Perhaps Juan Kouyoumdjian’s most famous innovation has been his modern take on hull chines, now appearing on numerous new production cruiser-racers. ‘But on most boats I see, they have no real effect,’ he explains to 0yvind Bordal…
We see them more often than not when a new production model is presented to the market. Distinct horizontal lines breaking up the rounded shape of the stern. A wide transom with sharp angles, instead of the traditional, unbroken arch.
At the same time a new buzzword has crept into the sailing vocabulary. It’s really an old term, describing a way of building boats from materials that can’t be easily formed in more than one direction, such as plywood, steel or aluminium. But nowadays the word has taken on a new meaning, and has a much more sexy ring to it. Chines are the new black.
Today’s chines carry a whiff of the Volvo Ocean Race, an image of full planing on the open sea. Chines symbolise something modern, efficient, stable and fast. But that’s all feelings. What are these chines really? What are the hard facts? What can they deliver, and how do they work? And can so many different boats really benefit from them…
Juan Kouyoumdjian, commonly known under the very-much-easier-to-spell moniker Juan K, is famous for being a straight talker. His fresh approach to yacht design, combined with a Latin temperament, has led to a few controversies in the racing design community over the years. But when we meet in the hotel lobby the first impression is a very accommodating, almost modest guy. And when he starts talking it’s obvious that he really tries to transform his very complicated trade into something understandable for outsiders.
We start out talking about the design environment where chines and other hardcore racing features are born, and how they may trickle down to more normal boats.
Juan K says: ‘As you know, I used to be very involved in the Volvo Ocean Race. Now, after a one-design was introduced, we’re not involved in the race any more. But there really was a lot of knowledge and information, a lot of experience that was built up with the V070s during the last few races. Not just by us, but by all the designers who were involved. And I think quite a lot of it actually can be used in more conventional boats. The V070s were quite extraordinary boats, and I think many of them will continue to be sailed for years to come. In terms of outright pace they will be competitive for many years yet …
‘But chines and wide sterns were not the only important dividend from the V070 era. As I see it, the more important developments related to the structure and building technology in the hulls and decks, and the impact of weight. I would also say canting keels, and the way boats are sailing with them, even if that might be less of a topic in the futrtre because most conventional boats don’t have a canting keel. .. and most owners don’t want one.
‘But in particular we learned a great deal more about slamming and the dynamic loads in the boat. That can be very useful in conventional boats as well.’
But what about the chines we see on a lot of production boats nowadays? Do they work? He laughs. ‘Yes, we see them in just about every boat now. In the V070s they were there for very specific reasons related to the rule-limited maximum beam and the stacking capacity. So there was a moment during the design process where we sort of … well, we had to cut off the rest of the boat. That resulted in the chine.
‘They also had some other benefits, but originally the chines came out of a rule constraint. And I must admit that today I see a lot of boats out there where the use of chines is more of a fashion statement than anything else. Some designers are exploiting them well but, yes, a lot of it’s about fashion.’
So how would he describe the effect of chines, when used properly? ‘V070s were designed for a certain angle of heel,’ he explains.
‘These boats are never sailed upright, not even with the wind from astern. For every different heel angle we optimised the hull shape for a certain boat speed. So in essence when you optimise hull shape, or more precisely the immersed volume at different angles of heel, you end up with a certain shape. And at some point you have to cut off the rest of the boat, to make it fit to the restraints of the rule. What comes out is what you’ve seen.
‘It’s not like we say … let’s put a chine there. It’s not an input. It’s an output. A result of something else. On some production boats it’s done properly. On most boats I’ve seen it’s merely fashion.’
But how to explain the advantages of chines, when actually used properly in production boats? ‘In these boats,’ he says,
‘you are allowed to end up with any hull shape you want, you can choose any beam at the back of the boat. There are no specific rules. That freedom allows you to exploit transom shapes that reduce dynamic drag as a function of heel and speed. So if you say what is the advantage – well, I don’t think there is an advantage per se, like “OK, we have a chine, therefore you have an advantage”. It’s more like, if you optimise the hull with complete freedom, no rules, you will most likely end up with a hull that has a chine at a very specific spot. So, like I said, the chine is a consequence, it’s an output.’
OK, but to be even more specific: the advantage of this hull shape, that for one reason or another ends up with chines – is it mostly present on broad sailing angles, maybe even planing? Or is it good upwind as well?
‘It can actually be very good upwind,’ Juan explains. ‘Particularly for boats with a symmetrical keel in the middle, like a regular production boat.
‘When the boat heels the chine helps in balancing the boat. It’s good for safety as well. On a boat with a wide transom and a single rudder, the rudder has to be very far forward on the hull to stay in the water when the boat is heeled. That reduces steering moment, and to overcome that it’s necessary to make the rudder bigger. Which gives you more drag. But even now, with the rudder moved forward on the hull, you will find it very difficult to press the boat hard, because the boat will lose balance with a lot of heel.
‘Putting the chine in the water helps balance the boat back. It’s almost like having an extra rudder in the water. When the chine is submerged the boat will have a tendency to bear away a little more. That makes it possible to load the sails harder, add some more power to the boat and take advantage of its form stability. Thus the chine can help take pressure off the rudder.
‘The same thing actually applies on broader angles – if the boat is fast enough. Fast boats will always have the apparent wind pretty much forwards, and basically experience roughly the same situation, when it comes to side force and heeling.
‘On normal displacement cruising boats, that almost never exceed hull speed, the whole concept of wide sterns and chines doesn’t really have any relevance – certainly from a performance point of view. Even on lightweight, faster boats the chines have to be designed properly and located properly. Otherwise they don’t do anything. Chines can only make the boat go faster within a very specific set of circumstances, and I don’t see these circumstances appearing very often on a normal production boat.’
Weight is the next big thing
What about the future? Are there some general design trends that he can see coming? Or to put it another way: what does Juan K believe will define the production boats that will be successful over coming years?