When your GPS fails, how do you navigate?

[Stu Jackson]

Current Sailing

I've wondered about "Dead Reckoning." The way I've heard it used sometimes amounts to; "Well--I reckon it must be over there!" Seriously, for how many hours of travel, at say 6.5 kt, should one trust a DR plot? If you're updating your position plot every hr w/ GPS (until it fails) you'd have a baseline for drift and set "behind you!" But then the tide reverses during a new moon and you still have, say, 9 hr of travel after dark to destination with another tide reversal in the offing. Where would you really be at the end of those 9 hr lacking a fix on a lighted ATON? Now I realize that big-time ocean sailors can go days to weeks on DR (if they have to) and not be too far off when a fix is finally gotten. But what about when traveling along the coast where tides, currents, and local eddies potentially come more into play? How often does anyone practice with the GPS TURNED OFF? My guess is hardly ever to never b/c the position up date is continuous while the GPS is working--no need for DR plotting until it STOPS working. Whereas in the old school, one had to maintain DR plots between fixes b/c they could be gotten only one or two times a day, maybe, unless passing within sight of charted landmarks, etc.

KG,

That's a very good question. Many of us are "experienced enough" (i.e., old f*rts!), who sailed around off the coasts before even Loran (gasp!). Most of us came back. While I didn't have an RDF, I did have a portable radio which I used when off the coast of California to check one line of position from the radio towers in San Francisco. Since I never was out of site of land, we actually, as was properly said, were PILOTING, not navigating.

If out of site of land, currents usually don't change very much, at least out here off our coast, and tend to trend to the south at up to one knot, not reversing.

Current sailing, however, in other places, like off the coast of Maine, can be quite tricky with the impact of all the rivers plus the normal tidal changes and associated impacts on currents.

Most of those are, however, pretty well known and documented. So, the answer is to learn how to do what IIRC Chapmans and Duttons call "current sailing" including all the factors you mentioned.

It's truly challenging, and very time consuming. It requires a LOT of planning ahead.

It's also very rewarding. I remember a trip outside the Golden Gate in unusual down-on-the-deck fog where I sailed without any instrumentation other than compass and speed and contours from the Gate along the south side (i.e., Baker Beach) to Mile Rock. I "hit" Mile Rock on the nose, almost literally!!! I was glad I "found" it and also glad I wasn't going much faster! That was on the last of an ebb.

I then turned NW to find the next buoy across the shipping lane, which I checked by VHF and VTS as clear of shipping.

I also "found" that buoy at the start of Bonita Channel and Four Fathom Bank on a building flood, by compensating my heading with the drift from the new flood and the boat's leeway.

The wind was steady and I was running a full main and a 110 jib, so other than the ocean swell and slight wind waves, it was a glorious sail.

I also learned that there are *********s out there who use their instruments to go from waypoint to waypoint on autopilot with no lookout!!! Big 40 foot sportfisher appeared out of the gloom at 20 knots! Never even saw me.

I now, as most advise, offset all waypoints to make sure those guys are at least a 1/4 mile away.

It was a great adventure.

I applied what I'd learned. In my case from Chapmans and Duttons, but Rich is right, learning in a class from the Power Squadron is a great idea, too.

I appreciate the instrumentation and finally got a Loran and then eventually a GPS.

A number of years ago I removed the old Magellan Loran 8000 from our boat (1986!). I shoulda saved it as museum piece - it looked like something from a Pentagon garage sail.

I think learning navigation is fun. Using it is more fun, 'cuz it means you're out on your boat! :dance:

And, it's handy safety tool to have, too.

 

[Charlie Jones s/v Tehani]

Not a problem.
If the GPS/Chartplotter fails, Turn on the I pad and continue, using INAVX. If the battery on the I pad becomes exhausted, turn on the I phone & continue using INAVX. If the I phone fails, turn on the Garmin handheld gps and continue. If the Garmin Gps fails, continue piloting with dead reckoning as I always do hourly position plots on a paper chart for backup & overall visualization. Obtain lines of position / fixes as possible. Talk about redundancy!!!

Plus one. I also when log position on a chart hourly

 

[Kings Gambit]

KG,
That's a very good question. Many of us are "experienced enough" (i.e., old f*rts!), who sailed around off the coasts before even Loran (gasp!). Most of us came back. While I didn't have an RDF, I did have a portable radio which I used when off the coast of California to check one line of position from the radio towers in San Francisco. Since I never was out of site of land, we actually, as was properly said, were PILOTING, not navigating.

If out of site of land, currents usually don't change very much, at least out here off our coast, and tend to trend to the south at up to one knot, not reversing.

Current sailing, however, in other places, like off the coast of Maine, can be quite tricky with the impact of all the rivers plus the normal tidal changes and associated impacts on currents.

Most of those are, however, pretty well known and documented. So, the answer is to learn how to do what IIRC Chapmans and Duttons call "current sailing" including all the factors you mentioned.

It's truly challenging, and very time consuming. It requires a LOT of planning ahead.

Stu, I honestly doubt that many could do it but it's probably preferable over attempting to maintain a DR plot/course to destination. Just thinking more on this, even w/o the tide and current variables, what do you have to do for DR? Steer a straight course that can be plotted as True. So, helm would have to maintain a compass heading, one correctable to a magnetic course (need deviation card). Would need to know the average STW. If all power fails at night then no speed log and likely no compass light. Someone has to go below and plot, leaving the helm to a crew. If no crew then cannot leave the helm to plot. Also, no autopilot if power is out and no depth meter to track a contour either. If you have not been plotting hourly on paper chart you might not know your position within 5 n.mi. when the units fail. Your hand-held VHF might not be fully charged and in any event you could not tell Vessel Assist your last True position since you never had one down on paper. Now what? You're only good option is to generally maintain your course but move inshore to search for a lighted ATON and get multiple FIXes!!! Better have good binoculars and a paper chart aboard!! Yes, situation awareness is also correct here IMHO!

 

[Allan12210]

When I learned piloting I was also taught that depth is a line of position. I've followed contours when trying to get into a harbor but what if your course crosses depths at an odd angle? Then awareness of where you were before the electonics failed will be a start. Keeping a constant speed and course allows one to set a pair of dividers to a distance after crossing two depth contours in a known time (D=S xT). The dividers are then oriented in the direction of travel and moved until the tips match the separation distance two contour crossed on the chart.

JK_Boston, I still have and use that same moving arm plotter. Its great.

 

[Calif. Ted]

I keep thinking of our home waters KG, I bet if you were dropped off 3 to 10 miles out between Santa Barbara and San Diego you'd know where you were on a clear day. Between the offshore islands, San Clemente, Catalina, Santa Barbara etc., the distinctive headlands, Points Loma, Palos Verdes, Mugu and then the oil platforms.
"Seamans Eye" using the chart in your head, you've see all those places at sea level and you remember the profiles.

 

[Stu Jackson]

KG,

You present two very different scenarios. One is when you are doing DR to a destination without "modern" instruments. This is current sailing or piloting and can be done in good visibility or bad, but preferably good, so if visibility dies you bail for your backup.

The second is when all things are good and then go to heck and you lose everything and only have paper to rely on. There is great merit in learning how fast your boat sails and motors to know STW, " 'cuz that's all ya got, buddy!" That and your compass.

But planning ahead should also include all bailout scenarios.

And I sail all the time with a bailout in mind: "What happens if a shroud lets go? Which way do I turn? Forestay or backstay failure... What happens if the engine dies?"

I don't live in fear, but I do plan, plan, plan, even as I'm merrily sailing along.

And the less instrumentation you have to depend on, the safer you are, 'cuz that's another bailout scenario: "What happens if the electrics go belly up?"

Obviously, worst case is zilch visibility.

One other thing: In all the navigation and piloting classes & books, all the courses and plots show so nicely as straight lines & points which seem to say: This is where you are.

One of the best things I ever learned about navigation was: A good navigator does his work so he knows where he is NOT, and pretty close to where he should be.

Those navigation lines, IN REAL LIFE, are simply approximations, not the "certainties" that seem to appear on our GPS chartplotters.

DR (sometimes also call ded for deduced reckoning - there was a little debate on this over on cruisersforum just yesterday !) simply is the best guess you can make.

It takes patience and discipline. And it's not always great for landfalls and tight spaces, in which case one waits for good visibility and more certain PILOTING.

 

[Kings Gambit]

I keep thinking of our home waters KG, I bet if you were dropped off 3 to 10 miles out between Santa Barbara and San Diego you'd know where you were on a clear day. Between the offshore islands, San Clemente, Catalina, Santa Barbara etc., the distinctive headlands, Points Loma, Palos Verdes, Mugu and then the oil platforms.
"Seamans Eye" using the chart in your head, you've see all those places at sea level and you remember the profiles.

Yeah, on a clear day, I would-as you say. We have lots of great, distinctive landmarks up and down the So. Cal. coast. It'd be hard to get too lost in daylight. But at night, in hazy conditions, with low visibility, it could be a challenge to [safely] run that 140 n.mi.-Ventura to Pt. Loma w/o the convenience of electronic navigation (oops, PILOTING)! (Especially if the weather is up!)

 

[jibes138]

I've wondered about "Dead Reckoning." The way I've heard it used sometimes amounts to; "Well--I reckon it must be over there!" Seriously, for how many hours of travel, at say 6.5 kt, should one trust a DR plot? If you're updating your position plot every hr w/ GPS (until it fails) you'd have a baseline for drift and set "behind you!" But then the tide reverses during a new moon and you still have, say, 9 hr of travel after dark to destination with another tide reversal in the offing. Where would you really be at the end of those 9 hr lacking a fix on a lighted ATON? Now I realize that big-time ocean sailors can go days to weeks on DR (if they have to) and not be too far off when a fix is finally gotten. But what about when traveling along the coast where tides, currents, and local eddies potentially come more into play? How often does anyone practice with the GPS TURNED OFF? My guess is hardly ever to never b/c the position up date is continuous while the GPS is working--no need for DR plotting until it STOPS working. Whereas in the old school, one had to maintain DR plots between fixes b/c they could be gotten only one or two times a day, maybe, unless passing within sight of charted landmarks, etc.

This is an interesting post. My first several years of sailing were only by dead reckoning very often in fog. My only electronic instrument was a depth sounder so sailing along contour lines on a chart was a very important skill. I finally splurged and bought a hand held loran that was amazing to me.
But here's a thought on DR and tide changes and errors. Before they had electronic instruments they figured out the height of Mt. Everest by plotting heights all the way from the coast at sea level until reaching the mountain. They were very accurate, because the inaccuracies average out over long periods of time. Some measurements too big, some two small. I wonder if the accuracy of DR has a similar effect, assuming a knowledgeable navigator ?

"In 1802, the British began the Great Trigonometric Survey of India to determine the location and names of the world's highest mountains. Starting in southern India, the survey teams moved northward using giant theodolites, each weighing 500 kg (1,100 lb) and requiring 12 men to carry, to measure heights as accurately as possible. They reached the Himalayan foothills by the 1830s,
In 1856, the Great Trigonometrical Survey of India established the first published height of Everest, then known as Peak XV, at 29,002 ft (8,840 m). The current official height of 8,848 m (29,029 ft) as recognized by China and Nepal was established by a 1955 Indian survey and subsequently confirmed by a Chinese survey in 1975."

 

[Stu Jackson]

A classic post from higgs

http://forums.catalina.sailboatowners.com/showthread.php?p=1053415&highlight=opinion

Not so much for the rant about electronics, but rather the nav stuff.

 

[JK_Boston_Catalina310]

I may come off like a jerk for saying this but I feel if you can't DR a course from a reasonable fix you shouldn't be on the water. We spent a fair amount of time working on this skill when we first started boating. You should be able to estimate your speed based on the feel of your boat. Same goes for steering a compass bearing. You should be practicing this along with other skills like heaving to, Williamson turns, reefing, etc.

We have actually had to DR before.



We hit waypoint 7 in fog with less than 50 foot visibility, we could barley see one boat length in front of us. We didn't have the chip for the area for our chart plotter and were using our garmin handheld. We also had our boat compass, hand bearing compass and paper charts out tracking our progress. Right after we passed that waypoint 7 our handheld died. Ended up being a problem with the memory chip. But the end result is we had no visibility and only our speed and depth meters. We used DR and made our way into the dock. Sure it was a little white knuckle for a bit but we had the skill and knew how to get us there.

We are at the end of our 50 ton Masters license as we speak. We have our sailing endorsement tomorrow and our exams the next two weekends. One of the 4 exams is on plotting and DR. To be honest it is the topic we are least concerned about.

When on the water we are generally more piloting than using our chart plotter, now our iPad as our primary tool. We use the iPad to verify our tracked progress and as a convenient way to view charts. That's part of the reason we don't get hung up on the accuracy of the iPad fix. We don't trust any GPS to be more accurate than a couple hundred feet. We base our location on what we see around us not on the screen.

Just my thoughts.

Fair winds,

Jesse

 

[JK_Boston_Catalina310]

http://forums.catalina.sailboatowners.com/showthread.php?p=1053415&highlight=opinion Not so much for the rant about electronics, but rather the nav stuff.

Thank you for sharing that Stu!

 

[Joe]

DR is simply estimating your position from your last known fix by analyzing your speed and direction over time. Part of dead reckoning is estimating how current is affecting your course.... the same way airplane pilots estimate drift.... it is a skill that can be acquired by practice.

Josh Slocum DR'd around the world with a tin clock, a compass and a speed log on a knot reel. Navigators throughout history, before the advent of reliable chronometers, relied on DR to estimate their longitudinal position, once they established their latitude by the noon sun observation.

No one... and I mean no human.. can steer an exact compass course.. it's an average heading at best... but you will recall that steering the big sailing ships by the quartermasters required them to record their course and speed at regular intervals on a chalkboard at the helm... they would often sail for great lengths of time without being able to get a sun shot.. and the sailing master used their data to predict the position with uncanny accuracy.
But then, again, those guys were real sailors... they knew their stuff.

So... pay attention to your last known position.... jot down your course and speed at regular intervals..... then estimate any adverse current... finally get out the chart and plot those intervals... then compare your results to the next fixed position you take..... It's fun and it may come in handy some day (or night).

 

[Doug4bass]

This thread reminds me when I was a private pilot learning navigation. They taught the acronym "True Virgins Make Dull Company". At the USCG Aux course a few years ago.......they cleaned it up. " Tele Vision Makes Dull Children". I laughed.

 

[Prime Time]

Having been sailing since the late 60s as a kid. Certain things come to mind. 60 D street. A stop watch. Doubling the angle on the bow. An old zenith RDF. Being able to look over the side and estimate speed. Fancy knot stick pitot tube. Compass, dividers and paper. Current charts in Eldridge. Calculating drift. Sailing bouy to bouy entering Yarmouth harbor in fog with the loran on the fritz. Finding Bermuda with an RDF. Sadly few out there have these skills or know they exist. My parents were excellent teachers. My dad continues in his 80s to share his skills with others via the US Power Squadron and just became Commander of his squadron after 48 yrs of membership. It is a phenomenal organization.

 

[Bill Roosa]

I don't use gps for navigation. I use pilotage and that round black thing at the helm, always points int eh same direction, think they call it a compass and chart.
GPS just tells you where you are, you still need a map to discover what that means in about 3 minutes when underway

 

[kappykaplan]

They're called charts!

snip
GPS just tells you where you are, you still need a map to discover what that means in about 3 minutes when underway

It's called a chart . . .

 

[capta]

I guess I'd have to dredge up all that old knowledge I've stored away somewhere in the back of my mind, from the days people actually piloted vessels before GPS was invented and available to the general public at an affordable price.
Drat. I was so looking forward to watching those movies projected on the main, while we sailed through the night, making sure all the alarm functions on the GPS were turned up full volume. Drat.

 

[KZW]

I've wondered about "Dead Reckoning." The way I've heard it used sometimes amounts to; "Well--I reckon it must be over there!" Seriously, for how many hours of travel, at say 6.5 kt, should one trust a DR plot?

Depends upon your compass and how much you pay attention. Dead reconking is still taught in USAF Navigator school. I works for airplanes, so it should work for you in a much slower boat.

 

[capta]

I've wondered about "Dead Reckoning." The way I've heard it used sometimes amounts to; "Well--I reckon it must be over there!" Seriously, for how many hours of travel, at say 6.5 kt, should one trust a DR plot? .

Like anything else, the more you do something, the better you get. The nice thing about coastal DR is that it can be continually updated with new factual information, which DR deep sea cannot.
With enough time spent on a boat, you should get a feel for the boat and know when a current is affecting your boat. If you are properly prepared, you have tide tables and other local information, to add to your DR, making it a pretty well educated assumption.
The longest I've gone is 6 days offshore, but we made a 25 mile wide pass in the Great Barrier Reef. I'm not saying it was worry free, but we did get through without difficulty.
DR is an act of trusting in yourself.

 

[Benny17441]

A professional Mariner will maintain and track his progress on a paper chart by plugging his position every hour even though he may be using GPS to navigate. If the GPS fails he will have a close indication of his location and then he can plot a dead reckoning course.