The chronicle of an adventure

Author: Penny Boviatsou

ECO40 is a Class 40 oceanic vessel (Length overall of 12,0 metres) that was equipped with a data acquisition system for both the met-ocean parameters recorded on-board (i.e. apparent and real wind speed and wind direction, atmospheric pressure, current velocity, air and sea temperature, etc.) and the kinematic characteristics of the boat itself (i.e. speed and course over ground). A team of professors from the University of Rome and the Polytechnic Turin recorded the boat’s movements by using three Leica GR25 GNSS reference receivers. With these they were able to:

• Calculate the height of waves along the ECO40 route by using the boat as a buoy and validate the numerical models of the United Kingdom - based Met (meteorology) office;
• Improve the structural design of the Class 40 sailboat by means of calculating the boat’s dynamic stress and boat material durability during the trip;
• Record the wave characteristics taken from the ECO40’s movements to produce a polar diagram of the boat’s speed, which would be useful for future Class 40 racing boats.

Miceli transmitted the data via satellite for analysing to Professors Paolo De Girolamo and Mattia Crespi of the University of Roma La Sapienza and to Alessandro Pezzoli of the Polytechnic Turin.

On his way back to Italy, after rounding the three capes and sailing for 25,000 nautical miles, the ECO40 capsized at the Equator. Matteo was about 600 miles offshore the Brazilian coasts. He was saved by a cargo ship. When he came back to Italy, he organised a first expedition to try to recover ECO40, which was not successful. After a month, the expedition team tried again and found ECO40 300 miles offshore the Brazilian coasts. Now the vessel is back in Italy.

Fortunately, the data were saved together with the boat and the researchers were able to do the final analysis of the journey.

The sailor’s journey

The planned route was the classic clipper route that runs from west to east through the Southern Ocean, taking advantage of the strong westerly winds. Namely the route consists in passing the Gibraltar Strait, then in descending the Atlantic Ocean and sailing around the Antarctic, at an average latitude of 50° S, from west to east rounding the most famous capes of the world: Cape of Good Hope, Cape Leeuwin and Cape Horn. Finally, sailing the Atlantic Ocean back to the Strait of Gibraltar and come back to the homeport.

“The data collected by the Leica GR25 GNSS receiver and the Leica AS10 antenna concerning the movement of the boat reported that ECO40 sailed wave heights of roughly 6 metres during the first storm with maximum waves reaching 10,0 m,” said Miceli. “After the end of the trip, we are now able to calculate the exact measurements.”

Gathering the data

A part of the measured data was sent to the land team on daily basis by satellite modem. These data, measured by the boat and transmitted almost in real time, helped significantly the team in charge of the safety of ECO40; the knowledge of the actual weather conditions the boat was really facing during the navigation could improve the route strategy and increase the boat safety.

“The measurements of the boat movements, obtained from the three GPS receivers, if properly analysed, can provide a measure of the waves that the ECO40 encountered during the navigation,” said Miceli.

The three high precision Leica Geosystems GPS receivers were placed on the left and right side of the stern along the boat cross axis while the remaining one was placed close to the boat entrance along the boat’s main longitudinal axis. The data were acquired by the system during the navigation of the ECO40 and stored on a flash-card by each receiver. The data analysis was carried out in post-processing after the recovery of the flash-cards.

Two different strategies were adopted in the post-processing:

1. The “Variometric Approach for Displacements Analysis Standalone Engine” (VADASE)
2. The moving base kinematic approach.

The two methods were used complementary in order to obtain the boat motion, and the boat motion has been applied to estimate the waves’ properties faced by the sailboat during its navigation around the world.

Indeed, the first (i.e. variometric approach) was used to calculate the boat heave, surge and sway motions, while the second one (i.e. moving base kinematic approach) was used to calculate the roll, pitch and yaw motions. The wave characteristics (i.e. directional wave spectrum) were derived by using the heave, pitch and roll motions.

When fast movements have to be detected and their effects suddenly evaluated, Leica VADASE can help researchers make the most informed decisions immediately. The solution adds additional value to traditional GNSS monitoring, providing accurate velocity information based on a stand-alone GNSS receiver that is continually available in real time for precise and reliable analysis of fast movements.

The boat performance data (i.e. speed and course over ground) can allow, after a certain amount of time that is required, to obtain a statistically meaningful database, to estimate the real polar velocity curves of the boat. Indeed these curves were used for the prediction of the optimal route made by the land team by using a route optimisation software, which was sent daily to Miceli.

The actual polar velocity curves of the boat differ from the theoretical ones estimated by the designer of the boat. This is due to several causes, among which plays an important role the ability of the crew to “push” the boat to the maximum of its performance and the presence of waves that normally is not taken into account when calculating the curves themselves.

These data are used mainly for two technical and scientific purposes:

1. The first purpose is the calibration and/ or verification of the numerical models output that are commonly used for the wind and wave forecast and/or analysis into the oceans, and the calibration of the remote sensing data (e.g. satellite wind and wave measurements).
2. The second purpose is directly related to the vessel design. Indeed the knowledge of both the movements and the loads that this kind of vessel can deal with, together with the response of the materials to the fatigue stresses, can improve significantly the design methods.

Analysing the measurements

This undertaking was the first time ever that a sailboat’s movement was accurately measured by GNSS on a global journey and data were transmitted via satellite every few hours. In terms of the met-ocean conditions and in terms of the boat heeling, the first violent storm experienced by the ECO40 during its navigation occurred in the Gulf of Lion 21-22 October 2014. The heeling of the boat was estimated by using the GPS signals that were analysed by using a moving base kinematic approach. This analysis allowed to estimate the heeling angle α during the whole storm event.

“Concerning the met-ocean conditions, we analysed the storm on the basis of the wind data that were measured and transmitted almost in real time from the boat,” said De Girolamo.

Wind data were measured on board of the ECO40 by means of an anemometer placed on the top of the mast. The first comparison was carried out with the European Centre for Medium-Range Weather Forecasts (ECMWF) and the second one was carried out by using the forecasted data, provided by the numerical model GFS (Global Forecast System).

This comparison, along with the results of the heeling analysis, showed that the wind measurement height plays an important role. The corrected measurements of the wind are comparable with the results obtained from the numerical models: a good agreement is noticeable within the first 60 hours. Nevertheless, a sensible discrepancy between the measured wind data and the numerical one is noticeable as the storm peak occurs.

The direct comparison between the forecast and the measured wind speed showed, in the present case, as expected, relevant discrepancies. These discrepancies are such to underestimate the forecast wind condition in the order of 50 per cent of the forecast wind for severe storm conditions.

The researchers and professors were able to put together a research paper based on the comparison between measured and numerical wind data.

“Still, despite the unexpected end of the journey, the data collected from the Leica GR25 GNSS receiver and the Leica AS10 antenna were enough to provide ocean scientific information for the development of new ocean knowledge and technologies for the benefit of society,” said Frank Pache Senior Product Manager, GNSS Networks and Reference Stations at Leica Geosystems.