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What you gain in accuracy of observation by this method is often lost in the lack of precision in your plotting instruments.  It also takes quite a bit of time to take horizontal sextant observations.

 

  I have done it, it works, but it is much slower.  All of my plotting tools are indexed to the nearest degree, with eye-ball interpolation good to about 0.25 degrees.  I don't see much use in measuring to the 0.1' of arc for such work.  Surveying is another game altogether.

 

Jeremy

 

See: NP 100 Extracts from THE MARINER’S HANDBOOK Edition 1.1 – December 2009

http://www.ukho.gov.uk/productsandservices/paperpublications/documents/np100%20edition%209%202009.pdf

 

I have attached p87&88

Horizontal sextant angles

11.8

Where great accuracy in position is required, such

as the fixing of a rock or shoal, or adding detail to a

chart, horizontal sextant angles should be used when

practicable. The accuracy of this method, which

requires trained and experienced observers, will

depend on the availability of three or more suitably

placed objects. Whenever possible about five objects

should be used, so that the accuracy of both the fix

and the chart can be proved.

A horizontal sextant angle can also be used as a

danger angle when passing off–lying dangers, if

suitably placed marks are available. This method

should not be used where the chart is based on old or

imperfect surveys as distant objects may be found to

be incorrectly placed.