We have developed a data logger to record the speed, course, and wind speed/direction simultaneously for the “Transitioning to Low Carbon Sea Transport” project in the Marshall Islands implemented by GIZ. The recorded parameters can be used to create polar plots to compare the performance of different sailing vessels. The device is open source, arduino based and works off-grid:

Data logger mounted on the kubaak of a traditional Marshallese canoe (Photo: E. Kokmeijer)

The logger can be mounted to any vessel. A detailed documentation and manual of how to build one can be downloaded here. One of the first tests was done on Proasis back in 2021:

Unfortunately, the conditions were not favorable with off-shore winds and lots of shifts in strength and direction (the wind shifts can be seen as the wavy course lines on the upwind tacks). In addition we were still using the small polytarp sail and the small leeboard.

Due to the bad conditions and the limited number of data sets recorded, the polar plot can only be seen as rough estimate of Proasis performance. The performance was further reduced by the tiny sail and the small leebard. We didn’t managed yet to conduct a another test with the new sail and leeboard but we expect the improvement to be at least 30% compared to the polar plot below.

The top speed of Proasis was recorded at 13.1 knots so far. This video shows sailing at 8-9 kn, which is something we score on a regular base in a good breeze.

The limiting factor for the speed is usually the sea state, not the stability. The Baltic Sea is known for very steep waves in winds of 20 kn and up, causing huge loads and a lot of spray at high speeds. Usually we slow the boat down to 8 kn at 20-25 kn of wind for comfort reasons.

As can be seen in the polar plot, the upwind performance, especially the tacking angle, is something we were not happy with at the time we recorded the data. The poor performance can be mainly attributed to two main reasons:

  • The sail we use was a 30€ second hand polytarp sail with lots of wrinkles, and a shape far from ideal. With 15 sqm it was to small, too. We already made a nice 19 sqm sail and are quite happy about it.
  • The leeboard was built 30% smaller than designed due to a measurement error. During the spring refit in 2023 a larger one was built and included into the hull. This greatly improved upwind sailing.

As mentioned above we didn’t manage to conduct a new speed trial yet but it would certainly be interesting to the the differences. We hope to present new data in 2024.