Two sights were taken last night almost an hour and a half apart - skies were clear and it was through a dish of water as an artificial horizon.
I had to put 1 shade (a light one) onto the Index Mirror because of the brightness of the MOON - so that I would be able to see both limbs come together.
Even though I know where I am, I went through the sight reductions without checking for mistakes as you might interpret with the results - as I am a little off.
If this was taken mid passage, no problem on being less accurate. Sometimes there is too much feedback when you compare the sight reduction to actual. It is better to rely on your wits without feedback on a real passage to test your accuracy on the final step - namely landfall.
My Notebook Page...
MOON Sight Reduction #1...
MOON Sight Reduction #2...
From the Almanac...
From Pub. 249, No. 3...
The Plot...
Forensic Review on Accuracy...
Well - a bit off. About 11 or 12 nm from Actual. Not what I was expecting. Remember I said that I completed the Sight Reductions and Plot without a serious review and took the results as being correct. If I didn't have the feedback from knowing where actual was I would not have known that I was off so much.
Also, remember at the beginning of a passage accuracy is not the main issue. Accuracy is an issue when making landfall, not when you have 2000 nm to go.
Usually when you make big mistakes it is pretty obvious, as you will be tracking your DR and unless you have just gone through a storm and been seriously blown off course - you will know pretty fast if there was a big mistake. Little mistakes may not be known unless you review your work carefully.
If there was no serious storm issue, remember that your DR may not be close to your position if you didn't factor in current and leeway.
So, did I make any mistakes? There is always a chance that I did and they are usually stupid ones.
My gut tells me that I felt that the sights were good sights and I should have had better accuracy so I will review and find out.
Again if we were on a real passage and at the beginning of it without knowing actual - I would have accepted the results and gone from there. If we were close to making landfall - check and check again to be as sure as possible on the results.
Corrected Sight #1...
Corrected Sight #2...
Corrected Plot...
Final Comments...
Well you can see on the corrected Sight Reductions and Plot that I did make the same mistake on both sights - and it was a dumb one as well. Even though I had the signs right for both d Value subtractions - I added the numbers instead!!!
The corrected results are much better showing that I was 2 to 3 nm off of actual. If this were for real and making landfall - it would be very good. But remember that this was done in my backyard with an artificial horizon with no waves and under very good conditions. The same will not be the case on the water.
Also, if we were really making landfall - is it day or night?
If it is day - you can be keeping a good lookout beginning before expected landfall and taking any opportunity for another sight to confirm position. You don't want to be going past your destination.
If it is night - you want to slow down to make landfall in daylight and to avoid getting too close to landfall especially if their are no lights on that side if it is an island, or if their are shoals or other hazards that must be avoided.
The things that may impact your decision to review your worksheets is where are you in the passage - beginning or end, or your gut feel on how good a sight you have taken. Knowing that you have a good sight comes from experience and as well from the progression that you have observed when taking multiple shots for a sight.
