Dipping a Light - SailNet Community
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post #1 of 12 Old 03-09-2012 Thread Starter
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Dipping a Light

Just ran into a fun term and concept for navigation.
"Dipping a light".

I've experienced it a few times but never used it for navigation.
Might come in useful some day?
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post #2 of 12 Old 03-09-2012
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Re: Dipping a Light

I've played with it, to see how close I come to estimating my distance off. It's something to do, in the middle of a night watch. I think it's good practice.

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post #3 of 12 Old 03-09-2012 Thread Starter
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Re: Dipping a Light

How close did you get
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post #4 of 12 Old 03-10-2012
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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.
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post #5 of 12 Old 03-10-2012
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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.

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The sea, once it casts its spell, holds one in its net of wonder forever. - Jacques Yves Cousteau
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post #6 of 12 Old 03-10-2012
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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.

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Re: Dipping a Light


1989 Hunter 30'
Southern Georgian Bay

The sea, once it casts its spell, holds one in its net of wonder forever. - Jacques Yves Cousteau
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post #8 of 12 Old 03-11-2012
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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."
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post #9 of 12 Old 03-31-2012
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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.


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post #10 of 12 Old 03-31-2012
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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
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