Wooden Boat Restoration Repair - WEST SYSTEM Epoxy

1.2 Why wooden boats fail
1.2.1 Loss of stiffness
1.2.2 Dry rot
Introduction 4
The nature of wood and the techniques required to build boats in the past have
contributed to both the beauty and the misfortune of wooden boats. The amount of
work necessary to maintain wooden boats tarnished their appeal, and lack of
maintenance resulted in many beautiful wooden boats being devoured by the elements.
Wooden boats may vary widely in age and condition, but most suffer in some degree
from two common problems.
Much of the appeal of wooden boats lies in the boatbuilder’s skill in joining many
individually crafted pieces of wood into a single tight structure and loss of the original
stiffness is a major cause of a boat’s deterioration. The forces acting on a boat during normal
use put each joint under a continual strain. For example, when a wave or swell passes under a
boat, it lifts the hull unevenly. Waves supporting the hull under the ends force the sides of the
hull apart; a wave supporting the hull in the middle forces the sides together. Waves or swells
crossing at an angle can lift the bow in one direction and the stern in another, causing a twist
that pulls one side of the hull and deck forward and the other side aft. Other loads come
from lifting the boat for storage, adding cargo and stressing the rigging under sail. Thus, a
boat is under a constant state of twisting, stretching and flexing. All of the joints must resist
this flexing to keep the structure rigid and watertight.
The smallest movement around a fastener can weaken the fastener’s holding power,
leading to more flexibility. Over time, every exterior joint that can flex is a potential
source of moisture penetration. Traditional caulking methods are intended to flex and
absorb the movement between adjoining pieces, but with the continual flexing, these
caulking materials will eventually break down. Without regular maintenance, the
caulked joints will leak. Then, high moisture content of the wood around the joint
leads to loss of wood strength (see Appendix–Wood data, page 75), loss of fastener
holding power, more flexibility and even more moisture penetration.
An often repeated misconception about wooden boats suggests that it is their nature to
be flexible, and that flexibility is desirable because it contributes to the “soft ride” that
makes wooden boats appealing. But, as those who race boats know, a flexible boat
absorbs power. It is harder to push through the water than a stiff boat and for the
reasons stated above it is not as durable. A stiff hull is faster, more efficient, and more
durable in the long run. A soft ride is better achieved with a good hull design. The
flexible approach implies that a wooden boat is at its best just before it falls apart.
Dry rot is another cause of wooden boat damage. It is a natural decay process caused by
the growth of brown rot, a type of fungus that feeds on the cellulose in wood fiber.
Along with severe loss of strength, dry rot causes the wood to discolor, crack across the
grain and shrink.
Dry rot is a misleading term, since wood must be damp for the fungus to exist. In fact,
all of these four conditions must be present for the fungus to survive:
FOOD—an adequate supply of wood fiber
MOISTURE—moisture content of the wood at or near the fiber saturation
point (above 20%)
OXYGEN
WARMTH—76° to 86°F (24° to 30°C) is ideal for rot growth (rot can be active
in temperatures as low as 50°F)
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