again illustrates my point of varied throttle to clear the shite.

The 4-107 was 2nd hand when fitted to my boat ... sat at back of HYCO shed for couple of years ... guy had replaced it due to age and smokey. Fitted it to my boat - took her out into harbour open water and thrashed the hell out of it ... 20 odd yrs later still running sweet !

 

[westernman]

If the engine is overpropped or even if it is not, do not run at full throttle, but back off the throttle so that the revs drop 200 rpm from the maximum.

Then you can run it like that all day and night.

 

[Refueler]

If the engine is overpropped or even if it is not, do not run at full throttle, but back off the throttle so that the revs drop 200 rpm from the maximum.

Then you can run it like that all day and night.

Ful throttle is really only good to check engine still gets full revs !

As I said earlier .. varied throttle gets good results ...

 

[LittleSister]

Bear in mind the 'throttle' on a marine diesel ain't a throttle!

It's just setting engine revs. The governor in the engine will provide as much or as little fuel as required to reach and maintain the revs you set.

Even at max revs, once the engine reaches those revs you will likely not be 'flat out', not be generating the engine's rated hp output, nor reaching its max fuel consumption, unless the engine is undersized for the boat and/or the boat is over propped or heavily fouled.

 

[Tranona]

Bear in mind the 'throttle' on a marine diesel ain't a throttle!

It's just setting engine revs. The governor in the engine will provide as much or as little fuel as required to reach and maintain the revs you set.

Even at max revs, once the engine reaches those revs you will likely not be 'flat out', not be generating the engine's rated hp output, nor reaching its max fuel consumption, unless the engine is undersized for the boat and/or the boat is over propped or heavily fouled.

That is not quite right. Look at the power curves in post#2. The only time the engine is under full load is when it hits maximum revs when the power curve meets the engine output curve with a fixed pitch propeller of the correct size. Clearly given most props are made with steps in pitch or diameter it is not always possible to get this exactly right so manufacturers usually give a range of revs of 2300 below the governed maximum which is near enough. The Yanmar in question has a governed maximum of 3200 and continuous rating at 3100 so can be run 2flat out" indefinitely - which Yanmar suggests you do periodically. as also explaine this gives a practical cruising speed at +/- 2400 which most posts have confirmed is common, although the actual revs used is often determined for an individual boat as what feels right - on one boat I sailed it was just before thegrid on the top of the cooker started rattling!

 

[LittleSister]

That is not quite right. Look at the power curves in post#2. The only time the engine is under full load is when it hits maximum revs when the power curve meets the engine output curve with a fixed pitch propeller of the correct size. Clearly given most props are made with steps in pitch or diameter it is not always possible to get this exactly right so manufacturers usually give a range of revs of 2300 below the governed maximum which is near enough. The Yanmar in question has a governed maximum of 3200 and continuous rating at 3100 so can be run 2flat out" indefinitely - which Yanmar suggests you do periodically. as also explaine this gives a practical cruising speed at +/- 2400 which most posts have confirmed is common, although the actual revs used is often determined for an individual boat as what feels right - on one boat I sailed it was just before thegrid on the top of the cooker started rattling!

The power curves (and 'fuel curve') graphs indicate only the potential max power output (and fuel consumption) at the various revs, including max revs, not the actual power, which will depend on load. The engine will generate whatever power is required (up to the maximum it is capable of delivering - about 29hp in that case) to first achieve and then maintain whatever revs you set (up to the rev limit set by the manufacturer).

If you set your engine to maximum revs in neutral, to take an extreme example, it will happily maintain that speed, but be generating nothing like 29hp (probably not much more than, say 1 or 2 hp, simply to overcome friction plus water pump and alternator loads), and it will be consuming very little fuel in deed, not the maximum consumption shown on the consumption graph.

You won't be able to rev beyond max revs, even in neutral, not because the engine doesn't have the power, but because the engine is limited to those revs.

In an ideal world, with perfectly matched engine/prop/boat (rarely exactly achieved), you will, in theory, be using the full power (and consumption) of the engine. In practice that's rarely the case, as (1) most boats these days have engines with more than enough power, so won't need (and can't use, as you have previously pointed out) their full power output at maximum revs and hull speed; and (2) even if you could achieve that 'ideal' your engine would not be able to maintain full power against a head wind and waves, and keep falling from maximum revs.

When you cruise at, say 2,200 revs (to take an example you gave above) the engine will rarely, if ever, be generating the c9hp power available (or c1.5l/h fuel consumption) indicated by the graphs, it will generate (and consume) only what is required to maintain those revs. If the wind pipes up from behind you while you are so cruising, the engine won't increase revs because of a reduced load, the governor will simply reduce further the fuel supply to maintain the revs you set, and yet the boat will probably increase slightly in speed.

The boat's engine control works nothing like the accelerator pedal in an ICE car. It is more like a cruise control: depending on loading providing more fuel to prevent slowing or less fuel to prevent overspeeding, except it's not maintaining car/boat speed, it's controlling engine speed only.

I don't understand why so many boating people fail to grasp this fundamental, and not very complicated, thing about the way their boats work.

 

[Refueler]

Governed Throttle is well known and a novel about it really is not needed.

One item that I do have an issue with - the statement of fuel used per throttle setting. Yes fuel is governed - but imperfectly. That is why such engine as my Perkins 4-107 which is underpropped (boat would be impossible with full prop) ... bit its big anyway !! .. why exhaust is black when past about 80% ... its partial burnt fuel ...

If Littlesister statement and 'others' were true - then there would be little or no black smoke of part burnt fuel.

Before suggestions of uncalibrated injectors - injection pump needing service ... etc. - they are all spot on ..

 

[Tranona]

The power curves (and 'fuel curve') graphs indicate only the potential max power output (and fuel consumption) at the various revs, including max revs, not the actual power, which will depend on load. The engine will generate whatever power is required (up to the maximum it is capable of delivering - about 29hp in that case) to first achieve and then maintain whatever revs you set (up to the rev limit set by the manufacturer).

If you set your engine to maximum revs in neutral, to take an extreme example, it will happily maintain that speed, but be generating nothing like 29hp (probably not much more than, say 1 or 2 hp, simply to overcome friction plus water pump and alternator loads), and it will be consuming very little fuel in deed, not the maximum consumption shown on the consumption graph.

You won't be able to rev beyond max revs, even in neutral, not because the engine doesn't have the power, but because the engine is limited to those revs.

In an ideal world, with perfectly matched engine/prop/boat (rarely exactly achieved), you will, in theory, be using the full power (and consumption) of the engine. In practice that's rarely the case, as (1) most boats these days have engines with more than enough power, so won't need (and can't use, as you have previously pointed out) their full power output at maximum revs and hull speed; and (2) even if you could achieve that 'ideal' your engine would not be able to maintain full power against a head wind and waves, and keep falling from maximum revs.

When you cruise at, say 2,200 revs (to take an example you gave above) the engine will rarely, if ever, be generating the c9hp power available (or c1.5l/h fuel consumption) indicated by the graphs, it will generate (and consume) only what is required to maintain those revs. If the wind pipes up from behind you while you are so cruising, the engine won't increase revs because of a reduced load, the governor will simply reduce further the fuel supply to maintain the revs you set, and yet the boat will probably increase slightly in speed.

The boat's engine control works nothing like the accelerator pedal in an ICE car. It is more like a cruise control: depending on loading providing more fuel to prevent slowing or less fuel to prevent overspeeding, except it's not maintaining car/boat speed, it's controlling engine speed only.

I don't understand why so many boating people fail to grasp this fundamental, and not very complicated, thing about the way their boats work.

Sorry but you are saying essentially the same as I did and that is illustrated by the power curve statement that you highlighted which clearly shows at any point other than full power with a fixed pitch propeller the power demanded will be less than the engine is capable of producing.

If, on the other hand you have a variable pitch propeller either mechanically operated such as on the SABB engines you can vary the pitch to match the engine power required for a particular speed. The engine in this case is almost running at fixed rpm and speed is varied by varying pitch. Very useful at low speed. Or you can have a propeller like the Bruntons where the pitch automatically adjusts to best meet the speed required depending on the conditions. If you have used one you will know that typically the boat uses far lower rpm than a fixed pitch propeller. You can also get "2 speed" propellers like the Gori "overdrive" feathering propeller that can mechanically increase the pitch to reduce rpm at cruising speed - effectively just like the overdrive popular in some cars before the days of 5 and 6 speed gearboxes.

In reality for most boats you cannot justify the additional complexity because as you say now most boats have enough power to achieve hull speed while the engine is sufficiently loaded at cruising speed not to have problems that can arise from long term low load running.

 

[boatmike]

I tend to think people get too complicated over technicalities and blind themselves with science sometimes. It really is fairly simple and all diesel engines are fairly similar.
ASSUMING the prop has been specified correctly and does not overload the engine at WOT the things to avoid are
1. running at light loads at low revs for long periods
2. running at WOT for long periods
3. not asked to do too much until warmed up to running temperature
4. properly maintained and not left for long periods idle without proper decommissioning/reconditioning

Most engines will last for years if run at 50% to 80% of full revs. (even better if the load/revs are varied as someone said previously) and the above points are followed. Just think how many road miles a diesel car or commercial vehicle can clock up without trouble if used and maintained properly. The relatively short life of most leisure boat engines is down to lack of care and maintenance which far more important than worrying too much about overloading them.

 

[dgadee]

2000 is out normal cruising. Sometimes up it to 2500 but not too often. Getting the proper prop made a difference.