Dead Reckoning vs. GPS?

[S/V Alchemy]

Spread over two boats, I have a 1993 aircraft version of one of these Trimble units:



One of these early Magellans:



A slightly newer Magellan 315:



A helm-mounted Raymarine 420 from '99.



and a new Garmin handheld, the 72H:



And that's why I keep my DR practice and coastal pilotage in order!

[sailr69]

when did DR ever go away?

[OldFrog75]

Originally Posted by sailr69

when did DR ever go away?

No one said DR went away. I asked when GPS replaced it as the primary means of determining one's location on the water for the majority of sailors.

One day we woke up and more people had GPS than didn't. Sounds like it was about 10 years ago.

[colemj]

Originally Posted by rebel heart

I'm usually within a pencil lead width's margin of error at twenty four hours.

Depending on the chart you are using, that can be a frightening amount of error.

Mark

[colemj]

Originally Posted by S/V Alchemy

One of these early Magellans:

We have one of those! It hasn't been used in well over 10yrs, but I pulled it out last week and it fired right up and got a fix that was as accurate as it could be (it only goes to 2 decimal places on the minutes).

Mark

[Hudson Force]

Originally Posted by goboatingnow

Before GPS ( and before NAVSTAR and loran) sailors still used fixes not dead reckoning. Costal used fixes from land and rdf. Ocean sailors used celestial fixes. ...........Dave

I'm with Dave and in agreement that there were numerous other primary means used to indentify position between dead rekoning and GPS. During our first trip offshore to the Bahamas in 1974 we used an RDF for occasional fixes. Loran was commonly used to, but the Radio Direction Finder was the simplest and cheapest reliable fix. We would use dead-reckoning too, but the varying speed of the Gulfstream was difficult to monitor and the RDF was more reliable.

[rebel heart]

Originally Posted by colemj

Depending on the chart you are using, that can be a frightening amount of error.

Mark

If I'm navigating at that scale close enough for it to matter, it's my own fault.

[JPA Cate]

1983, Jim and I took his Yankee (S&S) 30 from SF to Hawaii and back. We used celestial, had an RDF for coastal, and ran 15 min. DR notations. In the presence of overcast and fog, we ran DR for two weeks, headed east, and were getting nervous about the hard bits towards the end of it. The DR was astounding close; but Jim always said that was luck.

1984, Insatiable (1) had a SatNav. She had been set up for ocean racing, and that was one of the bells and whistles. Just about the time the Gulf War broke out, we managed to get a Trimble GPS, and have used it ever since! It's on Insatiable II now. Not a bad service life.

Ann

If it ain't broke, don't fix it!

[NewMoon]

Originally Posted by OldFrog75

I asked when GPS replaced it as the primary means of determining one's location on the water for the majority of sailors.

One day we woke up and more people had GPS than didn't. Sounds like it was about 10 years ago.

Don't know about the majority, but we got one of the first decent chartplotters, a Garmin 210, for our first Alaska cruise in 1996. The screen definition and charting detail weren't up to today's standards, but it worked well. Before that we used LORAN.

The Garmin 210's main limitation was the government's fuzzing of the signal, called Selective Availability, which could produce a position error of 300 feet or more. So you couldn't be sure you were in the right spot entering a narrow channel without visual or radar. This fuzzing was eliminated in May 2000.

[boatpoker]

Delivering a 45' powerboat from Toronto to Chicago, my son and I got caught in thick fog in Lake Erie, We were close to the Canadian shore and all our electronics went down. After about 20hrs we were low on fuel and one engine went down. We were afraid to try and make port because of all the shallows along the shore so we DR'd to Pelee Island and found the break wall at the marina by feeling with a 16' boat pole. Fortunately we are in the habit of plotting a DR even with the electronics so we had a place to start when they crapped out.

[a64pilot]

Originally Posted by S/V Alchemy

Spread over two boats, I have a 1993 aircraft version of one of these Trimble units:

Called a Trimble Flight mate, saved my arse in Bosnia, actually a little bit into Serbia where we weren't supposed to be, since then I won't fly or go out of sight of land without two GPS's

[S/V Alchemy]

Originally Posted by colemj

We have one of those! It hasn't been used in well over 10yrs, but I pulled it out last week and it fired right up and got a fix that was as accurate as it could be (it only goes to 2 decimal places on the minutes).

Mark

I treat mine to new batteries every year, and it lives in the crash box. It's the GPS of last resort, i.e. a foggy night in shoal water, with a dodgy anchor out on a battery-dead boat and the captain has pink eye. I have reasonable confidence that it would fire up and, after a characteristic wait for acquisition of satellites, would in fact work.

[S/V Alchemy]

Originally Posted by boatpoker

Fortunately we are in the habit of plotting a DR even with the electronics so we had a place to start when they crapped out.

That is an increasingly rare habit. Even on sunny days five miles off shore in Lake Ontario (say, on the 10 to 11 hour sail from Toronto Harbour to Cobourg), I will first take bearings on landmarks and handplot in fine pencil onto a Richardson's or the "big" Lake Ontario chart. Then I will see how steady my eye was with a GPS lat/lon.

That's when I learned that a sextant on its side is better than a hand bearing compass if you are comparing, say, a water tower eight miles aft and a chimney six miles forward.

I do maintain that all this "old school navigation" increases situational awareness, even on fine 12 knot days with the chute up. It also relieves boredom, frankly, and alertness should never slacken too much. I recall motoring in calm air into a fog bank... the type of "bright fog" that's only about 40 feet thick, but right on the water...on the lake and switching to "ear mode".

Sure enough, because I was keeping a DR track, I knew we were near a place where fishing boats gathered, and I was able to narrowly (less than a boat length) avoid hitting an anchored fishing boat because I heard them talking over the engine. I didn't SEE them until two boat lengths away. If I had been on plotter, I'm not sure I would have been quite so alert.

In fog, I will put a crew at the bow just to listen for potential traffic.

[colemj]

Originally Posted by boatpoker

Fortunately we are in the habit of plotting a DR even with the electronics so we had a place to start when they crapped out.

Wouldn't it be better to regularly plot your actual position rather than a DR? Then you would know exactly where you were when the electronics crapped out.

Mark

[Lodesman]

Originally Posted by colemj

Wouldn't it be better to regularly plot your actual position rather than a DR? Then you would know exactly where you were when the electronics crapped out.

Mark

Shhh. Don't question the methods of the old-school Vasco's

Actually the main function of the DR is to ensure the boat is not headed into danger. Now that we have real-time position info and whiz-bang plotters/e-charts, that is not so necessary. Back in the early days of GPS use, when we just plotted a GPS position onto the paper chart, we still used DRs from those fixes.