Cavitation

Reducing the effects of cavitation

Of all the four elements, water is the most powerful and uncompromising. Its expansion and contraction with variations in temperature cannot be constrained by any force – just one degree increase in temperature would rupture a vessel containing water alone. Water cannot be compressed and water’s forces, when changing state from solid to liquid to vapour, cannot be checked.

Water’s indomitability is sufficient to corrode steel and excavate craters by its explosive virtues. This huge power is seen nowhere more clearly than in the effects of cavitation.

The boiling point of water varies according to pressure. At sea level this is considered to be 100c, but a mountaineer at high altitude would be able to boil water at a much lower temperature because of the lower pressure. The differentials brought about by propeller propulsion are remarkably similar.

cavitation

effects of cavitation

Class or safety issues

Water aft of the propeller is put under great pressure as its force is used to advance the ship, but water forward of the propeller is subject to such a reduction in pressure that it will effectively boil and unleash all the latent capacity involved in this state changing process.

It is in these forward areas that water molecules expand and then explode with a force too great for even steel to withstand. Tiny molecules, in and around the metallic surfaces of the hull and rudders, are able to crater the surfaces and deplete the strength, integrity and efficiency of these essential parts of the ship. Eventually this depletion becomes a Class or Safety issue which, if unchecked, will necessitate dry-docking for extensive steel works or, alternatively, Class suspension from trade.

To counter this problem Brunel developed CaviCure, a product which incorporates many of the virtues of the EnviroMarine coating technology.

Brunel CaviCure comprises 100% solids and its exothermic cure is neither dependent on humidity, nor on the thickness to which it is applied. It does not shrink and it is smooth on its external surface, with no pores to harbour water molecules. It is extremely hard, yet has sufficient expansivity to accommodate the unbeatable forces of water that cause cavitation.

Since its introduction, four years ago, CaviCure has been applied to vessels to remedy existing cavitation problems.  As well as being applied in dry dock situations, CaviCure has also been applied to suitably trimmed vessels, whilst in port, allowing those vessels to sail within hours.

Whilst the problems of cavitation are widespread, no vessel repaired with Brunel CaviCure has failed to have class conditions removed – and despite being under the watchful eye of class, no vessel has suffered any further symptoms of the cavitation problems that previously affected it.

Avoid the problem altogether

EnviroMarine Coating, just like CaviCure, is also smooth, hard, and completely non-porous. It contains no material or molecule which can react to pressure change, yet its elastic modulus allows it to accommodate the huge energies that marine propulsion conditions generate.  Brunel has never been called upon to apply a cavitation remedy to any hull previously coated with EnviroMarine.

Brunel can cost effectively deal with existing cavitation problems by the application of CaviCure.  Brunel can prevent the problem from occurring in the first place by the application of EnviroMarine.

cavitation

Brunel Marine Coating System