| Nearly 40 years after the first cases appeared, | | | | which has been on a hard standing for a year or |
| we have learned a lot about osmosis - but it's still | | | | so, or which has not even blistered yet, will be a |
| a problem. What causes osmosis, how to prevent | | | | nigh on impossible task. |
| it and why treatment can fail? | | | | Could my boat get osmosis? |
| Boat owners were petrified of the word and | | | | Unless the boat was epoxy-coated, in a word yes! |
| many would simply not set foot on a boat known | | | | However, there are many variables that affect |
| to have dreaded "pox". A blistering boat? | | | | how likely anyone boat is to suffer from blistering |
| We have undoubtedly learnt a lot over the years, | | | | (early in its life). A boat kept in the warm waters |
| and most owners are now quite relaxed about | | | | is more likely to blister prematurely than one kept |
| sailing offshore on a boat with a few blisters on | | | | in colder conditions. Fresh water also accelerates |
| its bottom. | | | | the process, but not as much as temperature. |
| What is osmosis? | | | | Preventing osmosis |
| In short, osmosis is usually defined as: "The | | | | Cliche as it sounds; osmosis is best prevented by |
| equalization of solution strengths by the passage | | | | keeping boats well away from water. However |
| solvent (usually water) through semi-permeable | | | | unhelpful this may sound, but protecting the |
| membrane", or something similar. | | | | underwater hull a glassfibre boat with epoxy |
| In the field of biology, osmosis is used by plants | | | | before she is launched will, in most cases, prevent |
| and trees to draw water and nutrients from soil, | | | | osmosis from ever occurring. A properly applied |
| and plays essential role in the function of cells in | | | | osmosis prevention scheme should also resale |
| body tissues. The basic principle can be explained | | | | values. |
| by imagining container which is divided into two | | | | Osmosis treatment failures |
| separate chambers by a semi-permeable | | | | By and large, the owners of glassfibre boats now |
| membrane. Simply, boats with fibreglass bottom | | | | accept osmosis as an inescapable fact of life, |
| have a few millimetres thick gel coat (usually | | | | although for newer boats it is not the certainty |
| white, although other colours are present too). | | | | that it once was. Osmosis treatment has always |
| Water can eventually break through and reach | | | | been a challenge and even today a significant |
| fibreglass layer, and this is where blistering occurs. | | | | number of treatments fail, usually by blistering. |
| What we have learnt? | | | | Given correct preparation, an osmosis treatment |
| Firstly, we know that osmosis is a natural ageing | | | | should last between eight and fifteen years. After |
| process in glassfibre - in much the same way that | | | | this the epoxy coatings may start to break |
| steel and aluminium fatigue and corrode, and that | | | | down, and will need to be removed and reapplied. |
| wood rots, shrinks etc. On the positive side, | | | | Most of those treatments that fail prematurely do |
| glassfibre is comparatively cheap to fabricate, light | | | | so because glycol is not completely removed |
| in weight, yet remarkably strong and can be | | | | from the laminate before epoxy coatings are |
| moulded into complex shapes. Above all, is almost | | | | applied. |
| maintenance free. | | | | Failures in osmosis treatments are usually |
| Will osmosis make me sink? | | | | highlighted by blistering of the epoxy coatings. |
| Boats are unlikely to sink because of osmosis - | | | | Blisters connected to residual glycol will usually |
| although they can be difficult to sell. | | | | remain visible for several weeks or months after |
| Don't treat it too soon! | | | | the boat is lifted, and will contain sticky or oily |
| Early treatment of osmosis is rarely beneficial. | | | | fluid. |
| The reasons for this are not to difficult to | | | | In this regard, it is interesting to see how many |
| understand: osmosis is a very slow process, and | | | | boats are treated for osmosis two or three times |
| we know that it can take anything up to 30 | | | | over, yet in many cases their gel coats are still |
| years for the solutes to migrate in sufficient | | | | comparatively intact. |
| volume to form blisters in the gel coat. Osmosis | | | | The problem here is that unlike steel (which is the |
| treatment is best started at the end of the sailing | | | | subject of several worldwide preparation |
| season, as soon as possible after lifting out as the | | | | standards), there are no formal standards for |
| solutes will be most dilute at this time. By | | | | preparing glassfibre laminates. |
| contrast, removing solutes from the hull of a boat | | | | |