What is Osmosis?
Osmosis refers to the passage of water across a thin membrane from a dilute solution to a more concentrated one. In other words, water moves through the semi-permeable barrier trying to even out the difference in concentration between the two sides. 2) What is reverse osmosis (RO)? The other side of the coin is reverse osmosis. A pump is used to cause a difference in pressure. This difference in pressure means that that water is forced through the membrane. Pure water molecules (H2O) are small enough to pass through the membrane whilst larger solute molecules get trapped. When water is processed by reverse osmosis a large fraction of dissolved material is removed. The cleaner the input water the cleaner the output water will be. Conversely, if your input water is clean enough, you may not need an RO unit. 3) How does RO equipment work? There are 3 stages to R.O. filtration: 1. A pre-filter (PR1-25-OE) initially removes larger suspended particles from the raw water 2. Water is forced th
How Osmosis Affects GRP Hulls Osmosis is the condition of visible blisters on a boat’s hull, caused by water absorption. The process of osmosis is the same mechanism by which plants and trees draw water up from the soil to their branches and leaves. Main Causes of Osmosis. Long periods afloat without lay-ups. Warm tropical waters. Fresh water is worse than salt water. Resins that are coloured (including white ones) are more affected than clear resins. The Process of Osmosis. The fibreglass mouldings on a yacht hull are not completely waterproof. Individual water molecules are so small that they can find their way into the layers of glass and resin which form the boat’s hull. Problems start to occur when water molecules merge with other chemicals inside the laminate. These are chemicals such as water-soluble materials, emulsion binders for example. The water molecules can then have a chemical reaction with these substances, forming larger molecules of a new chemical, often acidic. Unlik
Osmosis quite simply is the physical process by which a liquid from a weaker medium is drawn through a semi-permeable membrane into a stronger liquid medium. So what does this mean and how does this relate to boat hull damage? The simple answer is probably not a lot! Contradicting earlier theories, the damage from “osmosis” is not caused by excessive water permeation. There are absolutely no osmotic forces involved as the gelcoat is an absorbing material which can never act as an osmotic membrane! Instead it is the process of hydrolysis, which creates the water soluble corrosive products which in turn create the familiar cavities. (Hydrolysis is the general term given to the reaction of any material with water, for example organic compounds like polyester resin, itself the main constituent of GRP laminates.) Once the cavities have formed, then excess water will enter giving rise to high moisture readings. This process may normally be slow, but the presence of free acids or alkalis will
Osmosis is based upon the fundamental pursuit for balance. Two fluids containing different concentrations of dissolved solids that come in contact with each other will mix until the concentration is uniform. When these two fluids are separated by a semi permeable membrane (which lets the fluid flow through, while dissolved solids stay behind), the fluid containing the lower concentration will move through the membrane into the fluid containing the higher concentration of dissolved solids (Binnie e.a., 2002). After a while the water level will be higher on one side of the membrane. The difference in height is called the osmotic pressure. What is Reverse Osmosis? By applying a pressure that exceeds the osmotic pressure, the reverse effect occurs. Fluids are pressed back through the membrane, while dissolved solids stay behind. To purify water by Reverse Osmosis membrane, the natural osmosis effect must be reversed. In order to force the water of the brine stream (high salt concentration)