Boatbuilding Glossary

The backbone: the timber, or moulded composite member, running fore and aft along the very bottom of the hull, to which the rest of the structure is attached. On a sailing boat the word is also used loosely for the ballasted fin below the hull, which is a different thing doing a different job.

See also Stem, Sternpost, Hog

The upright member at the bow into which the forward ends of the planking land. On a plywood boat it is often a simple stem post with the plywood bevelled onto it; on a traditionally planked boat it is a curved timber cut with a rabbet to receive the plank ends.

See also Rabbet, Apron

A reinforcing timber fitted behind the stem, giving the plank ends more wood to fasten into than the stem alone would offer.

See also Stem

The upright member at the after end of the keel. On a transom-sterned boat it supports the transom; on a double-ender it does at the stern what the stem does at the bow.

See also Transom

The flat — or nearly flat — surface closing the stern. A "wineglass transom" is one whose lower part curves into the hull in the shape its name suggests, and is among the harder things a first-time builder can choose to make.

The plank next to the keel — the first one fitted and, on most boats, the most awkward, because it twists hardest along its length.

See also Strake, Keel

One continuous line of planking running from bow to stern. A hull is described by how many strakes a side it has; a plank is one physical piece, and a strake may be made of several scarfed together.

See also Scarf, Garboard, Sheerstrake

The topmost strake, running along the sheer. Usually the one that gets varnished when everything else gets painted.

See also Sheer, Strake

The curve of the top edge of the hull seen from the side. A "sweet sheer" is the usual praise; a sheer that sags in the middle is the first thing a critical eye notices and very nearly impossible to fix later.

The corner where the bottom of the hull meets the side, on a hull built with flat or nearly flat panels. A round-bilged hull has no chine; a multi-chine hull has two or three, approximating a curve with facets.

See also Bilge

The curved part of the hull between the bottom and the topsides — and also, confusingly but universally, the lowest inside part of the hull where water collects.

The height of the hull above the waterline. More freeboard keeps water out and gives the wind more to push against.

The fore-and-aft curve of the bottom of the hull. A boat with much rocker turns easily and tracks poorly; a straight-keeled one does the opposite.

The angle the bottom makes with the horizontal, measured from the keel outward. A flat-bottomed skiff has none; a deep-V powerboat has a great deal, which is what lets it take a chop at speed.

The outward slope of the topsides as they rise, which throws spray away from the boat and adds buoyancy as she heels.

The opposite of flare: topsides that curve inward as they rise. Handsome, traditional on launches and canoes, and a little more work to plank.

The athwartships crown of a deck, which sheds water and makes the deck stiffer than a flat one of the same thickness.

Where the stem meets the keel — the part of the boat that enters the water first when she pitches.

A fin projecting below the after part of the hull, fitted to help a boat hold a straight course and, on a small boat, to protect the rudder when she takes the ground.

Drawing the hull out full size — traditionally in chalk on a loft floor — to turn the designer's table of offsets into shapes that can be cut. Many modern plans for amateurs supply full-size patterns precisely so that this step can be skipped, and say so prominently.

See also Table of offsets, Station, Fairing

The table of measurements defining the hull's shape at each station, in feet, inches and eighths. The compact form in which a hull was transmitted for about two centuries.

See also Lofting, Station

Making a line or a surface sweet — free of flats, bumps and hard spots — by eye, by batten and by sanding. It is the single activity most often underestimated by first-time builders, and the one that most decides whether the finished boat looks right.

Transferring the true shape a plank needs to be onto the stock, using a batten and dividers, rather than assuming it is a straight or regular curve. A plank cut without spiling almost never fits.

A long tapered joint used to make one long piece out of two shorter ones. In plywood a slope of about eight to one is the usual rule, and a well-made scarf in epoxy is stronger than the wood around it. Also spelled scarph.

See also Epoxy

A groove cut along the keel, stem or sternpost to receive the edge of the planking. Cutting one correctly, so that the plank lands fair along its whole length, is a traditional test of patience.

See also Keel, Stem

Softening timber with wet heat — an hour a inch of thickness is the usual rule of thumb — so it can be bent to shape and will hold that shape as it cools and dries. Oak and ash are the traditional choices.

See also Frame

Building a curved member up from several thin strips glued together over a form. Stronger and more stable than steam bending, and it does not need a steam box — but it needs clamps, and a great many of them.

The angle cut on the edge of a frame, plank or panel so that the next piece lands flat against it. Bevels change continuously along a curved hull, which is why they are cut and checked rather than measured once.

The general word for what holds the boat together mechanically — screws, nails, rivets, bolts. In salt water the metal matters as much as the size: silicon bronze and stainless behave very differently, and mixing metals invites corrosion.

See also Rivet

In clinker work, a copper nail driven through both planks and a washer — a rove — then cut short and peened over to draw the joint tight. The characteristic sound of a clinker boatyard.

A wooden plug glued into a counterbored screw hole and pared flush, so that a varnished surface shows wood rather than metal. Cut from the same stock, with the grain running the same way, or it will announce itself.

Driving cotton or oakum into the seams between carvel planks so that they take up and become watertight. A traditional operation with its own tools, and not to be confused with running a bead of modern sealant, which is a different thing that happens to share the word.

A four-sided sail set on a mast with a diagonal spar — the sprit — running from low on the mast to the peak of the sail. Simple, cheap, quiet and very old; the rig of the Thames barge and of a great many small home-built dinghies.

A four-sided sail hung from a yard that crosses the mast. Balanced, standing and dipping lugs differ in where the yard sits and what happens when you tack. Cheap to make, forgiving to sail, and easily struck and stowed in a small open boat.

A four-sided fore-and-aft sail with a spar — the gaff — along its top edge. More sail area low down than a bermudan rig of the same mast height, at the cost of more strings.

A rig whose yard stands nearly vertical, giving something close to a triangular sail while keeping the spars short enough to stow inside the boat. The usual answer for a trailerable dinghy that wants a tall sail.

The familiar triangular mainsail set on a tall mast. Also called marconi. Efficient to windward and demanding of the mast.

A pivoting plate lowered through a slot in the hull to resist leeway, and raised for shallow water and for the trailer. A daggerboard does the same job but drops straight down instead of pivoting.

See also Leeboard

A board hung on the outside of the hull doing a centreboard's job, leaving the inside of the boat clear. Traditional in Dutch craft and on flat-bottomed working boats.

See also Centreboard

To reduce sail area in a rising wind by tying part of the sail down. The interesting question about any small boat rig is how easily it can be reefed while afloat and alone.