engine synchronising

[Guest]

We have developed a way of showing the difference of engine rpm in the form of a bargraph. Center zero with the bar moving to the left or right depending on the difference between the engine rpm. We sense the engine rpm on deisel by a sensor on the fuel line. Is this Useful? and what display would owners of twin engines like to see? what accuracy between the engines would be practical?

Rob

 

[Guest]

How does the diesel flow give info about engine rpm. If the loading on the engine is slightly different (e.g. slightly different prop pitches) or the set up (injectors, fuel pump, degree of blockage in fuel filters, etc.) is not quite set identically will there not be slight differences in fuel flow for the same rpm or, conversely, same rpm gives different fuel flow? This question is genuine from an ignorant accountant! Myself, I tend to synchcronise my engines by ear. They sound right, almost as one engine, when they are in sync and there is a definite beat or thrumming noise when they are not. I have twin 200hp Volvos and when they sound right, the starboard engine is running very slightly faster than the port engine according to the tachos.

I agree, however, that the display you suggest sounds useful for a novice but is it accurate for the reasons above?

Nick

 

[Guest]

Since presumably the rev counters are receiving pulses it seems unnecessary to take pulses (or other readings) from the fuel lines. I like the thought of a visual display of rev alignment but it needs to look good on the instrument panel without adding to the complexity of wiring to the engine. Must be digital and accurate to 1 rev I suggest. Last thought...If boat rev counters were digital then there would be no need for your device. David

 

[Guest]

Years ago, in fact the late 60s I had a Coronet fitted with twin volo petrols, above the panel there was a guage and to have the engines perfectly in sync one had to adjust the throttles until the needle was dead centre. Don't know or can't remember any more excepting it wasn't a standard fitment and it came from the U.S.A.

 

[Guest]

To be fair he didn't mention fuel flow was being measured. I can guess that they have a transducer or load cell counting the pressure pulses on one of the injector lines, which of course is directly correllated to engine revs.

Having said that, I would agree that this is of limited use as most throttle controls of the Morse type would be difficult to set very accurately. I too adjust my two 306's by ear/feel, mainly to reduce the beating effect, to almost zero, and of course the tacho's may well be slightly different.

What would be of much greater use, is a servo system to actually SET the engine revs the same- but that takes money.

 

[Guest]

As far as I am aware, other than the latest Electronically controlled engine management systems, most rev counters are a voltmeter, whose voltage reading is proportional to revs and calibrated accordingly, hence variable accuracy between a pair on the same boat. This is the reason for the idea.

Unless it was cheap, then people would only buy it for novelty value. If both engines are 50 revs/min out, it is not going to cause any problems.

 

[Guest]

Analogue display.

I have exactly that on my Sea Ray and it works well. AW/Florida

 

[Guest]

Is the condition of the props/stern gear also a factor. If the pitch of a propellor is slightly out or it has slight damage, compared to the other it will produce more/less thrust and result in the "out of balance" sound made by twin engines. Obviously no amount a fiddling with the throttles will sort out the results of real damage to the stern gear but are props so accurately made that identical high speed rev's produce identical thrust?

For me, when the engines sound right i.e. sound in balance, they probably are right.

Nick

 

[Guest]

Depends on the cost, commercial synchronisers exist. Most common is made by Glendinning, you only use one throttle once it is engaged and this keeps both engines at the same revs. I used to have a boat with one and it was brilliant.