DS Marine Surveys

991 Ridgemount Blvd. Oshawa Ontario L1K2K7 Ph: 905-449-2176
Condition and Valuation Surveys for Pre-Purchase and Insurance - Consultations - Appraisals - Underwater Accident Investigations and Salvage Supervision

Surveyor - C. David Sandford SAMS® / AMS®

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Moisture Detection

Moisture Detection has become a big issue in boats manufactured with both fiberglass reinforced plastic (FRP) and wood hulls. For years FRP hulls were thought to be water resistant but time has shown that not to be the case with some hulls lasting less than a few years before becoming moisture laden causing a subsequent breakdown of the resin / fiberglass matrix and resulting structural damage. See: Osmosis the dreaded "O".

To compound the problem very few FRP hulls, manufactured recently, over approximately 25 feet are solid laminate but are manufactured with some type of core material surrounded on the inside and out by a FRP laminate. Core materials are usually End Grain Balsa, various types of closed cell foam or wood (plywood and cedar strip being most popular). See: Fiberglass Hull Construction The problem arises when water is allowed to penetrate the FRP laminate and it migrates into the core. The core then soaks up the moisture and may become soft or in some cases even crumbly.

The electronic moisture meter is the instrument most widely used by surveyors and industry professionals to detect elevated moisture levels in FRP and wooden hulls. These devises are useful tools but the operator needs to be aware of their limitations.

These Limitations Include:

1- Different FRP laminate and core configurations read differently making "apples to apples" comparisons difficult.

2- Many hulls are constructed of solid FRP below the waterline and some type of core installed in the topsides. This type of hull will also provide different readings if the operator attempts to make comparison readings using the topside for a baseline differentiating between it and the reading taken below the waterline.

3- Since moisture meters do not actually measure moisture content but in reality measure the electrical conductivity or capacitance of the substance in question and since many anti-fouling coatings and gelcoats contain metal this can also affect the readings.

Warning!

4- In Sub Freezing Ambient Temperatures moisture meters are virtually useless. This is because as water freezes crystallization occurs and the tiny air pockets which are formed in the ice are non-conductive. The noise meter will read this as virtually zero. Also because frozen substances are very hard percussive soundings taken on these surfaces will be inconclusive a well. Assessments of wood, fiberglass and composite structures performed when ambient temperature are below freezing cannot and should not be considered accurate.

Moisture meters are however very useful in indicating different moisture levels across a given area of an object therefore when used correctly and with care wet spots in a hull can be pin pointed. This method in conjunction with other methods such as percussive sounding can in many cases produce an accurate assessment of a particular object.