TACTICS By Design

in THE GOLDEN GLOBE RACE

BT Challenge skipper and IMOCA 60 designer Merfyn Owen, of Owen Clarke Yacht Design, explains what can be learned from the GGR

Flong-keeled, sturdy yacht – of the sort ew expected the ambitious Golden Globe Race (GGR) to go without a hitch, but as Event Director, Don Mcintyre, says even he was surprised by the number of boats being rolled in the Southern Ocean.

It has often been stated that a stipulated in the GGR rules – is the most seaworthy to take on a long oceanic voyage. With many of the sailors reporting pitch-poling, variously trailing warps, drogues, or nothing at all, is it time to reassess that view? And what can be learned from their experience?

Merfyn Owen followed the race and was not entirely surprised by this outcome. ‘Really, what we are talking about here is energy transfer,’ he told YM. ‘When a wave meets a boat, something has to happen to that wave’s energy – which is a function of the weight and speed of the wave. Some of that energy is therefore transferred into the vessel.

‘If you have a wave travelling at 30 knots, which hits a boat travelling at six knots, the relative velocity of that wave is 24 knots. If we have a trimaran, which weighs the same but is sailing at 25 knots, the relative velocity would only be 5 knots.’

For Owen, if you are sailing downwind with significant waves, maintaining as much speed as feasible is your best way of managing the situation. ‘I don't really understand trying to slow the boat in big waves. You are far safer going as fast as you can – so reducing the relative velocity of the waves hitting you. Keeping up boat speed also increases your control of the boat, not just leaving you at their mercy. Of course that is just in reference to a pooping wave, there is nothing we can do about a wave that hits you from a different angle in a confused sea – that all comes down to the righting moment of the vessel.’

This speed issue, he adds, is the reason why drogues or towing warps would not have helped the sailors. ‘It’s not that it wouldn’t work, they are useful for some situations, it’s just you never have to use one to slow yourself down in waves with plenty of sea ahead of you. You are far better off just sailing fast through it.’

Righting moment is the other main factor at play here and there is much that can be done at the design stage to increase that – bulb keels and increasing width being key factors as well as size: ‘A 40-footer would still be likely to be rolled in these extreme conditions. A 50ft boat, even though it has only gone up by 10ft, has the best part of 50 per cent more righting moment, which adds an extra level of safety, but is obviously not an option for that many people,’ explains Owen. There are, however, some steps

you can take to help. The biggest one being to lower the centre of effort. We do this anyway when reefing, not only reducing sail area but removing sail area from high up. Jean-luc Van Den Heede took this to a logical conclusion by reducing mast size so that, even when sailing fully canvassed, he had a lower centre of effort.

For the everyday sailor this would mean thinking about your sail plan in a storm. If you want to maintain speed, then keeping some sail up is a key concern and having sails that set low should be a priority. A storm jib is key if you are planning to cruise any distance, as is a storm trysail. The trysail can be notoriously difficult to control, however, so it is also well worth ensuring you have a fourth reef in the mainsail. Reefs are easier to put in and there is an argument that a reefed mainsail allows you to maintain better control. As ever, the advice here is to try both configurations to get a feel for which offers best speed and control.

UNDERSTANDING STABILITY

One of the reasons for the pervading sense that designs such as those used in the GGR are more stable is a misreading of the angle of vanishing stability curves, Owen says. ‘If you look at a typical sine wave stability curve, your classic long-keeled yacht of about 35ft would have an angle of vanishing stability where it crosses the zero axis of, say, 145°.

‘If you take a modern blue-water cruising design, the curve will probably cross that axis at a far lower angle. People might point to that and say the old boat is much more stable, as it doesn’t have a vanishing angle until 145°, so it’s a much safer boat.

‘However, for a larger or modern yacht, especially with a deep keel and bulb, the righting moment – the top peak of the curve – is likely to be quite a lot higher and the area underneath that curve is greater. It’s that area under the curve that is important because it’s directly equivalent to the energy required by a wave to roll the boat. The greater the area, the less likely to be rolled in the first place, irrespective of where the vanishing angle is. The area under the curve is also proportional to the energy required to re-right the boat.’