# Overspeed while surfing



## Piecesofeight (Oct 10, 2008)

A question for the engineers from a former R/O.

In 1986 I was working on a Greek built product tanker (Brassie/3FCG) as R/O. We were crossing the Pacific with a following sea and the ship was surfing. As the stern rose the prop was briefly relieved of its full load sometimes and when this happened there would be the most horrible noise from the engine room as it over sped. I presume the turbo was over running. Somebody did explain it to me once but I've long since forgotten what they told me. Lack of speed regulation on the turbo charger? It sounded like a horrible grinding of gears.

Perhaps somebody would be kind enough to hazard a guess at what was going on to cause such a noise.

Many thanks


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## Satanic Mechanic (Feb 23, 2009)

Yup Turbo charger surge aka ‘barking’

Physics is a little bit complicated , it’s not exactly over speed- not terribly good for the poor turbo. It’s essentially a transient condition caused by the turbo charger trying to supply more air than the engine needs which then leads to a back flow of air through the compressor. There are certain vibration characteristics as well which assist in the unholy sound it can make


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## makko (Jul 20, 2006)

I concur with SM - Take the load off, instantaneously, and the entire engine and auxiliaries run amok!

Basically, the turbo uses the exhaust gas to run a turbine to spin the compressor and provide more air - More air equals more fuel that can be burned per cycle, thus more power. I remember from college, probably Derek Burton telling us, that a turbo charged engine cylinder volume/power ratio is comparable to about 3 times a normally aspirated engine. Anyway, I digress. The diesel engine is not stochimetric like a petrol engine, hence the need for a governor. With the diesel, more revs, more air/fuel, more revs, more air/fuel ad infinitum - If ungoverened, the engine will run up it's speed until it disintegrates!

Getting back to your question and repeating, when the load came off the prop, the engine and, in consequence, turbos, were allowed to run up the revs. And boy, do they scream! That is, until the governor cut in and/or the prop dropped back into the oggin, like a giant brake on the revving engine!

A friend was on a vessel (Sulzer 9RND90 with 3x BIG turbochargers) that had to do "slow steaming" and the turbine side of the turbo became caked with combustible crud. Eventually, the crud flashed off and the turbo went off the clock (that is over 10,000 rpm), running efectively as a jet engine! He said the sound was terrifying. When they go truly bananas, they "shed blades" which can "exit the casing", think of a knife throwing act with multiple knives thrown at the same time. The only solution that occured to them was to insert floor plates in the inlet joint, thus strangling the turbo. and then copious cleaning.

Rgds.
Dave


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## Piecesofeight (Oct 10, 2008)

Thank you both for giving me some idea of what is likely to have happened. I don't know that the prop ever cleared the water, I'd be surprised but then perhaps once or twice with a heavy swell rolling under us from astern, it did. Certainly the noises coming from aft were alarming for a few days.


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## Varley (Oct 1, 2006)

makko. Stochimetric for the humble? (It appears ungooglable. Stoichiometric seems inapplicable).


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## Piecesofeight (Oct 10, 2008)

This looks to be relevant but frankly way over my head and I was happy with the rest of his explanation https://www.sciencedirect.com/topics/engineering/stoichiometric-coefficient


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## Engine Serang (Oct 15, 2012)

Wish I've had taken my Extra Chief's.


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## makko (Jul 20, 2006)

Varley said:


> makko. Stochimetric for the humble? (It appears ungooglable. Stoichiometric seems inapplicable).


Yes, spelling mistake. Air/Fuel mixture in a spark initiated internal combustion engine as opposed to the diesel's compression/ignition cycle. Hence, no governor on a petrol engine and governor always on a diesel engine.

Additionally, to my explanation, as the prop lifts out and the engine revs run up, the turbo will accelerate, When the prop is "braked", i.e. goes fully back in the water, the turbo will continue at very high revs, but the exhaust gas flow will drop (engine slows, very quickly). This will cause the turbo to surge then stall, hence the popping. Very basic Bernoulli, I suppose - p1v1=p2v2.

Rgds.
Dave


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## Varley (Oct 1, 2006)

Myself when young did eagerly frequent.........
.........
But evermore came out by the same door as in I went.

It's the link with no governor on a petrol engine that I cannot make.


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## Varley (Oct 1, 2006)

Dave, while I am obliged but I still cannot make the connection. If we had a large spark ignition engine would we leave it with a fixed fuel setting. Very easy to cut the spark to stop it but one would need something to measure the speed and do the cutting wouldn't we? Even some cars have some sort of governor to allow the driver to regulate the fuel automatically instead of with his foot.

We did have at least one rogue/uncontained event due to slow steaming after which a daily(?) increase to NCR was mandated in the hope of burning off the crud deliberately and daily. Rather than accidentally with a months worth. On Nordic Crusader/Cast Fulmar we came back nearly all the way from Dampier to Rotterdam with turbo chargers surging. We had a buggered fuel valve in one cylinder (8 Cyl B&W). Stopped to change it but even head turned upside down and wellied with much hammer it would not budge and the charter dictated we continue anyway. Since this thread started I have wondered for the first time if that one could have been blanked off and the pump adjusted to allow the other 2(?) to operated 'normally'/less stressfully. Not sure I am right about the number of fuel valves could there have just been one?


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## Stephen J. Card (Nov 5, 2006)

Varley said:


> Since this thread started I have wondered for the first time if that one could have been blanked off and the pump adjusted to allow the other 2(?) to operated 'normally'/less stressfully. Not sure I am right about the number of fuel valves could there have just been one?



Good question!!!!!

Would this cause a problem with a piston, liners and every other part running with different temperatures from the other cylinders?

Would it be better to remove the piston and cranks and let the others do the 'work' and get better burning?

Better if an engine was 'designed' just for this purpose of 'slow steaming'?

My only experience is with my scooter. Only 1 cylinder and I have found it runs better without it. No noise, saves petrol too.


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## Varley (Oct 1, 2006)

Stephen,

That cylinder was hotter and if I remember the load had to be kept so that it did not become damagingly so.

I think I have the connection with Stoichiometry. In the petrol engine the fuel and air must both be controlled according the quantitative imperatives of the chemistry that describes the burning reaction. (Stoichiometry, if I read it right, includes the quantifying of reagents in a reaction) The diesel burns in an excess of air and so only the fuel needs to be regulated. Overspeed protection, by governor or otherwise, operates to cut the fuel off but not the air. 

I do not think I will burden my tiny brain with it any longer. How a day can be consumed by stumbling across a strange word. I hope there are no more out there.

An engine can be 'rated' so that it is optimised to an operating condition within it's design. So that the a vessel strengthened for Ice will have, by Class, a power above that which it is contracted to use in normal waters it will be rated at its expected normal output but still have the higher power available with a less good fuel consumption. Only within limits that I guess would not cover 'slow steaming'.

Burmpac Bahamas (one of Houston's prizes being supported with considerable help from Glasgow) cracked a liner leaving Lisbon and we shut off the fuel rather than 'hang-up' the unit. All went well until the following morning when a loud bang followed by escaping steam (very like a compressor unloading except the hiss continued) not all the energy in the compression stroke was returned to the crankshaft and the water in the head had boiled building up enough pressure to blow out a joint in the jacket cooling piping.

We would have been for your scooter solution too, silence and Lisbon. Well, until the liner had been replaced anyway but Euan Davidson requisitioned me from TDU me and sent us off with "If she doesn't go now and stayed here and we repaired everything that needed doing she'll never sail". I stayed until Las Palmas where she picked up a spare liner. She continued to have an eventful life.


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## makko (Jul 20, 2006)

Stephen/David,

Large marine diesels can be "dead legged". That is, the piston "hung", disconnected from the crosshead. This is normally if a cylinder liner (for one example) fails and cannot be replaced. The engine timing can be tweaked and it will run fine, except for a decrease in available power.

There were two problems with the B&W's, late 70's, early 80's. One was as David described, erosion and dripping of the fuel injector nozzle. There were many failures due to pooling of oil on the piston crown (principally) with all the usual subsequent effects.

The other problem was the weld failure on the stem of the exhaust valve. The valve disc and stem were different materials (only the disc being stellited) and the disc would fall into the cylinder or jam in the seat with resultant, unwanted consequences! 

A friend (RIP) survived a typhoon in the S. China Sea on a T&J Harrison: The engine was (maybe Doxford) a five cylinder opposed and, due to liner failures, had two cylinders "dead legged". Another liner, thankfully, failed as they were manoeuvering into berth! I think the ER gang were all wearing brown boiler suits by the time it was FWE! If I remember, the problem was poor quality control during fabrication of the liners.

Rgds.
Dave


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## makko (Jul 20, 2006)

I will give you 7/10 for your stoichiometric description, David! Try no more.......


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## dannic (Mar 10, 2013)

Stephen J. Card said:


> Good question!!!!!
> 
> Would this cause a problem with a piston, liners and every other part running with different temperatures from the other cylinders?
> 
> ...


Slow steaming most older engines, required different fuel injectors being fitted. 
1 tanker was on with a 10 cylinder engine, 3 injectors per cylinder, was a major job changing out all injectors after telex from office.
And of course 2 days later another telex to say - resume full speed, 13.5 knots!
Modern engines can alter injection, exhaust, timing etc. with computer.
Dannic


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## Stephen J. Card (Nov 5, 2006)

It was easier in the old days when the fuel was burnt in a boiler!


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## Varley (Oct 1, 2006)

makko said:


> I will give you 7/10 for your stoichiometric description, David! Try no more.......


Relief. I will settle for that (before leaving school that would have been the best score ever. Afterwards I did better).


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## Varley (Oct 1, 2006)

Stephen J. Card said:


> It was easier in the old days when the fuel was burnt in a boiler!


Indeed Stephen. Do we not somewhere have a photograph of one notable ship of yours with much of the charterer's fuel, unburned, skypainting her progress in black all the way to the distant horizon?


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## spongebob (Dec 11, 2007)

This reminds me of a voyage from Auckland to Melbourne under charter to NZ Fruit Distributors Ltd to collect a ship load of Riverland Oranges.
We sailed light ship in ballast and mid Tasman a South westerly storm struck and pummelled us for about 48 hours or more .
The little Navua was punching into head seas and the 1500 hp five cylinder trunk piston Sulzer was not responding quick enough to the governor whenever the propeller broached the water and after a few scary over-speeds we decided to man the throttle full time .
The watch engineer stood at the controls feeling the stern rise and fall and closing the fuel lever at the right moment and putting the fuel back on as the prop re-entered the water while the standby engineer look after other matters as we bucked like an untamed rodeo horse. 
Things were to get worse , the stern gland was taking a hammering with each rise and fall to increase the sea water entry from a dribble to a flow while the tunnel bilge suction strum box blocked up with wood shavings from the workshop where we had all been doing woodturning on the otherwise unused Colchester lathe . 
The roll and pitch had washed the bilge water into every corner of the tunnel bilges to ac***ulated all this and other debris at the aft strum which saw the willing motorman almost diving to frequently clean it.
Then the ship dropped off a big rouge wave and buried her bow into the next one which sent solid wall of water over the ship, bridge and all and sending a huge amount of sea water up the goose neck vent on the galley fuel oil tank mounted just aft of the bridge , the egg beater effect of the ship's gyrations quickly turned the tank contents into a syrup of treacle like emulsion that would not flow down to the galley .
It fell on me and my watch motorman to go up to the tank and take the inspection door off to ladle out this sludge and flush the tank before we could get anything cooked from the galley.
The skipper was reluctant to heave to , no doubt thinking about his bonus from the Charterer! But after a while it was the engine-room controlling the progress as we settled down to a slow way on within the engine limits under those cir***stances.
The weather eventually abated and we made up time to reach the cargo within it ripening time limits .
Nobody got any real sleep during the storm but the engine room staff came close . We had just taken on board a couple of bales of washed old rag and a bale of cotton waste for engine room cleaning and the Second moulded this into a birds nest like bunk on the workshop floor that cradled the body in every direction so we all had a go at that luxury.

Bob


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## Steve Hodges (Feb 12, 2007)

Thanks to my esteemed colleagues for the detailed technical explanations of what happens to a turbocharged slow-speed diesel when the prop comes out of the water. The only time I had to be the "manual governor" no-one troubled to explain it to me, I was just plonked at the controls and told to pull the regulator back as the engine ran away and push it back up when the prop "bit". This was on a 20,000 tonne product tanker off Cape Leeuwin, worst weather I was ever in at sea. I was only a second trip cadet - Acting Junior Engineer - but because the 2/E had a heart attack everyone got "instant promotion" and I ended up keeping the 4-8 with an E/R rating ( who knew a lot more than I did). I did wonder what might happen if I got it wrong, it all sounded - and felt - rather alarming.


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