Saturday, November 25, 2006

T-Shirt Weather

Fernandina Beach, Florida

Oh it felt good to strip down to a t-shirt today and to enjoy the sunshine. We spend the day shopping and doing errands. This is the first time since Solomons Maryland that we had the chance to really stock our grocery supply.

I forgot to mention two things about the trip down. Thursday night we were treated to a spectacular meteor shower. Perhaps is was the Perseus Shower, I'm not sure. The sky was crystal clear, except the perpetual clouds over the Gulf Stream 30 miles to our east. The moon set soon after the sun so it was a very dark night. Perfect viewing conditions for a meteor shower. In those conditions I also like standing my watch sitting on the upper deck beside the dinghy. That gives me a great view of half of the sky.

The trip was uneventful, except for the final part. Arriving at the St Mary's River inlet we had to navigate to the end of the breakwater, about 2.5 miles from shore. Although the winds were light, when we dropped our sails and headed in the swell started violently rolling us. It was extremely hard to stand up enough to hold the tiller and see where we were going, even when braced. We arrived after dark, and the lights on the navigation aids were seen against the backdrop of city lights. I could see a light briefly, then the boat would roll and I wouldn't get a chance to see it again for 20 seconds. That made it extremely difficult to tell which light was what. To top it off, my mind was filled with memories of the story our friend Baird told us of counting the buoys wrong and running his boat aground on the rocks of the breakwater. We made it OK, but I depended extra heavily on our GPS.

The value of a chartplotting GPS is hard to overstate. We can't use it for navigation directly. It isn't necessarily accurate enough for navigation. One sill has to see the buoys or other aids visually. Also, the GPS database can have errors. Also, things change. In this case, when we encountered the first red bouy at our intercept with the entrance channel, I asked Libby to check the number with the spotlight. "It should be number ten," I said. She picked it out with the light and called back, "sixteen." Sixteen! I re-checked the GPS, and both sets of chart books we have on board. All three sources said it should be "ten." "Oh well," I thought, "they must be renumbered." It was the GPS that allowed me to be so calm. It is plenty accurate enough to tell me that this is the last bouy before the breakwater, no matter what the number. If we didn't have the GPS, I would have been panicked by the discrepancy. I would have reacted by sailing three miles more out to sea to meet the first bouy and then three miles back in following them all. It would have taken two hours more time. With the GPS, I was confident enough to know we were right despite the discrepancy.

A second major advantage of GPS is that it can be read even at night and even when one's hands are busy steering the boat. At night, and in bad weather, paper charts have to be left below. To consult them means abandoning steering long enough to go below decks. If one is making a near approach to a hazard like a breakwater, that is too risky. Without a GPS, and on a dark night in bad weather, we probably would have had to stand hove to off shore until the following morning before attempting a hazardous entry.

The bottom line: our GPS allows us to be much less conservative in our navigation without increased risk. The same is true with very many other technical applications of computers. Software allows operators of everything from airplanes to nuclear power plants safely with reduced safety margins. The more ignorant you are of the state of your machine, the more margin you must allow for uncertainty.

Oh, by the way, we were indeed at the correct bouy, and it had been renumbered.

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