Boat building

Not to be confused with shipbuilding.
The schooner Appledore II under construction.

Boat building, one of the oldest branches of engineering, is concerned with constructing the hulls of boats and, for sailboats, the masts, spars and rigging.


Boat building in Greece (Hellas).
Side view of the wooden frame.

Construction materials and methods

Damaged boat mid-reconstruction; carvel planking partially removed.
Caulking irons and oakum.
Caulking a wooden boat.
A sheet plywood sailboat during construction.


The traditional boat building material used for hull and spar construction. It is buoyant, widely available and easily worked. it is a popular material for small boats (of e.g. 6-metre (20 ft) length; such as dinghies and sailboats). Its abrasion resistance varies according to the hardness and density of the wood and it can deteriorate if fresh water or marine organisms are allowed to penetrate the wood. Woods such as Teak, Totara and some cedars have natural chemicals which prevent rot whereas other woods, such as Pinus radiata, will rot very quickly. The hull of a wooden boat usually consists of planking fastened to frames and a keel. Keel and frames are traditionally made of hardwoods such as oak while planking can be oak but is more often softwood such as pine, larch or cedar.

Plywood is especially popular for amateur construction but only marine ply using waterproof glues and even laminates should be used. Cheap construction plywood often has voids in the interior layers and is not suitable to boat building as the voids trap moisture and accelerate rot as well as physically weaken the plywood. No plywood is rot resistant and should be coated with epoxy resin and/or a good paint system. Varnish and Linseed oil should not be used on the exterior of a hull for waterproofing. Varnish has about 60% of the water resistance of a good paint system. Only boiled linseed oil should be used on a boat and only in the interior as it has very little water resistance but it is very easy to apply and has a pleasant smell. Note that used linseed rags should not be left in a pile as they can catch fire. A valuable 200-year-old waka (Maori canoe)caught fire in New Zealand in June 2014 when restorers left rags piled overnight. Raw linseed oil is not suited to boats as it stays damp and oily for a long time. Mildew will grow well on raw linseed oil treated timber but not on boiled linseed oil. More recently introduced tropical woods as mahogany, okoumé, iroko, Keruing, azobé and merbau.[2] are also used. With tropical species, extra attention needs to be taken to ensure that the wood is indeed FSC-certified.[3][4] Teak or iroko is usually used to create the deck and any superstructure. Glue, screws, rivets and/or nails are used to join the wooden components. Before teak is glued the natural oil must be wiped off with a chemical cleaner, otherwise the joint will fail.

Some types of wood construction include:

Steel (and before that iron)

Either used in sheet or alternatively, plate [14] for all-metal hulls or for isolated structural members. It is strong, but heavy (despite the fact that the thickness of the hull can be less). It is generally about 30% heavier than aluminium and somewhat more heavy than polyester. The material rusts unless protected from water (this is usually done by means of a covering of paint). Modern steel components are welded or bolted together. As the welding can be done very easily (with common welding equipment), and as the material is very cheap, it is a popular material with amateur builders. Also, amateur builders which are not yet well established in building steel ships may opt for DIY construction kits. If steel is used, a zinc layer is often applied to coat the entire hull. It is applied after sandblasting (which is required to have a cleaned surface) and before painting. The painting is usually done with lead paint (Pb3O4). Optionally, the covering with the zinc layer may be left out, but it is generally not recommended. Zinc anodes also need to be placed on the ship's hull. Until the mid-1900s, steel sheets were riveted together.

A punt under construction.
Wooden boats being built during the Klondike Gold Rush.


Aluminium is either used in sheet for all-metal hulls or for isolated structural members. Many sailing spars are frequently made of aluminium after 1960. The material requires special manufacturing techniques, construction tools and construction skills. It is the lightest material for building large boats (being 15-20% lighter than polyester and 30% lighter than steel). Aluminium is very expensive in most countries and it is usually not used by amateur builders. While it is easy to cut, aluminium is difficult to weld, and also requires heat treatments such as precipitation strengthening for most applications. Corrosion is a concern with aluminium, particularly below the waterline. It is most commonly used in small pleasure and fishing power boats that are not kept permanently in the water.

Fiberglass (Glass-reinforced plastic or GRP)

Typically used for production boats because of its ability to reuse a female mold as the foundation for the shape of the boat. The resulting structure is strong in tension but often needs to be either laid up with many heavy layers of resin-saturated fiberglass or reinforced with wood or foam in order to provide stiffness. GRP hulls are largely free of corrosion though not normally fireproof. These can be solid fiberglass or of the sandwich (cored) type, in which a core of balsa, foam or similar material is applied after the outer layer of fiberglass is laid to the mold, but before the inner skin is laid. This is similar to the next type, composite, but is not usually classified as composite, since the core material in this case does not provide much additional strength. It does, however, increase stiffness, which means that less resin and fiberglass cloth can be used in order to save weight. Most fibreglass boats are currently made in an open mold, with fibreglass and resin applied by hand (hand-lay-up method). Some are now constructed by vacuum infusion where the fibres are laid out and resin is pulled into the mold by atmospheric pressure. This can produce stronger parts with more glass and less resin, but takes special materials and more technical knowledge. Older fibreglass boats before 1990 were often not constructed in controlled temperature buildings leading to the widespread problem of fibreglass pox, where seawater seeped through small holes and caused delamination. The name comes from the multiude of surface pits in the outer gelcoat layer which resembles smallpox. Sometimes the problem was caused by atmospheric moisture being trapped in the layup during construction in humid weather.

Composite material

Originally "composite" referred to a timber carvel skin fastened to iron frame and deck beams. This allowed sheet copper anti-fouling to be employed without the risk of galvanic corrosion of the hull fabric. It was employed for fast cargo vessels so that they were not slowed by marine fouling. This use is now obsolete. While GRP, wood, and even concrete hulls are technically made of composite materials, the term "composite" is often used for plastics reinforced with fibers other than (or in addition to) glass. Cold-molded refers to a type of building one-off hulls using thin strips of wood applied to a series of forms at 45-degree angles to the centerline. This method is often called double-diagonal because a minimum of two layers is recommended, each occurring at opposing 45-degree angles. "Cold-molding" is now a relatively archaic term because the contrasting "hot-molded" method of building boats, which used ovens to heat and cure the resin, has not been widely used since World War II . Now almost all curing is done at room temperature. Other composite types include sheathed-strip, which uses (usually) a single layer of strips laid up parallel to the sheer line. The composite materials are then applied to the mold in the form of a thermosetting plastic (usually epoxy, polyester, or vinylester) and some kind of fiber cloth (fiberglass, kevlar, dynel, carbon fiber, etc.), hence the finished hull is a "composite" of fiber and resin. These methods often give strength-to-weight ratios approaching that of aluminum, while requiring less specialized tools and skills.

Steel-reinforced cement (ferrocement)

Strong, long lasting and, perhaps surprisingly, not necessarily heavy. First developed in the mid 19th Century in France. Used for building warships. Extensively refined in New Zealand shipyards in the 1960s and the material became popular among amateur builders of cruising sailboats in the 1970s and 1980s, because the material cost was cheap, although the labour time element was high. The weight of a finished ferro-cement boat is higher than wooden boats only in the case of small vessels. They are suitable for traditional hull forms of types such as the gaff cutter. As such they are often built as cruisers allowing more comfortable sea passages. Hulls built properly of ferro-cement are more labor-intensive than steel or fiberglass, so there are few examples of commercial shipyards using this material. The inability to mass-produce boats in ferro-cement has led there to there being few examples around. Many ferro-cement boats built in back yards can have a rough, lumpy look, which has helped to give the material a poor reputation. The ferro-cement method is easy to do, but it is also easy to do wrong. This has led to some disastrous 'home-built' boats. Properly designed, built and plastered ferro-cement boats have smooth hulls with fine lines. Amateur builders are advised to use a professional plaster to produce a smooth finish. Most ferro-cement hulls are designed as heavy displacement. See also concrete ship, concrete canoe.

Hull types

Further information: Hull (watercraft)

To build a boat, the type of hull used is of vital importance; for example, going to sea requires a hull which is more stable than a hull used for sailing rivers (which can be more flat/round). Some types include:

Boat building tools and use

Boat building uses many or the same tools that are common house tools such as hammers, cross cut saws, power drills, benches and vices. For building small boats under 5m some specialized tools are needed such as clamps (cramps) either G clamps or spring clamps. A minimum of 4 6inch(150mm) and 10 4inch(100mm) G clamps, plus 20 2 inch(50mm) steel spring clamps is need for ply on frame designs. More is better with clamps. Flat and round surform rasps are useful tools for shaping wood and ply. A drill set from 2-10mm, several speedbore drills for larger holes 12-25mm, (1/2inch-1 inch) rotary sanding backing pads and a range of replacement sanding pads from coarse (40grit) to fine (180grit), counter sinking drills for screws, a right angle set square, a set of manual screw drivers with blades to match screws being used are essential. A heavy craft knife, an 8m(25 ft) tape, flat and round files for metal and wood, a short(torpedo) level and a set of 3 chisels from 6 to 25mm are needed. Power tools make a job much easier and are relatively cheap. An 7 1/4inch (185mm) circular saw with a fine 40 tooth tungsten carbide blade, a jigsaw with a dust blower with a set of fine, medium and coarse tooth metal and wood blades is good for cutting plywood panels to shape, a rotary oscillating sander with medium and fine pads and a cordless drill for driving screws all save time and energy. A steam box is excellent for making planks easier to bend although hot wet rags are a messy, but easy substitute. A fine tooth hacksaw is not only essential for cutting metal such as trimming stainless steel bolts to the correct length but is handy for ultra-fine cuts in thin wood. A fine-tooth tenon saw is used to cut across the grain to produce a reasonably fine, accurate cut. Some boat builders have started using Japanese draw saws for fine cuts but while these are excellent they tend to be very expensive. A No 4 smoothing plane is essential but an electric plane is very useful (but extremely loud) for making rudder blades and centre boards. A much longer No. 7 plane is needed if the design calls for a wooden spars as used in many modern "traditional" yachts.

In boat building lots of sanding requires using either dry sandpaper, or wet and dry paper, to achieve a reasonable paint or varnish finish. Sandpaper is graded from 40 (very coarse) to 400 (ultrafine). Wet and dry sandpaper lasts longer than dry sandpaper. Wet and dry is best used on paint finishes, while dry paper is best used on dry wood. About 2 sheets of sandpaper for every foot of hull length is a good guide. Less sheet sandpaper is needed if power sanders are used. Spatula applicators, with a flexible stainless steel blade, are used to apply filler. A knife type and a flat 3"(75mm) type will cover most needs.

Silicon bronze screws are normally used in boat building but can be hard to locate. Brass fasteners are commonly available but apart from being softer and weaker the common brass alloys are much more prone to corrosion through depletion of their zinc content. Stainless steel screws may be used for attaching fittings to the hull above the water line. Type 316 stainless steel is the only stainless steel recommended. Even 316 may get stained with surface rust but this does not penetrate the surface. Staining comes from being in contact with other steels such as the anchor or incorrect cleaning in the factory. Staining near wields should be removed as it can pit. Experienced boat builders are reluctant to use even 316 below the water line in a boat permanently in salt water. This especially applied to long thin fastenings such as screws in boats that have motors. Sacrificial anodes are used to help prevent corrosion underwater but experts will inspect a sample of long thin screws or bolts annually to check for corrosion.

Epoxy resins and hardeners are universally used in boat building due to their superior holding power and ease of use.[15] In its thickened state it is used as a strong filler and for a range of joints that do away with more traditional fastenings. A large supply of cheap wooden tongue depressors is useful for mixing and applying epoxy resin. The curved ends are useful for shaping coved joints with epoxy. Silicon bronze ring nails are excellent for permanent fastening of wood and ply as they are strong and easily driven. Many small boats are almost entirely fastened by epoxy resin. In stitch and glue construction the hull panels are temporarily held together with either copper wire, nylon fishing line or plastic cable ties, until the epoxy cures, after which the stitching material is removed. Polyester filler is a quick setting (20mts), softer filler, suited to very small holes and scratches and is far more easily sanded to a fair shape than harder, stronger epoxy filler which takes 24 hours to set hard.

Boat building requires enough space, under cover, so that the builder can easily move around the hull during construction, or the boat can be built on a trailer so the hull can be moved out of the shelter for construction sessions. It also requires space at the bow and stern not only for working but for sighting down the gunwale and chine lines to check they are fair. Have the bow at the garage door end for this reason. This is especially important in stitch-and-glue construction where no jig is used, as the ply panels are very floppy until the glue sets.

Water-based paint is far easier and cheaper to apply, as undercoat, to produce a good smooth finish with a fraction of the time and effort of enamel paints, but harder and slower-drying enamel is best for the top coat on the outside of the hull, which is subject to a lot of bumps and scraps. Limit varnishing to smaller areas, such as grab rails, hatches, toe rails and trim, unless you have lots of patience and a very dust-free environment for varnishing. Use only marine gloss varnish on the outside, as interior varnish will peel off very quickly in hot sun and rain. Marine varnish has UV inhibitors to slow down peeling and fading. Never varnish a deck as it is slippery when wet. Even top-quality marine varnish is not as water-resistant as paint, so you must apply at least 4 coats. Often perfectionists will apply 8 coats or more to get a glass-like, reflective finish. Never varnish submerged parts like rudders.

Boats take a long time to build as there are almost no right angles. Amateurs working at night or in weekends commonly take a year to build a 12–16 ft (3.65m) craft. Builders with handyman skills will find that over time their skills will increase. For amateurs, starting with a boat built on a jig (temporary wooden frame) is useful as making the jig is all about right angles and basic carpentry skills. Sailboats require about 25% more time than a dinghy type because of the need for built-in buoyancy, centreboard case, centreboard, rudder, mast, boom and a range of special fittings such as chain plates, gudgeons, blocks cleats and tracks.

Essential safety gear needed is closed-in footwear, very high grade ear protectors (especially if using a high-revving electric plane or router), eye shields when cutting or grinding metal, disposable gloves when gluing, close-fitting clothes that will not get caught in drills. Good light is essential. Boat builders should not work when they are tired and should keep the work floor clean so they don't trip over tools or wood or electric leads. A fan is handy for extra ventilation if the work space does not have many opening windows or doors. Many boat builders like smaller tools to be bright-coloured tools so they can see them easily amongst saw dust.[16] With the recent technological advances in materials being used in modern boat building including GRP and FGRP repiratory protection masks have become essential in many workshops. The only suitable alternative being substantial dust extraction equipment by means of on-tool extraction or a fully fit out environmental cleaning workshop installation.

Other useful power tools are a belt sander, especially if using recycled timber or for finishing rough-sawn timber. A thicknesser/planer is only needed if building many boats or larger vessels, as it is usually cheaper to pay a joiner to do this for a small amount of timber. A bench saw is useful if you buy larger sectioned timber, which may be considerably cheaper and need to saw it to the correct size, but again a timber yard will do this for a small charge.[17]


Traditional boat building in India.[18]

Traditional wooden boat building in Vietnam. Photos taken January 2009.

See also


  1. TV1 news, NZ, 6 Sept 2012
  2. Zeilen:Van beginner tot gevorderde by Karel Heijnen
  3. "FSC certification". Retrieved 2012-06-14.
  4. "Boat building lumber". Retrieved 2012-06-14.
  5. "Carvel Planking for Boats, Sailboats - Richard Joyce Montana Tech". Retrieved 2012-06-14.
  6. "Strip Planking". Retrieved 2012-06-14.
  7. "Planking Methods Comparison". 2010-11-23. Archived from the original on 2010-11-23. Retrieved 2012-06-14.
  8. "Ply on Frame construction". Retrieved 2012-06-14.
  9. "Stitch and glue subdivision of sheet plywood method". Retrieved 2012-06-14.
  10. "Benefits of stitch and glue". Retrieved 2012-06-14.
  11. "European Dinghies build by amateur builders". Retrieved 2012-06-14.
  12. "Vaurien amateur building". 2009-05-02. Archived from the original on 2009-05-02. Retrieved 2012-06-14.
  13. ″The Gougeon Brothers on Boat Construction, Wood and West System Materials″
  14. "Welding, hot-riveting or drilling of plates". Retrieved 2012-06-14.
  15. West System International
  16. New Zealand Backyard Boat Builder. J Welsford. Reed. 1999.
  17. Backyard BoatbuilderJ Welsford. Reed.1999.
  18. "Sulkha shipyard". Retrieved 2012-06-14.

External links

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