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5.1. Osmosis" is not only cosmetic but severely harmful.
5.1. Osmosis" is not only cosmetic but severely harmful. Many boat owners believe that "osmosis" is only a cosmetic problem with superficial blisters. HYAB and other research tests prove that it is severely harmful. 5.1.1. 30% loss of strength before gel coat blisters form. The truth is, that already an "osmosis" type 1 causes about 30% loss of strength in the FRP due to the alkali penetration. This initial loss of strength will not be recovered by a repair without a heat treatment, (e.g. HYAB or IR heating) as indicated by the following test results.
5.2. Test of "osmosis" FRP panels before and after repair: Blow energy (J) needed for a 6 mm radius point to penetrate a test sample 80 mm in diameter and 10 mm thick was determined. The black bars in the diagrams below represent top and bottom results from 4 samples of each kind tested. The average value of each test is cross marked on the corresponding bar. Only FRP originating from PVA bounded fibreglass mat has been used. FRP with methyl acetate bounded fibreglass is generally claimed to lose less strength. As most FRP hulls are made from the PVA bound mat, there was no other object available to prove this theory. Samples of different types of "osmosis" to be tested have been of various thickness and age. The values obtained have been adjusted for correspondence to the average 10 mm test thickness and the charts are estimated to be > 85% accurate "Osmosis" of type 2 and 3 are impossible to cover with a few test samples. The unfilled bars beside the filled ones show an estimated range based on field experience. A FRP hull that can be penetrated by a force corresponding to a blow energy of J 27 in this test must be considered as not seaworthy. To achieve an approximation of "late stage osmosis", the test samples are boiled 7 hours in distilled water. This corresponds to about 5 years use in 15º C normal salt seawater.
TEST NR 1: Different types of "osmosis"
TEST NR 2: "osmosis" type 1 after repair
TEST NR 3: "osmosis" type 2 after repair
TEST NR 4: "osmosis" type 3 after repair
5.3. "Osmosis" often renders a hull not seaworthy. Analysing the above tables indicates that most types of "osmosis" will within a few years time bring the strength of a hull to below seaworthiness. Especially fin keeled sailing yachts will be considerably more vulnerable to grounding.
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