Nova Scotia sailboat trailer weld failure

Tom's forensic case. A farmer-built sailboat trailer with a slugged weld (bolt buried in the joint, then welded over) fractured on Route 24 south of Boston on the return trip from a Newport race, destroying the 40-foot sailboat. Used to illustrate why standards prohibit welding on tractor-trailer frames and what "slugging a weld" means.

Slugged welds were always something we used to joke about, because it went out after World War Two when people started seeing this. No one would ever select a weld with a bolt in it. I had never seen a slugged weld. They brought me this piece of a trailer, and the story is: this person had bought the trailer in Nova Scotia from a farmer who built it for him. It was a trailer for their 40-foot sailboat. They drove from Nova Scotia with their sailboat all the way down to Newport, Rhode Island for the races, and they had won the race. They were coming back up — it's Route 24, an interstate-like highway just south of Boston here — cruising along about 55 or 60 miles an hour with their trailer behind them, and they hear a bang. They slow down and put their brakes on, and there's a sailboat just passing them on the highway. The weld broke. The trailer let go. All of a sudden you had a freewheeling trailer and a 40-foot sailboat, and it crashed and destroyed the sailboat. They brought me the weld and said, what's wrong with this? They wanted to go back to the farmer who had welded up the trailer and complain to him. It wasn't hard — you saw about a three-quarter-inch bolt that had been put in there and just little welds put on top of it. It was not a fully welded joint. That's the only time I've ever seen slugging a weld. You sometimes look at this level of engineering and wonder about it.