I skip the log’s entries until they get to Mauritius Island.
The two vessels sail from Indonesia to Mauritius with no problem, except for a sail being torn on the Zeehaen on 30 August. Their speed is rather slow compared with that of our contemporary yachts. They average 33 nautical miles per day. Given that a nautical mile equals 1.8 km, it totals up to about 60 km. Over 24 hours it gives an average speed of 2.5 km per hour… they’re dragging!
4 Sept. (1642)
At noon we estimated our position as 19o 55' S, 85o 13' E. The wind a moderate to soft breeze. We kept our course west-northwest and sailed twenty-six miles.
About midnight we saw land and thereafter lay to for the rest of the night with reduced sails.Variation 22 degrees 30 minutes.5 Sept. In the morning seeing that the land was the island of Mauritius we made for it and came to anchor there about 9 o’clock. We calculated our position as 20o S, 83o 48' E. We were by our earlier estimate fifty miles east of Mauritius when we saw it.
The business of taking bearings every day at lunch time is a question of life and death at sea. If you don’t know where you are, you are lost and in such case survival is not warranted. The same applies to-day. On TV the sailboats of various sailing races around the world seem to be linked to a supporting team on land ready to go and rescue the sailors wherever they might be on the globe. That is Hollywood like… In any case in 1642 Tasman was on his own and had to rely on his sole capacity to face the unknown.
In order to know your position at sea in those days, you could calculate your latitude (vertical position north-south on the chart) but you had to estimate your longitude (horizontal position east-west). To do so the ‘dead reckoning’ method was used which consisted of giving the time and distance thought to have been covered in one precise direction from a known point of departure, as marked on the chart with a pin. Sure as eggs!
The short last sentence by Tasman on his entry of 5 September 1642 says that, when they sighted land around midnight the day before, the calculations on board made it out that they were 50 odd miles out to sea East of Mauritius. It is only in the morning, at first glance because they knew the place, that they figured out it was indeed the island of Mauritius.
What we have to note here is that Tasman was sailing upon the great ocean with a 50 mile error margin. It means he could very well ‘miss’ a continent, for it is not possible to see any land up to 50 miles away from your deck. You can see something on the horizon up to 7 miles away, no more…
Is there a sailor in the room? Please post your comments!