Chart errors (contd).

Several earlier posts covered inaccuracies in charts. Last week I came across yet another example in Cala de Portinax, a bay at the north end of Ibiza in the Balearics. This screen shot from my Navionics chart shows depths in a fair amount of detail: yet the numbers were wrong by a factor of three or four. IMG_2586 Because of the modest depths shown, we motored in with great trepidation in Olivia Jane, a Beneteau 43 with a 2 metre draft. Yet we found the depths in the middle of the bay were all in the 11-13 metre range and even close in to the rocky shore we anchored in 8 metres. In contrast, the C-Map chart on the cockpit plotter gave no depths at all inside the bay, which is a safer option than mistaken information. We’ve fed this back to Navionics and await a reply, but the nagging question will always remain in future, even if this proves to be a rare mistake: can we trust the inshore information on these charts? What if the mistake had been the other way, showing 11 metres when only 2 metres was there? Do other brands of charts have similar errors? Continue reading “Chart errors (contd).”

Maskelyne v Harrison – the longitude show in London

Harrison's third clock
Harrison’s third clock

 

We finally managed to take in the excellent Ships, Clocks and Stars exhibition at the National Maritime Museum, Greenwich, which runs only until 4 January. Among other things, it puts the record somewhat straighter on the eminent 18th century Astronomer Royal, Nevil Maskelyne, chief villain of Dava Sobel’s best selling nautical history of the race to measure longitude at sea. Maskelyne was the man who conspired against John Harrison, the genius who built the first true chronometer, or so the narrative goes in Sobel’s book, Longitude.

Not so, it is clear from the detailed story set out in the exhibition, Continue reading “Maskelyne v Harrison – the longitude show in London”