Mast Down at Midnight

It was midnight and my watch had just ended. I’d barely climbed into bed when Cathie starting bellowing from the helm,

“Alan, the boom doesn’t look right!”

What now? I’d already had enough excitement for one night. Barely two hours earlier, the gennaker had come tumbling down when its halyard gave way. It had been hard work carefully retrieving the sail in darkness, which had dragged through the water between Arriba’s hulls. Miraculously, the sail appeared to be undamaged. Disconnecting the sail completely would have required clambering out onto the end of the prodder pole while underway in darkness. Instead, I bundled the sail as best I could and lashed it to the prodder pole and the trampoline.

I joined Cathie in the cockpit and was stunned by what I saw. The boom was wobbling, but not in the usual kind of back-and-forth way, which happens when the traveler is loose. It was wobbling because the mast was nodding up and down like a giant broken metronome.

I shone a light forward to the bow and couldn’t believe the devastation. The seagull striker, normally vertical, had snapped in half and was horizontal, the prodder pole was nowhere to be seen, and the crossbeam was buckled in the middle. The forestay, attached to the latter, was loose and its foot was half ripped out of the beam.

I grabbed the spinnaker halyard, which is always shackled amidships, and scrambled to the port bow. Perhaps I could use the halyard as a temporary forestay? By the time I clambered to the bow, the mast was swaying like a tree in a storm, every bouncing wave pushing it closer to the brink. Before I could cleat the halyard, a particularly bumpy wave jolted the mast beyond the point of no return.

I screamed over the wind.

“Take cover! The mast is falling.”

I was still holding the spinnaker halyard, thinking (hoping!) that I could control the mast’s descent. In the past, I’ve guided felled trees to the ground by holding a rope. I held on until I could hold no more. My steering might have helped, as the mast fell down on the port side—the same side as me—and crashed on the hard bimini directly above the helm. It missed the solar panel by mere inches, then bounced off onto the port deck, before coming to a halt snagged in the safety lines.

Arriba was dismasted!

Seventeen hours earlier, with a fresh breeze and moderate seas, we’d departed from Lakes Entrance for Wilsons Promontory. Though notorious for its rough seas, Bass Strait was in a gentle mood. The wind seldom exceeded 20 knots and, until losing the gennaker, we’d been sailing at a modest 6.5 knots in 2m seas.

When the gennaker fell into the water, the normal upward force on the prodder pole was suddenly replaced by a downward force. Initially, a Dyneema line connecting the tip of the prodder pole to the top of the seagull striker prevented the prodder pole from falling down. I’ve had such a line there for the whole time I’ve owned Arriba, but I now realize it is a very bad idea. Dyneema, which is up to 15 times stronger than steel of the same weight, will easily break your seagull striker, and this is exactly what happened a short time later. Every wave over the bow hit the partially furled gennaker, pushing down on the prodder pole. Eventually, the downward force exerted by the pole applied across the length of Dyneema (the “moment arm”) produced a torque sufficient to bend the seagull striker. The role of the seagull striker is to apply a downward force on the catamaran’s cross beam (fore beam), to counteract the upward force of the forestay (on which the jib is rigged). Without that counteracting force, the forestay was ripped out of the cross beam by the mast. Then it was only a matter of time before the mast came down.

You may be thinking that such a failure shouldn’t happen in benign sailing conditions. Sure, in a storm, with the rigging under enormous strain, things can break due to sudden, high-force events. These are the well-televised events that force boats to retire from the Sydney to Hobart Yacht Race. In truth, the only thing we had in common with that race is that we happened to be in Bass Strait.

After subsequent conversations with riggers, my best guess is that the cause was aluminium fatigue of the cross beam. Unlike a single, high-force event that can cause immediate breakage, aluminium fatigue involves a gradual weakening of the material until it eventually cracks or fractures. When subjected to repeated stresses, microscopic cracks, invisible to the naked eye, occur within the aluminium.These act as stress concentrators and with each subsequent stress event, these cracks grow larger, eventually leading to a complete fracture.

Even so, why should the failure of the seagull striker have such a catastrophic outcome? In short, the rigging is an integrated system and if a critical part fails, unless there is redundancy, the system as a whole is jeopardized. As it turns out, I’d replaced almost all of Arriba’s standing rigging less than two years earlier, but there had been no reason to suspect that the crossbeam was compromised. At any rate, riggers don’t have the expensive testing equipment required to detect aluminium fatigue.

Those thoughts and conversations would all be in the future, though.

Now, all I was thinking was, how do I get Arriba and her crew safely ashore?


PS The story continues here.