Broken strop on my SEAL 28 - 5

​Replacing the strops.
 
Analie was built in the 1970s, so it is not surprising that Imperial measure was used—it is a Seal 28 (feet) after all. The strops have probably been replaced a few times over the years, and by measuring up the unbroken strop I determined its specification as follows:
 

• Stainless-steel wire rope, 7/19 strands, 6 mm diameter (7 large strands, each composed of 19 individual wires), breaking strain around 2,000 kg (two tonnes).
• One end crimped with a copper end stop, around 18 mm diameter.
• The other end crimped around a stainless-steel thimble with a 20 mm aperture, designed to be threaded by a 19 mm—0.75 inch—diameter stud.
• Length between the bearing surfaces, 137.4 cm—54 inches. 

 
Two cables each of two tonnes breaking strain lifting a 400 kg weight provide a safety factor of ten which may seem like overkill, but since each cable passes over two pulleys, radius of curvature around 2.4 cm—one bending the cable back on itself 180°—some substantial derating is necessary. 
 
The first problem was to acquire suitable thimbles. These are sized according to the diameter of the wire rope for which they are designed. Unfortunately, 6 mm thimbles have a clear aperture diameter of only 15 mm, 8 mm thimbles will accommodate 18 mm. 10 mm thimbles have a clear 25 mm aperture, but they are much bigger and would not fit the slots on the keel. Examination of the existing thimbles indicated that they were likely to have been of the 8 mm size. Two new 8 mm thimbles were purchased and modified by my Parker Seal mate Chris, by the expedient of banging a 20 mm diameter socket into the hole. This opened the jaws sufficiently to accommodate the 19 mm stud—Figure 8.  The original thimbles could have been reused but the one from the broken strop was badly corroded and pitted—worn right through at one point—and I wanted to keep the remaining strop in one piece as a precaution.

I sent the modified thimbles to GS Products, whose applications engineer, Lewis, had been most helpful via several emails and a telephone call. After three weeks, they had not arrived there… Chris modified two more thimbles for me, and I sent them Royal Mail Priority Tracked—they arrived the next day. Within a week I had two brand new strops—Figure 9. A week after that, the first two thimbles arrived at GS Products... Moral: if it’s important or time critical, send it tracked (or don’t use Royal Mail). 

With the glorious benefit of hindsight, it might have been wiser to make a new, smaller diameter stud, say 17 mm diameter, to fit the unmodified 8 mm thimbles—see below re strop length—but I was loath to modify anything unless absolutely necessary. Also, a new stud would need machining, with threading at each end and the central part supporting the thimbles left smooth—more delay and expense. Meanwhile, the winch had been stripped down—Figure 10 shows the constituent parts. The box was cleaned and painted, the screw, slider, pulleys, and cables were regreased with waterproof grease as used in my MaxProp propeller. The thrust-bearing was loaded with as much grease as it would take, the whole reassembled, and the strops fitted into the keel.[1] There was one irritation: one of the strops was a few mm or so longer than the other. This almost certainly arose from my request to the supplier not to clamp the cables tightly round the thimbles in order to preserve their modified opening. Some copper wire was wound around the cable next to the copper end stop until the tension in both cables was judged to be the same—see Figure 11.

[1] I could not see how to disassemble the thrust bearing; it may have been pressed into place. The plastic ring sealing the end adjacent to the handle could be removed. I used a thin blade to lever it out, and crammed the space inside with bicycle grease, hoping that pressing the plastic ring back in place would force grease into the business part.