Corchester SS

CORCHESTER

Research ... Paul Hennessey

Acknowledgements ... All underwater photography courtesy of www.sambeanimages.com

Built ... 1927
Position ... 52 55 927 N / 001 34 483 E
Type ... Cargo ship, Long raised quarter deck, x 4 holds, engines midships, counter stern, plumb bow
Depth ... 28mtrs
Tonnage ... 2374 grt
Dimensions ... 87 x 12.5 x 5.8mtrs
Material ... Steel
Engine ... x 1 triple expansion engine, x 1 propeller
Boilers ... x 2 scotch type boilers x 3 furnaces per boiler
Output ... 243 nhp
Speed ... 10 knots
Builder ... S. P. Austin & Sons Ltd (Sunderland)
Engine ... Swan, Hunter & Wigham Richardson Ltd (Wallsend)
Owner ... Cory Colliers Ltd (London)
Date of loss ... 19 / 2 / 1956
Cause ... Collision
Crew ... 21
Lives lost ... 8

Below ... S.P. Austin & Son Ltd (Builders of the Corchester)

Loss of the Corchester

At 1515 on the 18th February the Corchester left the Thames in ballast and proceeded off the Norfolk coast on route to Hartlepool. Whilst on route with heavy snow in a moderate sea, wind speed force 4-5 NE, at 0720 on the 19th of February the Corchester's 2nd officer observed an echo on the ships radar screen some 5 miles off the port bow. The Corchester's captain was at this point called. By the time he arrived on the bridge the other vessel was less than 1 mile away. Despite the low visibility due to the heavy snow, the Corchester had neither reduced her speed or sounded her fog horn. With less than a quarter of a mile between the two vessels, the Corchester swung to port whilst the other vessel, the 6,986 ton City of Sydney swung to starboard, this resulting in the two vessels colliding. The Corchester was struck on her starboard side and was cut in two accross the number 1 hold. Eight of the Corchester's crew died in the collision, six of these being situated in the Corchester's forcastle accommodation. A formal enquiry was held in July 1956 where the Corchester's master, George Northcott was found to be at fault.,

UKHO surveys

1956 ... Sank

1963 .... Dispersed, clear at 14.2mtrs

1973 .... Amend, clear to 13.7mtrs

1983 ... Swept clear at 15.4mtrs, foul at 15.7mtrs

The meaning of swept depth, swept clear and wire swept

Survey vessels lower a wire to a predetermined depth and slowly traverse the position of the wreck. If the wire does not snag, it is lowered in stages and the process is repeated until it does. The deepest depth at which the wire did not snag is then recorded as the swept depth, or to have been swept clear to that given depth

Below ... Triple expansion engine as fitted in the Corchester.

Double acting triple expansion steam engine.

High pressure steam (red) passes from the boiler and goes through 3 stages, HP cylinder (red), IP cylinder (orange), LP cylinder (blue). From here the steam from the LP cylinder goes to the condenser where it is returned to its former state, ie water and is returned to the boiler for re-use.

Note .... As with the engine illustrated, the Corchester's engine is fitted with Stephenson's link motion valve gear. These are the workings to the left of each con rod. Two eccentric sheaves are fitted to the crank shaft, these are attached to eccentric rods and then the valve rods which in turn open and shut the slide valve for each cylinder.

Whilst the Stephenson's valve gear arrangement was not exclusive to the Corchester's engine design, it was the most widely favoured amongst engine builders of the time.

Advantage of long raised quarter deck with engines midships.

With the engines located midships, this meant the prop shaft and in turn the shaft tunnel ran a great deal of length along the bottom of the ships hull to arrive at the stern. The disadvantage of this was that it took up a great deal of potential hold space astern of the engines. A solution to this was to raise the height of the deck above the area of the shaft tunnel, this in turn increasing the hold space available, this being known as a long raised quarter deck, the raised quarter deck would also include the bridge. Note ... From the photograph of the Corchester at the head of this page the two holds astern of the funnel are higher than the two forward of the funnel. This in turn increasing the hold space that would have been reduced due to the accommodation of the shaft tunnel.

Below ... x2 Scotch type boilers with x3 corrugated furnaces as fitted in the Corchester. Note ... The inside of the furnaces are corrugated.

There were two types of furnace available for the construction of boilers. Firstly the corrugated type and secondly the plain type. The advantage of the corrugated furnace due to its corrugation was that it proved to be more flexible, stronger and in turn extended the life of the boiler.

The Corchester today (2019)

Today the Corchester sits on a sand and gravel seabed at 28mtrs. Due to her depth and size you are able to navigate the entire wreck on one dive. The most intact part of the of the Corchester is her engine and boilers. The engine has sustained some damage to two of its cylinders, this either being caused during dispersal or with the above super structure collapsing onto it. The area in and around the boilers is littered with various pipework associated with the engine room. On the seabed to the port and starboard of the engine room lies much of the broken super structure, collapsed hull and life boat davits.

Below ... Left to right. Ladder, forward winch, Steering quadrant (background left), Boiler. (Courtesy of SamBeanImages)

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Aft of engine and boilers

Heading away from the engine and towards the stern, for the most part this area is well sanded in, none of the bottom frames or plates are visible. Sticking out through the sand, from what would have been one of her holds stands a ladder, this being about three to four rungs clear of the seabed. Heading aft, much of the hull shows itself port and starboard, this being some 1 to 1.5mtrs clear of the seabed. The end of the aft section is marked by the steering quadrant, this standing upright at a slight angle to starboard and being clear of the seabed by about 3mtrs. No prop shaft or tunnel bearings in evidence, sanded in.

Below ... Diver alongside broken wreckage (courtesy of SamBeanImages)

Forward of engine and boilers

Forward of the boilers and heading towards the bow, much of the single bottom is now exposed, the floors have long rotted away, this now exposing the frames and strakes. As with the stern, much of the hull to port and starboard is exposed for much of the forward section, port standing up to 2mtrs clear and starboard being 1 - 1.5mtrs clear of the seabed. There is still evidence of the decking to be seen, for the most part this is along the port side where the hull has fallen in on itself. In between what would have been holds 1 and 2 sits two winches, at this point also lies the forward mast, the top of which points towards the bows. A short way past the end of the mast and in the area of number one hold, the hull comes to an abrupt end. Reports at the time state that the forward section, from mid number 1 hold was sliced off in the collision with the City of Sydney. If this was the case, this could well explain the forward section ending so abruptly??

Below ...How the Corchester looks today (2019) Diagram by Paul Hennessey.