GPS - The hidden dangers

iangrant

iangrant

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GPS Waypoint collisions.

Something I'd not thought about until it was pointed out to me.

Lots of other people use the same waypoints - set up the Goto - all aiming at the same thing!!

Ian
 
Unfortunately it doesn't end there, the military can blot out areas of the gps signal using jamming techniques from an aircraft, the only way i knew it was happening was because it was on notices to mariners on the navtex..........keith
 
Ever since GPS became widely used I have had this mental image of 2 or 3 irate skippers clutching their bent pulpits in thick fog and yelling at each other!
 
I must admit that I don't fancy chugging though a foggy day towards a published waypoint.

I will never even look at the wayponts in reeds.
It is easy to pick a waypoint off a chart that is near by and easy to enter especially if you use the small craft folio charts with the grid at 1' centres.
 
We've been teaching this on YM theory courses for a few years now.
I once met a chap who was one of the crew of Channel Light Vessel in the days before 'automatic' and they faced a similar problem with their RDF transmitter in fog. Ships used to home on it, and with luck veer away just before they hit it! The LV crew lived in fear and trembling in foggy weather, he said
 
I wonder how many people have tapped in the contents of Peter Cumberlidge's Waypoint Directory - English Channel, only to discover they are 1 of 5 yachts converging on the same waypoint one foggy dayl!!

Make yer own up waypoints, the chance of two people choosing the same dot on a chart are pretty remote.

Don't make the mistake I did on a foggy day in Brittany. I put a lighthouse as a waypoint, thinking by the time we get there will be able to see it from some way out. Looking in the distance it came as a great shock to see the big French lighthouse towering above us!

It was quite a few years ago now, when GPS navigation was still a new thing, it was the first time I'd really tried it in thick fog, it was amazing to see buoys come out of the fog directly in front of us. We had 2 GPS's, no radar, and plenty of depth round the lighthouse, little wind or tide and considered neither yacht or crew to be in danger...Just before I get an ambush of replies about bad seamanship....;-)
 
Allways set waypoints on my old Magellon as the point I did not want to be.
That way it gave range and bearing to the danger.

Brian
 
Allways set waypoints on my old Magellon as the point I did not want to be.
That way it gave range and bearing to the danger.

Brian
 
But surely just because you have a waypoint entered, you don't have to approach it too closely even in GOTO mode.
I have buoys & lighthouses entered so I can display them on the screen which shows my position relative to them. In fog you can use a buoy as a waypoint but aim off (range ring) to ensure you don't hit it & then enter the next buoy waypoint & repeat the proceedure to work up a channel or down the coast. Of course DR, depth & chart are updated in case the chips go down.
 
When I was a Cadet ....

The MerchanT Navy Instructor told us ...... Collisions occur because two stupid sods try to be in same place at same time ..... QED.

I remembered that all my sea-going life .... simple but true.

Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !
 
280,000 Ton tanker ....

As Third Mate on a Tanker we were sailing into Arabian Gulf in Ballast ..... Master decided that he would take the inner traffic route around into the Gulf entrance. Now this has a TIGHT turn in it !!!! Most go the longer way round !!

Anyway we had wheel hard over to Port, speed about 12 knots .... I went on bridge wing to take a bearing of the lighthouse ..... I could NOT depress the back edge of the compass ring enough to elevate the prism to take a bearing of the light towering OVER us !!!!! We were CLOSE !

Masters comment ...... same as last time !! Sorry guys but that is the last time I ever agreed to that one !!!! I was not amused !!

Ships Name etc. withheld before you ask !!

Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !
 
Setting a waypoint does not absolve one from keeping a look-out.

If I set a way-point especially one at the end of a longish passage, I usually choose a convenient off-lying intersection of a latitude and longitude on a chart - reduces risk of errors of interpolation which can happen if you enter a WP when tired or distracted. If you are approaching in visual then you can refine when you get closer.
 
There is a waypoint danger, but I believe the greater danger is on passage. Take two high speed motor cruisers ignoring tidal effects and making a "rolling road" passage between say The Needles and Braye Harbour, their meeting speed may be 40 knots or more and using the same waypoints at both ends...

John
<A target="_blank" HREF=http://www.allgadgets.co.uk>http://www.allgadgets.co.uk</A>
 
The real rason why lightships are unmanned....

An awful lot of them are used as waypoints!

Current recommended big ship practice is to set a course several miles to one side of the rhumb line, on all well trafficked routes - the accuracy of GPS bunches ships together much more now. Standing a few miles to one side adds almost nothing to the distance, and, assuming some silly prat is not driving on the wrong side, it significantly lessens the risk of collision, which with todays manning levels affecting watchkeeping, is rather high.

When I was a lad I was told of a collision between two oil company tankers off the coast of Portugal - which was as far as the Decca chain extended in those days. One was northbound and the 2/O was trying to pick up a signal, the other v/v and trying to get a last fix...
 
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