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Old 06-19-19, 09:44 AM   #3
Pisces
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Join Date: Dec 2004
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Sorry Matt, but you are not getting of the hook that easily with the aspect ratio AOB video. You got your observed sizes wrong. If you find that the resulting angle is supposed to be right of 90 degrees on the angle disk then you need to re-asses them. The nominator (observed aspectratio) must be smaller than the denominator (real aspect ratio). Fudging by flipping the numbers may have worked here to get close but does not solve the problem.

Real aspect ratio: 150(.0)m over 28m (using 280 seconds or 4m40s on the time disk) points to 5.357-ish on the distance scale.

Observed aspect ratio: you took 14.6 length vs 2.7 height. You shifted the disks a bit too far resulting in 5.44. Proper placement of the marks would be 1460 distance against 4m30s time, pointing to just over 5400 on the index. 5.407 according to a calculator. Your nominator being larger than the denominator does not allow to compute the inverse sine. The division of observed over true aspect ratio must be below 1. I don't blame you though. I am sure it is hard to keep a good focus while making videos and providing commentary on what you are doing. Mistakes are easily made.

Personally I eyeball the observed length at 10m33 to be 14.3, and height at 10:59 to be 2.8. Resulting in a aspect ratio of 5.1(07) (using 1430 against 4m40s on the time disk) Making my inverse sine calculate to 72-ish degrees. But one has to keep in mind that the same inverse sine result applies to angles equally distant to 90 degrees. The sine of 80 degrees is the same value as the sine of 100 degrees. So the AOB based on my measurements could also be 108 degrees.

Now, me being able to compute a result does not mean that I am right in my measurements. From the view to the target when you can see that is showing the backside of the forward bridge structure. Indicating AOB is larger than 90 degrees, so close to 108. But infact a little time later the map shows the AOB to be 99. Which goes to show this method is not really appropriate to AOB angles close to 90 degrees. You will only get a ball-park result. On-bow or on-aft AOBs work out more precisely. But then beam-width also comes into play. Yeah, science is messy.

And if people have not noticed yet. It really helps to know your tables of 6(0 seconds) to come up with the equivalent mark on the time-disk representing desired numbers. Like 28 not having a mark on the time disk. But considering a full lap on the disk is a multiplication by 10, it is the same mark as 280. Knowing that 280 = 240+40 = 4*60 +40, it is then located at 4 minutes and 40 seconds.
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