Глиссирование

PLANNING MODE

There are three modes of boats’ movement: displacement mode, transitional mode and planning mode.

Water displacement mode

42. K 430

The vessel has the same draft, and the displacement is equal to the weight of the vessel at the movement, as well as without it. The movement in this mode is not speedy, the boat simply floats on water, taking the maximum surface. This mode is for boats with low-powered motors, and their speed is below 15 km/hour. The boat creates high wave.

Transitional mode

IMG_6941

The boat is moving with highly raised prow overcoming the waves created by the boat itself.  Such mode can be reached at the speed of 16-18 km/h with a high consumption of fuel.

Planning (hydroplaning) mode

The boat has a minimal contact with water surface. The speed is about 20 km/ hour. This is the most economical mode for the boat.

A BIT OF PHYSICS

Planning vessels have a specific hull form. It is specially designed so that when the vessel reaches certain speed the lifting force pushed the ship out of the water. The boat can develop a higher speed because the water resistance in planning mode is not significant. To bring the boat into the planning mode you need to make more efforts than to maintain a boat in this mode. Therefore in a boat with an outboard motor you first need to “give full throttle”, and after the boat goes into planning mode, you should decrease the power at a half. The speed ​​will not decrease, the planning mode will be retained.

French word “glisseur” means a light high-speed vessel. Planning (or hydroplaning) mode is a movement when a vessel is held on water surface only because of water pressure. When the boat goes into the planning mode the water resistance decreases and the boat’s speed goes up.

It is well known, that main resistance to vessel is created by waves and splashes. The prow of the vessel is cutting the water and creates the prow wave. The water streams flow along the sides of the vessel, face the stern and create the stern waves. Finally, the water streams that flow along the bottom create the transverse wave, which lifts water astern.

When the boat speed is approaching the speed of the wave, it turns out that the boat is trying to overcome the wave created by the boat itself. This is called the wave crisis. When the speed goes up the fuel consumption increases reaching its maximum point just before the moment when the boat comes into the planning mode. The boat won’t come into the planning mode if the engine does not have enough power. Planning mode depends on the boat’s frame construction, material it is made of, engine type and capacity, the angle of engine inclination, the size of a screw and a weight of cargo in a boat.