Engines in sync - by ear?

[Murv]

I hear a lot of discussion referring to people being able to tell if their engines are synced by the sound.
As someone very new to twin engines, and (relatively) large marine ones at that, could someone explain it a bit better?

Mine make a kind of warbling sound, best way to describe it would be that the sound volume/tone would be a sine wave peaking at around 1 second intervals (with the engines matched in rpm according to the tacho's.) Playing with the revs (very slightly) on one engine will speed up, or slow, the frequency of this warble.
What should matched engines sound like?
This is related more to a very slow cruise speed and probably iro 1200-1500 rpm or so at a guess. At higher revs it's more of a continuous roar.


Engines are Volvo TAMD61A's in a Fairline turbo 36 (6 cylinder, 5.6 litres, charge air cooled turbo diesels @ 306hp peak) if it makes a difference.

 

[BruceK]

I just wrote about that here post 23.

The answer for me is the higher the revs the more harmonic intervals there are so you cannot judge by the lack of harmonic interference alone. I tried but got it wrong. However if your tachs are balanced you can use that as a base and then use the ear to fine tune.

Theoretically your engines will be balanced in the absence of any oscillating harmonic interference thrumming and become a single unified hum.... if that makes sense

 

[Murv]

I just wrote about that here post 23.

The answer for me is the higher the revs the more harmonic intervals there are so you cannot judge by the lack of harmonic interference alone. I tried but got it wrong. However if your tachs are balanced you can use that as a base and then use the ear to fine tune.

Ah, gotcha, thanks for that. So you really need the tacho confirmation that they're synced, then you can "tune" your ear to the sound of the engines rather than the other way around. Makes sense!

 

[No Regrets]

Just tweak them so they sound happy. The engines don't really care, but you and your vibrating bits of boat interior do!

 

[CharlieAlpha]

The physics is interference, goes like this lets take two 1cyl engines if both cylinders go bang at the same time the sound form both bangs will be added together (louder), or if the banged at different times combined sound would be less. So if both engines are running at exactly the same rpm the sound level would be constant, but if their rpm's were different the sound would vary (oscillate as per your sine wave) as at some point the bangs would coincide and at other not.
Now we have 2 times 6cyl and thus loads more bangs that can coincide (harmonics) and we only have a mk1 ear so at best we might start to notice the sound oscillation as the rpm's get closer together and be constant when together then start to oscillate again if we carried on with one throttle.

So my suggestion is to get a laser handheld tacho they are very cheap these days http://www.ebay.co.uk/itm/GM8905-Digital-Laser-Tachometer-RPM-Tach-Test-Meter-Speed-Gauge-Handheld-/152233831244

 

[BruceK]

Tacho yes. Despite the love poured into these diesels, they are not musical instruments and there is so much noise being generated I wonder if I'm hearing or feeling the interference oscillations when underway. Either way it's been demonstrated (on my boat at least) to be not quite enough to tune to a perfect harmonised "note". On my boat I can get sync'ed oscillation intervals every ~200 odd revs. i.e. the engines will sound balanced when port is at 3200 and starboard is at ~ 3000 3200 3400 etc however when both are at 3200 the note is subtly different. It's almost as if there is a slight reduction to db but an increase in perceived engine loading. Which is slightly counter intuitive for me at least. (Very difficult to put words to sounds and I'm making a right hash of it I suspect but hope you understand my bumbling attempts here )

 

[Murv]

Just tweak them so they sound happy. The engines don't really care, but you and your vibrating bits of boat interior do!

They never really sound happy as such, it's more the sound of a suppressed rage to be honest. I love my engines

The physics is interference, goes like this lets take two 1cyl engines if both cylinders go bang at the same time the sound form both bangs will be added together (louder), or if the banged at different times combined sound would be less. So if both engines are running at exactly the same rpm the sound level would be constant, but if their rpm's were different the sound would vary (oscillate as per your sine wave) as at some point the bangs would coincide and at other not.
Now we have 2 times 6cyl and thus loads more bangs that can coincide (harmonics) and we only have a mk1 ear so at best we might start to notice the sound oscillation as the rpm's get closer together and be constant when together then start to oscillate again if we carried on with one throttle.

So my suggestion is to get a laser handheld tacho they are very cheap these days http://www.ebay.co.uk/itm/GM8905-Di...Test-Meter-Speed-Gauge-Handheld-/152233831244

Great explanation, thank you I do actually have a laser tacho, so will check the calibration on the engines ones. One does seem to read a bit lower than the other at tickover, so would be good to check if they are actually out or not.

 

[Spi D]

If memory serves Faria sell a Synchronizer instrument for not a lot of money (relatively).

 

[jrudge]

It maybe worth seeking to recalibrate / reset the electronics as i have not known a synced engine not sync ( i.e. one constant hum).

The electronics will take their feeds from the RPM input directly so taco inaccuracy is not relevant to the electronics, so it should be spot on if it is working.

Some Volvo engines have the ability to turn sync on or off. Mine just did it with no option!

On the Squadron 65 ( cat) there are two syncs .... the primary which is done by the control system , and the secondary that is by the CAT electronics.

The normal mode is the control system does it and the CAT system is off. I gather the switch is only there as CAT wont certify the installation any other way.

I dont know the boat or engines, but it maybe worth seeing if there is a similar thing going on on your boat and they are both on, which I imagine would cause an issues as the two system fight it out. I have never touched the button so I can't advise directly what happens when they are both on!

 

[BruceK]

My KAD42's dont have any of this modern electrical wizardry. I'm not sure if this is a good thing or not.

 

[Murv]

Tacho yes. Despite the love poured into these diesels, they are not musical instruments and there is so much noise being generated I wonder if I'm hearing or feeling the interference oscillations when underway. Either way it's been demonstrated (on my boat at least) to be not quite enough to tune to a perfect harmonised "note". On my boat I can get sync'ed oscillation intervals every ~200 odd revs. i.e. the engines will sound balanced when port is at 3200 and starboard is at ~ 3000 3200 3400 etc however when both are at 3200 the note is subtly different. It's almost as if there is a slight reduction to db but an increase in perceived engine loading. Which is slightly counter intuitive for me at least. (Very difficult to put words to sounds and I'm making a right hash of it I suspect but hope you understand my bumbling attempts here )

Actually, I do, thank you! I did struggle to phrase my initial question, I know what I wanted to ask, just not sure if it made any sense or not!
Very good point that the sound can appear synced when the revs are drastically different. Mine only rev to 2800 rpm max anyway, so a hundred rpm or so is quite significant

 

[Murv]

If memory serves Faria sell a Synchronizer instrument for not a lot of money (relatively).

They do indeed... http://fariabeede.com/products.php?calledGauge=2_synch and as a confirmed gadget/gauges fanatic, it looks really good!

 

[Murv]

It maybe worth seeking to recalibrate / reset the electronics as i have not known a synced engine not sync ( i.e. one constant hum).

The electronics will take their feeds from the RPM input directly so taco inaccuracy is not relevant to the electronics, so it should be spot on if it is working.

Some Volvo engines have the ability to turn sync on or off. Mine just did it with no option!

On the Squadron 65 ( cat) there are two syncs .... the primary which is done by the control system , and the secondary that is by the CAT electronics.

The normal mode is the control system does it and the CAT system is off. I gather the switch is only there as CAT wont certify the installation any other way.

I dont know the boat or engines, but it maybe worth seeing if there is a similar thing going on on your boat and they are both on, which I imagine would cause an issues as the two system fight it out. I have never touched the button so I can't advise directly what happens when they are both on!

These don't have any electronic trickery on them, just simple cable operation

 

[PeterBoater]

A laser tachometer isn't going to be of any use except to check that the regular tachometers are reasonably accurate. Having calibrated the regular tachometers with the laser, when making way set the engine rpm's the same, then adjust one throttle, it doesn't matter which, by tiny amounts so that there is no regular beat or throb. If the beat/throb increases move the throttle the other way. One way to make the required tiny throttle adjustments is to use two hands, one at the top of the lever and one at the bottom slightly opposing the top movement. It's an aural process; it can't be done on rpm gauges alone.

 

[steve930]

My boat has the faria sync gauge fitted. It works well at lower rpm's but when my superchargers shut down & the turbos take over at higher rpm's the gauge goes all to pot!

Interestingly mbm did a test on a boat years ago and also noticed the same issue ( no it wasn't my boat)

At higher rpm's I set up initially with the tachos and then fine tune by ear

 

[omega2]

We use the boost gauges to balance.

https://youtu.be/KqfZ6ZXl5pc

Tacho's are very difficult to sync due to the alternator drive pulleys and belts not evenly worn, being an old fashioned Ford set up it does not really bother us. LOL

we get load difference even when the auto pilot operates the steering to put us back on track.

 

[jfm]

It maybe worth seeking to recalibrate / reset the electronics as i have not known a synced engine not sync ( i.e. one constant hum).

The electronics will take their feeds from the RPM input directly so taco inaccuracy is not relevant to the electronics, so it should be spot on if it is working.

Some Volvo engines have the ability to turn sync on or off. Mine just did it with no option!

On the Squadron 65 ( cat) there are two syncs .... the primary which is done by the control system , and the secondary that is by the CAT electronics.

The normal mode is the control system does it and the CAT system is off. I gather the switch is only there as CAT wont certify the installation any other way.

I dont know the boat or engines, but it maybe worth seeing if there is a similar thing going on on your boat and they are both on, which I imagine would cause an issues as the two system fight it out. I have never touched the button so I can't advise directly what happens when they are both on!

J, the engine's in OP's boat are mechanically governed (centrifugal spinning mechanical governor)

The cat stuff you refer to is a switch that lets one engine's fuel timing and injection duration be dictated by the other engine's ECU, and vice versa. (remember, in an electronic diesel pretty much the only outputs that the ECU can decide, from the myriad of inputs, is fuel injector opening time and duration). The switch is more of a back up (in case one ecu fails) than a synching device. In fact, by definition, it won't create synched rpm because the load on the two engines is generally not perfectly matched.

So you'd only use the switch by exception. Normally, you'd let the normal control regime apply where each engine's own ECU decides its own fuelling parameters, and the control electronics synch the engines just by placing the same desired rpm value into the electronic governors.

 

[Newbroom]

Chris
Set your engine revs to what you want to run at, Bring one engine down from those revs and gradually increase it till you go above the other engine, you will hear the right pitch as you go through the band its a bit like tuning an old transistor radio to radio Luxembourg. For those of old enough to remember doing that.
Very often the difference will be 50 to 100 revs different but you will hear the difference when they harmonize.
Dave

 

[jrudge]

J, the engine's in OP's boat are mechanically governed (centrifugal spinning mechanical governor)

The cat stuff you refer to is a switch that lets one engine's fuel timing and injection duration be dictated by the other engine's ECU, and vice versa. (remember, in an electronic diesel pretty much the only outputs that the ECU can decide, from the myriad of inputs, is fuel injector opening time and duration). The switch is more of a back up (in case one ecu fails) than a synching device. In fact, by definition, it won't create synched rpm because the load on the two engines is generally not perfectly matched.

So you'd only use the switch by exception. Normally, you'd let the normal control regime apply where each engine's own ECU decides its own fuelling parameters, and the control electronics synch the engines just by placing the same desired rpm value into the electronic governors.

It is marked SYNC and boats.co.uk just told me dont touch! For once I did what I was told!

 

[Murv]

Thanks all