Spirit of Sark's crew feel the influence of the magnetic South Pole and pore over spreadsheets and data logs in their pursuit of speed
Been busy for a couple of 4 days trying to figure out why we can’t accurately identify our tacking angles. We have had the B&G instruments apart and then read the manual to no avail. We traced the issue back to the gyro-compass but the manual is in German so we are not as confident about taking that apart!
It all started when we noticed a large (20°) difference between the steering compass and our B&G heading. After many hours of investigation we have realised that we are crossing the Magnetic South Pole just 900 miles away at the moment and everything is getting weird, including the crew.
Driving has become challenging with the steering compass reacting so slowly and varying so quickly with the forces at work.
In addition, we have built a series of elaborate spreadsheets to analyse true wind direction, COG & VMC [velocity made good against course to the mark] and VMC rate to help us successfully identify when the wind has crossed our course and hence so we know when to tack. We are using 10-minute averages to find oscillations and two-hour averages to find isobar shifts. Even with this we sailed two hours further into a windshift than we intended yesterday…much to the disgust of the skipper.
Tactically, we are hanging out between the leaders and attempting to work on their respective leads. We are struggling, however. We can’t use leverage against both at any one time because the leaders are split north and south of us. We are excited by a ridge today with no wind in and the chance to close on the leaders as they stop first and we keep going.
We have a wedge-shaped ridge that is wider and deeper to our south. The wind has already dropped and we are hoping BP Explorer will see less than us and grind to a halt or at least slow up. Unfortunately, Imagine It. Done and boats north will be well out of this light wind patch and be in an even better situation than us so we may loose miles to them…