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Boat construction

A wide variety of materials and materials areThese can be solid fiberglass or of the
used  in  boat  building:sandwich (cored) type, in which a core of
balsa, foam or similar material is applied
Wood - The traditional boat building materialafter the outer layer of fiberglass is laid
that was and is still used for hull and sparto the mold, but before the inner skin is
construction. It is buoyant, cheap, widelylaid. This is similar to the next type,
available and easily worked. It is notcomposite, but isn't usually classified as
particularly abrasion resistant and it cancomposite, since the core material in this
deteriorate if fresh water or marinecase doesn't provide much additional
organisims are allowed to penetrate the wood.strength. It does, however, increase
Rot resistant woods such as cedar and oak arestiffness, which means that less resin and
generally selected for wooden boatfiberglass cloth can be used in order to save
construction. Glue, screws and/or nails areweight. Most fiberglass boats are currently
used to join the wooden components. Somemade in an open mold, with fiberglass and
types  of  wood  construction  include:resin applied by hand. Some are now
constructed by vacuum infusion where the
Carvel, in which a smooth hull is formed byfibers are laid out and resin is pulled into
wooden planks attached to a frame. The planksthe mold by admospheric pressure. This can
may be curved in cross section like barrelproduce stronger parts with more glass and
staves. Carvel planks are generally caulkedless resin, but takes special materials and
with oakum or cotton that is driven into themore  technical  knowledge.
seams between the planks and covered with
some water proof substance. It takes its nameComposite - While GRP, wood, and even
from an archaic ship type and is believed toconcrete hulls are technically made of
have  originated  in  the  Mediterranian.composite materials, the term "composite" is
often used for plastics reinforced with
Another method of building wooden boats isfibers other than (or in addition to) glass.
lapstrake, a technique originally identifiedCold-molded refers to a type of building
with the Vikings in which wooden planks areone-off hulls using thin strips of wood
fixed to each other with a slight overlapapplied to a series of forms at 45-degree
that is beveled for a tight fit. The planksangles to the centerline. This method is
may be mechanically connected to each otheroften called double-diagonal because a
with copper rivets, bent over iron nails,minimum of two layers is recommended, each
screws or with adhesives. Often, steam bentoccurring at opposing 45-degree angles.
wooden frames are fitted inside the hull."Cold-molding" is now a relatively archaic
This technique is known as clinker in Britainterm because the contrasting "hot-molded"
and  also  as  clench  built.method of building boats, which used ovens to
heat and cure the resin, has not been widely
Another method uses sheets of plywood panelsused since WWII. Now almost all curing is
fixed to a frame. Plywood may be laminateddone at room temperature. Other composite
into a round hull or used in single sheets.types include sheathed-strip, which uses
These hulls generally have one or more(usually) a single layer of strips laid up
chines. A type of the plywood panel boatparallel to the sheer line. The composite
building methond is known as thematerials in question are then applied to the
stitch-and-glue method, where pre-shapedmold in the form of a thermosetting plastic
panels of plywood are edge glued and(usually epoxy, polyester, or vinylester) and
reinforced with fibreglass without the use ofsome kind of fiber cloth (fiberglass, kevlar,
a frame. Metal or plastic wires pull curveddynel, carbon fiber, etc), hence the finished
flat panels into three dimensional curvedhull is a "composite" of fiber and resin.
shapes. These hullls generally have one orThese methods often give strength-to-weight
more  chines.ratios approaching that of aluminum, while
requiring less specialized tools and skills.
Steel (and before that iron) - Either used in
sheet for all-metal hulls or for isolatedSteel-reinforced cement (ferrocement) -
structural members. It is strong, but heavy.Strong and long lasting. First developed in
The material rusts unless protected fromthe mid 19th Century in France. Used for
water. Modern steel components are welded orbuilding warships during the war. Extensively
bolted together. Until the mid 1900s, steelrefined in New Zealand shipyards in the 1950s
sheets  were  riveted  together.and the material became popular among amateur
builders of cruising sailboats in the 1970s
Aluminium - either used in sheet forand 1980s, because the material cost was
all-metal hulls or for isolated structuralcheap although the labour time element was
members. Many sailing spars are made ofhigh. The weight of a finished ferro-cement
aluminium. The material requires specialboat is comparable to that of a traditionally
manufacturing techniques, construction toolsbuilt wooden boat. As such they are often
and construction skills. While it is easy tobuilt for slower, more comfortable sea
cut, aluminium is difficult to weld, and alsopassages. Hulls built properly of ferrocement
requires heat treatments such asare more labor-intensive than steel or
precipitation strengthening for mostfiberglass, so there are few examples of
applications. Corrosion is a concern withcommercial ship-yards using this material.
aluminium, particularly below the waterline.The inability to mass produce boats in ferro
cement has led there to being few examples
Fiberglass (Glass-reinforced plastic or GRP)around. Many ferrocement boats built in back
- Typically used for production boats becauseyards have a rough, lumpy look, which has
of its ability to reuse a female mold as thehelped to give the material a poor
foundation for the shape of the boat. Thereputation. The ferro-cement method is easy
resulting structure is strong in tension butto do, but it is also easy to do wrong. This
often needs to be either laid up with manyhas led to some disastorous 'home-built'
heavy layers of resin-saturated fiberglass orboats. Properly designed, built and plastered
reinforced with wood or foam in order toferrocement boats have smooth hulls with fine
provide stiffness. GRP hulls are largely freelines, and therefore are often mistaken for
of corrosion though not normally fireproof.wooden or fiberglass boats.



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