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Re: What constitutes Round The World (RTW) ?
From: Bill Lionheart
Date: 2021 Jan 31, 15:50 +0000

Well here is the definition from The ISAF/ World Sailing Speed Record Council (ISAF/WSSRC) which is what matters for sailing records.

To sail around the World, a vessel must start from and return to the same point, must cross all meridians of longitude and must cross the Equator. It may cross some but not all meridians more than once (i.e. two roundings of Antarctica do not count). The shortest orthodromic track of the vessel must be at least 21,600 nautical miles in length calculated based on a 'perfect sphere'. In calculating this distance, it is to be assumed that the vessel will sail around Antarctica in latitude 63 degrees south.
A vessel starting from any point where the direct orthodromic distance is too short shall pass one single island or other fixed point on a required side so as to lengthen his orthodromic track to the minimum distance. No starting point will be permitted more south than 45 ° south. 1 degree of longitude at 63 degrees south will be taken as 27.24NM

I think if we were navigating on a featureless spherical ocean with no special points we might devise a different and more mathematical definition. How about this: A closed path on the sphere is a circumnavigation if there is a great circle such that when points forming the poles are deleted, when if the great circle is considered as the equator, the path can be deformed continuously on the punctures sphere to the great circle.

Not really tested this completely, but on my featureless sphere what I mean is you are free to choose any equator, then you can weave N and S of the equator as long as you wind once around the poles. You have to adjust your equator so that your path does not include either pole. So on my definition if applied to the
actual earth you can do a pole to pole circumnavigation choosing the prime meridian (for example) as your " equator". The path will always be at least the length of a great circle (as deforming it, by definition of a great circle as a geodesic, makes it longer).

Hope this is of interest.

Bill

On Sun, 31 Jan 2021 at 14:31, Bob Crawley <NoReply_Crawley@fer3.com> wrote:

I've been avidly following the various RTW races Voyage Jules Verne and Vendee Globe. I applaud the superhuman abilities of the RTW sailors although, in a pedantic moment I wondered if they were really RTW.
Obviously if the course passed through the antipode to the start point then it would have covered at least a great circle and would be RTW. However, both the VG and VJV course (and Golden Globe) is the five capes to port leaving Antarctica to starboard which is same as sailing around Antarctica (non trivial I know). Even though the total distance sailed exceeds the circumfrence of the Earth the entire course can be fitted into less than one hemisphere so at no point does it encompass a great circle. To do so the route would need to go north of the South Island of NZ.
So are these races really RTW and, if not, how should one rigourously define such a route?
BobC
52N 1E

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