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Dead Reckoning

5K views 33 replies 19 participants last post by  nickmerc 
#1 ·
I've had my boat for about 4 years and haven't actually taken her on a "real" trip. Done some local overnighters but I haven't actually planned a trip to, say the Statue of Liberty or the Hudson River.
My question is really: Do you use Dead Reckonning to plan your trips? My familiarity with dead Reckoning is totally limited to the coastal cruising course given by the local coasty Aux. And it was mostly PB'ers. So How does a sailor plan a dead reckoning course without knowing which way the wind will blow? I can plan to sail due north and estimate my speed will be 5.0 Kts, and then drop the mooring and find that the wind is right on my nose and that I need to do some serious tacking. What then is the benefit of my having made my DR?
(Take it away, Boasun, Dog, Smack, et al.)
BP
 
#2 · (Edited)
Actually the DR line is the track line that you have plotted between waypoints. (waypoints are derived from your preplanning of the trip).
Doing the DRs and actual fixes will tell you what and how the local currents are affecting your vessel. There are many good books that will give you the knowledge on how to do this. One book is "Piloting & Dead Reckoning" by Shufeldt & Dunlap. Then you have 'Chapman's' & 'Bowditch' also, plus a few others.
Though you are following your planned route, you can depart from your planning if you so desire. You have the boat for good times and adventures... So sticking to a perfect plan is not always desirable for adventures.
 
#3 ·
Hi BP,

From Red Bank, to The Statue is more Piloting than Ded Reckoning. All the channels are well marked, you are never out of sight of land to obtain bearings/fixes from, Unless of course you get some very poor visibility or Fog.

For a trip up the Hudson from Sandy Hook Bay, I might plot my desired course. Then once you're in Sandy Hook bay, and know the sailing angles you can overlay ( plot) your actual course made good and speed taking fixes off the channel bouys, or by taking bearings off charted land objects. Use the Depth sounder as well. Fix your position at regular intervals ( one hour)

You can also then extend your new ded reckoning plot, if you want to recalculate based on the actual sailing angles.

Again, I think this is more of a piloting challenge, So you could simply fix your position at regular intervals. There's plenty of fixes available in those waters.
This way, if you lose visibilty, or need to radio a position...or need to alter course...and head somewhere else, you have a starting point plotted.

With GPS technology and affordability many people simply rely on redundant systems...I have a chart plotter and a hand held, and usually only keep a paper plot anymore when offshore.
 
#5 ·
I'm sure that you will get a lot of answers on this, but the way that we approach a trip seems to be consistent with most other sailors.

As boasun indicates, you establish a series of waypoints that you would like to achieve. You can enter them on a paper chart, a GPS, or a chart plotter. Regardless of the media, it's the same process. Of course, no plan survives action (von Moltke), so when you get offshore, you may find that you have to deviate from your intended course. In fact, you can virtually count on it due to current, wind direction, leeway, etc. Keeping track of those deviations is what DR is all about.

For instance, you intend to sail 000 deg, but can only make 040 because you're going upwind. As soon as you make the change from your intended path, you note the new course, speed, and time on the chart. At some point in the future, you advance your position on the chart and that is where you should be, but probably aren't. The other factors affecting your actual course are wind, leeway, etc. This is where the "art" in DR comes in. The better you know how your vessel acts in various conditions, the better you will be able to estimate the other factors. This is where boasun indicates that fixes are used. Near land, you can plot fixes and running fixes from known reference points on land; offshore, it's more of a challenge and usually relies on celestial sights.

IMO, DR is becoming a lost skill due to the ubiquitous GPS In many cases, we ignore all the external factors pushing us off course and simply plot a new course to the waypoint. For instance, on Victoria, we have a laptop running chart software, a handheld Garmin, and a iPod Touch with Navionics software. And I still DR just to keep up skills because a) the laptop can freeze, b) the Garmin batteries can die and c) the iPod isn't waterproof. IMO, DR is an essential skill that's being ignored. While at University, I took the Navy ROTC navigation course (DR and celestial) and have benefitted immensely. The CG Auxiliary offers similar courses (my uncle taught one). Every boater should have a working knowledge of DR.

True story: 30 years ago, just after I became engaged to Victoria, we were sailing up a channel in Ocean City, NJ at night. We had a beam wind and an outgoing tide so I was offsetting course to accommodate the conditions. The buoys were unlit and I couldn't see them due to background land light. Halfway up the channel, there was a loud crash and a nun buoy came rolling down the starboard side. Vicky and I still disagree on whether the collision was superb DR (my view) or idiocy (her view).

Another story: When I was 19, I DR'd the family Cat 30 from Ocean City offshore to Block Island with 2 friends. We noted each significant course change on the chart. When the wind veered to the west, I worried that we'd be offset east, missing Block Island. So we headed more northerly (noting time, course, speed), intending to intercept Long Island near Montauk. The plan worked and we turned east at LI, eventually arriving at BI without incident. DR is simply the techniques associated with position estimation.
 
#8 ·
.
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True story: 30 years ago, just after I became engaged to Victoria, we were sailing up a channel in Ocean City, NJ at night. We had a beam wind and an outgoing tide so I was offsetting course to accommodate the conditions. The buoys were unlit and I couldn't see them due to background land light. Halfway up the channel, there was a loud crash and a nun buoy came rolling down the starboard side. Vicky and I still disagree on whether the collision was superb DR (my view) or idiocy (her view).
.
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I say superior DR, great story. To the OP I have nothing to add but I am looking forward to the replies to your question.

John
 
#6 ·
I've had my boat for about 4 years and haven't actually taken her on a "real" trip. Done some local overnighters but I haven't actually planned a trip to, say the Statue of Liberty or the Hudson River.
My question is really: Do you use Dead Reckonning to plan your trips? My familiarity with dead Reckoning is totally limited to the coastal cruising course given by the local coasty Aux. And it was mostly PB'ers. So How does a sailor plan a dead reckoning course without knowing which way the wind will blow? I can plan to sail due north and estimate my speed will be 5.0 Kts, and then drop the mooring and find that the wind is right on my nose and that I need to do some serious tacking. What then is the benefit of my having made my DR?
(Take it away, Boasun, Dog, Smack, et al.)
BP
Bruce - dude, I'm flattered. But I must make it clear that I don't know squat about REAL sailing stuff. I'm just the color-commentary for the fun and adventure of sailing - not the nitty-gritty stuff.

So, there's NO WAY I'm in the same league as Boasun. Dog? Sure. But not Boasun.

But thanks for the props. I'm sure it made Boasun roll his eyes. Heh-heh.
 
#7 · (Edited by Moderator)
IF you are sailing on well marked waters all you have to do is select waypoints and sail to them however you can. If you really want to get your geek on you can plan your course like you are a power boat, look up the current for your route and adjust your course to steer accordingly. Then, just before you leave you can replan the route with the forecast winds and the courses you will have to sail to get to the waypoints. If the forecast info is close and you are are really good at DR you should be very close to your revised plan.

I used to fly all over the country with a compass, stop watch, and winds aloft forecasts. It is amazing how close you can come to your plan. I am not as good on the boat (yet).
 
#9 ·
We used to cruise from Florida to the Bahamas and back with dead reckoning and a RDF. I like to keep the skills available if needed, but the GPS is a great tool that takes the excess course made good as a sigmoid curve and turns it into an efficient straight line when you are dealing with current vectors. Take care and joy, Aythya crew
 
#10 ·
Where I sail in the Sandy Hook Bay area, it is a confluence of channel markers, range markers ( a little further out) and other locating features. So I'm pretty sure of where I am. and I do have a GPS. I was just curious to see if Dead reckoning was , excuse the pun, a dead art, and if others actually used it. I do like Nickmerc's idea and may try to plot a course, mod it to the actual conditions and see what happens.
BP
 
#11 ·
One minor detail: When you set your waypoints. DO NOT set them on the buoys but right of center of the channel. That way you don't find out which is prone to more damage, Your Boat or the Buoy... :eek:
 
#13 ·
DR is the process of using all info that is available to determine where you are. Usually this is only relevant to courses that take you away from visible constant landmarks such as shoreline detail. When you can see stuff that is noted on your charts, that's pilotage. DR is somewhat different.

If I have a fix derived from whatever source and then sail on for, say, a day, the course I have steered, the speed I have achieved, the leeway my vessel makes and so on are calculated together to provide a DR position of where I think I am now.

To this process, I add a GPS fix as one of the tools I use in the DR process because that provides, like a landmark or a celestial fix, a definite reference from which to start again. The course, speed etc should be constantly updated and whenever one substantiially changes, a new DR position should be noted.

A DR also provides a reference from which to plot a sight reduction when using celestial navigation because one needs to have a reasonable idea about where you are for the celestial data to be meaningful.

So resultantly, on any voyage away from visible landmarks, I use DR constantly to cover my a$$ for when the electronic toys stop working. Which eventually they will.

Well, that's my viewpoint anyway . . . .
 
#16 ·
Tempest,
Speaking of Fog, sailed into a fog bank up near Roamer Shoal with a friend the other day. Visibility dropped to about 200 feet. We decided to sail back the way we came and broke back out about 20 minutes later none the worse for wear. We had visions of getting "T-boned " by Seastreak the high speed ferry to NYC. Verry interesting.
BP
 
#17 ·
"We had visions of getting "T-boned " by Seastreak the high speed ferry to NYC. "
In general the express ferries are probably the most belligerent and dangerous vessels in NY Harbor for other craft. When they first came on the scene they seemed to think they owned the water--and the Staten island ferries and USCG Governor's Island ferries had to give them a comeuppance and make a few incident reports to adjust that attitude.
Since the express ferries really aren't constrained by draft or manueverability in the same way that the older ones are--they often really don't have right of way when they try to claim it. Don't let 'em bluff you, it's legal to torpedo those express ferries. You might even get some applause from the older harbor pilots.<G>
 
#18 ·
Deductive... reasoning...

Unless you are speaking in dialect and saying that you "reckon that someone died" you need to call it "Ded. Reckoning" which is just shorthand for Deduced Reckoning.
i.e. you Deduce your location or position now from the historical record you kept every so many minutes in your log and on your paper chart.
You have been logging direction with any changes, speed, depth, bearings on any identifiable land or fixed nav. buoys or structures. You might add in a position you obtained from a passing vessel if you are out wandering around the oceans.

From every information and data source, you then deduce your present position. The entry you make on your chart will show the level of confidence in any given "fix."
Sidebar: that wonderful lat and lon you get from your old GPS is one piece of data, too.

That's not all there is to it... but at least we can get away from citing someone's death as a necessary part of position finding! :rolleyes:
 
#20 ·
My habit requires that I continue to say that I used Dead Reckoning for many years, but I like the "Ded" reckoning derivation as explaind above; however, in a place like Raritan Bay where you are looking at visual references for your entire trip up to the Verrazano Narrows and to "The Lady", PARRALAX is the tool!. Parralax is the visual phenomenon of near objects moving at a relative faster speed at our view than far objects; therefore, when driving along the highway, The trees at the roadside pass quickly and the houses in the distance move by more slowly and the moon seems to not move at all. If you continue to sail directly torward a marker or bouy then it will stay at the same location compared to a more distant object, like a pylon of the Verrazano Bridge, during your approach. If you plan to sail between two closer marks, then these marks should each appear to move away from your destination on the horizon as you make headway. Parralax is a helmsman's tool more immediate and with more direct feedback than dead reckoning when coastal cruising with visual marks and a visual coastline. Take care and joy, Aythya crew
 
#24 ·
If you continue to sail directly torward a marker or bouy then it will stay at the same location compared to a more distant object, like a pylon of the Verrazano Bridge, during your approach.
This process is called "sailing up a transit" IIRC. The two landmarks that stay in line is the "transit".
 
#21 ·
Indeed....Captain.... since you can actually sail backwards in the hudson..if the winds are light and the current is running against you.
or simply sail in place...going nowhere...

I call it my sailing simulator...you can tack and gybe..heel over etc..but the only water flowing under the keel is the river....SOG is zero
 
#22 ·
Tempest - You did it. Here's my going backwards Hudson River story.

1978 - I raced for Villanova and we were at West Point on 420's. There was no wind and we were scattered all over the river. All of us were intently, athletically, racing backward. And then a ship came around the corner. You can really work up a god sweat sculling a 420 out of mid channel. :)
 
#26 ·
As Olson34 pointed out, the term "Dead Reckoning" comes from the oldest navigation technique known. You "deduce" where you are from figuring out where you were and adding such things as steering error, current, leeway etc. Deduced became shortened to "ded", but since that looked weird it was eventually pretty universally changed to "dead".

It is not a system for laying out your course in advance, that is a plot. It is only used to figure out where you might be when out of sight of navigational aids or land. In the days before gps or even loran, on the boats I raced offshore, each person would take a half hour trick on the wheel. After you were relieved you immediately went below and made your log entry, averaging the course you believed you steered and the average speed you believed you held. Of course, if you changed course significantly (a tack or a jibe or a major wind shift) another crew member made an entry for you at the time it happened.

Old time navigators were incredibly skilled (or at least the good ones were) at taking that information and grinding in the various other factors, such as current (filling the head with water and dunking a thermometer to see if you were in the Gulf Stream yet),including the previously measured leeway the boat made under the particular conditions being experienced and even using past experience with a particular helmsman who might have a tendency to exaggerate his skill sailing the boat to windward. Those guys were amazing - and navigation was a full time crew position.

When I took my first navigation course in the late nineteen fifties as part of my NROTC training we were taught to lay out our line of position and put a circle with a dot in the center along the line with the time and mark it with the words "fix" when we had a confirmed fix, either through bearings on known objects or through celestial. If it was a dead reckoning mark it would only have a half circle around your DR point and would be marked DR. All of that is of mostly historical value now with the incredible chartplotters available these days, but it is certainly a skill worth having in case the gremlins (or a lighting strike) mess with your electronics. That's why I keep an old battery powered GPS that only gives Lat and Lon in an insulated metal box. Accurate Lat & Lon is much more than I used to have and with the paper charts I always carry I feel I can get somewhere with ease no matter what happens to the rest of my instruments. And with regular fixes from the old gps I won't have to remove the rust from my dead reckoning skills.
 
#27 ·
I will sometimes take the old garmin from my car along on a trip turned off. It does not have any marine charts, in fact even the road maps are out of date. I have found that when turned on the little car icon dutifully shows its location even in the middle of the sound. If I tap the car a screen will show the lat and long. It then serves as an emergency positioning device to be used with charts the same way skip does above.
 
#28 ·
When in doubt, wake the crew up, have a consultation as to what the chart reads, what the instruments read. Plot where you are in the moment! There is nothing wrong about people with no sense of direction ( great crew criteria)! Ignore what the mind and eyes think is to sail around in circles!
 
#29 ·
Thanks Genieskip, that's an awesome backup plan. Now, time for the insulated box.

Funny, I'm attempting to learn this stuff, and have purchased charts, take them with me and study them all the time at home on the workbench in teh shop. Haven't actually tried to plot a course yet, as I'm on a river and I can easily ID landmarks, etc., visually. However, comma.

Went to a very large, nationwide sporting goods center and was told they don't even sell charts anymore, because everybody's buying GPS units.

I'm not going to get stuck in that rut. I do love my 441s though.
 
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