NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: I wish I had thought to bring 'that' along with me...
From: Bruce J. Pennino
Date: 2017 Jan 24, 23:02 -0500
Bruce
From: Bruce J. Pennino
Date: 2017 Jan 24, 23:02 -0500
Hello:
Some time back I needed to measure my height of eye from the deck of a
ferry. I estimated it on board, but before I left I looked online at a photo of
the ship noticing the “depth of loading lines” (I forget the proper name). Also
notice how tall a person appeared on deck. Using this info as a rough
scale, easy to estimate elevation of each deck floor above the load line. Close
enough all things considered.
Bruce
From: Brad Morris
Sent: Tuesday, January 24, 2017 10:33 PM
Subject: [NavList] Re: I wish I had thought to bring 'that' along
with me...
Hello David
You wrote
Number 17 on your
list – determining an accurate height of eye is ...
Once I tell you how
to do this, you will undoubtedly smack your forehead.
Measure it
directly. Use a string and a lead weight and dangle it over the side until
it touches the water. Make a knot at eye height. Measure the
string.
If you can't touch
through water directly, use the string to take a series of incremental
measurements.
You want to do this
from both the port and starboard bridge wings, where you are likely to be taking
your observations. Average the two readings. Try to do this just
after the cargo is loaded, in port, while not underway.
When underway, the
velocity of the ship will produce enough drag on the string to cause the weight
to deflect backwards, giving an erroneous measurement (too long). It's
possible underway, but with reduced accuracy. Use a monofilament
line to reduce drag.
Brad
