MV Derrycunihy Doxford engine start up procedure

25th October 2009, 22:43
Hello all,

Could anyone help with the start-up procedures for a three cylinder Doxford engine? My specific interest is in the MV Derrycunihy, which was mined off Sword Beach on 24th June 1944.

There are several accounts of the sequence of events, none of which seem to quite tally, so I would appreciate some technical advice to try and make the pieces fit together.

Most accounts have it that, after having received orders delivered by landing craft to run into Juno Beach to unload the armoured vehicles and the 583 men of 43rd Reconnaissance Regiment aboard, the Derrycunihy started her engines and immediately triggered an accoustic mine. This explosion caused the vessel to split in two, just aft of the engine room bulkhead. The engine room did not flood, although there was some flooding of the shaft tunnel, and the fore part of the vessel remained afloat.

Things were much worse in the stern part. Within twenty seconds or so the rearmost hold was under water and not long after No4 hold was flooded. The two parts remained attached for a short time by the keel plates but whilst rescue efforts were under way the keel finally gave way and the stern settled taking with it those still trapped. 189 men of the Recce Regiment were lost in 4 and 5 holds along with 9 crew and 7 DEMS gunners. Also lost was a 'Seaborne' Observer of the Royal Observer Corps, one of only two ROC personnel lost during the Normandy landings.

I have interviewed a member of the crew who was on deck at the time of the explosion and he remembers hearing the compressed air used during engine start up, and then the explosion. However, the Captain's report states that the vessel had been for moving several minutes and was under 'steerage way' when the explosion took place. As I am not familiar with the technicalities of this, can someone explain the apparent contradiction.
Most of the accounts seem to be of the opinion that the starting of the engines was the cause of the detonation of the mine.

In any case the effect on the vessel was catastrophic, compounded no doubt by the shallow water she was in at the time. I understand that shallow water can amplify the explosive force of mines and she was quite heavily loaded being full of armoured vehicles and ammunition etc.

If the technical spec helps it is as follows:

She was a traditional rivetted hull, 425' in length, 57' breadth, 7093 Gross tonnage, and was built by Burntisland Shipbuilding Company Limited, Burntisland, Fife.

Her engine was a Doxford three cylinder, 600mm cylinder, 2320mm stroke, 2500 BHP and speed, 11.5 knots.
She had two auxilliary boilers 120 psi, by Stockton Thermal and Riley Boilers Ltd respectively.

The Doxford was installed at a cost of 63,762 and the vessel was launched on Armistice Day 1943. The total build cost was 242,345.5/6d.

What I am specifically looking for is a decription of the start up procedure for such an engine and the likely number of crew involved in this. Also can anyone explain the Captain's account as having the ship underway for several minutes before the explosion. On a vessel of this type what speed would 'steerage way' have been?

All contributions welcome!



25th October 2009, 23:35
I would think that the Captain's version is the one you would have to go by; if he reported that he had steerage way on his vessel, i.e. 1-2 knots or more, then the engine had already been in operation for a few minutes or longer, and certainly well beyond the short time between admitting starting air into the cylinders and introducing oil fuel. Also, he is likely to have known whether he had way on the ship, as opposed to her simply moving slowly due to current, wind, etc. Also, would not have thought the action of admitting a short burst of starting air into the cylinders would have been sufficient to set off the mine, whereas the slowly thrashing propeller blades and combustion noises after the engine fired might be a different kettle of fish.

25th October 2009, 23:44
Hello Eriskay,

Many thanks for the quick response. I think that sounds much more likely. There is also the asumption/belief that it was an accoustic mine that caused the loss but pressure mines were also laid in the Sword Beach anchorage and such a mine could have been detonated by the passing of the Derrycunihy.

All of this is speculation of course but informed speculationis a lot more reliable!

Thanks once again.