How a cross-Channel ferry avoids collisions
This is the large and impressively quiet bridge of the Pont-Aven, Brittany Ferries’s 187m flagship. Mate Julien Lemesre, pictured here, was in charge today and kindly showed me round as I made my way back home after Francis Joyon’s arrival in Brest.
The three-year-old ship maintains a service speed of 20.1 knots from St Malo to Portsmouth on two of her four engines (amazing to think that this is only fractionally more than Joyon’s fossil-fuel free average round the world) and has a top speed of 27 knots. The Pont-Aven can alter course by 90° in less than a minute and will crash stop from full speed in under two miles.
Typically, says Julien Lemesre, the crew will alter course 30 to 40 minutes before the time to closest point of approach to avoid a big ship but will wait longer for a fishing vessel or a sailing boat because their movements are less predictable. He aims to pass a ship at a minimum distance of 1.5 miles, but in good conditions this morning was happy to pass a fishing vessel off Guernsey at a distance of 0.9 miles.
Julien says that he has confidence in the radar picking up yachts although, as we know, a small target can give an intermittent return in big seas. However, he tells me that the radar is so sensitive that if it’s calm it will even show large seabirds flying by.
It was interesting to see the AIS data available, and it reinforced my view that for our own safety we should be making it a priority to fit AIS transponders as well as receivers on yachts.
“AIS shows us things ahead of the radar range that we need to watch out for,” remarks Julien. What is a big surprise to me is how far AIS data can extend. The image below shows AIS information displayed aboard the Pont-Aven one day last summer when the VHF propagation conditions were exceptional and the bridge was able to hear Cork Radio.
The ferry’s position here is close to St Malo but look at the AIS data coming in from all the way west to Ushant and as far afield as the south of the Bay of Biscay.
When asked if he is concerned about the future likelihood of a mass of clutter from small craft AIS data, say during a yacht race in the Solent or Plymouth, Julien replies: “No. It would be better. If there are hundreds of boats around we still have to know, and if there is fog it would be a very good thing.”
However, he also points out that AIS sometimes gives erroneous information, particularly in relation to course, and they always use radar to calculate course and CPA.