# Innovations from the past



## Tim Gibbs (Apr 4, 2012)

Toward the end of the 1970s a number of companies formed a consortium to build eight similar second generation refrigerated container ships for the South African trade. 
The Ellerman ship was the City of Durban built at AG Weser in Germany. The capacity was c. 3000 teu of which c.850 were fridge. The main machinery was 2 X 20MW and the auxiliary power was 6x1500kW and it was a very interesting project to be involved as it provided a number of challenges for the technology of the time.
Early on it was realised that there was going to be an issue with the main engine torsional vibrations. Being an 8 cylinder 2-stroke, the normal crank angles would all be 45 degrees but some bright spark worked out that changing the angles would magic the problem away and so it was that we had crank angles alternating 42.5/ 47.5 degrees. QED and a zero cost solution.
Having solved the torsional problem there was some concern about propeller excited vibrations being a problem with this power and the chosen stern configuration and so the shipyard proposed what we thought was an outlandish idea; a way to electronically synchronise the main engines and vary the phase angle between the propellers to cancel out any vibrations without any mechanical or electrical connection between them. We remained sceptical right up to the sea trials but work it did; pressing the synchronise button immediately locked both engines into exactly the same speed with both simultaneously having No.1 at TDC and then we could vary the crank angle between the engines from 0 to 45 degrees. My memory is that to make it work required a very large actuator for the governor systems. Unfortunately (or perhaps not!) there was not a hint of the feared vibrations so the system turned out to be a solution to a problem that didn’t exist.
The engines had two turbochargers arranged for constant pressure exhaust inlet and there was concern that starting and manoeuvring with one turbocharger out of action would be problematic so a turbocharger booster system was devised. A nozzle directed starting air into the eye of the compressor which had a twofold effect – it helped accelerate the working turbocharger and pushed additional air into the scavenge system. It worked fine on the testbed, however I don’t know if it was ever used in anger with the ship service but I was surprised how relatively little starting air it used when we tested it. 
For reasons I never really totally understood, the consortium decided that the eight ships should have propeller and tailshaft interchangeability. This requirement was obviously a problem with a number of shipyards with different designs involved but a solution was provided by Araldite! With the passage time I cannot recall the exact details except that a changeable steel boss was Araldited into the propeller hub and this provided the ability to change between different propellers and tailshafts. I do recall it was a rather large pot of resin but I can’t help thinking this may have been another solution to a problem that didn’t exist.
The ship was quite complex for it time and to ease commissioning and trials the shipyard initially fitted the ship with fitted zero thrust propellers. This allowed the main engines to be run up to full power whilst at the fitting out berth so by the time we come to trials they had a run a couple of hundred hours allowing all the systems to be debugged and so we had a very uneventful trial charging around the North Sea for a few days at 25 knots.,
Technically the vessel was a success but unfortunately this was not the case commercially as the trade for which it was intended did not fully develop and she was eventually transferred to the ACT service and became ACT8.


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## blueprint2002 (Sep 7, 2011)

*innovative*

What an intriguing case! There is material enough for at least three technical papers for the learned societies, SNAME/IMarEST/RINA, or their equivalents in other countries. Maybe there already are?
I would guess, probably wrongly, that the adjustment of those crank angles could only have been done in the engine builder’s works, and hopefully this happened before it was installed on board. Corresponding adjustment of the cam angles would surely be needed too, and all this could be easy when you know how! Incidentally, do you recall the make and model of those engines?
The need (or not) for adjusting the phase difference between the two propellers was occasionally also found in the past. I seem to recall a case of a passenger ship of the thirties, maybe Dutch or Italian, on which this had to be done, in order to suppress the low frequency beats which resulted from slight differences in the two shaft speeds. Which meant that at fairly long intervals, the two would come into some relative position which reinforced each other’s pulses. Naturally, at that time, only a mechanical solution was practical, and if memory serves this was done by a kind of differential gear connecting the two governor drives: the direction and magnitude of the relative motion would effect an adjustment of the appropriate governor. Will try to find whatever reference I have in this connection
Not sure if I’ve correctly understood the turbocharger situation you have described; it sounds as if the two TCs would come into operation progressively i.e. one only at lower powers and both at higher powers? In parallel, not series, would seem more likely. Either way, innovative is the only way to describe the solution.
Thank you for sharing this unique experience.


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## Tim Gibbs (Apr 4, 2012)

blueprint2002 said:


> What an intriguing case! There is material enough for at least three technical papers for the learned societies, SNAME/IMarEST/RINA, or their equivalents in other countries. Maybe there already are?
> I would guess, probably wrongly, that the adjustment of those crank angles could only have been done in the engine builder’s works, and hopefully this happened before it was installed on board. Corresponding adjustment of the cam angles would surely be needed too, and all this could be easy when you know how! Incidentally, do you recall the make and model of those engines?
> The need (or not) for adjusting the phase difference between the two propellers was occasionally also found in the past. I seem to recall a case of a passenger ship of the thirties, maybe Dutch or Italian, on which this had to be done, in order to suppress the low frequency beats which resulted from slight differences in the two shaft speeds. Which meant that at fairly long intervals, the two would come into some relative position which reinforced each other’s pulses. Naturally, at that time, only a mechanical solution was practical, and if memory serves this was done by a kind of differential gear connecting the two governor drives: the direction and magnitude of the relative motion would effect an adjustment of the appropriate governor. Will try to find whatever reference I have in this connection
> Not sure if I’ve correctly understood the turbocharger situation you have described; it sounds as if the two TCs would come into operation progressively i.e. one only at lower powers and both at higher powers? In parallel, not series, would seem more likely. Either way, innovative is the only way to describe the solution.
> Thank you for sharing this unique experience.


The crankshafts were built up in Czechoslovakia and i know the office there was a bit confused when they first saw the drawing!
The turbocharger thing was to cover the situation where one was out of service so the engine had to start and self-sustain on just the one and this being a particular problem with the constant pressure exhaust syatem.


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