ASA 105: Skill 10, Calculating Deviation
10. Check compass deviation by a transit bearing or other means. Compass deviation is how we address the magnetic field of a vessel. Deviation may change over time as the magnetic field of the yacht changes. This is more common for steel or wooden hulls fastened with iron than for fiberglass yachts. There are two basic ways to check deviation. The first and oldest is by using a table of the sun's true bearing at sunrise and sunset for a given latitude. The other is by using a charted range (transit bearing). We will look at the range method. Nantucket Harbor Channel Range This is similar to the range used in the example, Cleveland Ledge Channel Range. The yacht should move right to get the ranges aligned The TVMDC AW formula is used. When D is unknown, the arithmetic result is D using TVMDC. In such a case, TVM and C are knowns so we solve for D. Turning to Chart 1210 Tr, observe the charted "Cleveland Ledge Channel" range for...