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-   -   Dipping a Light (http://www.sailnet.com/forums/seamanship-navigation/84781-dipping-light.html)

davidpm 03-09-2012 08:56 AM

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?

Tempest 03-09-2012 09:29 AM

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.

davidpm 03-09-2012 11:41 PM

Re: Dipping a Light
 
How close did you get

Capt Len 03-10-2012 01:37 PM

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.

flyingwelshman 03-10-2012 05:28 PM

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.

Tempest 03-10-2012 06:03 PM

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.

flyingwelshman 03-10-2012 06:57 PM

Re: Dipping a Light
 
http://i493.photobucket.com/albums/r...istanceoff.jpg

hellosailor 03-11-2012 07:00 PM

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."

Shawnibrion 03-31-2012 03:12 AM

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.

CaptainForce 03-31-2012 06:40 AM

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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