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Trevor Bell wrote, about the sinking of Rangitane in 1940-

"I agree - this is getting interesting. I acknowledge that the first 
waypoint was nowhere near the great circle - that was the intention of the 
naval control service routings - to sail off the normal direct routes but 
what the calculations have shown is that the total distance using the 
different methods varies by only a very small percentage.

Having re-read the 1941 inquiry into the Rangitane sinking I can confirm 
that the waypoint coordinates I have given are correct but I realise that 
there was another error in my previous post: I said that the NCS told the 
captain to sail a great circle route between waypoints. This is wrong - he 
was told Mercator but the captain said at the inquiry that he may have 
sailed great circle. From various other enquiries I have made I understand 
that it was virtually impossible to sail a great circle because of 
continuous changes in heading so the great circle was broken up into a 
series of rhumblines. If he had sailed an approximated great circle, this 
makes the position of sinking (see previous post 11695) much more acceptable 
at about 35nm, but still off course.

Just to lay another issue to rest - there has been some discussion in other 
posts about me using the term 'whole circle' instead of 'great circle' - 
sorry about that, it comes from my background as a civil engineer in which 
we use the term 'whole circle bearing'."

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If she was commanded to sail a rhumbline (Mercator) course to waypoint 1, 
that would have been at a course of 93.3º. When she reached the longitude 
where the sinking occurred, at W175º 22', the latitude would be S36º50'. In 
fact, she sank at a latitude of S36º58', just 8 miles further South. That 
would be exactly compatible with the ship steering that Mercator course of 
93.3º, but getting deflected a bit to the South by the South-East going 
current of 5 to 10 miles per day. We can conclude, then, that she was doing 
exactly what she had been instructed to do. (In practice, courses would be 
rounded to the nearest whole degree).

Was that sensible, though? In the absence of any wartime dangers, from 
Cuvier (not Curvier) Island, she would be expected to take a great-circle 
path to Panama, which was 6352 miles at an initial course of 92.4º, which 
would later be adjusted throughout the passage, at intervals. Note that this 
initial course was only 1º from the course that was actually specified, as a 
supposedly anti-interception measure! So she had been instructed to set out 
in almost exactly the same direction that an enemy vessel would be expecting 
to find her! Presumably, the most dangerous parts of such a passage were 
near the beginning and near the end, when vessels would be concentrated, 
scattering from the departure point and converging on the destination at 
Panama. It would seem most sensible for a ship to diverge from the 
great-circle, to one side or the other, immediately after leaving port. But 
it seems that no such divergence was programmed until later in the Pacific 
crossing.

If Rangitane had simply followed that great circle, by the time she reached 
the longitude of W175º22, where the sinking occurred, she would have been at 
a latitude of S36º23'. She was sunk at S36º58', only 36 miles further South 
than that. Indeed, she may have been intercepted at a much earlier time, and 
followed, which would have been easy to do, as her speed from Cuvier seems 
to have been no more than about 10.5 knots. Why so, for a 16-knot vessel?

This analysis appears to raise more questions than it answers.

George

contact George Huxtable, at  george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. 

   

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