|
Author
|
Topic: CelNav home study
|
Craig001
|
posted November 16, 2014 09:37 AM
I am working through the home study course. I am using a AH with my sextant and a DR within a degree of actual but when I get to the sight reduction I am consistantly around 2 degrees off between HO and HC so when I plot it's way off. I've done it numerous times but every time I am still off, any ideas?
|
|
Capt Steve Miller
|
posted November 16, 2014 10:21 AM
It would be helpful to see your work for a specific sight to try to determine what or where you need help.
Your indication that your DR is within a degree causes me to wonder why you cannot determine a DR much closer than 60 miles.
With an artificial horizon you need to divide the raw Hs in half to obtain the actual Hs.
From: Starpath
|
|
David Burch
|
posted November 16, 2014 10:22 AM
We will need more specific info to track this down.
First, may i ask why the DR you are using is not precisely correct? This you can get from your phone or without GPS you can get it from Google earth.
Then to track this down we would need to know exact times of the sights and the exact location used, then we can compute what you should see to determine which of the two numbers is wrong.
From: Starpath, Seattle, WA
|
|
David Burch
|
posted November 16, 2014 10:23 AM
well,,,, looks like two simultaneous answers. Very glad to see that we agree!
From: Starpath, Seattle, WA
|
|
Craig001
|
posted November 16, 2014 11:06 AM
I was using a DR close to so simulate a real situation at sea. Is there an e-mail address I could send some of work to?
|
|
Capt Steve Miller
|
posted November 16, 2014 11:35 AM
A DR at sea would be normally closer that 60 miles.
Post your work here on the Forum. That way all can benefit.
From: Starpath
|
|
Craig001
|
posted November 17, 2014 03:00 PM
I see what you mean about my DR. I changed them on some sun sights yesterday to my exact location and when I plotting them the fix was within 2 nm. With more practice that should improve, thanks.
|
|
David Burch
|
posted November 17, 2014 03:33 PM
Excellent. Thanks for the update. We are still standing by to help. There are a bit more challenges with the artificial horizon, but i think it would be fair to strive for 1 mi, but that is about the limit with a good metal sextant. Index correction is crucial and you might try our solar method to home in on that. It is especially good for land locked practice.
There are also limits set by the glass covers on the AH if you are using any of them.
From: Starpath, Seattle, WA
|
|
Craig001
|
posted November 17, 2014 04:36 PM
Yes, I did use the Solar correction, I have a Freiberger sextant that I bought used but after making sure the mirrors were aligned it showed no I.C. I usually use both tinted plates since the glass plates always start to get condensation. One of these weekends I will go to a lake not far from here to practice the Dip Short method.
|
|
David Burch
|
posted November 17, 2014 11:34 PM
OK. that should work, but please keep in mind that for dip short procedure to get you close to accuracy limit the input values of HE and distance to shoreline must be very accurate. You can use Google Earth to measure the elevation of the shoreline then add HE to that where you are above the water if not directly measurable, and also use GE to get distance to shoreline under the object. This must be done after the sight, to take into account the proper Zn which you will know from the sight reduction and time. experiment with ± x feet on both inputs to see how sensitive the dip correction is. Also must be computed, not found in tables, as they are (all the ones i know of) too coarse for this.
if you refer to plates that are on the artificial horizon to block out the wind, then they are suspect until proven innocent.
Also of course, need a GPS to know precisely where you are for best test.... or maybe get that from GE as well. and doing it this way, or at home, you can compute the exact Ho you should measure from USNO computer at www.starpath.com/usno.
From: Starpath, Seattle, WA
|
|
|
