Sunday, March 22, 2015

Navigation Plan B

Boot Key Harbor, Marathon, Florida

I've written before about how seductive it is to navigate exclusively with the aid of a GPS chart plotter. It is not only easier, but the result is so much superior to coastal piloting techniques. Because of confidence in the GPS, we can take short cuts. Using only coastal navigation techniques, we would have to add many miles (and many extra hours of sailing) to avoid coming close to hazards.

The picture below shows my favorite example, sailing from Everglades City, Florida to Marco Island, Florida. There are a number of shoals south of Cape Romano, arranged as parallel east-west sand bars with deep water in between. Using GPS, I feel safe using the red path, but with coastal navigation the yellow path would be the most aggressive route I would dare. It is very many much longer. In terms of time, it could be half a day. The more uncertain I am of my coastal piloting position and course, the more south (conservative) I would have to be.


But any prudent captain must plan for the day when the GPS, and all the backup GPS' on board will fail, and we need to fall back to paper methods. What then? Suppose we have a navigation plan A based on GPS. There will also be a plan B based on paper charts and coastal piloting methods. B will always be more conservative than A.

Today's question is, "Must one have both plans A and B in hand before leaving, or can it suffice to have a generic procedure C for creating a plan B on-the-spot?"

I should mention that this post was inspired by an airline captain friend who said that he felt uncomfortable leaving the dock with out both plans A and B in hand. It is true that the standards are different. When flying a plane you may not have enough time to invent plan B on-the-spot. On a boat you do. On a plane, the pilot seldom has a chance to repair failed equipment en-route, but on a boat you do.

  1. Strictly observe the Box Canyon Rule. Never put yourself in the position that plan A must succeed or else you're screwed. Preserve the opportunity to make a feasible plan B if needed.
  2. Always have paper charts available, and know on which page you are.
  3. Any procedure C to create a new plan B depends on knowledge of your current position. Therefore:
    • You may have used pencil and paper to record your current position (i make pencil marks on the chart itself). Use dead-reckoning to extrapolate your last known position to your current position.
    • Use any possible source to locate your current position. VHF radio calls to other boats, sextant, cell phone, visual bearings on landmarks, compare the depth to the charts, position of the sun and sunrise/sunset times, even call the Coast Guard if your situation is dangerous. (I'm sure that there are even more ways, than I listed.)
    • Be patient. Unless you are in imminent danger of going aground, you can take whatever time is needed to get a position fix. You might be able to anchor, or to heave-to to stay in more or less the same place. Urgency is usually not needed.
    • If your uncertainty is so great that you dare not proceed, is there a direction you could go that would be safe and would improve your ability to get a fix? Doubling back on the course you used to get here is probably safe. Unless you are surrounded by shoals in all directions, there should always be a safe direction. (If not, then you violated the box canyon rule.) For example, offshore along the east coast of the USA, I know that sailing West will make me sight land.

Once you have your position fix, and an estimate of the uncertainty in that position, you can look at your paper charts and devise a prudent plan that either gets you to your intended destination or at least returns you to safety.

It is that simple. Indeed, simplicity is mandatory.

Finally, let's not overdo it. Cruising is more demanding than day sailing. When day sailing, you have no plan A at all (other than have fun). But day sailing should be restricted to familiar waters where you always know where you are and how to get back and when reference to the charts is seldom needed.

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