Balance – Heeling
Balance and the Effect of Heel
We must also consider the effect of heeling, and how much that is caused by the under water shape of the immersed hull – we are not talking now about the keel and rudder, but the hull itself!
When the boat is upright, the hull shape is symmetrical – but as the boat heels, the shape becomes progressively asymmetrical.
The leeward side, the immersed side is the most curved side, and this has an hydrodynamic effect that is similar to the aerofoil made by the sails – in other words it is forcing the boat sideways to leeward, the same as the sails, but the opposite to the keel/rudder.
With increasing heel the boat hull effect is getting stronger, and the keel/rudder effect is getting weaker.
So,we can see that this gives more leeway, but less clear is the increase in weather helm. This is caused by a rotational effect of all aero/hydrofoils, and causes the bow to “round-up”. The wider the boat the greater the effect.
Now also consider the asymmetry of the underwater shape from bow to stern, and how that looks when heeled, and you can see that the“rounding-up”will be bigger