Broken strop on my SEAL 28 - 6

Lifting the keel
 
The most problematic part of the whole business was the need to lift the keel sufficiently high enough to allow proper cleaning. Although it had been unjammed, extensive use of both the lever and the bottle jack showed that it would still jam about three-quarters of the way down. Since the keel could not come down to be cleaned—the option already ruled out because it could only be done by the boatyard—it had to be lifted up. 
 
The bottle jack and blocks had been very successful in lifting the keel safely from below, and sufficiently high enough to allow the strops to be replaced. But the two nylon guide blocks had always been fully engaged with the slots on the keel box. Even with the strop stud removed, the two remaining studs clamping the blocks to the keel ensured that it was always secure from toppling. Lifting the keel another 10 cm or so would see the blocks rise above their guide slots, and all transverse and longitudinal stability would be lost; the risk of a topple in either axis was too awful to contemplate. It was clear that the only safe way to proceed would be to suspend the keel from above. I considered three options:

1. Build up a framework of timber from the loadbearing support-points on the top of the keel box, with the existing winch high enough to allow sufficient of the keel to be lifted above the keel box for cleaning. The worry with this option was transverse stability; the structure would be very narrow and need to be stabilised with transverse timbers against the cabin wall to prevent all possibility of toppling, and these would be a considerable inconvenience. Also, the framework, very close to the keel, would limit access for cleaning. The cabin roof would limit the height of the winch, meaning that the entire keel could not be exposed. Furthermore, the winding handle could not be used when the winch was close to the ceiling.
2. As 1, but build the framework from floor level, resting on cross-timbers under the floor, clamped around the keel box for lateral and longitudinal stability. This would be more secure than 1 but suffer from the same height restriction—and inability to use the winch handle. But by spacing the timbers out, more room would be available for cleaning.
3. Make a small hole in the ceiling/coach roof to admit a suspending strop secured to a four-legged ‘A’ frame straddling the deck. A chain hoist would be used for raising and lowering the keel, and the keel could be raised, safely, virtually to the cabin roof exposing almost, if not all, of the keel for cleaning.

 
There is a semi-permanent hatch, for’ard of the sliding coach roof, secured by four screws and sealed with silicone rubber. When this was removed, it revealed what appeared to be a small ‘removable’ panel suggestive of a port originally designed to admit a lifting strop for the keel… Unfortunately, on Analie it was attached with permanent bulk adhesive, probably epoxy, and quite definitely not removable. To execute option 3, a hole of suitable dimensions would need to be cut through this panel, some wood spacers underneath, and the ceiling moulding.
 
In various states of euphoria, depression, sobriety, and inebriation I considered these three options, favouring first one and then another. I had to get the keel in an operational state; I might need to sell the boat. Marina fees were accruing relentlessly and my indifferent health meant that my confidence in sea-sailing was waning. On the other hand, a bodge would be worse than useless; it had to be a decent job. 
 
The ‘A’ frame solution allowed access to virtually the entire keel with no timber framing in the way. Also, it should be possible to lift the keel entirely above the keel box, allowing some timber cross-pieces to support the keel on the box securely. This would enable some decent and safe cleaning of the inside of the stub keel also. Chris had a half-ton chain hoist I could borrow, and GS Products sell a range of galvanized wire rope and clamps enabling the various strops needed to be fabricated at minimal cost. The downside is that a substantial hole would have to be cut through the coach roof and the ceiling moulding under it. The position of the hole and apex of the double ‘A’ frame would have to be determined by dead reckoning adding to the difficulty. Furthermore, the ‘A’ frames could well foul the shrouds. 
 
An initial foray to the boat to measure up the position and size of the A frames was abandoned. The impossibility of making accurate measurements on a three-dimensional structure with curved and sloping surfaces soon became clear. I considered that the deck-loading should not be a problem, with each leg having to support, say 120 kg, but there were two further difficulties. Firstly, the substantial hole in the cabin roof would need considerable remedial work when the keel had been dealt with. Secondly, and this was the killer, the apex of the two ‘A’ frames and the fixing of the chain hoist would need to be around six feet above the coach roof. It would have been quite impossible for me to have worked on this securely and safely, and at the mercy of the weather.
 
I reconsidered options 1 and 2. Option 1, I discounted for the reasons given above. Option 2 used the transverse and longitudinal stiffness of the keel box—itself designed to hold and contain the keel, raised or lowered, under conditions of pitch and roll—to stabilize a frame sitting on the cabin floor. The floor was supported by transverse timbers directly on the hull. Option 2 had further benefits—no holes needed in the coach roof, and the entire procedure contained within the weatherproof cabin. Furthermore, some preliminary tests showed that with the sliding roof open, the winch handle could still be used with the winch quite close to the ceiling. This was the approach I decided to adopt.
 
Figure 10 (previous post) shows the underside of the winch with its mounting flanges and the substantial box girder containing the stainless-steel screw and brass ‘nut’ with its two slots to locate the ends of the strops. The winch is heavy, weighing 12-14 kg. The screw assembly is offset laterally to allow visual inspection of the keel and strops. The strops run to the two end pulleys where they are turned through 180º and led to the nut. It is evident that the centre of weight passes through the two pulleys on the central flange which has a triangular reinforcing web on the top side—visible in figure 12. There are fixing points on the keel box corresponding to the flange holes. The central rectangular flange bridges the keel box above the keel and the two slots accommodating the nylon sliders. Either side of these, the keel box is substantially reinforced—centimetres thick all the way down to the floor. To keep things simple, I supported the central flange closely behind the pulleys with a simple transverse timber beam. The resulting moment on the screw box transmitted just a few percent of the weight to the flange adjacent to the pulleys at the for’ard end of the screw assembly. Figure 12 shows the basic structure. I considered calculating buckling strengths and stiffness ratios for the timber, and the merits of ‘A’ frames rather than four parallel vertical beams. In the end, I opted for simplicity—the Stonehenge design—and decided that if it lookedright, using C24 grade building-quality 4 x 2 and common-sense constructional techniques, then it probably was ok. Furthermore, timber in construction has that quality, well-known to the old miners who used to use it for pit props, that it creaks and groans when pushed to the limit, thereby signalling distress before imminent failure. Note that the bridging transverse beam and the two side bridging beams, consisting of doubled 4 x 2, are ​arranged with the ‘4 inch’ dimension vertical. The stiffness of a beam varies with the cube of its depth, so a pair of 4 x 2s, not glued or screwed together and arranged thus, have eight times the stiffness of the same pair used with the ‘4’ dimensions horizontal. 
 
Each pair of vertical beams was located on a short length of timber on the floor to spread the load. They were braced at the bottom and half-way up. Separation was around 20 cm, this being a compromise between longitudinal stability and room to access the keel, and the need to limit the length of the bridging span at the top for safety. They were clamped to the keel box as shown using four horizontal members, screwed to the verticals and tensioned by studding at each end. The studding was positioned on the keel box using wedges. As before, there may well be more secure and/or efficient ways of doing this, but it was straightforward and was able to provide open access for rust removal and treatment. There was plenty of creaking from the floor as the cables took the full weight of the keel, but the frame seemed to be secure. One further benefit unlooked for as the design evolved, was the fact that the keel, at 450 kg, provides a considerable level of security when the strops are under tension by clamping all parts very firmly together.