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Furuno offers fix for GPS problem

Coast Guard safety bulletin only applies to some ships using the GPS’s position offset feature

Coast Guard safety bulletin only applies to some ships using the GPS’s position offset feature

GPS maker Furuno has introduced a software fix for a problem with the “position offset” feature of two of its late-model GPS receivers.

The Coast Guard identified the problem with Furuno’s GP80 and GP90 series of GPS receivers in a February safety bulletin.

It is only an issue on ships that use Furuno’s GPS and the GPS’s position offset feature along with the ship’s automatic identification system — a vessel tracking system used to transmit the vessel’s location to other ships and to port vessel traffic controllers.

“It is a very narrow problem because there are very few people who use the position offset function,” says Lee Luft, an AIS specialist at the Coast Guard Research and Development Center in Groton, Conn.

Position offset normally isn’t used except when a navigator uses the GPS to plot the vessel’s position on a paper chart that is uncorrected for position offset. Paper charts are drawn to different reference systems, resulting in slightly different latitudes and longitudes for the same point on different charts. Luft says charts in this country by and large have been standardized and corrected for these anomalies, called “geographical offset,” but in other parts of the world they have not.Mariners using GPS with a paper chart that has not been corrected for offset usually can manually program the offset into their GPS so the coordinates from the chart and GPS are identical. The amount of offset to be factored in usually is printed on the chart.

Luft says the Furuno units — when using the manual offset function — were passing GPS positions to the vessel’s AIS without alerting it to the fact that the coordinates had an offset built in. AIS is supposed to reject the offsets — but only if it is alerted to them — and send the coordinates using a standard reference, World Geodetic System 84. That way all AIS coordinates are based on one reference system.

If a vessel uses electronic charts, none of this is an issue because electronic charts already are corrected for offset, says Eric Kunz, senior product manager for Furuno USA Inc., of Camas, Wash.

Kunz says a software revision available on CD ROM will fix the problem, or a mariner can disable or not use the GPS’s position offset feature.

“A lot of peoplewere freaked out about this,” says Kuntz. But — he says — “almost nobody uses that offset function. … Unless you’re a pretty savvy chart user, you don’t even look for position offset.”

Luft says the matter came to the Coast Guard’s attention after navigators on commercial vessels operating in Australian waters began receiving AIS coordinates that were inaccurate. As it turned out, it was because Furuno units were adjusting coordinates for position offset without telling the vessels’ AIS that it had done this. Luft says Australia evidently has a number of charts with uncorrected position offsets. Kunz says the only place in the United States where the problem has reared its head is in Galveston-Corpus Christi, where — according to him — some charts require an offset of three minutes.

The GP80 and GP90’s software can be flash-updated via the PC serial port using a Furuno seven-pin data cable. The software revision (part number GP8-090-CD1) and updating instructions are available from Furuno.