SailGP’s St Tropez event two years ago saw some of the most spectacular racing on the circuit thus far. Team France, Les Bleus, hit 99.94 km/h (53.96 knots) on the opening day.
That speed was topped this year in Sassnitz Germany with Rockwool Racing hitting 103.93 km/h (56.12 knots) on the bear away after Mk1 – “the holeshot”, to use a motor racing phrase.
So how fast could these foiling catamarans and their intrepid crews go? And how do these speeds compare to world records?
When I started my career in sailing media, waaaay back in 1989 with good-old Yachts & Yachting magazine, the outright world speed sailing record was 78 km/h (42 knots) held by Frenchman Gérard Navarin aboard the catamaran Techniques Avancées.
If the Danish SailGP crew in Sassnitz had kept up their speed for 500m, the official World Sailing Speed Record Council’s set distance for outright world records, Nicolai Sehested and crew would have been king of the hill as recently as 2010.
Russell Coutts, SailGP CEO, puts me straight on this: “ROCKWOOL Racing’s speed was achieved in a bear-away, where the inertia of the boat is increasing the righting moment, rather than in a straight line, so it’s not the same.”
What are the limits for the current F50 set-up? “I think we might see a spike of 106km/h or perhaps 108km/h with the new rudders,” says Russell, “but that speed is unlikely to be sustained. Actually, for us it’s more important to increase speed in the light winds to create a more compelling or entertaining broadcast product. I think the boats are plenty fast enough in stronger winds!”
Paul Larsen is the outright world speed record holder, setting a 500m run at an average of 121.1 km/h (65.45 knots) aboard Vestas Sailrocket 2 in 2012. This was the first record above 60 knots. It’s still the benchmark 13 years on.
What’s his perspective on the recent SailGP speeds? “Things change substantially when you start introducing turns into the speed equation – as in a big bear away at the top mark. The inertia of the boat and crew wanting to go straight now shares some of the work of the foils in opposing the wind.
'That inertia effectively unloads the foils, which are the draggiest part of the whole equation. With less load, they are also less likely to generate the pressures required to start the process of cavitation – until they go faster where they do achieve the low pressures where water turns from liquid to gaseous vapour.
'The thing is, it's not a steady state. It's a trick involving inertia. It's not purely the forces of wind and water. It's wind, water and mechanics.”
I was lucky enough to produce a story for CNN Mainsail on Paul, who was based in Walvis Bay in Namibia for his long campaign to become the record holder. He’s a classic hard grafting, upbeat Australian. Technically minded, determined, exceptional. If anyone can give us an insight into sailing speed, it’s him.
“If you want to know how fast an F50 really is, wait until 200m after the top mark and then see what speed it hits," he says. "Sailrocket 2 would also likely hit higher peak speeds if bearing away was part of the program. Kite boarders and craft are well equipped to exploit this method of generating high peak speeds.”
What does Larsen think of SailGP?
“I'm a fan. I have quite a few friends racing in various teams and that makes it all the more enjoyable. I love how hard they’re pushing the boats and that you know how much the individuals want to win. I'm not a great fan of a lot of the hype but then I'd say that about most sports. I'd gladly swap that for more nuts and bolts geeky stuff. That's where my personal interest lies.
"I think the racing format and the nature of the boats showcase the skills of the sailors really well. It's a great overall package. And the boats are awesome in that they’re hitting these speeds and racing neck-and-neck around a complete race course. Full respect for that.”
When it comes to the technical side of speed on boats, Paul has been there and done it – so let’s pick his brains a bit.
What limits speed for sailing boats? “Usually drag... and stability,” he replies.
“When all your drag equals all your thrust... you stop accelerating. Sailing boats travel through the water and that liquid is around 800 times more dense than air. Broadly speaking, the less you mess with it the faster you go.
“That's why we try to avoid it with creations like hydrofoils that lift the bulk of the boat clear of the water. The fact is we still need hydrofoils to give us grip in the water to oppose the wind forces and to lift the static weight of the craft and crew out of the water. The thrust a boat can generate is often limited by its stability - its ability to stay upright and resist the overturning forces of the wind on the sail.
"Once the craft has reached its stability limit it has generated as much thrust as that configuration will allow. Then if it wants to go faster it has to generate less drag – i.e. foil higher so there’s less in the water, or make the boat more aerodynamic.
“There’s a physical limit with water when the low pressure areas of the foil get so low that the water turns from liquid to vapour. It’s called the vapour point. You can reach it with water by boiling it with heat or reducing the pressure of its environment.
"With hydrofoiling boats it’s the low pressure that does it. That's cavitation. The water is maxed out. It's like a tyre sliding around a corner. It loses traction. Putting any more power down will only cause it to spin/slide, or cavitate more and that all leads to more drag... and no acceleration. You're at the limit.
“Sailrocket was the first boat that showed that sailing boats could go faster than the traditional cavitation limits of conventional foils. It did this by using a concept that has no stability limits, very refined and dedicated aerodynamics for the angles it was designed to sail and a unique foil design that used a combination of concepts to move the cavitation point way up near 70 knots.”
Could the F50s approach your record? “On an average over 500 meters... hmmm. Not with the foils and foil shapes they’re using. Never. It's like a piston engine, propellor-driven plane breaking the sound barrier. Physics will stop it. I think you might be able to get a specifically modified F50 to go very fast. The question would then be... is it still an F50 or some ‘Frankenboat’ that would no longer be very good at course racing?”
Now for the journalistic version of the holeshot: How fast could a sailboat go?
“Crazy fast. The last stage is to go to foil concepts that have no limits. They would be... well... let ‘em work it out…”
Full disclosure, I’ve been working on the TV side of SailGP for the past three and half years. I’m as big a fan as any of you, I hope (!), who’ve read this far into a technical piece on sailing speed.
Back in 1989 there was no YouTube, or social media, or frankly anything we’d think of as the internet. Magazines were the popular form for sharing one’s hobbies and passions, with race reports, kit reviews, opinion from the likes of Bob Fisher and so on. Our letters pages in Yachts & Yachting often had moans about “why is there no sailing on TV – it’s a sacrilege!”
36 years on (gulp) I think we can say we have a decent racing series to follow on a regular basis. And at 100+ km/h (54 knots), let’s face it, by any metric, it’s bloody quick.
Digby Fox is a long-time sailing journalist and TV producer. As well as his work with SailGP he now lectures on Sports Media Production (BA) at Bath Spa University.
