Figuring out how to do back-bearings

From: rospa10 (wilmes2@mindspring.com) | Date: 2004-11-15 21:24:13 UTC

This weekend I tried to find Walking Back the Cat l.b. in Wellfleet,
MA. I just want to run my seeking technique by all of you and ask for
advice. 2 objects are given as bearings. The box is a certain degree
position from each object. I walked in a circle around one reference
point until the correct reading was shown on my compass. I then kind
of paced backwards to a spot that looked like it might hold a
letterbox. Then had my husband do a rough compass reading from the
second reference point. In other words, we were rather unscientific
to say the least. I tried to think of the search in terms of
geometry: the lines from reference points to letterbox are the rays
of an angle, with the l.b. as the endpoint. It seemed like we should
have each had a compass, then backstepped from a reference point
until we bumped into eachother. This would be where the box is
hidden. I did not find it but shall return in warmer brighter spring
time weather. Any comments on your experiences/techniques when
searching for back-bearings boxes? This was my first experience.
Thanks!
Catlover/teacher/gardener

Re: Figuring out how to do back-bearings

From: capecodletterboxer (capecodletterboxer@yahoo.com) | Date: 2004-11-15 21:48:08 UTC

I did the same thing with the same box. walked around that field for
over an hour trying to find it. and there was 3 of us with 2
compasses. Came up empty too. i emailed the placer and she was very
nice...told me how to do it but havn't had a chance to get back up
there. email her. thats your best bet :)
-CCL

Re: Figuring out how to do back-bearings

From: John (jprovetto@earthlink.net) | Date: 2004-11-16 04:14:11 UTC

I do this a lot. In surveying and mapping it's know as either a
resection or cross-bearings. One way to do it is to stand at one of
the sighting points and face in the bearing direction. Find a
natural landmark to walk towards. Before you begin walking in that
direction set the compass to the other bearing. Walk towards the
natural landmark until the second one lines up.

In the case of Walking Back the Cat, you could stand at Landmark #1
and face 212 degrees (32 + 180). Walk in that direction with 139
set on your compass and stop to check Landmark #2 as you get close.

Another option is to stand far away from landmark #1 facing 32
degrees and walk towards it with 139 set in the compass.

This is nothing. I once had to set targets along Newark Bay so that
a tug captain could line up a drilling barge to do test borings on a
precisely coordinated spot. It's all based on the same thing.

Good luck,

John