Solstice Planking

On the 21st June at noon local time the sun, directly overhead it seems had no problem tracing an imaginary path around the world at 23.5N latitude as the Earth rotated creating the Tropic of Cancer on Winter Solstice (for us down under).summer-solstice-large  Image – NOAA

My planks are not so easily directed and prefer meridians following a great circle path. Consider a plank running along a lines of latitude on each edge. The sphere’s radius is smaller on the pole side but the planks edges are the same length so it is deflected towards the equator.

The rugby ball approximates the Eric’s hull shape, the first green tape almost follows meridian and starts to kick up (downwards on the ball) at the ends. The orange and subsequent yellow tapes are displaced significantly down towards the ends.

P1040353S

As my planking progresses in parallel runs similar to lines of latitude it starts to get very unhappy as tension and compression forces built up in the opposite edges. This compounded by wind tension as the planks are twisted. Running a wider batten  flat against the hull surface establishes a happy curve for the planking to follow.

P1040286S

Cutting off bits of boat is not so happy.

P1040311S

The unhappy planks are soon replaced and with happy planks, much easier.

P1040348S

P1040347S

Despite happy planks progress is so slow, a tack to change course may be needed, but not just yet. The GGR 2022 has been announced by Don McIntyre in the TCP magazine a free e_magazine which is worth a read.

GGR 2022

For the GGR 2018 my goal is to improve on Suhaili’s time in 1968 of 313 days according to wssrc. Based on a distance of 30000NM the average speed was 4 knots. .
PT 1

Displacement yachts seldom exceed a speed to length ratio of 1.3 , with 1.5 just possible. The typical average Speed to Length ratios is 0.9.

Marcaj.C.A – Aero-Hydrodynamics of Sailing

Achieving an average Speed to Length of 0.9 would result in a RTW time of 265 days for an Eric design or 221 day for a Joshua Design.

PT2


 

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