Daily Archives: March 25, 2015

Heading, Drift, Route …. Some explanations from Pierre -

The compass on land or at sea gives the heading in relation to the magnetic north, which we must remember does not always correspond to the geographic north. This angle between the true north and the magnetic north is called magnetic declination and the angle varies a few degrees every year. When moving from a map to a compass and vice versa you have to take this magnetic declination into account.
A boat which navigates at a certain speed toward a point follows a route on the surface of the water to a heading (the angle in relation to magnetic north). This boat moves on the water and is subject to different forces which can prevent it from following its trajectory, such as wind or currents, and which produce drift, i.e. the route the boat follows on the surface may not correspond to the route at a certain depth. Any floating craft, whether it has an engine, sails or oars is subject to the same drift, keeping in mind that a very tall craft which is high on the water or a light one which has little of its surface on the water, will have drift caused by wind. Serge’s boat, Middleton, is an example of the latter.
So, it is of utmost importance to take these elements into consideration when calculating the heading given to a boat so it can get from one point to another, and to monitor the changes in the strength of the wind and currents in order to modify the heading so he will not miss the point to which he is heading. GPS has brought a precious aid to navigation because at any time the navigator can know what his position is relative to the seabed.
At night or during periods of rest, without anyone at the oars to give Middleton speed, Serge’s boat will drift according to the force and the direction of the wind and current. Serge can compensate a bit by activating the moving parts of the boat: the rudder blade or rudder and the drift (a small plank that slides vertically in the water and helps to somewhat reduce the “lateral slide” or drift of the boat. Naturally, Serge has to wake up often to check that he has not drifted too far from his heading and if that is the case he changes the trajectory by regulating the appendages.

Pierre Katz
Serge covered only 30 nautical miles in the last 24 hours, and there was always a wind and swell that relentlessly pushed him westward, rather than to the north. Conditions should improve today or tomorrow. Follow his trail to Sainte Marie.