TransomChainplate

I own a 1978 sloop rigged 424. I've had problems with the transom chain-plate for many years. In my opinion, Pearson designed the
boat to be rigged as a ketch and added the sloop and cutter options as an afterthought. My sloop has exactly the same rig as the
ketch except it lacks a mizzen. The ketch uses a split-backstay, but the cutter and sloop have a single backstay. Both share the same
transom chain-plate design. The chain-plate is about 16 inches long, 2 inches, wide, and 3/8 inch thick. It has a bend where it extends
above the hull. It is attached to the hull with four 3/8 inch bolts. The transom is not reinforced where the chain-plate attaches. The
transom is angled back slightly. Since the angle of the backstay is not in line with the transom, tension applied to the backstay will
force the transom inward. Without some kind of backstay tensioner, it is not possible to get more than about 2000lbs of tension on the
backstay. Even with less tension, dynamic loads on the rig when subjected to a pounding seaway can well exceed 2000 lbs. There
have been many reports of cutter and sloop rigged 424 having trouble with this chainplate.

At the suggestion of my marine surveyor, I glassed in a plywood backing plate many years ago before heading offshore. This
distributed the load somewhat, but still left the rig with a problem. The gelcoat just behind the transom toe-rail showed signs of stress
cracks. I attributed those signs to be old age. In retrospect, it was the beginning of a more serious problem. About a year after
returning from my offshore trip, I re-rigged the boat. Included with the new rigging was a hydraulic backstay-adjuster. This significantly
improved the pointing ability of the boat, but added to the rigging load on the transom. Cracks behind the transom toe-rail got larger
and the transom started to show signs of deforming. After taking the boat out in rough weather one day, I returned to find the transom
pushed in about two inches. Cracks appeared around the chain plate. I resolved to reinforce the transom. That winter, I removed the
small backing plate that I had installed and replaced it with four inches of layered plywood. The new backing plate was four feet wide
and three feet high. It was bolted to the inside of the transom with a row of 3/8 inch bolts. It conformed to the shape of the hull.
Although this didn't address the cracks in the hull and deck, I was confident that the backstay chain-plate would never pull out with this
kind of reinforcement. I expected the transom to hold its shape. I was disappointed the next season when the transom again
deformed under the load of the rig. I find it hard to believe that a four inch thick sheet of plywood could bend under load, but that is
precisely what happened.