Mainsheet Block Swivel: Should Have Been A Shackle?

I have long marveled at how light some of the hardware found beneath a sailboat's mainsheet tackle can be. Here you see the decidedly fragile swivel that previously secured the bottom end of Lunacy's mainsheet tackle to her traveler car. Fortunately, I detected the fracture before the bit let go altogether and all hell broke loose. It was one of those odd distracted moments during our recent SEMOSA cruise where my eyes were wandering and noticing things that might have otherwise escaped detection. What I noticed specifically was that the angle of the bottom block on the mainsheet tackle was slightly altered. It took only a brief inspection to discover the cause.

We were sailing at the time hard to windward betwixt Saba and Statia in a vigorous 20-knot breeze. Like any good sailor, I thought immediately that a bit of rope might save us from disaster and so lashed up the bottom of the block just so.

Afterwards, once we were moored at Statia and the rig was idle, we substituted an overly sturdy shackle in place of the swivel and felt most virtuous for our trouble.

For me it was a delicious bit of deja vu, as I had once before detected a fault of this type before it succeeded in making trouble. This was aboard Crazy Horse, my Alberg 35 yawl, during my there-and-back-again transatlantic gambit at the end of the previous century. Interestingly, what I noticed that time was a slight change in the pitch of the humming sound made by the vibrating main boom's topping lift as we lay anchored in high winds in the Cape Verde Islands. A zealous inspection as to the cause revealed that the tiny shackle beneath the mainsheet's bottom block had fractured and was on the verge of failure.

The larger question, obviously, is why this critical bit of hardware, be it shackle or swivel, should often be so chronically undersized. I realize, of course, that the mechanical advantage of the mainsheet tackle must reduce the load on the line that serves as the sheet. But it cannot reduce the load on the fastener beneath the bottom block of the tackle. Or am I missing something here???

Hardware manufacturers everywhere, please advise.

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