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On our way to Cape Town

A nice sailing day! During the afternoon we gradually start to brace a bit squarer, first just a little keeping the ship close-hauled, still doing great speed and heeling heavily to starboard and riding a moderate swell.

Later on, by 17:00h we change our point of sail from to a beam reach, on what it seems to be slightly increasing NW winds. For the moment we kept a course of about 075º and the speed above 10kn. It is forecasted that the wind will shift to the W or even WSW during the next hours. When that happens the idea is to follow this wind for as long as possible, even though at the end it looks like we will be on a straight downwind course to Cape Town. The high pressure system located now between Tristan and Cape Town has been growing bigger, and if we end up close to its centre, that will mean running out of those fair winds just before arrival. But for the moment, what we experienced in the late afternoon was a slight increase on the gusting winds and while facing several little squalls we took away the outer jib and the spanker.

From last evening at 20:00h to today’s eight o’clockie meeting we have been keeping an average speed of 10kn, meaning that the distance sailed was 240nm. It looks like our beloved Europa is getting restless with the proximity of land and her upcoming appointment for the “beauty salon session” during the Cape Town refit. During this fantastic day of good sailing the talks and lectures kept going on. Annukka repeated her explanations about weather and wind systems, and Eduardo also did again his popular discussion about "The Problem of Plastic at Sea" in which he addressed the global issues concerning plastic debris that ends up in the oceans of the world.

Also today, after many days of sail handling lessons and a few introductory talks about celestial navigation, we have reached the point with the navigation talks, to start introducing the use of the sextant and celestial coordinates. The sextant is a navigational instrument used to measure angles with high precision. In navigation the angle in degrees of an object above the horizon is called height and a sextant is an excellent instrument to measure heights. The instrument as such evolved from an earlier instrument invented probably by the Arabs hundreds of years ago during the Middle Ages named astrolabe. The astrolabe was the base to build the quadrant, which evolved to the octant. Both instruments receive their names because the first uses a fourth of a circle to measure angles, while the second uses and 8th of a circle. It was John Hadley who implemented the use of a sextant in 1730. In today's lecture we introduced the use of a sextant and the errors that need to be taken into account when making a measurement, namely the index error (associated to the accuracy in alignment of the mirrors of the sextant), the dip error associated to the height of the observer above the horizon and we discussed for the case of the Sun, the solar diameter error, associated to the intrinsic size of the sun in the sky which depends on the orbit of the Sun. Likewise, during the lesson, we discussed the celestial coordinates associated with the objects, geographical hour angle (also known as Greenwich hour angle) and the declination of objects. With this it was left as an exercise to find the true height of the Sun (after correcting the sextant reading for index error, dip error and solar diameter error. As the day ends and new one starts, the whole situation changes.The wind drops and backs starting to blow from a westerly direction. For a while we are busy on deck changing the sail configuration and bracing to sail on a broad reach.

Geschreven door:
Jordi and Eduardo | Guide

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