Dead Reckoning - Page 3 - SailNet Community
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post #21 of 47 Old 05-04-2012
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Re: Dead Reckoning

When dead reckoning in Arctic waters remember the sun is in the north at night and in the south during the day.
I'm confused?
The compass doesn't work if it's rough weather and mud bars don't reflect radar and waves do, so use the clutter dial. Large ice chunks caught on the bottom can indicate current in the fog and big waves can come from any direction.
I agree, ever see a compass free float no matter what?

Dick
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post #22 of 47 Old 05-04-2012
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Re: Dead Reckoning

In the 70's and 80's, I DR'ed from Ft. Lauderdale, Fla all through the Bahama's. At the time Loran was out but was way to costly for me. I was barebone cruising but didn't know any better. Didn't have a problem except one time crossing the Gulf Stream back to Ft. Lauderdale. Left West East about 8 o'clock at night in perfect conditions only to have a total change in weather about 4 hours into the crossing. Long story short made landfall next day in the afternoon in West Palm Beach. Dropped the hook just inside the Intercostal Waterway slept for the rest of the day and night and finished my trip the next day.
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post #23 of 47 Old 05-04-2012
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Re: Dead Reckoning

One tip I remember from my class is that in dead (or ded, as in 'deducted') reconing is to aim for shore a few miles to one side of your destination. When you make landfall, you will know which way to turn. If you aim for your destination and miss by a little, you won't know which way to turn. There are methods (which I am sure I would forget if my GPS pooped out) that you can use to calculate how much your COG deviates from your heading (due to current, sideslip, hand steering error, etc).
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post #24 of 47 Old 05-04-2012
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Re: Dead Reckoning

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One tip I remember from my class is that in dead (or ded, as in 'deducted') reconing is to aim for shore a few miles to one side of your destination. When you make landfall, you will know which way to turn. If you aim for your destination and miss by a little, you won't know which way to turn. There are methods (which I am sure I would forget if my GPS pooped out) that you can use to calculate how much your COG deviates from your heading (due to current, sideslip, hand steering error, etc).
Doesn't this put you beam to breaking waves in the surf zone? There is a video on the Farallones thread showing these dangers. I would plot a course for the sea bouy that marks the channel to the inlet as they are often as visible as a low lying landfall. Sorry, don't mean to hijack the thread.

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post #25 of 47 Old 05-04-2012
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Re: Dead Reckoning

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Doesn't this put you beam to breaking waves in the surf zone? There is a video on the Farallones thread showing these dangers. I would plot a course for the sea bouy that marks the channel to the inlet as they are often as visible as a low lying landfall. Sorry, don't mean to hijack the thread.
Would depend on the conditions. You would only have to approach close enough to identify where you are on the coast. That could be miles off shore. The point is, that you could spend a lot of time going in the wrong direction looking for some clue about where you are on some featureless coast. This is all assuming that you don't have GPS.

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post #26 of 47 Old 05-04-2012
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Re: Dead Reckoning

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There are methods (which I am sure I would forget if my GPS pooped out) that you can use to calculate how much your COG deviates from your heading (due to current, sideslip, hand steering error, etc).
We still folks how to account for set and drift and leeway.


Not sure how to deal with hand steering errors.

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post #27 of 47 Old 05-04-2012
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Re: Dead Reckoning

I guess I must be gettin' old. For me, at least, there's no thrill to DR my way to any destination. I have 3 GPS's, all work perfectly, and the accuracy is uncanny. Sure, I can use charts, and most of the time find my way to anyplace I want to cruise to. But, when the first consumer version of Loran-C became available I quickly ditched the RDF I had been using and never looked back. When GPS plotters became available, the same scenario was repeated. I purchased the GPS, ditched the Loran-C and never looked back.

Now, despite the fact that I'm old, it doesn't mean my mind has gone to Hell. I find it much more interesting to sail using the latest technology, thereby providing me more time to enjoy the scenery, watch American eagles soaring over Aberdeen Proving Grounds, and keeping a sharp vigil for barge traffic in the bay. I would rather be sailing at night, knowing exactly where I'm at at all times, and having that 3G Radar image superimposed over the GPS Plotter display.

Sitting down with a pile of charts, plotting courses, etc... is the last thing I want to do while sailing--even in the open ocean. Yep, the charts are on the boat, sitting in waterproof cases where they're dry and safely stored. So, if I lost all 3 GPS plotters, and all 5 batteries suddenly went dead, I'm confident I could find my way home--especially in the confines of Chesapeake Bay. I'm equally confident that if the same failures took place 200 miles off the coast of the lower Delmarva Peninsula, finding a particular inlet, especially while cruising on a sailboat in marginal weather, would be a WAG (wild-assed-guess) at best. Having covered that shoreline from end to end for many, many years I can assure you that it all looks the same--no markers to determine your position within 30 miles in any direction.

Guess I am getting old!

Cheers,

Gary
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post #28 of 47 Old 05-04-2012
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Re: Dead Reckoning

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Originally Posted by Flybyknight View Post
When dead reckoning in Arctic waters remember the sun is in the north at night and in the south during the day.
I'm confused?
The compass doesn't work if it's rough weather and mud bars don't reflect radar and waves do, so use the clutter dial. Large ice chunks caught on the bottom can indicate current in the fog and big waves can come from any direction.
I agree, ever see a compass free float no matter what?

Dick
How do you navigate the northwest passage without using GPS? The compass must be unreliable. And to take say a noon shot with celesitial navigation must be very inaccurate (sun rotating around the horozion in the summer). How did early explores navigate in these waters?

Last edited by casey1999; 05-04-2012 at 01:58 PM.
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post #29 of 47 Old 05-04-2012
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Re: Dead Reckoning

Strictly navigating by GPS is not the best way to get from pt A to pt B if you are crossing a long distance with a cross current. In that case (as in crossing the Gulf Stream) you should maintain a heading at right angles to the current. The GPS will head you increasingly into the current to maintain a straight line. It is much better to plan on drift while in the current, making up distance on either side of the current. This requires calculating current speed and drift so your course made good is actually an S. There is a good explanation of this in the Explorer Chartbooks for the Bahamas. This is similarly true in plotting great circle routes using Mercator map projections where waypoints need to be on the curvature, not on a direct line connecting distant points.

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post #30 of 47 Old 05-04-2012
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Re: Dead Reckoning

Relying on the the GPS to tell you anything more than a position or bearing to a point can lead you astray It's telling where you've been and CMG and thats got little to do with where the bow is pointing .Set, drift and inconsistant steering need deducing either on a plot or by the seat of your pants. I'm of the latter school and have changed them more than once. .
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