GPS Coverage can experience short gapsJan 1, 2003
|From Ocean Navigator #114 |
Arnold Grubin lives in Southern California and has been sailing the Caribbean for the last 15 years, currently in an Amel Super Maramu - based in Tortola in winter and Grenada in summer.
Contributing editor Bill Brogdon, former head of the Coast Guard's office of navigation, responds:
I have seen GPS receivers lose lock for a few minutes on a number of occasions. This may have been due to receiver problems or antenna shielding or something else rather than signal problems. In all cases I was using a relatively low-cost receiver.
I don't believe that using an external navigation system to direct the autopilot is an especially good idea. The reasons should be obvious, and one of them is the effect of short-term signal loss. Another is the zigzags from small signal errors. More important, you lose any way to measure set and drift. It's better to set a course in the autopilot and let 'er go. That way you can find the course and speed made good on a specific course. You also can tell autopilot zigzags from signal zigzags. But there is a strong theory: if it's technically feasible, it must be desirable. This theory is nearly immune to performance facts.