Gunpowder Magazine

After another successful Heritage Open Days in Berwick, someone asked on this blog how the winch mechanism inside the magazine worked.  Good question, so I went to have a look.

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Berwick gunpowder magazine

Berwick’s  is an outstanding example of an 18th century gunpowder magazine.  It was built by 1751 but was planned in 1748 following a threat to Berwick in 1745 after Jacobite victory at the Battle of Prestonpans:  it had been found that the gunpowder was damp and useless.  It is a popular belief that the powder was stored within the flankers of the bastions and other smaller stores such as the New Tower and Coxons Tower.  However, a map of 1682 shows a large magazine on the same site as ours.  For more on this and the story of gunpowder in Berwick see my earlier piece.

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Plan and east elevation of proposed magazine 1748.  This was obviously much simplified as the outer, ancillary buildings were not built.

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Replica barrels on racks either side of the central aisle in the magazine.

The barrels of powder were stored one on top of another on racks in bays either side of a central aisle.  This is accessed by a door at the east end of the building.  A second door exists at the west end above which is a window.  The building is heavily buttressed to mitigate any accidental explosion and is set within a yard within a high enclosing wall.

Longitudinal cross-section and east elevation of Berwick’s magazine (based on the 1748 plan). The east entrance is on the right.  A window is drawn at the west end where now is a door.  The high level window that exists now is not on the original plan but indicated by the dashed red lines.  
The crane jib (red) is set within the movable frame (yellow).  

Above the central aisle is the crane mechanism—an crane arm, or jib, mounted on a frame, set within upper and lower rails, that can be pulled one way or the other by means of ropes.  The moving arm has no hooks; presumably a block-and-tackle was suspended from the end.

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Crane jib (colourised red) swung back towards the frame (yellow).

Rope set into lower rail used to pull the frame and jib along the rails. The upper level west window can be seen as well.

The questioner reckoned he/she could see how the mechanism could lift barrels off a horse-drawn cart but not how they would be moved into place on the internal racks.  At first glance I think I can see what they meant.  It certainly looks like a cart with its load of barrels might be drawn up to below the window at the west end, the jib run to that end and poked through the window.

West end of magazine showing the window above the door.

There are only two problems with this, a) the door through the enclosure wall is only about 1m wide—hardly enough room for a cart to get through, b) you can see from the cross-sectional diagram that the jib is higher than the top of the upper level window, and c) the original plan had no high level window.  All these reasons indicate the jib operated internally only.

So the barrels must have been rolled in and out of the building, presumably, preferably on dry days.  The only time the jib would be used would be to raise or lower the barrels on to the racks.  

Longitudinal section showing block and tackle mechanism.

The barrel would be raised up by means of a block and tackle (now missing), the jib swung round into the barrel storage bay and the barrel carefully lowered into place. 
I had thought that if they needed to move a barrel from one bay to another maybe the barrel could be held aloft under he jib while the frame was pulled along to the new bay, but that would necessitate the tackle rope running over the crossbeams that support the lower rail.  This would have been extremely awkward at best and downright dangerous at worst, as the  tackle rope would have to be let in or out as the frame/jib moved, while maintaining the barrel at the correct height. One would expect the end crossbeams to have grooves worn into them if this was the case.  There are none, indicating this is not how barrels were moved.

 If they needed to be moved from one bay to another, the jib would be swung round over the bay, the barrel lifted, lowered to the aisle, rolled along to the new bay then raised into place once more. Easy!

Good question. Thank you. Keep ‘em coming folks!

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