Cruising Tips – Navigation
Chart Smart (July 2006)
We arrived off Suva, the capital of Fiji, after a 10-day passage from New Zealand. While we knew the island of Viti Levu was about 5 miles off our bow, we couldnt see it because of a heavy rainstorm. My husband, Bob, turned on the computer and looked at the electronic charts we had added to our navigation suite a few weeks earlier. We wanted to use them to help us get through the pass in the reef but were unwilling to trust them, knowing charts are often inaccurate in this part of the world.
We hove-to, hoping the visibility would improve, after two hours we concluded conditions werent going to change quickly. We got on the radio and called boats we knew were already anchored in the harbor. We asked whether they had used electronic charts to get through the pass and, if so, whether the data was spot-on. After we heard from three boats whose judgment we trusted, we felt better about the accuracy of our charts.
As we went in, we kept our paper charts laid out with the route carefully plotted; I stood watch on the bow. We motored through the rain at a snails pace and used the radar and depthsounder to keep track of our location. We had no problems, and everything worked out fineincluding the electronic charts. But the moral of the story is that you never should rely on just one form of position finding. Even though electronic charts can guide you through potentially hazardous waters, you should always use as many different sources of position data as you can and constantly evaluate all of them as you check and double-check your position. Younot the equipmentare responsible for your navigation decisions. Cary Deringer
Radar piloting (June 2006)
The most accurate tool for estimating your distance to a solid target is radar. When you have to traverse a narrow channel close to the shore with off-lying dangers and you cant line up two objects to see you through, select the most appropriate range setting, then set the variable range marker (VRM) to a safe distance from whichever shore seems likely to offer the best radar target. You can then sail or motor along and be sure of your distance off. Double-check everything, make sure you have a bailout plan in case the radar goes on the blink, then forge ahead while keeping the VRM just touching the echo of the shore. Tom Cunliffe
GPS and Great-circle Courses for Ocean Navigators (March 2006)
Most GPS receivers are capable of delivering the bearing to a waypoint as either a rhumb-line or a great-circle course. When sailing along the coast or making an offshore passage, the two are synonymous for all practical purposes. However, when making an east-west ocean passage well away from the equator, following a great-circle courseso far as wind and wave permitcould save a day or more. Thanks to your GPS, you need not immerse yourself in tortuous calculations involving spherical trigonometry or plot new courses repeatedly from a gnomonic chart. As long as you have specified great-circle course on the setup page, you have only to create a destination waypoint, hit the go-to button, and read off the course. The figure you get will be the great-circle heading from your current position. Tom Cunliffe
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