# HMS Dasher -propulsion machinery



## Steve Hodges (Feb 12, 2007)

My late father-in-law was a survivor of the disastrous explosion and sinking of the escort carrier HMS Dasher in the Firth of Clyde in 1943, which was I believe the Royal Navy's greatest single loss of life in home waters ( 379 crewmen killed ). In reading about the ship I came across some details of her machinery which aroused my curiosity.
HMS Dasher was originally built as the merchantman "Rio de Janeiro" by Sun Shipbuilding in the USA in 1941, and subsequently converted to an escort carrier of the "Avenger" class. Her main propulsion machinery is listed as four William Doxford diesel engines driving a single shaft with a total of 8,500 shp. Can anyone help with the following questions?
- Would these have been the familiar opposed-piston Doxfords, or an earlier conventional design?
- Were Doxford engines built under licence in USA? I was not aware of this, but it seems inconceivable that we would be sending ship's engines to USA in wartime.
- Does anyone know how the four engines were coupled to the shaft? Was it via a mechanical gearbox, or some sort of diesel-hydraulic or diesel-electric arrangement?
- I have recently bought a very good video programme about the disaster, which mentions repeated problems with the main propulsion machinery throughout her short career, but without giving details. Can anyone throw any light on this?
- One of the suggested possible causes of the catastrophic explosion and fire has been an initial crankcase explosion which damaged and ignited the ships aviation spirit storage tanks. Does anyone know if crankcase explosion was a known problem with Doxford engines of this era?
Here's hoping that someone in SN-land can throw some light on this - I can't think of a better place to try!


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## Tim Gibbs (Apr 4, 2012)

Steve. I don't think she has 4 engines, I think she had a "twin-bank" engine ( 2 engines mounted on a common bedplate and permanently geared together) driving a single propeller. The engines were built under a very loose licence from Doxfords by Sun Shipbuilding in Chester, Pennsylvania but was still recognisable as an opposed piston Doxford. Over a period of over 20 years Sun built 49 Doxford engines, twin-banks and single and with cylinder bores ranging from 535 to 815mm with several variations in between. 
The published data I have about 'Dasher's engines appear to be wrong and I would prefer to believe the data for the 'Charger, 'Biter & 'Avenger.
This says it was a twin-bank 6 cylinder 535mm LB engine developing 9.000bhp. 
Yes, crankcase explosions were a serious problem in the past but my feeling is that with the Doxford, being a steel fabricated structure as opposed to bolted steel castings, the effects of a crankcase explosion could be slightly less catastrophic ....... but never good! 
I had a lot of Doxford experience (not much of it good!) but never had anything near to a crankcase explosion despite having more than my fair share of bearing problems where the explosions normally originated from.


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## sternchallis (Nov 15, 2015)

Typical Yanks, more cubic inches.
Sounds overly complicated to put 2 Doxfords onto one shaft rather than twin screw, particularly considering its use as an auxiliary carrier.
Presumably there was a clutching arrangement as knowing Doxfords they had their problems. The 535mm bore would have been close to medium speed, one shudders at the thought of one doing more than 100 rpm.

As for the names, a Doxford is more liable to Charge, Bite and Avenge, than Dash.


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## Tim Gibbs (Apr 4, 2012)

sternchallis said:


> Typical Yanks, more cubic inches.
> Sounds overly complicated to put 2 Doxfords onto one shaft rather than twin screw, particularly considering its use as an auxiliary carrier.
> Presumably there was a clutching arrangement as knowing Doxfords they had their problems. The 535mm bore would have been close to medium speed, one shudders at the thought of one doing more than 100 rpm.


I'm not sure there was a conventional clutch as there may have been an issue with torsional vibrations that might have required the cranks to be correctly phased - like the Mirrless & Sulzer twin-banks. So perhaps a dog clutch arrangement?
We had 67LB6 engines running at 118rpm and *once* had a 75LB6 at 108rpm for a full passage from Canada to the UK. Most of us lived to tell the tale!


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## Steve Hodges (Feb 12, 2007)

Tim Gibbs said:


> Steve. I don't think she has 4 engines, I think she had a "twin-bank" engine ( 2 engines mounted on a common bedplate and permanently geared together) driving a single propeller. The engines were built under a very loose licence from Doxfords by Sun Shipbuilding in Chester, Pennsylvania but was still recognisable as an opposed piston Doxford. Over a period of over 20 years Sun built 49 Doxford engines, twin-banks and single and with cylinder bores ranging from 535 to 815mm with several variations in between.
> The published data I have about 'Dasher's engines appear to be wrong and I would prefer to believe the data for the 'Charger, 'Biter & 'Avenger.
> This says it was a twin-bank 6 cylinder 535mm LB engine developing 9.000bhp.
> Yes, crankcase explosions were a serious problem in the past but my feeling is that with the Doxford, being a steel fabricated structure as opposed to bolted steel castings, the effects of a crankcase explosion could be slightly less catastrophic ....... but never good!
> I had a lot of Doxford experience (not much of it good!) but never had anything near to a crankcase explosion despite having more than my fair share of bearing problems where the explosions normally originated from.


Thanks Tim. My initial information was straight from Wikipedia. After a bit more ferreting I learned that the four "Avenger"s were laid down as sister ships for MooreMcCormack, and that HMS/USS Charger was converted after the war into Sitmar's passenger liner "Fairsea" and survived until the late 1960's. I'm wondering if she was re-engined or if she retained her original Sun- Doxford engines to the end - if she did, she must have been quite a curiosity, to say the least. 
I read somewhere else that the "Avenger" class's Doxfords ran at 180 rpm which seems terrifying, I hope it was a mis-print. I sailed with an LB Doxford, and as an apprentice was involved in building the prototype Hawthorn- Doxford Seahorse; it was supposed to run at 300 rpm I think, although I never saw it finished. I have been trying to get my head round the concept of two early 6-cylinder opposed piston units on a common bedplate and geared to a single output shaft - it sounds like the stuff of nightmares, even without 180 rpm! From what I have read, all the "Avenger"s had engine troubles - now I have to start researching the "Fairsea" to find out if she was re-engined or not.


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## Tim Gibbs (Apr 4, 2012)

Steve Hodges said:


> I sailed with an LB Doxford, and as an apprentice was involved in building the prototype Hawthorn- Doxford Seahorse; it was supposed to run at 300 rpm I think, although I never saw it finished. I have been trying to get my head round the concept of two early 6-cylinder opposed piston units on a common bedplate and geared to a single output shaft - it sounds like the stuff of nightmares, even without 180 rpm! From what I have read, all the "Avenger"s had engine troubles - now I have to start researching the "Fairsea" to find out if she was re-engined or not.


I saw the Seahorse managing >7000Kw and think it might just have had a future with more development but British Shipbuilders pulled the plug on it.
If the 'Dasher's 2x535LB6 had the normal Doxford LB bore/ stroke ratio the piston speed wouldn't have been too excessive but I would admit it might have looked a bit scary on the top platform! I had the misfortune to be involved with the 58JS3 which ran at 220 rpm but with the very short top piston stroke that looked ok . Shame it was only the looks!
Sun certainly weren't bound by convention; as well as twin-banks some early engines had the scavenge pumps replaced by electrically driven blowers and they also built 2 cylinder opposed piston generator engines of c. 150 hp.


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## blueprint2002 (Sep 7, 2011)

Steve Hodges said:


> My late father-in-law was a survivor of the disastrous explosion and sinking of the escort carrier HMS Dasher in the Firth of Clyde in 1943, which was I believe the Royal Navy's greatest single loss of life in home waters ( 379 crewmen killed ). In reading about the ship I came across some details of her machinery which aroused my curiosity.
> HMS Dasher was originally built as the merchantman "Rio de Janeiro" by Sun Shipbuilding in the USA in 1941, and subsequently converted to an escort carrier of the "Avenger" class. Her main propulsion machinery is listed as four William Doxford diesel engines driving a single shaft with a total of 8,500 shp. Can anyone help with the following questions?
> - Would these have been the familiar opposed-piston Doxfords, or an earlier conventional design?
> - Were Doxford engines built under licence in USA? I was not aware of this, but it seems inconceivable that we would be sending ship's engines to USA in wartime.
> ...


Two references that may be helpful, if only partially:
1. The Royal Navy Research Archive website has a page on Dasher (under Escort Carriers) which states that the ship had two Doxfords geared to a single shaft, power not stated. I'm sure you've seen this already.
2. The Dutch magazine "Schip en Werf" featured a 3-part article on Doxford by a G G Jackson, who was Technical Manager Liaison for Doxford at the time. Part 1, in the 15 Feb 1980 issue, mentions a twin bank engine built by Sun in 1925, and even has a picture and a cross-section of it. This particular engine drove two shafts, but it is easy to see how they could be coupled together by a single gear wheel between two pinions. This is available on the magazine's website. And in case you are wondering, this particular article is in English, not Dutch. They did that sometimes.


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## Tim Gibbs (Apr 4, 2012)

A bit more on Sun Doxfords;
Apparently they built a 330 mm bore 4 cylinder twin-bank in 1925 which was fitted to mv Sialia - Henry Ford's yacht. All the main engine structure was in cast aluminum. 
It produced 750hp at 200rpm and each bank drove its own propeller!
As far as I can see the crankshaft centres were about 1750mm so the props must have been very small, or overlapping!
It didn't appear to have a detuner on the front of the cranks but there was a large balance weight in it's place.
You've got to hand it to them - they weren't bound by convention!


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## Tim Gibbs (Apr 4, 2012)

A bit more on Sun Doxfords on the escort carriers; the third one HMS Charger survived the war ( probably no thanks to the engine!)and was converted to the passenger /. immigrant ship "Fairsea" in 1949 and remained in service 'till 1969 so someone must have got the hang of running that strange engine .


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## Rocket_Ron (Jan 25, 2013)

I`ve a book by a Seafire pilot who said that that particular ship always stank of fuel. He wasn`t surprised at all it blew up. But it wasn`t a class thing, he`d flown from others of the class which were fine.


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## Tim Gibbs (Apr 4, 2012)

Rocket_Ron said:


> I`ve a book by a Seafire pilot who said that that particular ship always stank of fuel. He wasn`t surprised at all it blew up. But it wasn`t a class thing, he`d flown from others of the class which were fine.


But did he look down below ? ! HMS Avenger was a real horror apparently and spent a lot in various dockyards have the engine "fixed" before she was lost to a torpedo in November 1942


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