Pit­falls of nav­i­ga­tion

Yachting World - - On The Wind -

The ar­ti­cle by Daria and Alex Black­well ‘Can You Rely on GPS?’ in the Au­gust edi­tion con­tains a num­ber of er­rors:

• Lo­ran-c worked on time dif­fer­ences not tri­an­gu­la­tion. It was not just in the US, there were chains else­where; Bri­tain used the tech­ni­cally sim­i­lar Decca sys­tem.

• The pro­posed re­place­ment is elo­ran (En­hanced Lo­ran), which uses a dif­fer­ent tech­nol­ogy, crit­i­cally in­clud­ing pre­cise time sig­nals and dif­fer­en­tial cor­rec­tions. It pro­vides a sen­si­ble PNT al­ter­na­tive to GPS, which a dif­fer­ent GNSS sys­tem does not do as the trans­mis­sions are much more pow­er­ful and dif­fi­cult to jam.

• GPS ac­cu­racy is usu­ally bet­ter than 15m, but to achieve 10cm re­quires a pro­fes­sional re­ceiver and time to take av­er­ages. Sig­nals are prone not just to jam­ming and anom­alies, but also to out­ages and on­board faults.

• UK mar­itime qual­i­fi­ca­tions, for un­lim­ited range, re­quire com­pe­tency in as­tron­av­i­ga­tion, which has never been dropped from the syl­labus, as it was in the US.

• It is the sur­vey data that dates from the 1800s, not the charts. Read­ing NP100 would as­sist in un­der­stand­ing what is shown on mod­ern charts, which is not for the rea­sons as­sumed by the au­thors.

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