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6.1. Visual inspection of a test hole
6.1. Visual inspection of a test hole Based on the new understanding of "osmosis", its varying forms can be easily identified prior to the repair. Use the tip only of a drill bit with the same diameter as the laminate thickness to drill a conical hole through 2/3 of the laminate. If the laminate is cored, drill just into the core. Drill about a dozen such holes around the underwater hull where
the moisture readings are higher than average. The conical walls in the hole will then show dark discolouring of any affected laminate layer. Mostly in large hulls fluid may seep or well out (use protective eye glasses when drilling). Place a strip of litmus paper against the inside of the hole. If the pH is below 4.5 and no fluid seeps out, the discoloured layers are affected but not yet de-laminated. If fluid of this acidity seeps out, the layer has lost some bond. The lower the acidity (higher the pH) the worse the delamination. Should low acidity fluid (pH above 5.5) well out of the hole, there will be very severe de-laminations in one or more layers. When the hull is to be launched after the inspection, the holes must be cleaned with acetone and filled with a high quality epoxy filler.
6.2. Measurement of hull deformation at dry setting. With a type 3, and bad type 2 case, the keel can usually be seen to sink into the hull a few centimetres as the vessel is left standing on the keel by dry setting. A ruler can be held across the bottom behind the keel during the dry setting for measuring. A common dry and shield repair will have no influence on the softness of the hull. By HYAB repair or repair involving relamination the back of the hull must be jacked up to proper position before the repair. Otherwise the deformation will remain after launching.
6.3. Meter readings when IR or dehumidifier are used. During and after the drying phase when IR heating or dehumidifiers are used, a Tramex Skipper moisture meter can also give a hint as to the type of "osmosis". Gel coat and degraded laminate must be removed before drying. 6.3.1. Green readings remain. If the meter after a normal drying shows green and also shows green when drying equipment has been disconnected for 24 hours, it is a type1 "osmosis" or interfacial blisters. 6.3.2. Red readings return. When red readings return after the drying equipment has been disconnected for 24 hours, it indicates an "osmosis" type 2 and shielding will not stop the "osmosis" without further treatment. In such a case extended drying is not sufficient! The laminate will contain substantial amounts of water bound to glycol and salts. Dehumidifiers will have no effect at all. An extended IR heating combined with steam- or pressure wash every other day might create green readings on a Sovereign or on range 1 of a Skipper meter. The Skipper range 2 will still show red because all of the glycol will not be removed and there is at least a 60% risk that some styrene and acid residues are left in the FRP and will keep the "osmosis" going on.
6.4. Moisture meter readings after open air drying. Using open air drying after gel coat and degraded material have been removed, the hull must be pressure washed at least every second week, or acids and glycol may clog the capillaries and prevent the moisture from escaping. Normal drying time needed is 2 - 6 months depending on the climate. 6.4.1. Readings become green after the drying period. In the case of a type 1 or a mild type 2, the readings will be green after a normal drying period. Surveyors will at this point accept the hull as ready for water shield application. However there is a big risk, that small amounts of acids are left under the surface. Styrene enclosures in the deeper laminate layers will always remain after open air drying. 6.4.2. Readings remain red after a normal drying period. If the meter still shows red figures after the normal period of drying, a type 3 or a far developed type 2 is indicated and further open air drying will be futile.
6.5. How to choose the proper range of a moisture meter. If the moisture meter is marked for the material to be measured, e.g. "wood in salt water" or "fibreglass reinforced plastic", one must be aware that those ranges are meant to show when the material is ready for painting. They are not designed for "osmosis", even if some brands propose to be. 6.5.1. Palm of hand inside of hull behind meter indicates range to use. To be sure of which range of the meter shall be used, ask somebody to put the palm of his hand against the inside of the hull behind the meter. Choose a spot where the readings are low without the hand. The proper range will clearly react and just reach the red area, when the hand is put in place. 6.5.2. Many meters are not suitable for osmosis control. If no range of the meter clearly reacts with the hand, this type of meter is not suitable for "osmosis" measurements!
6.6. All blisters are not a sign of "osmosis"! Especially in the water line area algae may penetrate the gel coat, where the roots decompose and form blisters. Check the contents of the blisters with a litmus strip. If there is no acid reaction, there is no "osmosis"!
6.7. "Osmosis" does not always form blisters! Sometimes one will find other damages or no damages at all in the gel coat. 6.7.1. Woodworm pattern. On older boats one may find damages in the gel coat and the first FRP layer looking like the ones woodworms cause between wood and bark. The pattern will mostly show through the surface of the gel coat. Theories about anything from "sea worms" to plastic eating bacteria are all wrong. The damage is caused by any of the three "osmosis" types, and is a function either of the first FRP layer applied over insufficiently cured gel coat, or that the polyester was mixed with talcum or chalk when the hull was moulded. This type of worm-like pattern only occurs when methyl acetate powder bound fibreglass mats were used in construction. 6.7.2. Cracks in the gel coat. Some types of gel coat will crack allowing the osmosis surplus to escape out into the sea. 6.7.3. No signs at all in the gel coat. Especially when some layers of heavy roving have been used in the laminate, the "osmosis" process can carry on for many years inside without showing any blisters or other signs. 6.7.4. Recurring "osmosis" without blisters in the shield. Certain water shield types as well as osmosis repair including re-lamination of more than one layer are too hard to allow blister formation. As a result often recurring "osmosis" separates the water shield or the new laminate from the original hull without any visible signs.
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