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Doxford Engines 3-legged

55K views 107 replies 55 participants last post by  thomas25 
#1 ·
I am researching details of 3-cylinder Doxford Engines built prior to turboblowers becoming standard about 1940.
A few main features I've found out so far but need verification: 1. They are famous for economy (helped win the battle of the Atlantic). 2. The throw of the crank for the Upper Cylinder was half the throw for the Lower Cylinder. 3. Some may have had open crankcases. 4. The scavenge pump was driven by a pair of parallel levers connected to the upper No 2 cylinder con rods. 5. Their Engine Frames were cast rather than fabricated.
I've been trawling the www for details so I can build a representative model. There must have been hundreds of these 3-legged Doxfords built but now its hard to find enough drawings to show how they were made and operated.
I'd be very appreciative if any reader could throw some light on this not-too-distant piece of Marine Engineering history.
best regards,
Jolee
 
#33 ·
I was under the impression that the classic Doxford was a victim of it's own design in that the crankshaft was unable to handle the increasing horsepower of it's rivals and they reached the design limit.
Still a wonderful engine and a famous part of maritime history.
 
#36 ·
That's always been my opinion because there are only 4 ways to increase the power of a reciprocating engine:

1) Increase the cylinder diameter but this increases the distance between the main bearing centres, in the case of a Doxford this distance is already large because of the presence of the side rods and bearings. This would result in the crankshaft bending too much between the main bearings.

2) Increase the piston stroke - this would lead to an over long cylinder liner with associated casting problems, the tripartite liner as an attempt to overcome this was never really successful

3) Increase the mean effective pressure in the cylinder - this would increase the bending moment on the crankshaft - see 1 above

4) Increase the number of cylinders - this would lengthen an already long engine increasing the size of the machinery space and eating into cargo space.

Mind you, material science and technology has come on a great deal in the 30 years since the demise of the Doxford, maybe these problems could now be overcome.

One other problem was the additional survey requirements of the bearings for the side rods, 2 bottom ends and crossheads.
 
#34 ·
Ellermans "City of Bristol" (ex Sacremanto) had twin screw 3 cylinder Doxfords. The engines were installed displaced by one cylinder as their side scavenge pumps were on centre cylinder. Built by Cammell Laird 1945, 670mm bore I think. The 'wrong way' alarm was in very frequent use during manoeuvring !
 
#97 ·
#50 ·
Hmmmmm! Increasing RPM does not necessarily increase power as fuel burn time (cetane index), scavenging efficiency and gas flow rates are all going to compromise power output after passing through the "sweet spot" where max power and torque are produced.
 
#45 ·
Doxford Three Legged

Teb advised of the Carronpark and Lylepark of Denholms, in addition
managed by them were:
Arisaig
Clarkavon
Clarkeden
Craigallian
Crinan
Naess Trader
Wellpark
All operated satisfactory and gave good service over their respective
lifes.
Served on a few of them from J/E TO 2E.

Archie
 
#48 · (Edited)
A little off topic as it relates to later engines:-
I sailed as 2nd Mate and Chief Officer on 5 ships operated by Ellerman City Liners from 1981 though to 1988 that had the last Doxford 3 legged engines built. They were supplied to the City of Plymouth Class 300TEU "paragraph" ships built at A&P Addpledore in devon - a 6th Engine was also built but never fitted to a ship and the last I heard had been donated by Ellermans to the Glasgow Museum of Transport. The first engine was supposed to run on a homogenised coal dust/ oil slurry but it didn't work............... the engines were way too powerful for the ships giving a Dead Slow speed of 7.5knots and really should have been mated to a contollable pitch prop. They weren't terribly reliable but once started they ran beautifully smoothly. The unreliablity was on the starting and stopping but this was resolved with some major redesigning of the liners and piston crowns of the City of Oxford that transformed the engine's manoeuvrability. Part of the starting problem was a "dead band" detector that soemtime didn't detect that all 3 units were "in line" and the start assister didn't engage to give the engine a half a turn by hydraulic ram............. IIRC the City of Plymouth had the start assister detect a dead band start situation while the engine was turning at 220rpm, which didn't do it or the rest of the engineroom a lot of good. I left Ellerman's in 1988 to join P&O Containers and remember seeing the City of Oxford trading in the Malacca Straits in 1992/3 as the Hyundai Malacca. Prince Line also had two vessel fitted with the same engine - Crown Prince and Royal Prince I think. They were handed over to OOCL when Furness was taken over by C Y Tung Group. I am now in command of some of the Maersk Line ships at the other end of the size/ power scale.
 
#49 ·
They weren't terribly reliable but once started they ran beautifully smoothly. The unreliability was on the starting and stopping but this was resolved with some major redesigning of the liners and piston crowns of the City of Oxford that transformed the engine's maneuverability. Part of the starting problem was a "dead band" detector that sometime didn't detect that all 3 units were "in line" and the start assister didn't engage to give the engine a half a turn by hydraulic ram............. IIRC the City of Plymouth had the start assister detect a dead band start situation while the engine was turning at 220 rpm, which didn't do it or the rest of the engine room a lot of good.
L.S.
The STARTING ASSISTER (JS3 DOXFORD ENGINES)

The S.A. consist of 2 pneumatic power cylinders (1) , on for ahead and one for astern
They are mounted vertically at the forward end of the engine and pivoted at the top so that the roller at the end of the piston rod can be engaged to a wheel (2) at the forward end of the crankshaft to turn the shaft the required amount.
Each power cylinder is brought in engagement by means of an engagement cylinder (3) acting through a lever mechanism (4)
They are disengaged at the end of the stroke and brought back to their storage positions by means of return springs (5)

These springs (5) will keep the power cylinders firmly away from the wheel (2) while the engine is running.
Special plates on the wheel prevent the ahead power cylinder from engaging in the astern grooves, and vice versa.

According the above story from "XFullFatTim" was the starting assister not ALWAYS a big success?
(Perhaps the spring 5 was broken in the above mentioned accident?)
Who can tell more about his experience with the starting assister?

Kind Regards
Alfons
 

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#51 ·
I was going to let that one slide, but as well as the issues that you raise Ian as the rpm increase the propellor efficiency starts to fall due to the effects of cavitation etc, whilst these can be alleviated by the use of tandem propellors the overall efficiency of conversion of potential chemical energy in the fuel to propulsive effort will fall. For most shipowners (warships being a notable exception) the overall plant efficiency for a given service speed is a prime concern. Also increasing RPM markedly will have considerable inertial effects which can be overcome by reducing cylinder diameter and increasing cylinder numbers which quite nicely brings us back where we started.
 
#59 ·
Certainly on the 58JS3s we only designed the ships to carry 1 spare liner but I seem to recall City of Bristol (2 x 60[?]LB3) that there were "quite a few" although I' not sure why as she ran on diesel and the wear rates were very low. However I think in her early days she had a few liners crack.
Someone was asking about the 58JS3s having the starting assister when the old LB3 didn't - I think that was 'cos the LBs had side cranks at 180 degrees to the main crank but all the turbo charged engines had the side cranks leading by about 8 degrees
B R
Tim G
 
#60 · (Edited)
I sailed on a four cyl Doxford which carried four spare liners, which did not inspire confidence.
Curiously, it carried only one of each top and bottom pistons.
I think that some companies used their ships as a sort of a spare gear store.

The picture in #58 does not appear to be a three legger. Looks suspiciously like a centre scavenge at top of picture.

Happy New Year

Derek
 
#61 ·
The picture in #58 does not appear to be a three legger. Looks suspiciously like a centre scavenge at top of picture.
Derek
Derek,
That is exactly what I thougt too, so I mailed this person for an explanation, but no answer yet
Although, this picture from the same ship (Shell Tanker mv BELA) looks like there are 3 starting air valves.
And I believe - I am not sure -, but you must know, that on a 4 cylinder there were 2 sets of 2 starting air valves?
Regards
Alfons
 

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#63 ·
The way I see it, the bottom one in the pic is the usual cast aluminium bottle guide cover while the top one is a fabricated scavenge pump cover.

I must admit I am stumped by the pic of the three air start valves which indicate a three legger. Did any of them have a mushroom scav pump?
I never sailed on one.

Derek
 
#64 ·
L.S.
I got this answer
"Hi Alfons

Yes that is the top of the scavenge pump which was on the back of the
engine behind number 2 cylinder. The seawater, fresh cooling water and
lubricating oil pumps were directly below, all driven by a rocker arm
from #2 cylinder cross-head. When I started with Shell as a fifth
engineer, I sailed fron New Zealand to Singapore as a passenger on a
Nowegian tanker. It was fitted with a six cylinder Doxford with the
scavenge pump between four and five.

The "B"s were unique in the Shell fleet. They were the only Doxford
engined ships although I understand that there were some equiped with
Doxfords later on when Doxford went onto HVF. All other motor ships in
the Shell fleet ran on HVF but the fuel valves fitted to the Doxfords at
that time wouldn't allow it. Personally I was pleased. HVF wasn't much
fun for the engineers. We had a lot of problems on a Harland and Wolf,
B&W copy, that I sailed on.

I didn't think about it at the time, but in retrospect, 2 spare liners
is a bit much but that's what was supplied. I doubt if they were ever
used. We did a re-ring on number two cylinder and the bore was in good
condition.

Using my images will be fine. Would yu like me to email higher
resolution copies?

Regards

Derek

( I found a picture on Internet concerning the mv Bela Engine Room, I enlarged it and give the Engine a color, so it is indeed a 3-Legged)
Regards
Alfons
 

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#65 · (Edited)
The 3cyl. only had a side lever scavenge pump and were in the middles and could not be seen from the tops(as in the photo).The photo. shows the back of the engine tops(no hoses and protection covers).So the mystery deepens.(Center scavenge pump cowlings are much higher than the tops).
BELA /BORUS were a Empire "Intermediate" type.sisters EMPIRE COMMERCE,EMPIRE GAIN (BARBATIA),EMPIRE RUSSELL (BATISSA),EMPIRE CREST (BURSA),EMPIRE CROSS (BALEA),EMPIRE MALDEN (IMPERIAL HALIFAX),EMPIRE GANGES (BOLMA)(AUSTRALITY),EMPIRE ENSIGN (BRITISH DRUMMER),EMPIRE ARROW(BRITISH BUGLER),EMPIRE SENLAC (BULLINA)

View attachment 32478 View attachment 32480
 
#66 ·
The 3cyl. only had a side lever scavenge pump and were in the middles and could not be seen from the tops(as in the photo).The photo. shows the back of the engine tops(no hoses and protection covers).So the mystery deepens.(Center scavenge pump cowlings are much higher than the tops).
A.D.F and other readers
I fully agree with your sight on the situation
So I asked Derek again, with a sketch, where I showed the direction of the yoke (transverse beam) in red, that it was NOT a Lever Driven Scav. pump.
Here was his answer:

Hi Alfons

The Bela had the lever type scavange pump. The six cylinder Norwegien Doxford had the crank driven pump. The Bela engine was basically laid out as shown. I think that the perspective in the photo is confusing. The top of the pump was lower than it appears. Unfortunately the old photographs are beginning to fade and are not in very good condition now.

I'm not certain about the horsepower but I think that it was around 3000. I could be wrong though. It was almost 60 years ago. I remember that it was similar to the much larger six cylinder B&W four stroke. Much against my wishes I had to give up the sea after 2 1/2 years because my father wanted me to help him start up a Motor and General Engineering business.
Regards
Derek


I give up now!
Regards
Alfons
 

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#70 ·
Alfons asked:
Who can tell more about his experience with the starting assister?

I was on the builder's sea trials of the "City Of Plymouth" out of Appledore Shipbuilders and I believe the problem with the over-enthusiastic dead-band assister occurred during that trial. I can't supply much detail as I kept out of the way, it seemed to me that the Doxford men had enough on their plates without me poking my nose in as well.

I thought it best to concentrate on the Blackstone generators that I was there to look after, but I seem to remember they had quite a bit of bother with flexible pipes failing and covering the job in oil prior to the big bang. The engine was a 58JS2, I believe.
 
#79 ·
I was Ellerman's Project Engineer for that class of ship built at Appledore. Great ships - shame about the 58JS3s! I had wanted the engine to drive a CP propeller at constant speed but the boss wouldn't have it. I think it was killed by the yard wanting a £45k extra which is a shame as it would have transformed the engine by doing away with the starting assister and probably considerably reduced the piston ring and liner wear problems encountered in service. Interestingly we found that the dead band was not as big as the theory suggested and it was further improved on the second shop when we changed the phasing of the propeller with the crankshaft .
At the beginning of the contract we were badly deceived by British Shipbuilders and Doxfords who told us the 58JS3 was a slower speed(220 rpm) version of the "fully developed"Seahorse. Unfortunately that was totally untrue but it was too late before we found out the full truth. The first engine was over 6 months late and development had to continue with the ships in service .
Perhaps a TM410 or K Major wouldn't have been so bad after all !!
 
#74 ·
I have posted copies in the Gallery, taken from the Motorship November 1949 which gives a good account of the engine. Built by Doxford and the ship towed to Sunderland for the installation.
I have a little more information if anyone is interested. Thanks to John ( Jack ) Jordan, who kindly gave me this information
Hamish
 
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