that I have roundly criticized the Coast Guard for their role in
the EL TORO II tragedy, its only fair that I should offer some effective
solutions on how to prevent these casualties in the future. I fully
recognize that it is easier to be critical than to solve the problems
being criticized. Yet, in the EL TORO II tragedy, a wooden vessel
which sank and killed three people because of wasted hull fasteners,
the NTSB and the Coast Guard blamed a lack of "adequate guidance"
for the CG's failure to locate these faulty conditions on EL TORO.
This essay proposes to fill the alleged gap by
offering a general discussion of how to approach the survey of a
wood hulled vessel. In addition, I would recommend a thorough study
of WOOD: A Manual for its Use As a Shipbuilding Material,
Department of the Navy, 1957, ISBN 0961060204, and Ian Nicholson's
Surveying Small Craft, Sheridan House, 1987.
I also recognize that in this day and age when
very few wooden boats are being built, and most have gone the way
of buggy whips, there's not much opportunity to gain experience
in wood vessel survey. Yet the overriding feature of the surveyor's
art is just that: experience. And since the Coast Guard is reported
to survey over 1400 wood vessels annually, certainly no one has
a better opportunity to gain that experience rapidly and amass a
large body of comparative data rapidly.
As their own studies and data has shown, the U.S.
wooden boat fleet is aging and deteriorating. Because of that, the
of accidents like EL TORO are likely to increase unless the CG does
not only a better job of surveying them, but also of mandating repairs
or condemning them once structural deterioration has reached the
point of no return.
Let start with the point that most independent
surveyors I know are no longer in the business of performing prepurchase
surveys on wooden boats and the reason is simple. Surveyors have
learned the hard way that surveying wood boats is very difficult
and fraught with risks. As private individuals, marine surveyors
cannot fall back on lame excuses such as not having adequate guidance,
or not finding any evidence or being inhibited in one way or another
at locating serious safety defects. The civil courts charge us with
the utmost degree of care in conducting that survey, and we are
held accountable when we fail, an accounting that more often than
not destroys our careers.
This is not to say that serious structural defects
cannot be found with relative ease if one knows what he's looking
for. In my 30 years experience with wooden vessels, its a maxim
that structural problems always manifest telltale signs.
The difficulty is that the inspector must be expert, and must have
a great deal of experience in knowing what to look for in order
to find them.
It should be recognized that the following discussion
covers only the most basic aspects of wood hull surveying. It would
require an entire book or series of books to address the subject
in its entirely.
Before getting into the heart of the matter, lets
first consider the nature of the materials that we are dealing with,
for this will give us a far better understanding of why severe problems
frequently go undetected.
Wood is a natural, organic material that
has no consistency from one species to another, or within a species.
Each tree grows differently and yields different qualities of wood.
Consistency may or may not exist. There are literally hundreds of
varieties of species wood used in construction, and these species
also have an equally wide range of strength and other characteristics.
Of all these species, only a very few have the ideal characteristics
of good strength and resistance to deterioration. (here deterioration
means fungicidal micro-organisms and electro-chemical degradation).
Woods like teak, cypress, fir, long leaf yellow pine, mahogany and
only two of hundreds of varieties of oak fit the bill. But over
several thousand years of boat building, these most desirable species
have been consumed and all but disappeared, causing builders to
have to utilize ever lower grades of material.
"Wind shakes" are a phenomenon caused
when a tree is hit by high winds, causing the whole trunk to twist.
This can damage the wood in ways that aren't easily detected. It
causes minute splits in the fibers which will make the wood more
porous and cause a plank cut from that tree to rot much quicker.
This is why we often find just one plank on the whole vessel that
rots badly with no apparent explanation for why.
Teak and cypress, among others, are highly valued
for their fungi resistance. That resistance comes from certain chemicals
in the tree that are toxic to fungi (and man as well). These trees
can also grow in soil where those chemicals are absent, meaning
that they will not be present in the wood and therefore not be rot
resistant. This also explains why rotten planks and frames will
appear in places where it is not expected.
Strength of Wood is degraded by a variety
of factors: soaking in water for 10, 20, 30 or more years, micro-organisms,
shipworms, ants, termites, the normal stresses imposed on the hull,
sunlight, constant wetting and drying and chemicals introduced into
the interior of the hull such as spilled battery acid, petrochemicals,
detergents and chlorinated cleansers, etc.; all work to take their
toll on wood. In other words, unlike materials such as fiberglass
and aluminum, wood is degraded by a large variety factors.
Metals Wood construction, of course, must
utilize some sort of metal fasteners to hold it together. As with
the quality of the wood, the quality of the fasteners used in the
trade can run from very poor (steel) to fairly good (silicone bronze)
to excellent (monel). As with everything else in this world, the
higher the quality, the more it costs. Thus, the ever-present tendency
to reduce quality to reduce the cost of the product. This is one
thing the surveyor should never loose sight of, for it can also
come back to bite him if he does.
Metals , of course, are all subject to corrosion,
a phenomenon which is subject to much myth and little understanding.
In industry, corrosion is still one of the most highly studied areas
of metallurgy. Even after billions of dollars of research, all of
its causes and effects are still not fully understood. So when we
think that we have some understanding about the nature of corrosion,
we should think twice.
The final consideration of materials leads us to
consider how they all work together, and it is here where the general
understanding of wooden vessels usually falls short.
Corrosion is a natural process that works to degrade
all materials, whether its gold, rock, plastic or steel. Corrosion
occurs in many forms, most of which are not common knowledge, even
in the marine industry. The ones we experience most often are oxidation
reduction, galvanism and electrolysis. I will start with the last
first because it is so misunderstood.
Electrolysis is the same identical process
used in electroplating. It occurs only with DC current and essentially
moves material from an anode to a cathode. Theoretically, electrolysis
cannot occur from AC current, although in reality stray AC current
can be converted to DC current through naturally occurring diodes
such as salt crystals. That's why electroplating can only be done
with the very expensive process of using DC current. Otherwise,
plating would be cheap and not as expensive as it is.
Electrolysis only occurs on boats when there is
a ground fault and it is leaking current, usually from bad wiring.
Small current leaks are commonplace and are rapidly dissipated in
surrounding metals without doing damage. Larger current leaks, as
when a significant part of a large conductor has a ground fault,
can produce very damaging corrosion. People often see heavy pitting
on propeller blades and rudders and attribute this to electrolysis
when, in fact, it is usually the result of yet another form of corrosion,
erosion corrosion caused by fast streams of water laced with air
bubbles. Erosion corrosion is strictly a mechanical form of corrosion.
Galvanism This is a from of corrosion caused
by a current flow generated between two materials with greatly differing
electrical potentials. Contrary to popular belief, galvanism does
not occur just between two different metals; it can occur between
other materials, such as carbon rubber and a metal. Carbon rubber
mated against aluminum, for example, is a disastrous combination
that will destroy aluminum very quickly. This is often found in
carbon rubber hose joined to aluminum or copper pipes and is often
referred to as electro-chemical degradation (ECD).
On wooden boats, galvanism is rarely a factor except
in small isolated areas. When two dissimilar metals are mated electrically,
they generate a very small amount of current that has little power.
That means that the electricity generated has little capacity to
flow very far before being dissipated. Wood is an extremely poor
conductor, and sea water wet wood is not much better, although it
will conduct current for short spans before being generally dissipated.
For this reason, stray current in a wooden hull does not have the
capability to generally damage hull fasteners, even when underwater
metals are bonded. When zincs are attached to the system, all potential
for galvanism is eliminated so long as the zincs remain effective.
Bottom fasteners, of course, are not normally exposed
to water, and thus their chance of being affected by stray current
or galvanism is even further reduced. Thus, galvanism rarely, if
ever, is a factor in hull factor corrosion.
Stray Current is the cause of true electrolysis
and can cause damage to fasteners if the leaking voltage is high
enough, has sufficient power flow (amperage) and continues long
enough under ideal conditions. However, I have never found a case
where stray current damage to fasteners was not also accompanied
by severe corrosion damage to exposed, submerged metals such as
propellers, shafts, sea cocks and the like. Absent such damage to
exposed metals, there is no reason to suspect stray current damage
to fasteners as fasteners are the last to become damaged in the
chain of events.
||The effects of stray current are usually
unmistakable. This is the remnant ofa zinc anode attached
to a bonding system that was subjected to a full twelve volts,
leaving an obvious burn pattern. The zinc did its job and
the problem was caught in time before serious damage occurred.
Electrolysis, or stray current corrosion is usually
notable by the very bright appearance of the corroded metal. When
the pitted part of the metal is bright, that means that the corrosion
is so rapid that oxides have no chance to form. That's particularly
true with all copper-based alloys like brass and bronze. When the
surface is dull, but still brightly colored such as pink or orange,
this tends to indicate a less rapid rate of corrosion, but stray
Oxygen Starvation This is the primary
cause of corrosion to hull fasteners, also known as crevice corrosion.
Oxygen starvation is not the simple form of chemical reaction with
water that causes rust or other surface oxides, but the result of
water being trapped in a small, confined space where the oxygen
supply is cut off. Surveyors are familiar with this phenomenon on
aluminum fuel tank bottoms mounted on a wet plywood deck that results
in rapid and severe corrosion pitting. What most surveyors have
never understood is that this same phenomenon occurs with metal
fasteners joining two pieces of wood together, or any other material
for that matter.
By the time a surveyor has pulled a thousand bronze
screws out of hull bottoms, it becomes readily apparent that the
wastage of the screws, or necking as its sometimes called, always
starts at the center of the screw. This coincides with the interface
between the plank and frame. The reason it does is because the seam
between plank and frame is subject to the capillary effect which,
as we know, is the tendency of water to follow along cracks, seams
or fissures. Therefore, anytime the plank/frame interface is wetted,
the water is going to head straight for the screw.
Now, the screw, being spiral threaded, creates
the tendency for that water to follow the treads right up and down
the shank of the screw. Occasional wetting of the fastener is not,
of course, a problem in and of itself. But once the fastener is
wetted a few times, it acquires a slight layer of soft and very
porous oxides. Normally, these oxides would serve to protect the
screw from further corrosion, but something else interferes. The
oxides on the screw surface further enhance the capillary effect
the same way that beach sand absorbs water. Thus, once the corrosion
process starts, it can only accelerate.
||Corrosion of stainless bolts by crevice corrosion
or acid attack. The prominent feature is that the active corrosion
areas are bright metal.
Unfortunately, yet another factor gangs up on our
poor fasteners: crevice corrosion. The water entrapped within the
screw cavity or interface between the planks does not have a good
oxygen source. i.e., air flow. The chemical reaction of oxidation
of the metal robs the water of oxygen and turns the water to an
acid. So what we now have is first, oxidation followed by acid attack
which really does the most damage. These processes are endlessly
repeated over the years, at an ever accelerating rate until the
fastener is finally destroyed.
||This is erosion corrosion on a rudder blade caused
by propeller wash. It is often mistaken for electrolysis.
The feature that often leads surveyors and investigators
to the conclusion of galvanism stems from the fact that oxidation
reduction or acid corrosion usually leaves the eroded metal bright-looking
and without the usual covering of granular oxides. Based on what
we usually see of galvanic or stray current corrosion, this seems
like a reasonable conclusion but its not. Acid corrosion is usually
recognizable by pink and black residues on a bronze fasteners. On
a steel fastener it tends to be very black. If there is no black
but just pink residue on the bronze fastener, then water is getting
to it on a continuous basis.
Climate The effect of climate on wood vessels
simply cannot be understated. In the Baltic sea archaeologists have
been recently pulling up very well preserved parts of wooden vessels
that are 600 to 1,000 years old. In the tropical waters of Florida,
vessels sunk as little as 60 years ago have completely disappeared.
Of the many Spanish galleons of the silver fleet sunk on Florida
shores 300 years ago, almost no wooden parts remain. Such is the
effect of warm, tropical waters on wood. Cold water, of course,
has a preservative effect on both wood and metal.
The other great enemy of wood are very damp and
rainy climates, especially moderate and tropical climates. In itself,
salt is a preservative because fungi can't survive in a salt environment.
But nothing advances fungicidal attack on wood like nice, fresh
rain water. Of course, one of the greatest maritime myths of all
time is the notion of "dry rot." Wood does not rot unless
it has a source of water. Fungi does not live, and wood does not
rot in the desert. Therefore, there is no such thing as dry rot.
Fresh water often does its worst damage when it
leaks into a hull. This happens in several ways. First, water from
the decks runs down the sides of the hull and gets absorbed into
open seams in the planks. Second, deck leaks run down the inside
of the hull where the same thing happens, but also ends up laying
in the bilge where there is often a perfect environment of nutrients
for fungi to blossom.
The problem for surveyors is that boats don't stay
put and you don't know its past history and where it came from.
Therefore, one has to expect the worst.
Hull Stress The deep bilge of course is
always the first place the surveyor looks for bad fasteners, for
it is here where there is a constant source of water. Yet boats
are not monolithic structures and they are subjected to stress and
thus work and torque and wrack and twist in all directions. Often
not enough to be visually detectable, but enough that all the seams
and joints are indeed moving. Projected over thousands of cycles
over the years, this creates the potential source for water entering
virtually any seam in the hull bottom, not once but hundreds of
Any surveyor who has spent a significant part of
his career surveying wood boats knows that, other than the garboards,
wasted bottom fasteners can occur anywhere, and just about any point
in the life span of the vessel. He knows its not reasonable to apply
any particular time limit, for it is entirely dependent on whether
open seams are allowing water to get at the fasteners.
||Hogging, a condition in which a hull is actually
sagging with age, is an accurate indicator that a wood hull
has reached the point of severe structural degradation and
can no longer be considered safe. This condition is plainly
evident on the above yacht.
Water The structure of wood is made up of very oblong cells
of cellulose fiber. Living wood conducts water soluble nutrients
along the grain of the wood, or from end of cell to end of cell,
ultimately to the top of the tree. Wood does not transmit water
across the grain very well at all, either from the edge or the wide
surface. We have only to stand up a plank in a pan of water to understand
how well this works. Very soon, the plank will empty the pan of
Because a plank is no longer a living organism,
it has lost much of its ability to transmit water along its length.
Eventually it reaches what is known as equilibrium level and will
absorb no more. Complete saturation of the open cells will only
occur a short distance from the end grain unless rot sets in and
then it will advance further.
When it comes to fasteners, the effect of this
point should be rather obvious: fasteners near the ends of planks
are the ones most vulnerable.
How to Survey A Wood Hull
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
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
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
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.
Appendix A - Hull Planking Types
Carvel Planked Planks butted edgewise with beveled
& fitted edges. No other method of sealing other than caulking.
The primary means of sealing is swelling of the wood. With age,
very prone to leakage and fastener corrosion, to which all areas
of the bottom are subject. Required great deal of construction skill
to make a leak free hull.
Seam Battened Utilizes a batten over seams on inside.
A very effective and strong method of construction, used mainly
by Chris Craft.
Double Planked Same as carvel only uses light inner
layer with heavier outer layer, parallel longitudinal. Vastly superior
to single carvel. Much less prone to leaking, working and fastener
Double Diagonal Most often seen on PT boats and
minesweepers and Huckins Yachts. If heavily fastened, this method
very strong and long lasting. Both edges and centers of planks need
to fastened to prevent warpage. If not heavily fastened, planks
subject to cupping because of thinness of planks. followed by water
leakage transmitted in the void spaces formed by the warped planks.
In that case, were highly prone to deterioration and fastener failure.
Warped planks spell big trouble.
Plank on Plywood Another very effective method
that is very good at keeping fasteners dry. Used mainly by Chris
Craft. Very strong, long lasting.
Bay Bottom This method utilizes longitudinal hull
side planking and transverse bottom planking. Vessels built mainly
for fishing in protected waters of Chesapeake Bay and Carolina sounds.
A cost saving method that greatly compromises vessel strength. Often
steel nailed. Not meant for ocean use, short-lived.
Cold Molded Usually three plies of thin planks
in di or triagonal laid up with resorcinol glue and small nails
of monel, copper alloy or bronze. Smaller boats used staples. Makes
for very strong hull but subject to the same warpage and water ingress
problems as double diagonal. Because of molded nature, fastener
problems are usually not relevant but hull shell deterioration is.
Plywood This material has gained a bad reputation
because of a great deal of bad design and poor quality plywood.
Good quality plywood is little different than cold molded material,
and is superior in that it doesn't warp. Marine grade ply using
mahogany or fir is extremely expensive and not often used. In recent
years, plywood hulls built with.
epoxy glues and resins have proved capable of producing
hulls with 30+ year life spans, but only if done right. Lydia of
Florida and several other head boat builders have produced some
noteworthy examples. The prevention of leakage and sealing of panel
edges is critical. Larger boats with double layers are very strong.
Strip Planked Appears in a variety of forms including
edge nailed and the West System. Usually the strip planks are glued
on edges and nailed. Produces a very strong, long-lasting hull,
not prone to leakage. West System uses large amounts of epoxy glue
and is highly rot resistant. Both these types tend to be monolithic
and will tolerate a great deal of fastener failure before structural
failures will occur.
Lapstrake Longitudinal planking with edges overlapped.
Produces a hull prone to wracking and leaking seams and therefore
fastener failure. Not many of these around anymore.
Recommendations for Safety Equipment and Systems
CFR 46, Subchapter T requirements for safety and
life saving equipment are woefully inadequate. Many private yachts
voluntarily have better safety equipment than what Subchapter T
Water Tight Compartments Regulated vessels should
be required to have no less than three water tight compartments,
designed so that should any one compartment be completely flooded,
the other two are capable of maintaining the vessel afloat. This
is easy to achieve and usually involves little additional cost.
Bilge Pumping Bilge pumping requirements are completely
inadequate. Most yachts have better pumping systems than inspected
vessels. A standard needs to be developed that addresses the numerous
factors that go into making up an effective system. Inspected vessels
should have both primary and emergency pumping systems, as do many
yachts. Adequate information is available and retrofitting costs
would not be excessive.
Bilge Alarms Marine surveyors are routinely recommending
of the installation of bilge high water alarm systems in yachts.
Many yacht builders provide them as standard equipment. Such systems
can be installed at very low cost and should be mandatory.
Life Rafts It is criminal that CFR 46 does not
require life raft capacity for the total passenger carrying capacity
of the vessel. It should. Further, life rafts must be capable of
keeping victims out of the water, meaning no bottomless life rafts.
The high cost of immersion suits can be avoided if sensible life
raft requirements are adopted, combined with a requirement for water
resistant wind chill protection such as water resistant "panchos"
Heat Packs The Japanese have developed very effective,
small chemical heat packets. These are about the size of post card,
designed to be placed in clothing pockets, and are very inexpensive.
They last 4-6 hours and combined with wind chill protection, would
go a long way toward reducing deaths associated with extreme loss
of body heat and hypothermia.
Navigation Limits The EL TORO victims were in the
water for as long as 80 minutes even though the vessel sank within
15 miles of one of the highest concentrations of marine search and
rescue agencies, stations and equipment. Had this accident occurred
in a more remote area, or out on the open ocean, it is entirely
possible that there would have been no survivors. By no stretch
of imagination did the vessel operator act responsibly by taking
the passengers out in the face of posted gale warnings. All necessary
weather information was readily available and the tragedy would
not have occurred had the operator heeded the warnings.
A huge body of data exists linking vessel design
and construction to sea capability and survivability. The designation
"small craft" needs to be further defined and vessel capability
linked to predicted weather conditions.
Emergency Transmitters Known as E.P.I.R.B.'s -
Emergency Position Indicator Radio Beacons, these devices are voluntarily
carried by most offshore yachts and should be mandatory on public
conveyances. Their value is not only in allowing rescuers to locate
offshore vessels quickly, but permitting more rapid location in
fog, rain and other low visibility conditions. These should be mandatory
for every life raft.
About the Author Dave Pascoe began his surveying
career in the heyday of wood boat building, the early 1960's when
the very first mass produced fiberglass hulls were being built.
He started his career on the Great Lakes and moved to Florida in
1972 so that he has experience in both fresh and sea water vessels,
cold and tropical climates. He has traveled extensively and conducted
surveys and accident investigations for marine insurers in North
and South America, the Caribbean, Mississippi River, Great Lakes,
Pacific Northwest, Europe and a number of Pacific Islands. In addition
to having many years experience on the international yacht racing
circuit (even back in the days of wooden yachts), he has training
in yacht design and has attended numerous seminars and training
courses on topics such as metallurgy, welding, marine engines, failure
analysis, fire investigations, corrosion, electrical systems, maritime
law, marine insurance and so on. He has been a guest lecturer on
the subject of marine surveying at Florida International University
and several private schools, as well general lectures to government
bodies such as the Japan Ministry of Industry and Trade and Nippon
Ocean Racing Committee. He is the author of numerous articles on
marine related subjects. During his career he has conducted nearly
3,600 surveys of vessels of all types, and than 500 marine accident
investigations of all types.