Cabo Finisterre Offing

After starting,  so easily said,  a course of approximately 221 T must be set to give sufficient offing to Cabo (cape) Finisterre at the South West corner of the Bay of Biscay. Cabo Finisterre ( finis terrae) is translated as the end of the earth,  it was the extent of the know world in roman times.  This is very fitting as we steer well clear of the known world to the Southern Ocean. The real issue is to avoid entrapment in the Bay of Biscay due to prevailing onshore winds.

Finis

The coast around here is known as Costa da Morte, the coast of death, apparently due to the number of wrecks along its rocky shores exposed to the Atlantic. So the idea is to stay well clear.

My initial planning is based on long term averages from Pilot Charts. First, from the Route Planning list, waypoints are placed on the chart.

Capture

The cyan line to the right is the planed course to waypoint 2 from the start. The round symbol with feathers of direct length indicate the probability in percentage of wind from each direction. The number of feathers indicate the wind speed in Beaufort Scale Force. The number in the centre of the symbol indicates 3 % calms. Current sets to the South at about 0.6 knots. There is a chart for each month.

pilot

The distance from start to waypoint 2 is 428 Miles and this can be multiplied by the percentage of wind for each of the wind directions from the wind symbol on the Pilot Chart. Then subtracting the course from the wind direction gives a distance in Miles at each Point of Sail.

PoS 1-2.JPG

So roughly for this leg and based on my true wind angles for each point of sail it is easy to multiply the total distance by the percentage for that point of sail and find a total for each.  I’ve taken Beat as 50 degrees true wind angle, the apparent wind will be less. Eric will not like beating so probably best to sail free.

I’ve entered some rough polars (boat speed for each point of sail) and determined a rough average speed.

Not shown here is that the wind averages are F3 – F4 (7 – 15 knots) and 3% calms.

The more detailed results give miles for each point of sail and at each wind strength. Example below.

beau

Wind speed is determined with true wind angles to heading, incrementing at 10 degrees.

This is a very rough approach, it gives a quick idea of what to expect  and useful for preliminary work on the sail wardrobe and rig


 

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