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by
David Pascoe |
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Illustration
of Water Absorption From a Hull Interior
Many Water Saturated
Hulls Don't Blister
Photos by David
H. Pascoe, Marine Surveyor
1.
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Photo
#1.
This photo is taken in the forward cabin
just above the point where the sole is taped into
the hull sides and below the waterline. When I first
lifted the carpet here, I was taken aback because
my first impression was that the cabin sole tabbing
had been laid over painted fiberglass, since the
aft section of the interior hull was painted. As
you can see, the tabbing is a pink color while the
hull laminate seen at the top of the photo is not
translucent like the tape but completely opaque.
(Tape or tabbing are the strips of fiberglass used
to join parts together, such as a bulkhead to the
hull in this case.) |
2.
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Photo #2.
This is one of the most graphic illustrations
you will ever see of differing rates of water
absorption in various areas of one hull. This is
looking straight down at the centerline bilge in
the forefoot where a bit of black water lies at
the bottom of the vee (the black vertical line).
The yellow section at the center is a separate layer
of fabric which has absorbed far more water than
the surrounding laminate and turned yellow. Whereas
in the upper part of the photo, you can see a different
layer of fabric that is pinkish and is not as opaque,
meaning that it has absorbed less water.. Notice
that the coloration is the exact opposite of that
in photo #1, where it is only the tabbing that remains
pink and translucent. Since both sections of laminate
are equally hard, most likely what this is telling
us that two different kinds of resin were used in
this lay up. Because of the hardness, cure rate
does not seem to be a factor as it is in many cases.
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3.
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Photo #3.
This photo was taken a few feet further
aft. it's the hull bottom between the keel and the
stringer (top of photo). Here the laminate has a
blotchy appearance - its whiter toward the left
and center, while a more translucent area is seen
at right. At the bottom is an oily bilge high water
line. The stringer has absorbed very little water
and remains translucent, whereas the bottom laminate
has turned opaque. The differing colors, which
are not just surface contamination, suggest that
chemicals in the bilge water have also played a
role in the discoloration.
What is most distinguishing
about this photo (#3) is the progressiveness in
the change of color of the laminate down toward
the keel; the deeper in the bilge, the more opaque
the laminate. When a laminate, or plastic, absorbs
water it turns cloudy or opaque. We take this as
clear evidence of just how much water a hull can
absorb from the interior. |
Go to Article
First Posted in 1997 at David Pascoe's site www.yachtsurvey.com.
Post: June 16, 1998
, Last reviewed 11/28/98
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