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This article discusses osmosis on boats and yachts.
FRP is the perfect material for yachts and pleasure boats (but chance of osmosis)
GRP, Glass Reïnforced Plastic, or rather better FRP (Fibre Reïnforced Plastic) is probably the most perfect material to build boats with: it’s light, fairly strong, relatively cheap to fabricate, we can make the most fantastic shapes with it and it’s low maintenance. But it’s not all roses and moonshine. A number of moisture measurements can cause a panicky reaction among boat owners when osmosis is detected.
Moreover, even after 50 years since this material has been used in shipbuilding, the most diverse misconceptions about osmosis in boats and yachts are still circulating, even among ‘specialists’.
What is osmosis?
Osmosis is, simply put, the transition of a liquid through a membrane that is slightly permeable to the other side of the membrane where there is another liquid.
This phenomenon occurs in a certain direction: from the one with the least density to the one with the highest density. Trees use this method to ‘suck up’ water.
In this article we look at FRP and water. The ‘membrane’ in this case is gelcoat or epoxy paint. Both materials allow water to pass through.
How osmosis occurs on hulls of boats and yachts
However, we often find that small parts of polyester are not perfectly cured (this can happen by applying the ‘mix’ too quickly, for example) and that there are also small air bubbles in the polyester (these are normally pushed out with a roll during construction). If these products come in contact with water, they will bind with the water and an acidic solution will form, which is denser (more concentrated) than the original product and which in turn will ‘suck up’ much more water.
Letting the boat dry against osmosis is pointless
Just ‘drying’ is useless in this case. The water has bound itself and made another product that simply does not dry out. The products formed by osmosis have to go. That is why rinsing is necessary, as well as ‘freeing’ too large spots of liquid (by grinding away, for example).
Osmosis on boats and yachts has a self-reinforcing effect
If this doesn’t happen, the osmosis process continues and strengthens itself, the pressure increases and blisters appear. This is still not a major problem for the ship. The blisters usually form just behind the gelcoat, which has little to do with the strength of the hull.
But now comes the point: if the laminate of the FRP does not contain enough resin in certain places, the pressure caused by the osmosis can weaken the laminate by separating the different layers. And then it becomes dangerous because the hull strength is so compromised. This can have very disastrous consequences.
And now what? Don’t panic, in most cases solutions are possible if you don’t wait too long. The longer the osmosis process remains untreated, the greater the cost of repair. Remember that the osmosis process is NOT reversible.
Be there in time to prevent problems with osmosis
We therefore advise, especially for boats older than 10 years, to have the hull regularly inspected by a yacht surveyor in order to determine at what stage the boat is at. The cost of a short inspection is negligible compared to the cost of repair if you wait too long.
Why a surveyor through BYSC? A BYSC yacht survey is neutral while another company will always give the advice that suits them, and not necessarily you, best.
Read also: the BYSC services in osmosis