Compass Navigation run on obtuse triangle

[CT-Rich]

Seems to me that you should take a surface bearing before dive and swimming the reverse on the on the way back. If visibility 50-100 feet a beacon on the anchor line will get you good enough. If this is a dead reckoning situation, you could plan out how far you were out were swimming on the original heading and have pre-plotted return headings based how you far you swim left (a bearing of 270) of your original course. Prior planning prevents poor performances. If you are running some sort of search and we are only talking a few hundred feet, with no obstructions (like a sand bottom) you might try running a line and then your return vector is based on winding in the line. Math skills are supposed to deteriorate before you become aware of narcosis, so trying to calculate a return vector will be hard unless you do the math topside.

 

[Motojack]

Unless you can do the law of sines calculations in your head, if you dont want to backtrack or guestimate (like I do), you can complete the parallelogram. Swim back 57ft due South at 180 deg heading then left 30 ft at 135 deg heading

Jack

 

[CT-Rich]

I get 81 ft at 165°. YMMV Too bad that road flares don't work underwater.

Actually, they do...

https://www.youtube.com/watch?v=r-SKYwOc0Fk

 

[NAM001]

I did a compass course contest in my younger days, the rules were go north for 5 minutes and then turn 90 degrees left for 5 minutes and then find your way back. The issue of 5 minute legs called for a 45 degree turn for a return course. We did the run in pairs. one navigated and the other towed the flag. The run is not an easy one to do. As time is distance only if you maintain constant speed. on the first 2 legs. The third leg can be done at any speed. It was ok for me as I was ding the nav but the poor guy towing the flag was beat by the end of the run. I had rocket fins and did not know my own strength so to speek. At the time they had much more thrust than my buddy's fins and he had the flag for drag. The unknowns you are concerned with provides a lot of learning in the end so long as you keep the basic course simple. like others have said you shouldn't need a log table to do it.

I am looking at running a underwater compass course involving an obtuse angle. I know all the particulars (side lengths, angles) but I am trying to figure out how I would execute this course without all the knowns, a real live situation.

Assuming I can accurately measure my swim distances and there isn't any current:

Starting at a point, say a boat anchor, swimming due North on a 0 deg heading for 57 ft.
I vector left and swim 30 ft on a 315 deg heading.

Beside surfacing and looking to see where the start point at the beach or boat is, how would I determine what my return vector is to get back to my start point?

Doug