After a long hard passage back from the Azores we pulled into an anchorage in Plymouth. We tacked and the chainplate of the aft lowers popped out the deck with a big bang!
Ok so the chainplates were now 23 years only and I should have lifted and inspected them before this happened but the aft lowers and babystay had the notoriously bad U-Bolt chainplate arrangements.
Back in the 80/90s the after lowers we’re not seen as a primary part of the rig. However, various yachts have lost their mast when the after lowers have parte due to the pumping action of the rig under sail. In fact they are arguably the most important part of the rig!
As such we commissioned David at www.allspars.co.uk to come up with an uprated chainplate with 14mm bolts. The flange is welded both horizontally between the bolts and over the top of the counter sunk M14 bolts. This cross weld should be very strong. They also angle the plate to the exact pull of the aft lower rigging. However as you can see from the photos below the final angle wasn’t quite matching the pull. Not the end of the world but I believe it should have been angled more.
Below you can see the drawings and the outcome. Note that the core of the deck is plywood and it was wet. We consulted some engineers and they said this was all too common and unless we were in warmer climates and willing to let it all dry out then the only feasible option was to have two stainless bushes made which are exactly the right length to go between the bottom of the new chain-plate and the internal chain-plate to which the bolts are fixed. This would prevent any deck compression or flexing.
Note the angle of the flange to maximse strength of equalise pull on the bolts. 
