Osmosis Detection in Yacht

Osmosis is generally considered a chronic and common issue for laminated and gel coated yachts (more often hidden). Its early detection and treatment are important in order to extend the life of the yacht hull. This article intends to highlight the inherent issues of Osmosis and how it is so dangerous to the gel coated yacht hull.

Osmosis by definition is “a process by which molecules of a solvent tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one.” In the context of a yacht hull, it’s the passing of the water molecule through the gelcoat to the fiberglass lamination. Generally, gelcoat absorbs the water and then dries up on its own when removed out of water. The problem starts to occur when the water molecule enters the lamination layer from the inevitable air pocket or dust between the lamination layers. These air pocket and dust particles in between the layer of the lamination commonly develop at the fabrication and molding stage of the hull. This is sometimes inevitable, the water in that air pocket stays and reacts with the surrounding substances present in the lamination of the yacht hull like polyester resin. This reaction is called hydrolysis.

When hydrolysis reactions occur in the air pockets between the laminations, they expand and tend to loosen the bonding between the two layers. This results in blistering on the hull (mainly submerge area). So, the visible blistering means the 1st later of the lamination is already affected and a prime suspect for detailed inspection for finding the number of layers affected and its economical repair.

Osmosis and hydrolysis is a slow process that takes time and it will be visible as blisters only after the 1st layer of lamination is affected. But there is also NDT testing which could determine the occurrence of this process at an initial stage. The two main NDT testing for yacht hull inspection is Moisture Content Evaluation and Percussion Testing.

Hammers can be of plastic, or rubber. As long as an audible sound is made when the tool taps the hull being inspected. The surveyor here is searching for differences in acoustics when tapping on the hull. However, the skill required for hammer testing to identify the sound difference is something that is gained through experience.

It’s a good practice to carry out the moisture content evaluation at regular intervals as a precautionary measure for hull check-ups to maintain life. We at constellation marine have a decade and more of experience in Percussion Testing and Moisture Content Evaluation by a team of Master Mariners and Engineers. We use certified moisture meters and have completed over 22,000 nominations between our team of 15 full time staff surveyors.

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By: Fahad Ansari