NavList:

Greg Rudzinski wrote:

"A time sight of Arcturus combined with a latitude by Polaris would have been part of the twilight star observation set."

Thank you Greg, as a CN "newbie" here - I appreciate such sage advice.

This morning I wondered how accurate would a DR be, using a Traverse Table.

A "flat earth" land surveyor can use them over short distances, but what about going "over the horizon" at sea I wondered.

So back to the Titanic and some fun with numbers.

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Experiment: Find the Iceberg !

Compare a DR between a Traverse Table and Rhumb Maths.

41:51:54" N, 047:52:18" W  (Geoff's location for Titanic C.N. fix)

Now determine location of Iceberg:

Course = 266 Degrees, Distance = 91.74 NM

Using Traverse Tables:

Distance to nearest NM = 92 NM
From Traverse Table, D.Lat = 6.4'
Dep = 91.8
From 42 Degree Page of Traverse Table, Dep of 91.8 -> D.Lon = 124'

Add 124' to  47:52:18" W
Longitude =  49:56:18" W

Subtract 6.4'from 41:51:54" N
Subtract           0:06:24"
Latitude =        41:45:30" N

41:45:30" N, 49:56:18 W = Iceberg location using Traverse Table
41:45:30" N, 49:55:00 W = Iceberg location using Rhumb Maths [1]
41:45:30" N, 49:55:00 W = GPS referenced Iceberg allision [2]

Delta between Traverse Table and Rhumb Nav = 0.97 NM !
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[1] Rhumb Calculator:
http://www.movable-type.co.uk/scripts/latlong-nomodule.html

[2] Collision Point by Samuel Halpern, July 2007
http://www.glts.org/articles/halpern/collision_point.html
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My use of the term Allision:

From the English Oxford Dictionary:
1843   Merchants' Mag. Dec. 543   The term allision applies to the act
of one vessel striking against another; and the term collision, to the
act of two vessels striking together.

An Allision With An Iceberg
http://www.titanicology.com/AnAllisionEvent.html
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Brad Morris wrote:

"The navigation officers on the Titanic did not use any stars, unless you count the Sun as a star."

Brad, here are relevant quotes selected by Paul Hirose, with the day number of the U.S. Inquiry into the Titanic sinking at the end of each quote.

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"When you take stars you always endeavor, as they did that night, to
take a set of stars. One position checks another. You take two stars for
latitude, and two for longitude, one star north and one star south,
one star east and one star west. If you find a big difference between
eastern and western stars, you know there is a mistake somewhere. If
there is a difference between these two latitude stars you know there is
a mistake somewhere. But, as it happened, I think I worked out three
stars for latitude and I think I worked out three stars for longitude."
Boxhall, US Day 10.

"Capt. Rostron said it was a very, very good position. After I had
worked these observations of Mr. Lightoller's I was taking star bearings
for compass error for myself, and was working those out. That is what
kept me in the chart room most of the time. I was making computations
most of the time." Boxhall, U.S. Day  10

"Yes; we took stellar observations and also observations for compass
deviation... No, sir; I did not take the stellar observations myself. I
took the time for them, and Mr. Lightoller himself took the
observations of the body... We just took a set of them at sunset, or
just as it was getting dusk, when the stars were visible. It was about
6 or 8 o'clock that we took them... After that I started working out
the observations... in the chart room; in the chart house... I was
there alone until 8 o'clock... I did not finish them. Mr. Boxhall took
on then and finished  them." Pitman, U.S. Day 4.

https://www.titanicinquiry.org/
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Regards, Geoff Hitchcox, Christchurch, NZ