Hull moisture meters are considered reliable instruments to determine the amount of moisture levels within composite hulls, non-invasively, and to an extent, without causing any hull damage.
However, if given in the hands of an inexperienced surveyor who believes that meters always produce infallible results is a recipe heading for disaster.
Very few surveyors understand that the instrument is generally subject to varying and limitless conditions, for many of which there are no absolute answers, and thus the use of meters is part science and part skill.
With over 21,700+ varied assignments under our belt, it is prudent to understand that while moisture meters are reasonably simple to use, it is not without its caveats, and coupled with inexperience, it comes as no surprise that its incorrect use has led to far more unnecessary bottom repair jobs to fiberglass boats than all other causes put together.
At Constellation we understand that Moisture Evaluation
is considered a core step during to conduct a pre-purchase
survey for fiber-reinforced Yacht hulls, however under
no circumstances should every reading of elevated moisture
be construed as an indication of osmosis and the surveyor
must take great care to corroborate finding by alternative
methods. In other words, we are rather explicit in stating
that there is no simple and direct correlation between
moisture meter readings and hull condition, and we are
not tempted to make a diagnosis based solely on moisture
meter readings. While this may sound contrary to popular
belief, let us look at why this is the case:
A composite boat hull is generally a mixture of a various
material matrix reinforced with fiber glass, and due
to the way these are molded, contain minute gaps and
voids, which form the base of what is commonly known
as Osmosis.
Water can diffuse into the laminate hull, collect within
the voids, and over a period of time, and as a result
of the internal build-up of water collection, the size
of the internal voids tend to increase to an extent
where blisters are formed, commonly known to compromise
the structural integrity of the hull. These Blisters
become the visible evidence of progressive hull moisture
content and osmosis.
This is where Moisture meters are generally useful,
however, there are some major considerations to account
for before some surveyor is declared to a potential
buyer – “The entire hull has elevated moisture reading”.
(May we hastily add, there are not practices at Constellation
Marine Services or their trained yacht surveyor.)
Testing on wet and recently hauled boat hulls:
We have significant and objective experiences that indicate
a varied difference in Moisture readings between boats
tested on haul-out, versus those tested when “dried
out”. This is because of the very nature of the hull
property of the yacht itself, which will produce aggregate
results much lower than when tested immediately after
it being hauled out.
It is thus prudent to appreciate that surveyors DO NOT rush into moisture measurements soonest a boat is out of the water, doing so will generally lead to obtaining elevated levels of moisture associated with residual wetness, and not in line with the actual condition of the Hull. End clients need to be informed that a certain level of time be made available for boats to be dried out before moisture meter measurements are initiated.
Gel Coat Testing:
Very few surveyors understand the behavior of Gel
coats. There are Gel coats that are prone to water absorption,
and thus when tested will lead to higher than actual
moisture results.
In an ideal situation, Hull moisture content testing
is recommended to be conducted on surfaces stripped
of gel coats and anti-fouling coating, however in reality
sellers will be very reluctant to have their boats uncovered
from the coating and it is reapplied once again.
Conducting only exterior testing
It is common fallacy to report on moisture results of
tests carried out on exterior hull areas only, and this
is often an erroneous modality adopted by inexperienced
surveyors.
The correct procedure would be to corroborate readings
with tests of the inner surfaces of the hull, which
are not submerged, and out of the way of compartments
such as bilge keels (with water trapped), freshwater
tanks, compartments housing hydraulic equipment such
as stabilizers, etc.
Conducting only exterior testing
It is common fallacy to report on moisture results of
tests carried out on exterior hull areas only, and this
is often an erroneous modality adopted by inexperienced
surveyors.
The correct procedure would be to corroborate readings
with tests of the inner surfaces of the hull, which
are not submerged, and out of the way of compartments
such as bilge keels (with water trapped), freshwater
tanks, compartments housing hydraulic equipment such
as stabilizers, etc.
It is important to thus understand that after inner hull areas, assuring that the surface is made clean and dry – will be a positive indicator of a wet core, than just assuming the readings tested over the exterior hull plating.
Blistering
The common thought that high moisture readings are a
forerunner to blistering is debatable and in general
incorrect.
The rather correct way to report would be that high
moisture may result in blistering.
It needs to be understood that boats built with high-quality
materials have little tendency to blister, so to assume
that high moisture readings will lead to blistering
is not true.
Low quality resin combined with excessive use of CSM Hypelon are generally considered as primary causes of blistering, it is thus important for the surveyor to have knowledge on the material and construction of the particular boat being surveyed.
So how is it to be done?
The International Institute of Marine Surveyors
“Code of Practice for the Measurement and Analysis
of the Wetness of FRP Hulls” recommends that
"The surface must be carefully cleaned. A large number
of random 4" x 4" areas must have paint or other coating
removed down to the gel coat. The vessel should be out
of the water for at least 24 hours. The minimum number
of measurements must be equal to approximately, one
per square meter (3.3 feet) or 50-100 on the average
35-40-foot boat".
Experienced surveyors will use a moisture
meter in one hand, with a rubber hammer in another.
The time-tested tapping acoustics produced between a
wet and dry hull provides a clear indication of the
status of the hull.
The only reliable method would be to have the hull surface
tested by moisture meters from the INSIDE.
Care should also be taken to ensure that surfaces are
clean and without salt residue, and this can be overcome
by cleaning with a damp cloth.
We avoid reporting moisture readings as a percentage
because that is basically inaccurate.
A major benefit of moisture meters is in locating the presence of water penetration in and around areas of hull fittings, and this provides a good indication of a POTENTIAL problem, and therefore an assurance that this could be fixed with a good quality marine sealant.
In our experience, moisture meters are useful instruments, if used with care, judgment, and experience, and surveyors must resist the temptation to only rely on readings from moisture meters to make a definite diagnosis.
Contributed by Capt. Vispy Rusi Dadimaster
