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by
David Pascoe |
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| From
Article
Hull
Design Defects
Part I
Photos
by David H. Pascoe, Marine Surveyor
| Here's a good example of poor design and
construction detail.
Utilizing a glass over plywood framing system, there are
no fillets under the frames or stringers which are butted hard
against the hull.
This creates hardspots with the propensity
for stress cracking.
In addition, the length-to-height ratio of the tall stringers
creates instability where the stringers are likely to buckle
under impact loading. Additional framing between the stringers
is needed to stabilize them. Also note that there are only two
hull side stiffeners so that flexing of the sides is likely
to cause hull/deck joint breakage. In the forward section, a
dog leg in the stringer profile can be seen. |
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Dog leg in stringer which
was cut down to make the engine fit. |
The stringer proved to be so
weak that the engine bounced every time the hull
hit a wave, ultimately bending the shaft and wrecking
the transmission. Also notice the hard spots created
by the fuel tank mounting pads at top of photo that
caused stress cracks in the hull. |
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Here's what often happens
when a large cut out is made in a structural bulkhead.
In this case, the 3/4" plywood
was fractured in three places. |
| This is another good example of the structural
integrity of a bulkhead being defeated by cutting
it full of holes.
It is perforated like a postage stamp and is destined
to fail.
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Floor frames under main
mast of large sail boat.
Properly designed by the designer,
the builder apparently saw nothing wrong with drilling
the frames full of holes. |
Here you can follow the fracture
along the perforated effect of the holes at right
and left sides. Frame was so weakened that ply separation
also occurred. A marine surveyor got sued because
he either did not find or report this condition,
which was far more extensive than this photo shows. |
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Stringer system of a 48'
Hatteras Hi Performance Convertible.
Note that the width of the top
hats are about the same as the width of the bottom
panel spans. |
This is a good example of structural
overkill, yet demonstrates the builder's concern
with strength. Also note the webs between stringers
under the engine mounts that provide extra stability.
Despite the appearance, these top hats are actually
quite thin. When slamming occurs, the thin sections
will absorb much of the impact, hence the web sections
to increase stability and insure that the engine
beds do not move. |
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The importance of stringer
stability is revealed by this stabilizing strut,
in addition to the mounting frame above it.
Yacht: 56' Magnum, 2600 HP. With
this kind of horsepower, the mounting system and
shafts will not tolerate movement. |
Go to Article
Related Photos: Hull
Design Defects Part II
First posted 6/10/97 at David Pascoe's site www.yachtsurvey.com.
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