in Tech Topics
Fixing a Broken Boom Fitting
March 19, 2017
Anytime we take Alembic offshore we expose her to conditions that can make things break. We try to sail conservatively and stay on top of our preventative maintenance. In spite of best efforts, we still have unexpected gear failures. During a recent passage from Cayman Islands to Belize we had the goose neck on the main boom partially shear off the mast. I discovered the failure when I went forward to put in a reef to prepare for an approaching squall. I immediately dropped the mainsail and we finished the passage with Mizzen and Genoa (Jib and Jigger). Luckily we have an extra mast on Alembic!
So what made the goose neck fail? The conditions were not particularly rough, however, they were conditions that can cause a bit of wear and tear. Specifically, we had wind directly astern and wind speeds that were abating after days of high winds. The seas were still running 5′ to 7′ but the winds had been dropping to <15 kts especially in the interval between squalls. These conditions can be particularly annoying because it causes the sails to slat. We were controlling the slatting as best we could with a tight preventer working against the main sheet. In spite of this, several times an hour the boat would roll in a big sea and the boom would swing toward the centerline and then back out with a load THWACK! This action creates a tremendous load on the goose neck fitting.
The goose neck of our boom attaches to a short track on the back of the mast. The top most 1/4″ machine screw sheared allowing the track to pull away from the mast. If the failure had gone undetected for a longer time, it is likely that more screws would have sheared and the goose neck pulled completely free of the mast.
Once in port, I quickly dove into the repair effort. Luckily the goose neck track was easy to disassemble. Who ever originally installed the track used sealant on the threads of the SS screws so there was no corrosion between the screws and the aluminum mast. One contributing factor to the failure was the goose neck car was positioned at the top of the track so that a single screw was taking much of the load. Instead of remounting the track in the same position, I moved the track up a few inches on the mast. I then drilled and tapped all new screw holes. Finally, I remounted the track to the mast using plenty of sealant to minimize future corrosion.
This repair was a good test to see how well prepared we were with the correct tools and spar fasteners. I would give myself a “B” for this effort. We have a great cordless drill and a good selection of drill bits. We had the necessary spare fasteners for the job (1/4-20 x 1″ stainless machine screws). We had a 1/4-20 thread tap in new condition. The only thing we were lacking was a larger 3/8″ tap that we needed for one particular hole. The hardware store in Placentia did not have the necessary tap. Luckily, I was able to borrow one from my neighbor in the anchorage at Placentia. So now I have a new item on my shopping list. Next time I find a well stocked hardware store, I will purchase a Tap and Die kit that has a full range of sizes. I will also add to my fastener collection which is something I do continuously.
The lingering question we always have when events like this occur is would we have been able to deal with this problem at sea if it were to occur on an extended passage. In this case, I am confident we would have been fine. I could have completed a partial repair quickly and easily while offshore and made a more complete repair while in port.
Finally, this event serves as a reminder that things break while cruising and putting them back together is part of the adventure. It is essential, however, to have the skills, tools, and spare parts to handle these events with minimal stress and disruption to the lifestyle.
