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P F wrote:
> What this coastal nav course proposed was taking the same three 
> corrected bearings but plotting from the fix position onto clear 
> material from a point on the plastic sheet representing the side 
> opposite to the land � the seaward side. So three position lines 
> radiating outwards.
>
> Then placing this clear sheet upon the chart and adjusting it until 
> all three position lines are placed over the features they point 
> towards � and beyond. You can immediately see the advantage � there is 
> no ambiguity about the fix as the triangle proposes; the fix is a point.
For this purpose a nice instrument was constructed: the protractor or 
"station pointer". The station pointer consists of a divided circle with 
three legs and was used mainly for sextant observations using beacons on 
shore. The legs could be adjusted by either a vernier or drum 
micrometer. The two measured angles (or reduced bearings as in this 
case) could be set on this instrument, after which the whole instrument 
could be placed on top of a chart of the area. After moving the 
instrument around until the three legs crossed the beacons on the map 
the middle the station pointer would then be your position.

Examples of the instrument can be found on my web-site:
http://www.dehilster.info/instrumenten/stationpointer1/index.html
http://www.dehilster.info/instrumenten/stationpointer2/index.html

The first one comes with a whole range of plotting aids like a 
push-button pin and a cross-hair with pencil hole. The second one simply 
has a ruler in the centre with a small notch in it.

Nicol�s


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