Navigation the Rite Way.. or Is GPS Reliable???

[Captain Smollett]

Even simple math makes my brain hurt.

Well, with the calculator programs (either mine or somebody else's, they are out there), you simply have to enter the data.  In the case of my sample problem above, you'd only have to enter the lat-long of starting and ending points.

The program does the rest.  :)

Anybody use a nautical slide rule like this one?

Those are pretty good for what they are, but are essentially single-purpose. They solve the distance-time-speed equation, and that's it.

It's probably a matter of personal preference, but I try to avoid single-purpose devices.  Using them not only adds space/storage issues, but it also tends to breed dependency on a specific tool for even simple tasks.

[Norm]

So, the GPS is broken.... must be time to use my brain again. 

Seriously, GPS units are more likely to lose their signals at critical moments than "break" altogether.  Everything on board can break.  As serious sailors, we have to have a backup plan.

I am a sailing instructor and work mostly with cruisers.  The question of what to do if GPS fails comes up every cruise.  My remarks are that we start observing the circumstances that surround us.  This isn't a math problem yet.

Practice on the good days as training for the not-so-good navigation days.

First.  Keep track of departure times, directions, speed, etc.  Draw the course and distance travelled on the chart.    The process is called "ded reckoning" with the d-e-d being an abbreviation for deduced.  I make a new DR fix every two hours if no course changes have occurred or every time I change course.  It works very well.

Second.  It is possible to estimate speed and arrival times using a couple of simple "guesstimates."
Speed... if you are really ripping along, the speed is 5 to 6 knots.  A comfy sailing speed?  Guess at 3 to 4 knots.  Slower than that?  Who cares?  The speed ranges are a function of boat type.  The Olson 30 racing boat I spent so many years on loafs along at 6 knots on the same day a Pearson 30 (a favorite of mine) sails briskly at 5kts.  Experience will teach us about our own boats.

Time.  Use this simple table that is easy to derive.
6 kts is a nautical mile in 10 minutes
5 kts... in 12 min
4 kts... in 15 min
3 kts... in 20 min

Anyway, there are a myriad of ways to navigate without GPS and breaking our brains on math.  It all starts with observation.  A navigators first job is to observe.

electronics help us keeep schedules.  Eyeballs and brains help us go sailing.

One of the fun things about my job is doing this with new-to-cruising sailors.

In case it matters to anyone why a "big boat sailor" is here.  A) I am a little boat sailor stuck in a big boat body.  B) my customers ask questions discussed here.  This provides me with insights into questions, thinking, and solutions.

Best,
Norman
Boston

[s/v Faith]

In case it matters to anyone why a "big boat sailor" is here.  A) I am a little boat sailor stuck in a big boat body.  B) my customers ask questions discussed here.  This provides me with insights into questions, thinking, and solutions.

  Just glad you are here Norm.  Thanks  ;D

[Captain Smollett]

Time.  Use this simple table that is easy to derive.
6 kts is a nautical mile in 10 minutes
5 kts... in 12 min
4 kts... in 15 min
3 kts... in 20 min

A similar useful technique I've read about and used is the 'how far in six minutes' method.  You travel 1/10th your speed in kts in six minutes - 3 kts = .3 nm in 6 minutes, etc.  Useful on it's own or for recreating the table above 'in your head.'

I also agree ded reckoning should ALWAYS be employed.  It's better to know where you are than to have to try to figure out where you are.  I don't always plot a DR position on the chart (okay, I rarely do if in pilot waters), but I do make notes of times that I pass certain features, aids, etc.  I made a "log chart" that I keep with my nav tools that has columns for the following headings:

Position, Time, Speed, Course (Mag), Course (True), WX Notes, WX Forecast and General Comments.

For position, I simply write "Mark 31 200 yds to stbd,"  a position line from an object or a Lat Lng, etc.

There's lines for 36 entries per page.

The "problem" that began this thread was one of knowing a start position and a desired ending position (whether destination or waypoint) and computing the course and distance.  For small distances, you can strike both directly off a large scale Mercator chart; for larger distances, that would give the wrong course and distance due to the mathematical nature of the projection.

[Norm]

getting back to the original idea... I used a gnominic chart a few years ago while planning a trip across the Pacific.  Should we start talking about that?

I was trying to make the point that not all navigation is math and there are non-math workarounds.  Problem is... I type so slowly.

[Captain Smollett]

If you strike a 'straight line' between two points on a gnomic projection, don't you get a great circle rather than a rhumb line?  I've never used a gnomic chart personally.

not all navigation is math

True. I guess it might depend on how you define "math."  :)

Navigation is data processing.  The data is measured values - courses, speeds, time, postions (in some coordinate system), etc, and the manipulation of that data is intrinsically mathematical in nature.  Of course, there's more to math than arithmethic.  Plotting a position on a chart is technically math.

For example, I offer that if you are looking at a daymark and trying to determine if you are on a course to clear it, you are doing math.  You may not be writing numbers on a piece of paper or punching them into a calculator, but you are processing angles and delta-angles visually.  I'd say you are doing math.  Others may disagree.

Maybe it's more of semantic point than one of practical value.

there are non-math workarounds

For some problems that may be true.  I've never seen any kind of written material (books or on the web) that deals with navigation or pilotage that does NOT deal with mathematical problems explicitly.  I know Bowditch is one of the navigator's main resources, and that book is nothing but math.  Even cel nav with HO 249 requires some basic math.

Is there a way to solve all of those problems without math?  I would love to learn any navigational trick there is.  I am fascinated by all navigational techniques, both as theoretical problems and practical tools for my toolbox on the water.

[Joe Pyrat]

Wouldn't the simple way to do this be to just shoot an angle on Polaris and start sailing north paralleling the coast until you get a reading of 43.40, then head due west?  After all this is what sailors use to do before they had timepieces accurate enough to allow them to determine longitude.

[AdriftAtSea]

While that would be one way to do it, it would be far longer a distance to sail, as you'd be doing the two legs of the triangle, rather than the hypotenuse. 

[Joe Pyrat]

In fact you would be sailing roughly the hypotenuse.   Green represents approximate course paralleling the coast.  Course based on coastal observation and angle on Polaris.

[AdriftAtSea]

But Joe, Cap'n Smollet said:

We are going to ignore Massachusettes and the fact that Georgetown is several miles inland from the ocean.  Let's just pretend we want to sail from the lat-long of Georgetown to the lat-long of Portland over 'open' water.

[Joe Pyrat]

I was responding to your assertion:

While that would be one way to do it, it would be far longer a distance to sail, as you'd be doing the two legs of the triangle, rather than the hypotenuse. 

The intent of the graphic was to demonstrate that I would, be sailing, roughly, the hypotenuse.

Regarding the original parameters:

We are going to ignore Massachusetts and the fact that Georgetown is several miles inland from the ocean.  Let's just pretend we want to sail from the lat-long of Georgetown to the lat-long of Portland over 'open' water.

I don't see where I would be in conflict with this basic premise.  I am offshore, not using the ICW so I would not be in violation of the "open water" requirement, and I did ignore that Georgetown is inland.  If you are referring to the fact that my theoretical sailing route in green went around Massachusetts, OK, it was a quickie, ignore that part of the route and just go straight.  I would not be using a GPS, only something to give ma an angle on Polaris and, depending on what else you want to limit the use of either my radar or binoculars to periodically observe the coast.

[CapnK]

In case it matters to anyone why a "big boat sailor" is here.  A) I am a little boat sailor stuck in a big boat body.  B) my customers ask questions discussed here.  This provides me with insights into questions, thinking, and solutions.

  Just glad you are here Norm.  Thanks  ;D

Ditto. :)

Hey - we 'outed' Norm. lol ;)

As to the original post - good thinking, John, and a neat idea for the calculators. I'm one of those people who gets sleepy when doing thinking about math, so it'll take me a while to unravel all of those sofistycated formuli up there and really understand it. :)

Right now, I'd most likely wind up doing what JoeP talks about - set a course offshore of the nearest cape, sneaking in for an observation when near it to confirm my DR, and/or nearing shore again when my sights/latitude indicate that I am close to where the destination was.

Inbetween approaching land, I'd have the GPS taken apart, as I tried to fix the cursed thing and make it work again... ;D

[Captain Smollett]

First Point:

I really, REALLY like JP's idea - for when it will work (which is admittedly a LOT of the time).  It's a low tech solution that is time tested.

There are some caveats, though:  One, you may have cloud cover and cannot get that Polaris site right when you really need it.  Two, you have may to make the trip as quick as possible due to a sick or injured crew member, or some critical failure on the boat.  In the SAMPLE exercise, you do have a nice coastline to follow, but what about otherwise?  It could get tricky, and sailing to the lat then following it E or W could add a bit of time to the trip.

Just some thoughts to throw out there.

Second Point:

There are many places where one may wish to follow pre-selected "waypoints" without the luxury of visual aids.  South Pacific reef rimmed islands come to mind, or even a poorly marked North American channel in fog.  True, both are circumstances that prudence MAY demand an alternative plan.

My point in introducing this thread was to:

(a) present the underlying technique the GPS and other nav computers use to compute course and distance when you know the lat and long of your starting point and destination, NO MATTER the scale or the conditions (or whatever other technique might serve as well or better).  If I chose a poor example to set up my hypothetical, please don't let that detract from the fact that knowing how to do this is a GOOD technique to learn (if for no other reason than just to build navigational confidence).

(b) to 'connect' with the navigators of the 'old days' that did stuff like this all the time, without GPS or even calculators.  Like Joe Pyrat's example, the technique listed at the head of this thread has been in use on the high seas on sailing vessels for hundreds of years.  If it were not really useful, I doubt it would have stuck around long enough or been deemed important enough by Nathaniel Bowditch to include in his masterful collection of PRACTICAL seamanship.

(c) to reiterate that reliance on electronics is, in my HUMBLE opinion, not the safe, prudent approach.  I know of boaters that routinely go 'to sea' without paper charts aboard, don't know rule of thumb techniques and certainly don't practice cel nav.  They follow the little blip on the chart plotter - that's navigation to them.  I merely wanted to emphasize that using a GPS was cool, but if it DID fail, one was not LOST with the waypoints one selected to follow.

In the end, when it comes to learning new tools and techniques, we must all pick and choose which we think we will find useful and which we won't.  I will post the links to the calculator programs here on sailfar (when they are done).  If anyone wants them, the will be free.  If not, for any reason, not-clicking a link to download a file is ALMOST as easy as clicking it.   ;)

[CapnK]

John -

As well as posting links to the software, would you consider doing up a simple tutorial for those of us here who are admittedly ignoramuses? ;D Maybe put in which calulators it'll work on, where to get them, and how to load your programs into the calculators? I like the idea of having a yet another backup method for navigation.

BTW - approx how much does one of the calculators cost?

Thanks for the expanded description of what you were posting about - I understand much better now.

Signed -

Ignoramus #1

;D

[Captain Smollett]

As well as posting links to the software, would you consider doing up a simple tutorial for those of us here who are admittedly ignoramuses? ;D

Absolutely.  Free tech support - but only for SailFar members!.   ;D ;D

Maybe put in which calulators it'll work on, where to get them, and how to load your programs into the calculators?

Right now, the code will only work on the TI-Voyage 200 (ya gotta love that name for a calculator to use on a boat, eh?).  Programs written for the older TI graphing calcs (such as the very popular TI-89) will work on the V-200, but ones written just for the V-200 will not work on the older ones.

But the V-200 is an AWESOME calculator.  I have been extremely impressed with it.  To give a brief idea of what this puppy is, it has the same family processor as the original Macintosh desktop computers had (M68000 family). Uh, that means this little handheld calculator is roughly equivalent to one of those, but with modern software, flash memory, etc.  It's a heck of a device.  Well worth the money, and there are TONS of useful programs for it.  I bought it in 2004 at the specific recommendation of one of my clients for the project I was doing for him, and as I say, have been impressed.

BTW - approx how much does one of the calculators cost?

The best recent price I've seen for a V-200 is $172.  The Celesti-Comp runs close to $500.  So, with my (or someone else's) sun/moon/planet/star epherimides, site reduction programs, and other programs like the rhumb line one discussed in this thread, you could have the rough equivalent to a Celesti-Comp for over $300 cheaper.  That's what I am moving toward.

Thanks for the expanded description of what you were posting about - I understand much better now.

No problem.  Actually, I saw something in one of your earlier posts,

Right now, I'd most likely wind up doing what JoeP talks about - set a course offshore of the nearest cape

that I thought would help clarify it further.  How are you going to determine that course to the nearest Cape?  That was the whole point of this exercise .... compute the course and distance when you know the geographical coordinates of the endpoints.  If your position and the destination (your Cape) are on the same chart, you should be okay measuring it off the chart. BUT, if they lie on different charts and there is significant different in latitude between your position and the Cape, trying to get the course this way will be technically incorrect.  The issue is: "Is such a course incorrect enough to cause a problem."

I meant it as just another tool, and not one to replace simpler techniques when they are adequate or appropriate.

[Joe Pyrat]

The tutorial idea is great.  Hmmm, The University of SailFar.   :)

[oded kishony]

Check out this article about the effect of solar emissions on GPS.

http://www.washingtonpost.com/wp-dyn/content/article/2007/04/07/AR2007040700916.html

Oded

[AdriftAtSea]

Key line from the story—A major electromagnetic storm at the end of October 2003, for instance, had some GPS units down for as much as 19 hours.

That's why I have a sextant, charts and other traditional navigation tools on-board.  :) 

[Captain Smollett]

Thought this important enough to lift from another site and repost here, especially for Chesapeake area sailors.  The GPS coords given are for Pax River NAS, and anywhere within 35 nm may be effected.

THE GPS NAVIGATION SIGNAL MAY BE UNRELIABLE FROM 01 APR 08 - 31 OCT 08 DUE TO INTERFERENCE TESTING ON GPS FREQUENCIES USED IN SHIPBOARD NAVIGATION AND HANDHELD SYSTEMS. SYSTEMS THAT RELY ON GPS, SUCH AS E-911, AIS AND DSC, MAY BE AFFECTED WITHIN A 35 NM RADIUS OF POSITION 38-15-41N, 076-26-01W DURING THIS PERIOD. GPS USERS ARE ENCOURAGED TO REPORT ANY GPS SERVICE OUTAGES THAT THEY MAY EXPERIENCE DURING THIS TESTING VIA THE NAVIGATION INFORMATION SERVICE ( NIS) BY CALLING (703)313-5900 OR BY USING THE NAVCEN'S WEB SITE'S 'GPS REPORT A PROBLEM WORKSHEET' AT WWW.NAVCEN.USCG.GOV"

[newt]

That is really interesting...I had my GPS go haywire last November at Baca Grande in SW Florida. Suddenly showed us out in the Gulf when we were almost to Burnt Store Marina. It was a charter, and the charter company just shrugged their shoulders and said "sunspots".
After the crew settled down, we did got out the paper charts and did a fix on a couple of buoys and vola', we made it home ;D.
All the more reason to learn the old ways to navigate.