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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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  #1  
Old 09-23-2010
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Dead Reckoning

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
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Old 09-23-2010
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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.
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Last edited by Boasun; 09-23-2010 at 10:17 AM.
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Old 09-23-2010
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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.
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Old 09-23-2010
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this is kind of a neat site

Dead Reckoning
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Old 09-23-2010
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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.
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Old 09-23-2010
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Quote:
Originally Posted by bruceyp View Post
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.
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Old 09-23-2010
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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).
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Old 09-23-2010
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Quote:
Originally Posted by Sabreman View Post
.
.
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).
.
.
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
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Old 09-23-2010
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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
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Old 09-24-2010
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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
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