Broken strop on my SEAL 28 - 4

​So far, I had been using pieces of wood roughly sawn on site, but the keel needed to be lifted by another 15 cm or so to access and undo the nuts and withdraw the stud threading the strop thimbles. I photographed the keel from the top—Figure 6—and made a scale drawing of the central part—Figure 7. I wanted to make three stacks of blocks, mostly from 4 x 2, precision square-cut using a radial-arm saw, sized to fit within the stub-keel slot without too much room for transverse slop, while allowing the stacks to move up and down without catching on each other or the sides of the slot. The central stack would sit atop the jack; the stacks either side would support the keel while the central stack height was being adjusted and vice versa. I dare say there may be simpler and better ways of doing this, but I could not think of any.

The process was as follows starting from the point shown in Figure 5:

1. The jack was used to lift the keel up by a little more than a block thickness.
2. One by one, blocks were pushed into the stub keel slot between the top of the axle stands and the keel.
3. The keel was lowered onto the new blocks—being now one block higher.
4. The jack was lowered, and an extra block was inserted above it and the keel. This process was repeated until the keel was high enough.

​(Berridge, in his book The Girder Bridge, describes this as ‘giggling’. He used the reverse process in the controlled dismantling of the old Brunel railway bridge at Chepstow, where a large wrought-iron tube was slowly lowered by steadily reducing the height of the supports at either end from the bottom. The Oxford English Dictionary does not recognize the term.)

The process was not entirely without issues or risk. A steady hand was needed to avoid the stacks toppling as new blocks were added at the bottom of the stack. To limit this tendency, I used double-sided tape between some of the blocks. As a safety measure, one of the stacks was always securely in place under the keel, with a second stack no more than 7 cm or so below the keel. I manipulated the stacks from the side, avoiding placing my fingers anywhere where they could be in danger should one of the blocks slip catastrophically. 
 
The method worked well. I was able to lift the keel so that the stud and its securing nuts were above the keel box. Using the largest socket in my set—32 mm—to undo the nuts, and with a bit of encouragement from a drift and hammer, the stud was withdrawn and the strops removed.