Osmosis expertise


Osmosis expertise

Owners of yachts made of GRP (glass fibre reinforced plastic) have to deal with the issue of osmosis, as untreated osmosis can permanently destroy the structure of the vessel. This issue is often underestimated.

Osmosis occurs when the underwater hull is not optimally protected and moisture can penetrate through the gelcoat. There it collects in cavities in the laminate that are inherent in the construction of every ship. Since the laminate is not “waterproof”, the resin that binds the glass fibres decomposes and forms an acid. It draws – through its chemical tendency to dilute – further moisture into the cavity. The pressure in the cavity increases and pushes the gelcoat outward as a bubble. The brittle gelcoat bursts open and the laminate is exposed to seawater without protection. In the further course of osmosis, the laminate increasingly decomposes. What remains are glass fibres without cohesion – the laminate is destroyed.

Possible causes are not always fully documented or are not always mentioned by the seller.

Was there grounding with possible structural damage to the keel section?

  • Was there storage/transport damage, especially in the areas of the supports that are heavily loaded at certain points?
  • Were there collisions of any kind e.g. with flotsam?
  • Has the boat ever had osmosis, and if so, how was it remedied?
  • Is there any traceable documentation including photos?
  • Etc.

In order to detect osmosis damage, E/M/S performs a visual inspection of the hull as well as a moisture measurement with a special device. For this purpose the boat has to be taken out of the water and the hull has to dry for several days before the test can be performed. The result of the inspection is documented in the E/M/S inspection certificate.