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Machinery Horrors

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  #101  
Old 9th March 2020, 11:15
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Duncan112 Duncan112 is offline  
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Originally Posted by Tim Gibbs View Post
Our 750 mm Doxfords were indeed horrors. They all had new crankshafts before the ships were 5 years old and one of them broke the replacement shaft 8 years later when I was 2/E and then that second shaft was badly damaged by microbial attack after another 4 years when I was Superintendent.
Interestingly, the Doxfords with 670 mm bore or less were relatively trouble free by comparison.
Too many millimetres spoiled the broth?
We did have a twin screw 3 cylinder 60LB that ran on diesel . That was really good (if you could hold the fuel pressure!). However, you were never quite sure which way the engines were going to start but as far as I know it was never the cause of a City of Brooklyn / Cato type disaster
I think you are right about the increased bore increasing the rate of bearing failure, at least initially. The reason to my mind was the distance between the main bearings, already large because of the side rod bearings increasing the bore caused more flexing over the increased distance increasing the risk of main bearing failure.

This brings me to another thought, the reason for the demise of the Doxford. Ship Owners wanted higher powers, there are only 3 ways of increasing the power per cylinder:

1) Increase the MEP, this will increase the crankshaft load, causing more flexing....

2) Increase the bore - this increases the bearing distance....

3) Increase the stroke - we now run into the difficulties of either casting a very long liner or go back to the difficulties of sealing a tripartite liner

Could these difficulties be solved with modern technology - maybe. Is there any appetite for investment to do so - almost certainly not
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  #102  
Old 9th March 2020, 13:50
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I think you are right about the increased bore increasing the rate of bearing failure, at least initially. The reason to my mind was the distance between the main bearings, already large because of the side rod bearings increasing the bore caused more flexing over the increased distance increasing the risk of main bearing failure.......
Yes, on the 75LB6 the " perfect" centre crank deflection at No.6 was 0.045 inch(1.1mm) ! In fact if the deflection gauge didn't fall out it was sometimes considered okl! Goodness knows what the deflection was in the running condition. On the ship I was on that fractured the crank at No.4 side crankweb ,we fitted a huge strap around the crankweb and had to cut a bit out of the bedplate to allow it to rotate. However, when we started the engine for a trial there was a clonk, clonk at about 40 rpm and inspection showed we had to cut out a bit more! In my experience with these engines the cause of many of the bearing failures was locked sphericals, either from incorrect adjustment or ridges being allowed to develop.
I agree about the 3-part liners of the "J" type. We had sister ships, two with 76J7 Doxford engines and one with a 6RND90 Sulzer. If it wasn't for the liner sealing problems the Doxford would have been a much superior engine. Your analysis of the Doxford demise is probably correct in the long run but I'm convinced they would have been keep in production for longer had it not been for the seriously c**p British Shipbuilders management
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  #103  
Old 9th March 2020, 20:20
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Yes, on the 75LB6 the " perfect" centre crank deflection at No.6 was 0.045 inch(1.1mm) ! In fact if the deflection gauge didn't fall out it was sometimes considered okl! Goodness knows what the deflection was in the running condition. On the ship I was on that fractured the crank at No.4 side crankweb ,we fitted a huge strap around the crankweb and had to cut a bit out of the bedplate to allow it to rotate. However, when we started the engine for a trial there was a clonk, clonk at about 40 rpm and inspection showed we had to cut out a bit more! In my experience with these engines the cause of many of the bearing failures was locked sphericals, either from incorrect adjustment or ridges being allowed to develop.
I agree about the 3-part liners of the "J" type. We had sister ships, two with 76J7 Doxford engines and one with a 6RND90 Sulzer. If it wasn't for the liner sealing problems the Doxford would have been a much superior engine. Your analysis of the Doxford demise is probably correct in the long run but I'm convinced they would have been keep in production for longer had it not been for the seriously c**p British Shipbuilders management
Tim
Doxfords Liverpool and Hull Sulzer London. Coasted Hull and London
Alan
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  #104  
Old 10th March 2020, 12:37
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..... In my experience with these engines the cause of many of the bearing failures was locked sphericals, either from incorrect adjustment or ridges being allowed to develop.
.....
All this has given me a severe attack of RAS*
Not unreasonably we had become paranoid about the 75LB6 crankshaft alignment but then the company decided to check the immediately post war built 67LB6s although they had run without any significant alignment problems. I have a memory that one of then was found to 40mm low at the forward end so the engine was realigned. What a trip we had after that. We had several BE bearing failures and all showed signs of locked sphericals - the sphericals that had previously been able to move to suit the crankshaft position couldn't now move to the required position due to the ridges that had formed by running so long in that original position.
*Repetitive Anecdote Syndrome
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  #105  
Old 11th March 2020, 13:38
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This is an aside but I was told (Can't remember where, possibly an IMarEST event) that sometime after Doxford's final closure a vessel required a new crankshaft. A world wide search revealed no one capable of building one!!
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  #106  
Old 11th March 2020, 17:45
Steve Hodges Steve Hodges is offline  
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I only sailed on one of this class, and we had field days fro drydock to signing off some 6 months and boiler water and its purity, and generation in the scam vaps was a problem, as the ships grew disgracefully older? They broke many a budding engineer. The stories of any of the six IT ships was a Story book to behold-Grimmes Fairy Tales.
Shakespeare clearly had a premonition about BP's Eyeties..... to quote from "Macbeth" - " O horror, horror, horror! tongue nor heart cannot conceive nor name thee! "
One of these beauties was my first trip as engineer cadet, so I didn't know any better at the time. I think the steelwork was all from recycled Fiats, you could almost watch it corrode before your eyes, and I quickly became adept at applying Thistlebond bandages to the bilge mains. That and sootblowing by hand - all the wiring to the electric motors had rotted away. If any ex-BP engineers want a walk down this particularly nasty memory lane, my cadet's logbook has
full details of most of the engineroom systems drawn on the back of old charts. Six separate steam systems! ( Superheated; desuperheated; auxiliary exhaust; high, intermediate and low pressure bled steam) What were they thinking! Perhaps it was their revenge for losing WW2?
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  #107  
Old 12th March 2020, 00:24
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Varley Varley is offline   SN Supporter
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I thought their revenge was the Grande Motori di Trieste.

A quick Google suggest then Bard knew them: Affliction is enamoured of thy parts, And thou art wedded to calamity.
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  #108  
Old 12th March 2020, 08:07
Engine Serang Engine Serang is online now  
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I thought their revenge was the Grande Motori di Trieste.
Or the Fiat 131. Or ham and pineapple pizza.
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  #109  
Old 12th March 2020, 10:41
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........Six separate steam systems! ( Superheated; desuperheated; auxiliary exhaust; high, intermediate and low pressure bled steam) What were they thinking! Perhaps it was their revenge for losing WW2?
There was certainly a correlation between complexity and the number of field days on the 1970s era steam ships. It was all supposed to improve efficiency and probably looked great in the design office but the through-life costs would have told a different story.Sadly those responsible for the design and approval of these systems were rarely around to take responsibility when the truth emerged.
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