NavList:

David C.  For your delectation, a genuine Mercator Sailing (as opposed to a textbook example) between Muckle Flugga, the most northerly point in the British Isles, and Traena Island, Norway.  I calculate it must have been completed in the Houlder Bros/Ore Carriers iron ore carrier MV Oremina in late 1957 whilst enroute in ballast from Port Talbot, S. Wales and Narvick, Norway, to collect Swedish ore brough overland via the Lulea-Narvik Iron Ore Line, the Gulf of Bothnia being frozen in winter.

I found it in an old notebook of my father’s, and it is the only example of his navigational prowess I’ve got.  The values appear to tie in with Norrie’s (Terrestrial Spheroid Compression 1/293.465), probably the ship’s copy.  Although I was being taught logarithms in school using bar notation around the same, my father preferred to stick with 9s.  This is hardly surprising when you realise he first went to sea from West Hartlepool aged 15 in 1930 and was taught to navigate by ships’ officers who might well have first gone to sea around 1900.  His neatness is exemplary and is probably the result of the strict British schooling system of the 1920s.  When adding and subtracting he keeps his 1 carries in his head, something I’ve never been able to do.

Being a lowly Air Navigator, I find I must revise Mercator Sailings every time I look at them.  Meridional parts allow you to mathematically model the trigonometry of a Mercator chart where latitude scales stretch, and meridians are parallel.   Diff long/diff MP gives you tanCo.  Having got Co, distance = diff lat x sec Co.  Purely by flook, you could check this particular sailing, because diff long=diff MP, so Co is 045, and distance =diff lat x root 2. DaveP

File:

File: