The balances

Static balances #

The center of gravity #

The drifter has a center of gravity noted

\(CG\) , like any object entering the field of attraction of a planet, point of application of Newton's force: Gravity.

This force is exerted vertically from top to bottom.

If we take the dinghy alone (without its crew), its center of gravity is invariable whatever the position of the boat.

On the other hand, once its crew is on board, this center of gravity can be modified according to the position of the navigator(s).

It can also vary depending on how much water has entered the boat during navigation.

The center of hull #

The hull center (CC) of a dinghy is the center of gravity of its submerged part.

At the center of the hull, Archimedes’ thrust applies.

It is exerted vertically from bottom to top.

Desalting #

In the lateral stability of the dinghy, gravity and buoyancy form a pair of forces.

Dynamic equilibrium #

Downwind balance

Lateral balance downwind is often tricky.

At issue is the force couple created by the aerodynamic force (Fa) and the resistance of the hull (Fr) .

To eliminate this torque, on round-hulled dinghies, a slight counter-heel is preferred so that the point of application of the aerodynamic force and that of the hull drag align and balance the boat.

Balance under other points of sail

Flat boat #

Let’s assume that gravity, buoyancy, aero and hydrodynamic forces, and hull drag all act in the same vertical plane.

We therefore assume that there is no problem of lateral trim.

If the point of application of the buoyant thrust is aft of the anti-drift force, the sailboat luffs because it is fiery.

Conversely, it will sink if the velocity force is on the front (the boat is slack). principle that windsurfers use among other things to control their direction.

Reversing or advancing the centerboard is possible in dinghies thanks to: The forward or backward movement of the mast Adjusting the mast rake The modification of the boat’s pitch (forward or backward movement of the crew) Adjusting the sail draft

Heeled boat #

With heel, in the dinghy’s lateral balance, the luffing torque between the velocity force and the hull resistance increases (note: The anti-drift force also accentuates the heel). If my boat is luffing, this luffing reduces the incidence of wind on the sails (the velocity force) and my boat will then level out on its own.

On the other hand, counter-heeling offers a torque that brings the dinghy down. Hence the importance of sailing a flat boat to avoid course corrections with the helm, which slows the boat down enormously.

If in light weather, it is better to have a little heel, it is to help the sails position themselves correctly.

Summary table #