Osmosis

[Captain Butterfly]

On reading many messages concerning osmosis, I noticed many a comment about osmosis never causing a boat to sink.

About thirty five years ago my Cape Dory Typhoon, a nineteen foot weekender, was sinking at her mooring off the yacht club in Toms River, NJ. Fellow members bailed her out before she could fully sink (she had a full fixed keel) and called me. I went immediately to the boat and found a spot below the waterline where water was seeping through a wet circular patch about four to five inches in diameter. I sailed her to a boatyard downriver and had her hauled. There was no apparent delaminating. Before leaving the mooring the seeping area of fiberglass was like blotter paper, soft and flexible to the touch and leaked perceptibly more when gently pressed.

Fortunately it was the end of the sailing season anyway. I stripped off the bottom paint and sanded down the gel coat, punctured and cleaned out the blisters, let her dry out until spring and then filled the pits with epoxy and coated the hull with West system epoxy, seven coats plus bottom paint.. I sailed her another couple of years before selling her as I was moving.

The leak could have been caused by some sort of temporary delamination that I didn’t detect on haulout, but I fully believe osmosis was a major factor. No sign of delamination was seen as I sanded down the gel coat.

 

[oldgit]

A mystery !
Yachts appear to be under attack from osmosis from first launch and must be kept ashore for at least half of the year to dry out.
Motor boats which are obviously made from completely different materials stay in the water all year round with only a few days ashore for antifouling.
Why is the river bed not littered with sunken motorboats ?
Think we should be told ?

 

[dankilb]

I think the 'never sunk from osmosis' is directed more towards mass-production boats of a later era (say late 1970s onwards). Not that I can say I've ever heard of earlier boats sinking from osmosis, either. But I think the presumption is that production techniques had progressed enough after the initial decade(s) of GRP to mean that osmosis was confined to relatively minor blistering.

Having an area of the hull go soft like that sounds like a manufacturing error to me - such as a dry patch in the laminate or a poor batch of resin - rather than purely the result of osmosis typically seen across larger areas of hull/laminate.

 

[Stemar]

Having an area of the hull go soft like that sounds like a manufacturing error to me - such as a dry patch in the laminate or a poor batch of resin - rather than purely the result of osmosis typically seen across larger areas of hull/laminate.

I agree. The kind of "osmosis" that produces blisters doesn't go through the thickness of the layup. If it's soft to the touch, it has to be because there wasn't enough resin, and it's the resin that keeps the water out. I could well imagine a dry patch being fine for years until the inner and outer surfaces get damaged, when the rest of the hull, being porous, lets the water through.

 

[RunAgroundHard]

There are quite a few cases of large scale damage to hulls caused by so called osmosis / hydrolysation, with blisters the size of dinner plates and visible de-lamination of the GRP. They are usually associated with boats built in tropics or more humid areas. Likely culprit is poor environment controls when mixing resin with an elevated moisture content and maybe skill level applying resin.

Some information in the book "Osmosis Myth and reality about hydrolyse blistering and delimitation in FRP boat hulls", Bengt Blomberg

https://montymariner.co.uk/wp-content/uploads/2014/02/Osmosis-handbook-9a.pdf

While the claim tends to be a considered by some as truism, I think it is more a generalisation.

Some good examples of gell coat separation as a result of blistering, and indications of delimitation inside GRP.

Is this delimitation due to Osmosis or something else Delamination? - Cruisers & Sailing Forums

There can be lost of reasons for shit lay up in GRP, so called osmosis being one of them. Interestingly that a lot of the images of crap hulls come from the USA.

 

[Refueler]

On reading many messages concerning osmosis, I noticed many a comment about osmosis never causing a boat to sink.

About thirty five years ago my Cape Dory Typhoon, a nineteen foot weekender, was sinking at her mooring off the yacht club in Toms River, NJ. Fellow members bailed her out before she could fully sink (she had a full fixed keel) and called me. I went immediately to the boat and found a spot below the waterline where water was seeping through a wet circular patch about four to five inches in diameter. I sailed her to a boatyard downriver and had her hauled. There was no apparent delaminating. Before leaving the mooring the seeping area of fiberglass was like blotter paper, soft and flexible to the touch and leaked perceptibly more when gently pressed.

Fortunately it was the end of the sailing season anyway. I stripped off the bottom paint and sanded down the gel coat, punctured and cleaned out the blisters, let her dry out until spring and then filled the pits with epoxy and coated the hull with West system epoxy, seven coats plus bottom paint.. I sailed her another couple of years before selling her as I was moving.

The leak could have been caused by some sort of temporary delamination that I didn’t detect on haulout, but I fully believe osmosis was a major factor. No sign of delamination was seen as I sanded down the gel coat.

Sorry - bit this sounds like a poor application of resin etc. Until fairly recently - GRP layups relied on employees and their manual applications of resin etc.
There is no way osmotic action could lead to such an event - unless left for substantial number of years .... decades in fact.

Think about it .... to be like "blotter paper" immediately indicates lack of resin application to saturate the Glass Fibre.

 

[dombuckley]

Some good examples of gell coat separation as a result of blistering, and indications of delimitation inside GRP.

Good o' Patrick, getting stuck in and taking the practical approach. 07:03 "I'm 69 years old...and time is ticking..." Ouch, that hurts.

 

[fisherman]

Someone who worked at a local moulder told me he would sometimes hear "Did you put catalyst in that pot? I didn't....."
However, I put a patch on my hull then realised I had only used 0.2% cat instead of 2%. I took it off and binned it. Six hours later it had gone off. When I'm doing general work I'm strict about % mix, but reduce the catalyst as time goes on, as I use the same pot, it goes quicker and quicker.

An osmosis treatment man told me he (very) occasionally saw hulls that had such big blisters on such a thin layup they had to be scrapped.