One of the most widely used instruments for the marine surveyor is the hygrometer or “moisture meter.” This instrument is produced by various companies in the world.
There are different types of hygrometer, but the purpose remains the same: quantifying the percentage of moisture present in the solid and sandwich laminate.
What this tool cannot do
Give an absolute value, that is, the value will be referable only to the boat examined; each boat and each processing will start from a different moisture content so it will be useless to compare one hull to another to draw conclusions. It also cannot determine or define a dry or wet boat because the value will have to be understood and contextualized by the appraiser. Finally, it cannot determine osmosis but only help to understand how “fertile” the soil is to the development.
Why is the hygrometer necessary?
First and foremost, as mentioned above, the hygrometer can help understanding the moisture content of the laminate and then contextualizing the value obtained with the age, type of construction and distance in time from hauling, the surveyor will have an idea of how much the gelcoat, for example, has lost its waterproofing function. How can he/she assess the state of the hull and what intervention is most appropriate, then?
The measurement as mentioned requires experience in analyzing the data. A boat will be able to tolerate a high humidity value even for many years without developing osmosis or vice versa. A professional hygrometer will also help the appraiser to assess the state of the sandwich of even a teak-covered deck, just find from the inside an uncovered part and measure it.
There is no rule about the boat’s previous hauling time for optimal measurement. Certainly a dated boat if hauled a few days earlier will be harder to understand. But – as mentioned – the marine surveyor will be able to put the measurement in context. Just as a newer boat may safely be measured a few hours after hauling.
My way
By using various hygrometers over time and comparing their data, I have chosen a digital readout that I trust quite blindly. It is my practice to test the instrument on the upper part of the boat I am going to survey to get a comparison on the lamination. It is also advisable to scrape the anti vegetative paint to check the gel coat directly.
You should never forget that false measurements are often obtained due to: layers of epoxy-based insulation, water in the bilge, tanks etc etc.
In short: it is not enough to have an instrument to christen a boat… There’s the sea, in between.