NavList:
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Re: Silico Sea 26 AND 28
From: Peter Fogg
Date: 2004 Jul 4, 17:11 +1000
From: Peter Fogg
Date: 2004 Jul 4, 17:11 +1000
Good on you, Mike.
"What is meant by Force 4 regarding wind?"
This may refer to the Beaufort Wind Scale, a table
recording the velocity of winds and their speeds.
Beaufort No: 4, Moderate breeze, 11-16 knots, sea height 1
metre, 'small waves becoming longer, more frequent white horses'.
"hints on solution using the sailings given Lat and Long?"
There are a number of methods to estimate the distance
across an arc of the earth's surface. They differ in simplicity and
accuracy. The simplest is possibly to measure the distance on a chart or map or
globe. Then there are a number of mathematical formulae. The least involved
assumes the surface is a plane, and has that name. There are other methods.
Possibly the most accurate uses meridional parts and differences, tables
that take into account the spheroid shape of the earth.
A rhumb line method calculates the distance as a straight
line across a chart that uses mercator projection. Its advantage is that the
course is expressed as a straight line across that chart, and the bearing of the
course does not change as lines of longitude are crossed. Its disadvantage is
that it is a longer course across a curved surface (the earth) particularly
courses to the east or west in high latitudes. The alternative is a Great Circle
calculation that gives you the shortest distance, but the bearing will change as
it is followed, unless that bearing is due north or south (lines of longitude
are Great Circles) or east or west along the equator (the equator is also a
Great Circle). Use a globe or some ball of convenient size marked with these
lines, compared with a map showing mercator projection, to assist in
conceptualizing this.
If you enjoy this then find out how to calculate all of
them - none is particularly difficult (although that is always easier to say
once you've done it!) and practise them all. Bowditch has much information, as
always, and is freely available chapter by chapter online. Other books on
navigation may present material in an easier form to follow.
----- Original Message -----From: Mike BurkesSent: Sunday, July 04, 2004 5:22 AMSubject: Silico Sea 26 AND 28Hi folks! I have 2 questions regarding SS 26 and 28: First I cannot find the archives on them so I appeal to you folks!SS 26: Problem no 1: What is meant by Force 4 regarding wind? It must play a key role in the solution I.e. used in conjunction with the current?Ss 28: Problem no 1: Any hints on solution using the sailings given Lat and Long? I cannot help think I am missing something obvious!I know these are old problems but I enjoy working them most challenging! Your replies would be most appreciated!!Yours Truly, Mike Burkes
