I do not see how two ships can alter their bearings when stopped Lord Mersey


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Dave Gittins

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Mar 16, 2000
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Personally, I don't use the formula. I just look it up in Norie's Tables, as Captain Smith and most British mariners of his day did.

Norie's uses 2.095 * square root of the height of eye in metres. I make that 1.1566 * square root of the height of eye in feet.

It's hardly worth worrying about it when we remember that the earth is not perfectly round, refraction varies quite a bit and even the height of eye varies during a voyage as fuel is used up. Also, some older books used a British nautical mile of 6,080 feet (1,853.184 metres) and newer books use the modern nautical mile of 1,852 metres.
 
May 12, 2002
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Hi Paul,

I asked this question a few years ago, having obtained a similar coefficient myself. Apparently the values of 1.13 to 1.17 include a semi-empirical correction for refraction by the atmosphere.

Cheers

Paul
 

Dave Gittins

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Looking more closely at Norie's Tables, I see its tables include an allowance for average conditions and refraction.
 

Paul Slish

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Thank you Dave and Paul. So the 1.13 to 1.17 multiplier is an attempt to account for refraction. Nories uses 1.16 in round terms.

As far as the earth no being perfectly spherical, I don't think it would make much difference when we are talking about distances in nautical miles of 30 or less. That is pretty small compared to the earth's radius of 3959 statute miles.
 
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