Good
New member
Is it true that if you leave the Boat "polyesterfiber" in the water over winter then
your are in bigger risk to get Osmosis in the future?
your are in bigger risk to get Osmosis in the future?
Osmosis
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Footpad
New member
That is certainly what they say - based on the fact that osmosis is the transfer of liquid through a semi-permable membrane (your gellcoat) - ergo the longer you leave it in the water the higher the risk of the transfer taking place and without regular drying out the greater the risk of the chemical changes that cause the blisters (I think?) and it is worse if the water is fresh rather than salt.
vyv_cox
Well-known member
The driving energy for osmosis is dilution of a concentrated solution by a weaker one. In the case of polyester the concentrated solution is uncured hardener, resin, additives, etc left behind by incomplete curing. The weaker the solution outside the semi-permeable membrane (the gelcoat) the greater is the energy available. Hence the effects are worse in fresh water. The phenomenon is purely physical, no chemistry involved at all. It seems likely that once the diluting force reaches the inside of the gelcoat no further dilution can occur, because the layup GRP does not have the properties required of a membrane.
airbubble
New member
proven true. Osmosis is a reversable process, specially in its early form. So any moisture (not even water) absorbed over summer will evaporate during winter lay-up keeping the dramatic effects at bay a long time.
steffen
New member
Vyv, you are right in stating that osmosis is purely physical and not chemical. Then again, it is not osmosis that is the problem in GRP hulls, it is hydrolysis that does the damage.
When water molecules get into the GRP (by a form of osmosis) the collect in the voids that have been formed in the curing process. Usually those voids contain uncured substances like resins and other unbound chemicals that can react with the water to form an acid. Teh resulting molecules are bigger than the original molecules and hence expansion takes place. The result is that the GRP is forced apart; delamination. The osmosis (ingress of water molecules) process then is reinforced by the acid formed and more water comes in.
The process is thus self-supporting and if neglegted can cause damage.
On the other hand if you take the boat out of the water in winter and check for blisters and treat them there is absolutely no cause for alarm
Before you think i am a chemical expert, read
"www.cps-ecp.org/squadrons/1407/OSMOSIS.pdf " or
"www.yachtsurveys.co.uk/faq_osmosis.htm"
Happy sailing, Steffen
When water molecules get into the GRP (by a form of osmosis) the collect in the voids that have been formed in the curing process. Usually those voids contain uncured substances like resins and other unbound chemicals that can react with the water to form an acid. Teh resulting molecules are bigger than the original molecules and hence expansion takes place. The result is that the GRP is forced apart; delamination. The osmosis (ingress of water molecules) process then is reinforced by the acid formed and more water comes in.
The process is thus self-supporting and if neglegted can cause damage.
On the other hand if you take the boat out of the water in winter and check for blisters and treat them there is absolutely no cause for alarm
Before you think i am a chemical expert, read
"www.cps-ecp.org/squadrons/1407/OSMOSIS.pdf " or
"www.yachtsurveys.co.uk/faq_osmosis.htm"
Happy sailing, Steffen
steffen
New member
True, osmosis is reversible but the resulting hydrolysis is not and thats whats causing the damage.
Happy sailing, Steffen
Happy sailing, Steffen
