Moisture, humidity measurements
Moisture measurements are carried out on the underwater hull, when hauled out and preferable dried for some hours, day’s. But measurements can of course also be done on other parts of a ship, such as deck, superstructure etc.
A moisture measuring device is an appliance for determining the overall condition of a polyester, fiberglassed or wooden hull.
The measurements should be considered as indicative and can be influenced by presence of metal, moisture on interior hull etc etc.
Prior or during the measuring locations of metal fastening materials or parts such as tanks are to be located.
The non-destructive moisture meters as the Tramex or Sovereign also react to the presence of such metals.
If there is reason to do so, we can also measure with probes which are pressed into the material. This obviously results in damage to the paint or lacquer, and we do not use such equipment without the permission of the owner.
With moisture measurements signal penetrates deep in the material, so to detect moisture present, or the humidity of the surface with less penetration depth.. The indications on the meters when measured deep in the material are not a percentage for moisture, but a number on a scale of 1 to 100 (or equivalent). By comparative measurements of known ‘dry’ material the readings are compared. The value gives an indication of moisture absorption, often related to time that the yacht is on the shore, has been lying in the water.
For the measurement of moisture on the surface of a material, the meter can be set to indicate moisture presence as a percentage. Such measurements can be useful before coating the hull.
The manufacturer has indicated a maximum humidity of a surface which is to be coated. We often hear that the humidity was somewhat above this maximum, but the painting job was without problem. Well ….. at that time it looked ok, but to high humidity is the basis for problems with the coating after some time.
A little, almost dry enough does not exist ….. if a higher humidity was allowed, the manufacturer would indicated such for his product. (it would give him a sales argument.
Often we notice that yacht are boats are condemned to be wet, thus having osmosis, by measuring the with wrong scale setting on the meter, the presence of metallic parts, or even in the building material (eg ferro-cement). The is often the case when measurements are performed by users, with non or little experience with the usage of the meters and and interpretation of the readings. Every one can hold a meter in it’s hand, but it takes experience, and integrity to perform an objective survey. Have moisture measurements therefore always be taken by a independent qualified yacht surveyor, who has the experience and knowledge.