NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Role of CN at sea, was Re: Averaging sights ...
From: Bill B
Date: 2004 Oct 12, 19:15 -0500
From: Bill B
Date: 2004 Oct 12, 19:15 -0500
> Has anyone ever heard of a vessel loosing all of its GPSs while at > sea? If it hasn't happened yet, I suspect it will. In approx.. 700 hours of land and water operation over the past 3 years, I have experienced five loss-of-satellites-signal situations, usually lasting from 5-15 minutes. Three were on land, one due to a detour through the mountains in Pennsylvania after a 50 car/truck pile up in front of me. With mountains on all horizons and a blinding snowstorm overhead, would hardly blame that on the system or unit. The other two land situations I have no explanation for. Great weather, flatlands, no military bases nearby. Of the two on water (Lake Michigan) all units (my Garmin 76, an older Magellan, and the owners chartplotter) all failed to get adequate signals for 10 minutes or so. Partly cloudy sky. In one case an older Garmin showed our speed-over-ground on a broad reach in a 34' Catalina as 33.8 kn. Not too shabby--lucky the rudder stayed attached ;-) I have seen people sit on their unit left on the cockpit cushion and it lost all of its waypoints. A friend's older Magellan unit failed to find satellites after 3 hours. It is been replaced by a new unit. Have also seen two different Loran C units go haywire, with errors of more than 5' lat and lon. In talking with about a dozen sailors on the 600 dock at Michigan City, each and every one of them has experienced unexplainable signal loss of 5-15 minutes while on the water. Perhaps the Great Lakes don't meet the definition of "at sea," and is mostly coastal piloting, but there is ample evidence a single unit can malfunction, and even with multiple units, there are periods where signals cannot be received. Not a big deal on the southern half of Lake Michigan where it is pretty much point-and-shoot, but uncomfortable in the area where Michigan, Huron, and Superior merge. Bill