Thanks for that Rob.Quote:
Originally Posted by robpage
We had a greaser on the Pretoria who had been on the Cape Town at the time and claimed it was caused by clearing of tubes, but as I said, so many rumors
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Thanks for that Rob.Quote:
Originally Posted by robpage
We had a greaser on the Pretoria who had been on the Cape Town at the time and claimed it was caused by clearing of tubes, but as I said, so many rumors
Air Start Explosion On The Capetown Castle is a good detailed explaination because what he said is also correct , drains to pipes were blocked with carbonQuote:
Originally Posted by happy daze john in oz
#42... Rob you being a certifiablele or should say certificated marine engineer, have asked this question before and got various answers . I served my time mostly on a 3 cylinder doxford. During the nearly 3 years I was there can remember during one of the nearly daily stoppages due to scavenge fires I was told. One of the junior engineers was slightly concussed due I was told that on restarting the engine someone had left the turning gear in which somehow managed to have a collision with his head. When repeating this story various engineers of various ranks have told me it would have been impossible to do so, however I think that fiver would disagree. Also we made passage from BA to Japan on two pistons only cutting one out as didn’t have the spares to fix. It took us 98 days to do but we got there and got the necessary bits and pieces in Durban en route. Again I have been told by various experts that it would be impossible to go on two legs, maybe the mates got lost and wasthe reason it took so long to make Port. Engineers have told me various answers. However a mate of mine who writes articles for Sea Breezes sentme an article some time ago about another ship which did similar on a North Atlantic run and was hailed as special and one time effect. We had done the same previous andgot no kudos, just part of the job for engineers of that day and era. Cheers JS. pS That was before Cappy got on this fine vessel and broke it with his chipping hammer. JS
this is very simplistic and well explained but VERY basic from Reference: The Operation and Maintainence of Machinery in Motorships By N.E Chell
One of the most common reasons for a fire in a ship’s engine room, scavenge fire is the deadliest of all fires. Scavenge fire has been the reason for several major accidents on ships in the past and it is for this reason that it is termed as the most dangerous cause for accidents on a ship.In order to understand scavenge fire it is important to learn the basics. In this article we have brought to you everything you ever wanted to know about scavenge fires – from causes to actions. Understand and fight scavenge fires the way it should be.
https://www.marineinsight.com/wp-con.../crankcase.jpg
Getting the Basics Right: What is Scavenge fire?
For any fire to occur we need three elements which make the fire triangle. The three important elements for any type of fire are:-
1. Oxygen –this is available plenty in the scavenge space.
2. Heat source- this could happen because of blowing by of gases between piston rings and liner or as a result of any rubbing between two surfaces.
3. Fuel- this can be from un-burnt fuel, carbon or cylinder lubricating oil leaked into the space
When all these elements are present in a proportion ratio and lie within the flammable limit inside the scavenge space the later become a hot spot for eruption of fire. The fire which thus results is known as the scavenge fire.
Causes of scavenge fire
There are many reasons for scavenge fire. However, the main ones are as below:
1. Excessive wear of the liner.
2. The piston rings might be worn out or have loose ring grooves.
3. Broken piston rings or rings seized in the grooves.
4. Dirty scavenge space.
5. Poor combustion due to leaking fuel valves or improper timing.
6. Insufficient or excess cylinder lubrication.
Indications of scavenge fire
There are a few signs which indicates a scavenge fire. One should be extremely cautious in case any of the below mentioned conditions are observed.
1. Scavenge temperature will start increasing.
2. The turbochargers will start surging.
3. High exhaust temperature.
4. Loss of engine power and reduction in rpm. This happens because a back pressure is created under the piston space due to fire.
5. Smoke coming out of the scavenge drains.
6. The paint blisters will be formed on the scavenge doors due to high temperature but this will occur only in large fires and extreme cases.
Actions to be taken
Action taken in case of a scavenge fire depends on the type of the fire, whether small or large. In case of large fire the following signs will be easily visible – the peeling or blistering of paint, large reduction in engine rpm and surging of turbocharger.
For small fires
1. Start reducing the engine rpm and reduce it to slow or dead slow.
2. Increase the cylinder lubrication of the affected unit. Special attention to be given for this as this does not feed the fire. In case of increase of fire do not increase the lubrication.
3. The fire can be due to leaky fuel valves, so lift up the pump of the affected unit.
4. Keep scavenge drain closed.
5. Keep monitoring the scavenge and exhaust temperatures and let the fire starve and wait for it to burn itself out.
6. After confirming that the fire is out start increasing the rpm slowly.
7. Keep monitoring the scavenge temperature for any signs of re-ignition.
For large fires
1. Stop the engine immediately and engage turning gear, and keep engine rotating with turning gear.
2. Extinguish the fire with fixed fighting system for scavenge fire. This may be co2 system or a steam connection for smothering the fire.
3. In case fixed system is not available on very old ships an external cooling is provided to prevent distortion due to heat.
4. Once after confirming that the fire is extinguished. The scavenge space is allowed to cool down and later opened for inspection and cleaning of the scavenge space.
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Turning gears often just had a micro-switch and light , so it was easy to start up , some would launch and fly across the flywheel , some would make noises and throw big bolts at you , 3.5 hp turning gear against 4000 hp main engine , been there , done it , lived to cover it up
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Hanging a cylinder is just shutting the fuel off simply , and letting it idle so you need to either let it cycle , or take bits out of the liner so there is an empty space , I have heard anecdotal stories of that but always third and fourth hand , with the two firing spaces per cylinder you would have to disconnect all the pistons from the crank and physically lift them in that cylinder , big job at sea , but do-able , you would be lucky to get 1/3 power , so slow ahead
for the nostalgic
https://www.youtube.com/watch?v=BMb5GLMdFNY
John, Most of my time at sea was with Doxford engines, generally five and six cylinders versions. they were reliable and easy to work on except for one. The life span of one particular engine No 5 cylinder was a couple of hundred hours only due to misalignment and then the scavenge fired started and after one particularly ferocious fire the company ordered us to dock in Shimizu in Japan. We thought this was very strange but we docked there and within 24 hours the entire engine had been lifted ashore and taken to the workshop. It was completely dismantled and the engineers started to measure up the bed plate and entablature to check if they were built to the correct specifications. They found the bedplate was 25mm shorter than the entablature and so modified that section of the bedplate so that all cylinders were running up and down when the engine was re-assembled. It took the workshop about five days to do this and the engine was re-assembled and lifted back into the ship. Nine days after arriving at that port we were sailing away and never any problems, the ship did another 20 odd years of trouble free service !!! The original entablature had been built in Italy -- need I say any more !! Regards Peter in NZ.
Thanks Peter, the eleven years I was with Runcimans they were always Doxfords as were tied up financially with same I believe. Runcimans home address was Doxford Hall. I was only on one 3 cylinder ship and think the last one was the J type believe it was called. When on the 98 day’s at sea run it was also the side effects away from the engine side that was a downer in those days, as meant water rationing for starters, and was back on the old lime juice as a substitute for vegetables. Was bred into one the value of fresh water and seen us chasing rain clouds and the main deck engine room feed tanks air pipes taken off to catch.Today with distillers and evaporators water is rarely a problem. Cheers JWS
Thanks Peter, the eleven years I was with Runcimans they were always Doxfords as were tied up financially with same I believe. Runcimans home address was Doxford Hall. I was only on one 3 cylinder ship and think the last one was the J type believe it was called. When on the 98 day’s at sea run it was also the side effects away from the engine side that was a downer in those days, as meant water rationing for starters, and was back on the old lime juice as a substitute for vegetables. Was bred into one the value of fresh water and seen us chasing rain clouds and the main deck engine room feed tanks air pipes taken off to catch.Today with distillers and evaporators water is rarely a problem.; Cheers JWS
The Southern Cross was the only British Merchant Navy ship lunched by a reigning monarch, who also chose the name of the ship. From a suggested list supplied by Shaw Savill.
She bunkered at Curacao and Last Palmas and top up with diesel at the ports Tahiti, Durban heavy and diesel. She had six, eight cyld. DC generators. Round trip 77 days three trips thro Panama and one round Cape-town every year. Northern Star was AC 3turbo alternators and two stand by Diesel, and ran the other way round the world.
GWB
Re #48. Northern Star had two Pamatrada turbine sets as the main propulsion units and at the time the largest fresh water distillation plant on board any ship, built by Weirs. Cheers Peter in NZ.
Seeing as the Southern Cross was built by H&W Did they bid for the contract for the Northern Star, or because Canberra was financially a disaster for H&W did they not bother tendering for the contract?