One of the excitements of sailing in BVI waters is the remote possibility that your mooring might fail. The likelihood, while slight, is sufficient to have the fine print on the National Parks permit require that a member of the crew stay aboard to handle the boat in case of trouble. Most people generally ignore the advice and blithely go about their snorkelling and diving without a care and, usually, without a consequence.

Recently, though, I got a reality check whilst on a diving trip. Our party was aboard a 45-foot dive boat which moored to a white diving ball. The party entered the water and descended the mooring line to 50 feet or so. After spending our allotted time below we returned to the mooring line to begin our ascent. The water was clear and the stainless steel eye of the mooring screw, anchored into rock on the sea bottom, was easily visible and obviously securing the mooring line. As soon as we reached the mooring line and began our ascent, the eye of the mooring line suddenly and inexplicably detached itself from the mooring screw. One second it was attached and the next, it was floating free below us. Nothing obvious had happened—nobody touched the shackle or interfered with it in any way. As we ascended, the end of the mooring line ascended with us. The fact that this was the line holding our dive boat in position above us barely registered as we made our safety stop, then continued to the surface.

It was only when aboard the boat and probably 10 full minutes after I had first observed the mooring eye come free from its attachment below, that the penny finally dropped. In the midst of a conversation with the dive leader and the boat's skipper about the strange events below finally I was able to observe, “You know, we're not actually attached to anything.”

Everything was suddenly clear—we were drifting closer to the rocks! Captain and crew sprang into action and we were able to manoeuvre to a safe position and drop our anchor. In the course of so doing, we managed to tangle the original mooring line around our starboard propeller. Luckily, we had two props—once we were anchored, it was a simple job the free the line.

So what wisdom is to be learned? Well, first, you never know—sometimes the impossible happens. In this case, there was someone aboard who could handle the boat but he had been oblivious to the danger. He had been monitoring things and was on the cusp of deciding we were drifting, when my words clinched it for him. But he was faced with the complication of having a dozen or so divers in the water beneath him. Perhaps the only thing to do in this situation is, when first tying off to a mooring ball, back the boat down as if setting an anchor. Put some decent strain on the system. If it holds the boat, you should be good for a couple of hours at least. Or, if you're really concerned, leave someone aboard the boat who can handle the boat!