A heavyweight in a world of lightness!
When you look at an IMOCA boat, you can imagine it made up of very light carbon fibre or titanium parts. But to sail fast and well, our IMOCA needs a keel made of lead and stainless steel!
To help us discover this jewel of know-how, we went to meet Laurence Crespel and Fabien Dillet at the AMPM in Vendée. A milling and turning factory, where all the keel sails of the IMOCA boats are now manufactured. Large parts are their speciality..
A one-design keel since 2014
Before 2014, every architect designed his keels without constraints: a carbon fibre sail here, mechanically welded steel here (sheet metal assembly), with lead bulbs often too heavy. After many setbacks, exploding budgets and accidents linked to the breakage of this part, which is essential to the stability of the boat and the safety of the sailor, the organisation of the IMOCA class rules has imposed standardised parts. This is when AMPM was chosen to equip the future boats that would meet these standards. This company was already present on the IMOCA circuit having built the keel for a certain Michel Desjoyaux in 2000..
What's an IMOCA keel?
It all starts with a six-tonne piece of stainless steel, transformed into a forged block weighing three tonnes and five metres long. Stainless steel is a metal with a high elastic limit, which guarantees a very high strength of the piece. This part is then machined for more than a month, 24 hours a day! The most impressive thing is that when it leaves the workshops, the keel hull weighs 950 kg, leaving behind almost two tonnes of shavings..
The quality department intervenes throughout the manufacturing process, because we have to guarantee perfect equity between the IMOCA's. " Imagine, a tenth of a millimeter error on the milling machine is a kilo more on the scale!" says Fabien Dillet. "All our pins come out with a certificate of conformity and have all passed through our test bench. "In conclusion.. "For this Vendée Globe, I'm setting out with confidence, the safety factors are largely respected."
The IMOCA boats have all reinforced the keel wells, since the Hugo Boss problem, as these boats are subject to major impacts, which damage the structure. Only the keels that have not been modified remain solid against the elements!
The future is being written, as the next IMOCA boats, which will be taking part in The Ocean Race, are currently having their keels delivered.
When this part is finished, the keel sail joins the lead bulb, this torpedo gives all the stability to the IMOCA. The weight of the bulb varies according to the expectations of the architects and the skipper...! According to the information that can be gleaned, a bulb currently weighs around 2700 kg. This is an average, as it is said on the pontoons that the lightest ones are below 2500 kg! Impossible to know more, it's top secret... With these foilers and the desire to get the yachts off the ground, weight becomes a war, let's be sure that the weight of the keels is closely monitored in order to relieve a nine-tonne boat as soon as possible.
Safety remains the number one priority. In 2014, the resistance calculation predicted a 3000 kg bulb. Nowadays, all the IMOCA boats are all below this red zone, so let us be serene, this Vendée Globe will surely be less marked by keel loss. Except in the event of a collision with a UFO, but that's another matter..
