Surveying Wood Hulls
PART 2: How to Survey A Wood Hull
by David H. Pascoe, Marine Surveyor
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Introduction
PART 1:
Materials and Causes of Problems
(with 4 pictures)
PART 2:
How to Survey A Wood Hull
PART 3:
Appendix
Contrary to common belief, a great deal can be
learned about the condition of a hull from examination of its interior.
One just has to have experience and know what he's looking for. I have condemned
hundreds of wood hulls long before the survey ever got to the haul out stage
and I'll explain how and why.
Opening Up Concealed areas within a hull are
always a problem but, most wood vessels are constructed in such a way that
enough access is available to make a fair assessment. It is usually
possible to pull up floors (such as screwed in place plywood panels and
the like) and remove enough paneling that one can get a fairly good
glimpse of the bottom and lower sides. Carrying an electric screw gun is a
must in order to do this quickly and effectively.
Yacht surveyors do carpeting and beds. That means one has to move a lot of
mattresses, bedding, carpets and emptying out of lockers, etc. Once the
interior is opened up as best possible, he's ready to begin. The above
discussion provides a lot of clues as to what to look for.
Planks & Frames Three important tools are a
slim but heavy gauge pry bar - of the sort used for pulling nails - a
heavy hammer and a large standard blade screwdriver. Check the joints
between planks and frames visually, looking for gaps or any sign that the
plank is not tight against the frame. Then use the screw driver to test
the wood for softness on both plank and frame near the mating surface. If
the frame is cracked or the wood is soft, one doesn't have to go any
further. Soft wood and cracked frames are dangerous conditions that
mandate repair.
Try to slip the pry bar under the frame and pry gently. Does the frame
move or rock slightly? If so, there is a fastener problem. This should be
done at every opportunity along the keel or garboard area. If the frame
ends are split or soft, repairs are necessary. If dealing with tall, sawn
frames, one can hit the frame with the hammer to see if it is loose.
Weepage Weepage is a process of very slow
leakage, very often involving the capillary effect in addition to just
water pressure from outside the hull. Weepage is not referred to as
leakage because the rate is so slow that the water evaporates nearly as
fast as it enters the interior. It can occur with no sign of wetness, but
inevitably leaves some trace of its existence such as stains, accumulation
of salts and so on.
Certainly its not feasible to go through the entire hull testing all
frames and planks in this manner, and fortunately it is not necessary
except for the keel area where this needs to be done wherever possible.
Further up from the keel, we can limit our physical testing by looking for
signs of weepage. Anytime there is evidence of water migrating through
seams, corrosion of fasteners has to be suspected. Weepage shows up in
various ways, often depending on whether the wood is painted or bare, its
age and so on.
In addition to water stains and evidence of corrosion such as rust or
green copper oxides, accumulations of dried salts and so on, angle
hair, or shredded wood fibers is a dead give away of weepage. Contrary
to mythology, angle hair or fuzzing is not caused by electrolysis but
rather the constant wetting and drying of salt crystals within the wood
fibers which damages the wood cells. This effect was first recognized in
the cypress timbers used to shore up the Morton Salt Company mines under
Lake Erie. It was found that exposure to raw salt over time caused the
wood to become badly shredded. This is a condition which only occurs in
sea water and is often found around sea cocks, butt blocks, port holes and
engine room vents, along with any other location where water is leaking
from the decks above.
On the hull bottom and lower chines, it means weepage and that hull
fasteners in any area which reveals this condition must be considered as
suspect. This condition is not associated with fungicidal attack because
the high salt levels preclude fungus. Scrape the fuzzy area hard with the
screwdriver blade. If it is only superficial, this condition can be
stopped by wire brushing and sealing the wood, followed by finding the
cause of weepage and stopping that too. This condition only affects the
inner surface that is exposed to air and evaporation, but once the surface
is fuzzy, it has increased evaporation capability through wicking and must
be addressed. This condition will not extend between the plank and frame,
but will draw water into the fastener area because the accumulated
salts are hydroscopic and attract and condense moisture out of the air.
Use the large screwdriver for testing the hardness of the inner planking,
particularly in the deep bilge or any place that is wet or looks suspect.
I suggest not using an awl or ice pick because this tool penetrates the
wood too easily and may give you a false impression. The screwdriver blade
is just right, and if it goes into the wood, you know for sure that its
deteriorated. Poking around like this is quick and easy so that most
vulnerable areas can be quickly covered.
Chine Areas The chines are an area not only of
high stress, but an area that is also prone to leakage. And it is this
leakage that endangers the fasteners. The surveyor should take every
opportunity to inspect the chine areas and when evidence of weepage is
found, the area should be targeted for special attention. Remember that
weepage is the precursor to corroded fasteners.
Bottom Frames are often joined to side frames with knees that are through
bolted. Looseness or corrosion on these bolts are a warning sign that all
is not well.
Forefoot The two most common areas for
sprung planks to occur is the garboard and the forefoot area. The forefoot
planking is difficult to check because this is the point where the planks
narrow into the stem. But, again, signs of weepage or leaking is usually
present when fasteners are wasted and planks are loose. Use the
screwdriver and insert the blade into the intersect of plank and stem and
push hard. This should be done on both sides in every area that can be
reached. Again, this does not take long if the area is accessible and will
readily show up rot and looseness.
Transom The intersect of bottom and side
planking to the transom is yet another area where leakage and
deterioration are prevalent. This area is also often difficult or
impossible to reach, being obscured by fuel tanks and exhaust pipes and
whatnot. Yet the surveyor still has a few diagnostic tricks.
If reachable, probe the wishbone transom frame from both above and below.
Probe from the intersect of bottom planks and frames, and transom plank
and frame. If the wood is at all soft, the problem is serious and needs
further opening up and investigation. Examine the intersect all the way up
to deck level. Is there water leaking in from above? If so, what is it
doing to the wood and fasteners? Check from the exterior: are there open
seams and signs of rot on the corners? If you see it above the waterline,
what's going on below? Remember that open seams are allowing rain water
in, and fresh water can be disastrous.
Keel Bolts, Keelson, Clamps and Stringers Check
these major structural members for signs of working. Look for unevenness
of scarph joints or any other signs of movement or working. Probe the
keelson with the screwdriver for evidence of softness. Check the
intersects of transverse frames for signs of rubbing or chaffing that
indicates movement. Check visible bolts and bolt heads for corrosion. Also
check for discoloration around the bolt heads. If the wood appears white
and soft, this is an indication of weepage and the same condition that
produces angle hair. Be careful about diagnosing this as "electrolysis."
Its probably not.
If there is water getting at the bolts, a serious corrosion must be
suspected. The only conclusion to be drawn is that the bolts must be drawn
and inspected. Don't rely on just tapping these bolts to see if they're
loose. They may be tight now, but may go loose when the hull is working at
sea. Bear in mind the forces that operate on a hull while underway.
Be wary of oily bilges and wood that can obscure this evidence. Poke
around in the wood surrounding the bolt head. If its soft, you can be sure
that there is weepage and the bolt is subject to corrosion.
Inaccessible Areas These are the areas
that almost invariably cause the surveyor his greatest problems for he
can't get at them to check. Frequently, these are the areas where
structural deterioration takes place because neither interior inspection
or maintenance is possible.
- Outboard and under fuel tanks
- Behind large exhaust pipes and mufflers
- Under refrigeration and freezers
- Under fish holds
- Under shower pans and stalls
- Under lined rope lockers
- Behind hulls that have full hull side ceilings
There's one thing you'll notice about most of the above listed areas
and that is the potential for condensation and lack of air flow in these
obscured areas which is highly conducive to causing deterioration of wood
and metals. These obscured areas should be viewed with extreme caution.
The only acceptable conclusion is guilty until proven innocent. To prove
soundness, fasteners or planks must be pulled.
Fuel & Water Tanks Failed or improperly designed
fuel and water tank foundations are a common cause of catastrophic hull
failure. Because of the extreme weight of tanks, if supports fail, or were
never properly designed in the first place, the planking or individual
frames could end bearing a major part of the tank load. When this happens,
hull failure usually results.
Be they cylindrical or square, tanks on saddles or on decks not fully
supported by hull girders must be considered as suspect and the entire
load bearing structure examined and evaluated. This is usually not as
difficult as it might sound, for anyone with a good knowledge of proper
construction can quickly size it up if the structure is accessible. If
there is any doubt at all, particularly on aging structures, then other
means of evaluation must be found.
The Exterior There is one example of aging
wooden structures that I can give that nearly everyone is familiar and can
relate to. That is driving through the country side and seeing a very old
barn that is starting to fall in upon itself - the kind with the sway-back
roof and bulging sides. If you would like to understand what happens to
old boats, all you have to do is look at that old barn which is subject to
nothing more than wind, rain and gravity.
Because boats are subject to much greater stresses, old boats rarely ever
get to that point without breaking apart first. Even so, aging boats will
reveal the same signs of age. The first sign is open seams that just won't
stay closed no matter how much caulking the owner does. As the wood
weakens and the fasteners corrode, the entire hull structure just keeps
getting looser and looser. Eventually it reaches the point where the whole
thing is working every time it goes to sea and it then becomes just a
question of time before something pops loose and an accident happens. Or
if the owner is lucky, it just quietly sinks at the dock, as most do.
Open hull seams above the waterline that won't stay closed are what
surveyors should be looking for. That and bleeding fasteners, loose guard
rails, leaky decks, warped or cupped planks, butt ends standing proud,
fungicidal rot and so on. If the hull sides don't look good, how much
better is the bottom?
The Bottom Survey If the surveyor has done a
good job with the interior, then his work on the bottom is going to be the
easiest part of the job. By this time, he already knows if there are loose
planks, bad frames, deterioration, weepage or leakage and where all these
things are located. Long before it comes out of the water, he has a pretty
good idea of whether this is a sound hull, and in many cases he'll already
know that it isn't, so there's no point in hauling.
How likely is it that an old wood vessel could have bad fasteners and yet
show no evidence of that fact on the interior? By my experience, that is
not possible at all. Yet there are always a few cases that seem borderline
and the surveyor hasn't enough evidence to say one way or another. In that
case, he's got to go to a hauled survey.
Steel Fasteners Its true that wooden ships have
been built with iron fasteners for several hundred years and
archaeologists have found some that are still in good condition. But those
iron fasteners involved huge planks and beams and were as precisely fitted
as a rivet, but that degree of care was abandoned long ago. Steel
fasteners, whether galvanized or not, are a very poor way to fasten a
vessel if you want it to last a long time. My attitude toward them is one
of fear - for myself and the passengers.
On the other hand, bronze fasteners haven't fared a whole lot better
because they are very expensive and so builders have skimped on their
size, and the dimensions of the framing into which they are set, thereby
reducing their effectiveness as well. Chris-Craft yachts and others were a
prime example of vessels with light scantlings and small fasteners that
have disappeared from the scene after only twenty years or less.
Nailing hulls is fraught with all kinds of problems, not the least of
which is the problem that nails tend to split the wood. When this happens,
water gets at the fastener immediately, so whether a vessel is 5 or 30
years old may have nothing to do with soundness. Further, when water is
getting at the fastener through the interface between plank and frame, its
also going to corrode rapidly.
Ultimately, the problem with nailed boats involves so many factors and
hazards that coming to any conclusion of soundness is nigh impossible.
Nails cannot be pulled without causing much damage to the plank, if they
can be gotten out at all. Inspecting the heads only tells one the
condition of the head, not the rest of the nail. And tearing planks off
means that they have to be renewed and the cost far too high.
Nondestructive methods such as X-ray are both costly, difficult and not
necessarily reliable.
Taking all these factors into consideration, steel fastened vessels are a
hazard to everyone who gets involved with them.
Screw Fastened Vessels Utilizing all the
techniques outlined above, along with removal and inspection of fasteners,
can provide a reasonable degree of certainty as to a hull's soundness.
Moreover, screw fasteners can be replaced if they have good holding
ground, meaning that planks and frames are not split or deteriorated.
To evaluate a screw-fastened bottom, first isolate the likely problem
areas, including all of the garboards, under fuel tanks, fish holds and so
on. One should not resort to the practice of laying out a pattern of
evenly spaced points and pulling fasteners in this method as it is
strictly hit or miss. First examine for:
- Cupped or warped planks
- Open seams and weepage from interior after bottom is dry
- Planks with split ends or splits anywhere
- Loose seams
- Sound planks with heavy hammer for sound of looseness.
- Discoloration around screw heads
- Special attention to butt ends
- Under tanks and engines - stress from heavy loads
- Damp environments like under fish holds, refrigeration, etc.
All of the above areas should be marked and targeted
first, for it is here where the problems are likely to be. Then, if all
these suspect areas prove out okay, you may not even need to pull
fasteners in the non-suspect areas and this will reduce the work load
greatly.
Unless a plank is cupped, go to the butt ends and edges first and pull
fasteners. If there are splits and open seams and other suspicious
indicators, and yet the fasteners are still in good shape, the surveyor
isn't going to have to go much further. Planks with split ends must be
replaced. If these fasteners prove thinned down, then the logical thing to
do is to then work outward from the most highly suspect areas. The
objective here is to determine whether the hull has a general condition of
wasted fasteners or whether it is isolated due to the initiating factors
discussed above.
To reinforce my findings, and to reduce work load, I like to find a spot
on the interior where that looks very good and then to pull a few screws
on the exterior. This gives me a good indication of whether I'm dealing
with local or isolated conditions. If isolated, I then need only to
determine how isolated.
All of these judgments are either reinforced or eased by my knowledge of
particular builders - the size of fasteners, planks, overall scantlings,
materials and construction methods. There's nothing like knowledge of a
particular builder's methods and how well they hold up to help one along
in his work.
Acceptable Degree of Wastage Essentially
there is no acceptable degree of wastage in a fastener. If water is
getting to the fastener, then it must be considered as subject to an
accelerated rate of corrosion and will fail soon. Removed fasteners should
be clean and dry. When a fastener that is tight is backed out, friction of
the threads against the wood should remove any trace of corrosion and
should generally the threads should appear bright. If the metal is pink,
dezincification is occurring and the fastener weakening and should be
replaced.
Tight fasteners should be hard or impossible to move. If it won't turn,
don't bother trying to force it because its okay. Fasteners that just spin
without backing out are bad and one needn't waste his time trying to get
them out.
Summary of Structural Strength
The most important thing to understand about wood hulls is that they are
in no way similar to any other material as far as aging is concerned. As
wood hulls age, they deteriorate and weaken generally. The constant
destructive action of stress, working, weakening of
the wood and corrosion of the fasteners means that the hull is getting
weaker and all the connections looser and looser. This process is very
highly progressive, meaning that the rate of deterioration and weakening
advances rapidly once the general weakening process has set in.
Once it reaches this point, the whole structure is at risk. Its no longer
a matter of this area or that area being bad, but a matter of the overall
weakened state of the entire structure. Thus, when approaching wood boat
surveys, there must be an holistic evaluation. And owing to a lack of
consistency in the nature of wood and construction methods, it is not
reasonable to attempt to ascribe a certain number of years as a viable
life span. This simply cannot be done because of the diversity of the
product. Every vessel must be evaluated on its own condition and merit.
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| Page |
Contents |
| Introduction |
|
PART 1:
Materials and Causes of Problems
(with 4 pictures) |
Materials: Wood - Metals,
Corrosion: Electrolysis - Galvanism - Stray Current - Oxygen
Starvation, Other Factors: Climate - Hull
Stress - Wood and Water |
PART 2:
How to Survey A Wood Hull |
Opening Up - Planks & Frames - Weepage - Chine Areas
- Forefoot - Transom - Keel, Bolts, Keelson, Clamps and
Stringers - Inaccessible Areas - Fuel & Water Tanks - The Exterior -
The Bottom Survey - Steel Fasteners - Screw Fastened Vessels -
Acceptable Degree of Wastage - Summary of Structural Strength |
PART 3:
Appendix |
[A] - Hull Planking Types
[B] - Recommendations for Safety Equipment
and Systems |
First posted 5/25/97 at David Pascoe's site
www.yachtsurvey.com.
Page design changed for this site.<
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