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I'm aware of an hydrometer, I believe lumber mills also use them to QC check their drying processes. The instrument I was referring to operated, I believe, on transmitted frequencies. Wet wood bounces a different frequency tan dry, just like a rocky bottom vs. mud. It's some type sonargram. I think Whaler uses something like it to locate posssible void cavities in hull molds that need more foam. Marine surveyors use the device to measure the degree of hull saturation. It gives them an idea as to stringer integrity and added weight on large vessels. A boat in the 35 - 50 foot range can easily have hundreds of pounds of water imbedded in its below deck structure due to crack seepage or severe blistering.