Keel design for shallow water
by Andrew Rice
Iñigo Toledo is also a fan of the centreboard concept and sees considerable hydrodynamic benefits compared with a conventional keel.
A fixed keel in a big yacht is limited by draught the keel has to be short in height and long to accommodate the amount of area required [for lateral resistance]. With the daggerboard you get something higher aspect, deeper and narrower which is more efficient, more like a glider wing, he explains.
Also you have to build [a conventional keel] with a certain thickness and geometry so that it holds the weight of the ballast. There are structural constraints, whereas when you make a daggerboard you can actually just make the most hydrodynamically efficient profile.
Toledo also believes the specialist nature of daggerboard manufacture results in a higher quality fin.
When people make daggerboards they somehow make much more effort to achieve a really good finish, more than when the keel is part of the hull. When you order a daggerboard from a composite materials company, the result is much better.
McKeon sees more centreboarder superyachts, and Toledo agrees: I would say in the future you will probably find 50 per cent of boats with fixed keels and 50 per cent with some kind of movable appendage, says Toledo. Probably about 10 per cent will be lifting, and maybe the other 40 per cent will have daggerboards.
The compromise between draught and performance is the perennial challenge of yacht design
Quite a prediction, given that every designer we spoke to acknowledges that a centreboarder will always struggle to match the performance of a lifting keel equivalent. What happens when you decide to take your shallow-draught cruiser to a regatta?
The problem with regattas is that the comparison is too fair and too cruel, admits Toledo. You find out exactly where you are performance-wise. Some owners just dont accept it.
Better then to stay away? McKeon offers an alternative view.
What I think is great is when owners participate in these regattas, they can experience the full performance potential of their yacht. Some owners when theyre cruising are nervous about pushing the boat and how much one can safely heel over, whereas during a regatta the yachts are pressed a lot harder and they achieve more speed and ultimately the owners have more fun sailing their yacht.
The compromise between draught and performance is the perennial challenge of yacht design. Whatever kind of configuration you prefer, Briand encourages all owners to take an interest in the appendage package of their yacht.
When you design a racing boat, its the first area you study, he says. However, because appendages are underwater and never seen, theyre easily forgotten, but the appendage package is a big part of how the yacht performs. It is hugely important to determining the final quality of the yacht.
Originally published: September 2011.
Kos Picture Source, Rick Tomlinson