SailNet Community - View Single Post - What is wrong here??
View Single Post
post #9 of Old 05-03-2010
Senior Member
AdamLein's Avatar
Join Date: Nov 2007
Location: SF Bay area
Posts: 1,939
Thanks: 8
Thanked 7 Times in 6 Posts
Rep Power: 10
Originally Posted by RandyBC View Post
What I think now after more consideration is that the error of 1 degree 8' does not necessarily translate into 68nm between assumed and actual position.
To my understanding, an intercept (difference in computed and observed altitude) is exactly the difference along the azimuth from the assumed position to the celestial line of position.

Actually, it occurs to me you could be plotting the intercept in the wrong direction.

You should be plotting the azimuth line towards the the sun and through the assumed position. Sounds like you are indeed doing this.

If the observed altitude is greater than the computed altitude, then you mark the intercept in the direction of the azimuth. If the computed altitude is greater, mark the intercept in the reciprocal direction. For example, if the azimuth is SW and computed altitude is 20 degrees, then:
- observed altitude 1852' --> intercept is plotted 68 miles SW of AP.
- observed altitude 2108' --> intercept is plotted 68 miles NE of AP.

If you plot it in the right direction, you should be just right.

If you plot it in the wrong direction, then you will be approximately 136 miles wrong.

In general if your error is double one of the numbers involved in the computation, sounds like a positive/negative or direction problem.

s/v Laelia - 1978 Pearson 365 ketch
AdamLein is offline  
Quote Share with Facebook
For the best viewing experience please update your browser to Google Chrome