Join Date: Nov 2007
Location: SF Bay area
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Re: practicing with sextant on land
Fitting the vector representing the travel distance and bearing between two lines of position, I think, is similar to St Hilaire intercept method with the Azimuth and bearing between the deduced reckoning latitude and the observed latitude.
I think I see what you mean. In a running fix you move an LOP, keeping it parallel. In the intercept method, you do something similar although you don't draw the first LOP, just the one that results after it is moved to the intercept.
I've tried a couple of artificial horizons, one was a mirror levelled with a digital level and the second was a bucket of water. The bucket was more convenient to move to sunny areas but is rippled by any breeze. The mirror took a few minutes to level each time it was moved but isn't affected by brreeze.
Apparently you can get an artificial horizon from Davis that is a liquid tray but also has a wind shield. It's a bit decadent for my tastes.
One thing you might try is heading to English Bay and taking sights from the beach. Sometimes the thing you're shooting will be over the western horizon and then you are set. If you want to shoot something that's over the land, you can use the Short Dip tables; I think it's Table 22 in Bowditch but I'm not sure. I've been meaning to go and do this for a while now, but never seem to get around to it. If you feel like meeting up one evening for some twilight sights, let me know.
s/v Laelia - 1978 Pearson 365 ketch
s/v Essorant - 1972 Catalina 27