Downwind – Flat or Kite?
An important skill in downwind sailing is prioritizing whether to sail the boat flat or healed to windward by the lee, referred to as kiting. Sailing by the lee means that the air is flowing into the sail from the leech towards the mast as opposed to normal sailing when the air is flowing from the mast towards the leech of the sail. Every class of boat has different requirements, so it is important to understand what these are and when to change mode.
Whilst most double handed dinghies will sail faster downwind, flat single handers often sail faster when kiting.
In this blog we will discuss key classes such as Optimist, Laser, foiling and planing boats.
An important note: generally the faster the boat, the flatter we would prefer to sail it.
Let us begin with the slowest boat around, the Optimist. Maintaining flow over the sail going downwind will ensure optimal power generated by the sail, so we can sail it flat on a run or we can sail it by the lee heeled to windward. In the optimist the windward heel is both determined by moving the center of effort above the center board to minimize rudder pressure and the shape of the hull. In this case, sailing the boat flat will mean creating more drag as the bottom is flat and the bow shape hits the water like a wall. When we sail healed to windward we are practically altering the shape of the hull causing it to have a ‘V’ shape, which eliminates a lot of drag as well as changing the shape of the bow so it is able to cut through the water rather than hit waves.
The Laser is a bit more complicated, whilst in lighter winds the boat would usually sail faster kiting, the purpose of the windward heel is to keep the center of effort over the center board since the hull shape is already V shaped from the center board forward which allows the boat to cut through the water. As the wind increase there is a need to steer the boat in order to surf the waves, for that reason we would use a leeward heel to luff up and a windward heel to bear away.
In survival conditions it is recommended to avoid sailing by the lee as the boat will have a tendency to death roll (capsizing while rolling the boat to windward), in this case it is safer to sail the boat flat keeping the leech of the sail considerably open.
We may also encounter conditions which allows us to jump waves downwind. This will usually occur in relatively strong wind and choppy waves, whilst it might be safer to sail the boat flat in such conditions which means the boat speed will be limited by the speed of the waves kiting at the right timing will allow the boat to jump to the next wave hence allowing the boat to sail faster. This technique must be well trained in order to be worth a while.
Foiling single handed classes such as the Waszp and the foiling Moth uses apparent wind to sail fast and low downwind, if we keep the boat flat we will generate pressure on the rudder as the center of effort will be to leeward of the boat in most conditions. For this reason, this boat will be sailed heeled to windward in order to bring the center of effort above the center board and allow us to minimize any rudder pressure. As these boats will sail faster than the wind we are unable to sail them by the lee, if we try to do so the boat will sail considerably slower and most likely cease to foil.
The 470 and similar boats (conventional displacement boats with symmetrical spinnakers) sail almost flat downwind – however, they have a distinct “sweet spot” where the heel balances all pressures and makes the boat feel fast with a light tiller pressure. On all planing boats, such as 49er, flat is the only way!
During our sailing sessions at Toplevel Sailing we train our sailors to prioritize the ways to sail the boat as fast as possible downwind and understanding how the hull shape will affect the different methods of doing so.