Osmosis: how to recognize it and what to do (hoping you never need it)

With spring approaching and the season close to restarting (for those who are not afraid of the cold), what is approaching is one of the most quotable times to haul the boat out to dry and give the hull a checkup, thus taking the time to fix any problems in due time. In fact, especially for boats of a certain age, it is not just vegetation and dog teeth that can postpone a happy return to the water. Less obvious, of course, but far more worrisome, is in fact osmosis, a phenomenon as tedious as it is potentially detrimental to the health of one’s boat.

Osmosis: how to recognize it and what to do (hoping you never need it)

The jobs and chores that can be tackled independently on a winged boat are not few. From cleaning sensors and through-hulls, to check-ups of everything concerning the live-work, you name it. The osmotic phenomenon, however, is often the one that is the most challenging and complex to combat, requiring not only a somewhat more trained eye, but also not inconsiderable timeliness. As is often the case, in fact, intervening right away is always the wisest solution (in this case, for one’s wallet as well), and as we age (and especially for Classic Boats), there is little we can do about it; osmosis becomes a more common thing. In this article we will briefly explain how to monitor, recognize and intervene in case of osmotic phenomena.

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Osmotic Phenomena – What they are and how to recognize them

In chemistry, the term osmosis denotes the diffusion of a solvent (seawater, in our case) through a semipermeable membrane (which lets solvent and not solute pass through). What does it mean? Unfortunately, it means that if air bubbles are trapped inside the fiberglass laminate, water will seep in to fill the spaces. In short, if at an initial stage the seawater will simply fill the air bubbles present, from there it will also begin to ‘eat’ everything around it. According to the osmotic process, the water (solution) will draw more water back to itself, through the gelcoat and so on, giving rise to a process that is indeed slow, but degenerative and inexorable. Intervening in time, in short, is crucial. How, then, to recognize a possible osmotic phenomenon?

First of all, this is a job to be done with the boat dry. Only then, in fact, will you be able to visually check whether the gelcoat has bubbles or, at any rate, certain irregularities. These, although not necessarily implying osmosis, are an obvious symptom of it. If this is the case, it is therefore a good idea to ask yourself two questions to take the best possible action. Figuring out whether your boat is suffering from osmosis, in a nutshell, is quite simple. Less easy, however, is to understand the extent and depth of the phenomenon, so you will have to rely on experts, or a boatyard, so that appropriate measurements can be taken. Using a professional hygrometer, in fact, you will need to measure the moisture at various points on the hull, thus understanding the potential extent of the problem.

In fact, based on the composition of the solution detected within the hull deformations, one can tell both how long the osmotic phenomenon has been going on and the depth to which it has reached. Be careful, however, when talking about osmosis, it is also important to know whether the hull has undergone previous repairs or anti-osmotic treatments. Combinations of different materials (fillers or epoxy resins) used in any previous refitting could imply different thermal and hygroscopic characteristics, and it will therefore be the responsibility of specialized experts to figure out how best to intervene.

Osmotic phenomena: the treatment

In the event that osmotic phenomena has been established, unfortunately, there is little that can be done: it is necessary to intervene as soon as possible with a specialized treatment. Remember, osmosis is a degenerative and inexorable phenomenon; it will not be enough to keep the boat dry for long to stop it; it would resume its course as soon as the hull is put back in the water. The stages of anti-osmotic treatment, moreover, vary depending on the state of the phenomenon, so, as you will see, the sooner action is taken, the better. Case histories can be identified in three main stages:

• the first, and least serious, involves the presence of osmotic bubbles under the surface layer of gelcoat, with extent, however, limited to these only;
• In the second case, however, the water moved past the first osmotic bubbles below the surface of the gelcoat, going on to affect the surface mat layers as well;
• In the third and worst case, osmotic phenomena have gone beyond gelcoat and mat, reaching deepest tissues. In this case, new lamination is required.

Generally, although there are other techniques, a well-done and complete job (once the presence of osmosis has been defined), involves sandblasting the bare hull after removing the layer of antifouling paint and gelcoat. This phase will be followed by a period of hull drying (about 3-4 months, depending on weather conditions), during which pressure washer cycles will be performed. Once the boat is dry (and thus without any more internal moisture), a coat of epoxy will then follow, followed by grouting and sanding, as well as potential and additional coats of epoxy. Only then can the primer and antifouling be applied.

If the boat is laminated with a traditional system (with polyurethane ribs and longitudinal members and a fiberglass hull), drying will occur sooner, whereas with sandwich constructions, moisture is more persistent and there is a need for hygrometric verification at regular intervals.

Are you looking for or want to sell a Classic Boat?

• If you are looking for or want to sell a Classic Boat, remember our Used Boat Market(HERE), the ideal place for anyone looking for a Classic Boat to buy and/or, even more so, the ideal platform for those who have a desire or need to sell their vintage gem. If you have a Classic Boat to sell, or if you were looking for one, remember the Marketplace. Using it is as simple as it gets.
• Want to learn more about the world of Classic Boats (1967-1998), the iconic boats of the period, the legendary designers, the stories and races of the “golden age” of sailing? Check out our section dedicated to Classic Boats!