Compass Navigation run on obtuse triangle

[DiveLvr]

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

 

[Bob DBF]

Off the top of my head, I'd head back about 85' on 165 heading, and look for the boat. I'd be closer to the boat when I surfaced than out at the other end of the dive. All that being said, my dives are usually not so precise that I need to bring a set of trig tables with me.


Bob
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I may be old, but I'm not dead yet

---------- Post added April 11th, 2015 at 08:38 AM ----------

If my trig skills haven't completely gone, by my calculations it is 78' on a heading of 170. Of course by the time I figured that out I would have been OOA, and have to come up at the wrong end of my dive anyway.

If you are that particular, look around for a PADI Nav-Finder, it is a circular slide rule that lets you track headings and distance and will calculate a heading and distance to your start point. Mine is for display purposes only, but it does work if used properly.



Bob
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My hero is "Wrong Way" Corrigan.

 

[Hatul]

Good luck measuring distances under water and working this out there. Be sure to take your trig tables and pencil and paper.

 

[g1138]

I'd head back somewhere between 180 & 135 with some Kentucky windage.
Note some landmarks off the left peripheral on my way out on the 0 heading and try to spot them on my way in.

Navigation is an art form. Some art looks like sh-t.

Similar swim pace and use time as a measure of distance. Assuming no current.

Realistically, unless you're trying to hit a knife stuck in the sand at your starting point, getting within 100ft of the starting point is pretty stellar by me.

 

[Jax]

Parallel Lines, a Transversal and the angles formed. Corresponding, alternate exterior, same side interior...

---------- Post added April 11th, 2015 at 07:00 PM ----------

.
.
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Bob's right. I get 167, close enough to 170.

 

[waterpirate]

Can you execute this drill walking in unknown terrain? Basic orienteering. I would practice on land before a "wet" run.
YMMV
Eric

 

[Charles2]

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

 

[Jax]

Blinking lights hung on the anchor line do work underwater.

 

[Necklinsberg]

Check out 'navfinders' as used in PADI's underwater navigation specialty course. Use that tool to track your kick-cycles and directions.

 

[radtype]

I'd cheat and go 30 feet on a heading 135 degrees and south for 57 feet. If you have decent visibility, head south for about 80 feet.