Ran some tests this week coming down the Washington coast with a Garmin 76Map. Accuracy with WAAS on and off does not seem to be significantly different. In fact, with it turned on the accuracy numbers deteriorated. I do not know what Remember...WAAS is Satellite based and line of site. Also, WAAS was not meant for ground, or water based use. It was specifically meant for aircraft use. DGPS on the other hand uses a land based antenna, and the signal (srapping itself around everything) is more conducive to boating, or hiking, or driving. When DGPS is up and running, it is a safer bet for boaters. RJ Bay-B-Grand

I am not quite sure how Mike manages to tell how accurate his positon is. What you see on a Garmin is the EPE (Estimated Position Error). This is a proprietary Garmin parameter for which Garmin declines to provide any technical description. It is known to involve DOP parameters which are based on the geometry of the satellites among other things. It may or may not include differential corrections depending on which model and who you talk to. It is however known that a Garmin GPS will favor WAAS or other differentially corrected satellites to those which are not. This can lead to use of satellites with a less desirable geometry and a worse DOP leading to a worse EPE. The objections to WAAS deal almost exclusively with multi-path errors. These should almost always be negligible at sea though perhaps real in urban ports. The CG and IMO are putting out pretty much pure propaganda that there are problems with WAAS. Seems more like the stakeholders in differential don't want to see their hard won agreements dissolved by the implementation of a similar scheme of much lower cost. It is of course true that WAAS has not yet achieved fully operational status. But how in the world would one decide that the open sea is different than the open air? Maybe airplanes never fly in valleys? While the error sources for WAAS and DGPS are different I am not aware that any advantage goes to DGPS for marine use. Lots of things interfere with the differential beacons - one certainly being thunder storms. Jim > > Remember...WAAS is Satellite based and line of site. Also, WAAS was not > meant for ground, or water based use. It was specifically meant > for aircraft > use. > > DGPS on the other hand uses a land based antenna, and the signal (srapping > itself around everything) is more conducive to boating, or hiking, or > driving. > > When DGPS is up and running, it is a safer bet for boaters. > > RJ > Bay-B-Grand > > >

.........It is known to involve DOP parameters which are > based on the geometry of the satellites among other things. It may or may > not include differential corrections depending on which model and who you > talk to. > > It is however known that a Garmin GPS will favor WAAS or other > differentially corrected satellites to those which are not. This can lead > to use of satellites with a less desirable geometry and a worse DOP leading > to a worse EPE. > > The objections to WAAS deal almost exclusively with multi-path errors. > These should almost always be negligible at sea though perhaps real in urban > ports. .............. Just curious, where did this information come from? Richard