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


Thread: Dipping a Light Reply to Thread
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Topic Review (Newest First)
03-31-2012 11:21 AM
jackdale
Re: Dipping a Light

You can also use a nomograph.

03-31-2012 09:31 AM
Tempest
Re: Dipping a Light

Captain,

You are correct, the above chart reads in Miles. Here's the full link to the website that contains that particular chart.

Sailtrain: Navigation and Chartwork, Rising and Dipping Lights.
03-31-2012 07:40 AM
CaptainForce
Re: Dipping a Light

flyingwelshman, I like the convenience of the chart that you presented, but please help me with a simple clarification. By international standards of measurement I believe the symbol "M" designates meters; however, this can't be the case with this chart. I'm assuming the data within the body of the chart is miles. Is this correct or would these be Kilometers? Take care and joy, Aythya crew
03-31-2012 04:12 AM
Shawnibrion Lighthouses are indicated on a chart with the height of the centre of the light (in metres) above MWHS. Be mindful though that both the lighthouses below are 40m high, but the yacht on the right might be expecting to see a tall tower from the lighthouse on the left.
03-11-2012 08:00 PM
hellosailor
Re: Dipping a Light

Useful, especially when you are looking for a distant light, even the markers on bridge towers, and someone says "I see it. No, wait, I don't. No, I do. Wait, I don't."

Now you know they've dipped the light and a quick look-up gives you the range. Or you can put a pencil line on the chart with your compass, i.e. where you expect to dip the light, and when that happens you know "We are here. Ish."
03-10-2012 07:57 PM
flyingwelshman
Re: Dipping a Light

03-10-2012 07:03 PM
Tempest
Re: Dipping a Light

Yes, the formulas yield you the distance from each object to the visible horizon, added together they give you the distance from the Light. Take a bearing draw a line that distance and bearing and you should arrive at your EP. Take a look at your depth..see if it matches up to the chart. I've come pretty close when using it. You can also use tables that are already pre-calculated, just match up the two known heights in a box to see the total distance. Height of tide will make a slight difference..a pitching sea will have an effect.
03-10-2012 06:28 PM
flyingwelshman
Re: Dipping a Light

Is this another term for establish distance off a known object?

I learned these formula:

If you are working in feet:

d=1.17 x √height of object(ft) + 1.17 x √height of eye(ft)

In metres:

d=2.1 x √height of object(m) + 2.1 x √height of eye(m)

(d = distance off in nautical miles)

You have to take tides into account where they apply.
03-10-2012 02:37 PM
Capt Len
Re: Dipping a Light

Let me guess . If you are looking up at a light house you know to be 300' high, you are pretty close.
03-10-2012 12:41 AM
davidpm
Re: Dipping a Light

How close did you get
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