Hello, a total newbie here. On my Davis Mark 25, I seem to be able to zero out index error by adjusting the knobs on the horizon mirror with the index arm and micrometer drum set to zero. Is that not correct?
On Homework problem #1, my answer was 41° 47.8’ vs. your answer of 41° 46.8’. 1.0’ is obviously very small, but I’d like to know where I went wrong. Hs 42° 06.4’; IC 1’ OFF =+1, = 42° 07.4’; Dip -2.7’ = Ha 42° 04.7’ Ref -16.9 = Ho 41° 47.8’ vs. published answer of 41° 46.8’
Wonderful introduction Is the micrometer drum set at zero just before the sight of sun? do you turn it clockwise or counter clockwise when sun just touches the horizon
There are a number of methods to bring the sun down to the horizon, and starting at zero while learning is best practice. When adjusting, a c-wise turn of the micrometer drum will increase the reading (moving "up" the arc). When making adjustments at the horizon, by turning the drum it'll be obvious which way you have to adjust to bring the sun up/down to the horizon.
You have probably figured it out by now, but 1.2 - 0.4 = 0.8, or another example 2.2 - 1.4 = 0.8. At 29:23 he does 45.2 - 3.4 to get 41.8' I presume that is what you were referring to.
Well, I will say that using celestial is not like reading a GPS! You don't get an immediate position, but one that is for a time a few minutes previous (depending on how fast you reduce the sight and plot). Celestial is best used on ocean passages, where "right now" positions are not as important as in coastal navigation where they may be lots of obstructions.
As far as accuracy, the more you use celestial the better you get at it. I am usually within 1-3 miles when comparing to a GPS position which is fine for a passage.
the way i understand it, the horizon mirror can be adjusted around 2 axes but the index mirror only has one axis for adjustment. is that correct? and if so, why does the index mirror only have one adjustment? if it had 2, it would be possible to eliminate the index error.
I don't know if anyone else is having this problem, but I'm getting about one new advertisement every minute. Massively annoying, and I don't know how to stop it.
Hello, a total newbie here. On my Davis Mark 25, I seem to be able to zero out index error by adjusting the knobs on the horizon mirror with the index arm and micrometer drum set to zero. Is that not correct?
On Homework problem #1, my answer was 41° 47.8’ vs. your answer of 41° 46.8’.
1.0’ is obviously very small, but I’d like to know where I went wrong.
Hs 42° 06.4’;
IC 1’ OFF =+1, = 42° 07.4’;
Dip -2.7’ = Ha 42° 04.7’
Ref -16.9 = Ho 41° 47.8’
vs. published answer of 41° 46.8’
I think your answer is correct and that Andy made a mistake. It seems he forgot to add 1’ to correct for the index error.
I lost track of comments so apologies for the delayed response. Yes, I forgot to add the IC so you are correct! (correction made in the notes) Thanks!
Wonderful introduction Is the micrometer drum set at zero just before the sight of sun? do you turn it clockwise or counter clockwise when sun just touches the horizon
There are a number of methods to bring the sun down to the horizon, and starting at zero while learning is best practice. When adjusting, a c-wise turn of the micrometer drum will increase the reading (moving "up" the arc). When making adjustments at the horizon, by turning the drum it'll be obvious which way you have to adjust to bring the sun up/down to the horizon.
I feel naive asking this, but how does .2-.4 = .8?
You have probably figured it out by now, but 1.2 - 0.4 = 0.8, or another example 2.2 - 1.4 = 0.8. At 29:23 he does 45.2 - 3.4 to get 41.8' I presume that is what you were referring to.
@@karhukivi thank you! I missed that it was infact 1.2, not .2
I'd already be 10 miles away by the time I did all this. How big is the error margin
Well, I will say that using celestial is not like reading a GPS! You don't get an immediate position, but one that is for a time a few minutes previous (depending on how fast you reduce the sight and plot). Celestial is best used on ocean passages, where "right now" positions are not as important as in coastal navigation where they may be lots of obstructions.
As far as accuracy, the more you use celestial the better you get at it. I am usually within 1-3 miles when comparing to a GPS position which is fine for a passage.
@@thenavstation how long does it take you from start to position fix usually
Out of interest. ?
@@thenavstation I am starting an rya celestial nav course in a week or so
So am trying to get some prep done.
@@farqfarq2225 Reducing a sight typically takes me 10-15 minutes at most, assuming no errors which means going back and reviewing.
the way i understand it, the horizon mirror can be adjusted around 2 axes but the index mirror only has one axis for adjustment. is that correct? and if so, why does the index mirror only have one adjustment? if it had 2, it would be possible to eliminate the index error.
The Index Error is a “vertical” error only, so just needs the one adjustment. the Horizon mirror has one adjustment In the other plane
I don't know if anyone else is having this problem, but I'm getting about one new advertisement every minute. Massively annoying, and I don't know how to stop it.