Setting of Latitude and Longitude on GPS

[Jim Seamans]

As I was bumping along in 15kts of wind this morning. I was checking settings on my GPS and the one thing the struck me odd was the setting for latitude and longitude. My GPS was set for hhh mm.ddd I then set it for hhh mm ss.dd which is hours minutes and seconds. Which way is the preferred way to report a position, say to the Coast Guard or someone else? Or does it really matter?JimS/V Java

 

[Rick D]

Decimals, I Think

The calls I here around SoCal as I recollect use decimals for the seconds position typically. I don't think it makes a difference as long as you are clear as to which configuration you are using. Rick D.

 

[Rich]

decimal is standard

According to our ASA navigation course book you use decimal because it's standard in Aviation and commercial shipping. It allows for easier calculation in manual computation. I'll leave it to the professionals to provide examples...

 

[Stu Jackson]

See what the Light Lists use

and use that.

 

[Ross]

It is DEGREES minutes and Decimals

NOT hours minutes and seconds.

 

[Rick Webb]

Coast Guard Will Know Where You Are

With their new system they automatically get a triangulation that is very accurate. If your GPS is plugged into you VHF they know exactlly where you are. Most all GPSs default to a decimal they can be set to a seconds format. I think that will make you out of sync with most other folks who do not even realize the difference. I keep mine on decimal. I suspect it is kind of a defacto standard. If in doubt ask the person you are communicating the position from or to and when they answer "huh" you can pretty much bet it is a decimal position.

 

[Brian D]

Personally...

I would give my position in D:M:S and not use a decimal system. Some people cannot agree on the term "decimal" or "dot" or "point", know what I mean. But if you give, i.e., "33 degrees, 22 minutes, 15 seconds, North" it is understood. Or even 33 22 15 North.Just my opinion, you mileage may vary.

 

[Bill Roosa]

ddd mm.m is sufficient

If you give degrees, decimal minutes you will be fine. Seconds is not very useful to the CG anyway. Get out a chart and try to distinguish between ddd mm 45 and ddd mm 46, your pencile lead is lots bigger than that. If you give down to decimal minutes they will be able to find you as they will be within 0.1 NM of you or about 600 ft. It also makes ploting on your chart (you do still have paper charts right?) much easier.

 

[Malcolm Young]

Plotting your position

It is not possible to directly plot your position on a paper chart in seconds as the latitude and longitude scales on all charts are in degrees, minutes and decimal minutes. During a distress (Mayday) situation if you gave your position in degrees, minutes and seconds you can be assured that time will be taken up by potential rescuers converting that to decimal minutes - or worse still they may mistake the seconds reading for a decimal reading unless you state it is in seconds.

 

[patrick]

As an air crewman, I say decimal

such as "location is dd degrees and mm decimal mm minutes" It is quicker than saying " location is dd degrees mm minutes and ss seconds. I usually just leave off the fractions of a minute. Time is money.Flying along at 90 knots in a fixed wing aircraft, a minute of latitude takes 40 seconds of time to cover. The minute of longitude takes less time than that. Thus for an air search, it doesn't really matter too much which system you use. There isn't much chance of seeing something closer than a half a mile because of the speed and your ability to see something when you pass by so close and so fast. Thus you do not try to fly directly over the target if you want to see it. Degrees and minutes is usually close enough.A helo or surface search is a little different since it goes slower but I don't think that it makes that much difference then either. If you are looking for something from the air, half a mile is likely close enough. I would leave off the fraction of a minute unless it is requested and then be quick as well as specific which you are using.

 

[Malcolm Young]

Include the decimal minutes

Patrick,We agree on use of decimal minutes except that you then say just use minutes because you can see so well from the air. Perhaps you are correct about your arial view in half decent weather and visibility is good. However, if you are in trouble it may be because the weather is not so good. One minute of latitude is one nautical mile. For rescue you may have to depend on a surface vessel (either Coast Guard or some nearby samaritan). They don't go a mile in 40 seconds.If you broadcast a Mayday giving only degrees and minutes and then your boat sinks and you are floating in rough weather in a life jacket, you may wish you had included the decimal minutes. Have you ever done a search from a small boat in poor conditions? I am a member of the Canadian Coast Guard Auxiliary and I have been on such searches and search practices. You are lucky if you can see something the size of a persons head in a lifejecket in the water 100 yards away. It takes a long time to execute a search pattern over a square mile from a boat. Use degrees, minutes and decimal minutes if you have a GPS position available (if it is possible also provide a rough position relative to some charted object as a cross check and to alert nearby boaters that they may be able to help).

 

[patrick]

Agreed, Malcolm

If your boat is sinking, give it all, speak clearly, and use degrees, minutes and decimal minutes. I would advise saying the word decimal to remove ambiguity. We often get ambiguous position reports but it usually gets sorted out.

 

[Cap'n Ron]

EPIRB RESCUE

I'll jump in here with an experience I had, since the bottom line here is being found by a rescue expedition.My crew and I were rescued four years ago, yeah it was on CNN, and a big deal in Europe, the upshot was that that C-130 showed up 5hr & 40 min after we set off the EPIRB.We had a 25mm flare gun and started shooting off flares as he was circling, until we ran out.It was a bright sunny day, but we had 18ft rollers still from the previous gale.The USCG crew finally spotted us from a pair of mirrored sunglasses I had on, they never saw the four red flares we'd shot.They dropped a small smoke flare for wind direction, then a five gallon waterproof-sealed can on 100 meter line, the center fell perfectly at the bow where we retrieved it.Inside was, water, snacks, and an ICOM HH VHF.That is when they told us that they had a postion from the EPIRB but did not see the flares, but did see out "signal mirror" reflecting the suns rays.Great guys, they stayed with us, circling untill we could talk to the rescue ship that had diverted they're course hours before.This was 980nm from the Hawaiian chain.The USCG uses decimals in reading GPS positions, and can be contacted on 16 or 22 by VHF.

 

[Jim Seamans]

Just Called the USCG at Baltimore

Told the office of our discussion.He stated it really didn't matter since they can convert to either. As long as you report acturately.Interesting thing was when I asked him what the rescure aircraft uses he stated "dd mm ss".So either way is fine.JimS/V Java