Learning the HARD way...
Join Date: Jan 2007
Location: Boston / Ft Myers Area
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A calibrated Electrophysics CT-33 detects the level of capacitance that can be established between the 2" plate at the back of the meter and the surface under examination. Among the things that can cause an increase in capacitance reading are proximity to metal (backing plates, copper in bottom paint, aluminum embedded in the core, chain rode in the anchor compartment), surface moisture, as well as moisture in the core.
Tapping with a hammer (phenolic hammer) is used to detect delamination, through a change in the sound of the tap. Without delamination there is a solid "tap" sound, and where there is delamination, there will be more of a "clack."
Moisture in the core can eventually lead to delamination in two ways. First, as the core turns to mush from constant exposure to water (this can take years). And second, in climates that drop below the freezing temperature of the water in the core, as the freeze-thaw expansion and contraction of the water separating the core from the GRP laminate.
Let me try to net this out for you; High readings on the CT-33 meter do not necessarily lead to delamination.
Also, when was the last time that you calibrated the meter?
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USCG Licensed OUPV Captain, ASA 101/103/104/105/106/118 Instructor - Also certified in Marine Electrical Systems