Build boats of planks that carry a family and its goods, row them with oars sized by rule, and add a sail only to a boat that passes the stability test.
A replica of the Gokstad Viking ship being built in Tønsberg, Norway, 2026: clinker planks overlapping, riveted through the laps and held by frames inside.TØNSBERG Norway 2026-06-10 SAGA GOKSTAD viking ship replica arkeologisk kopi bygging skrog clinker-built wooden hull akterstavn sternpost Vikingodden byggeplass building site IMG 6856 · 2026-06-10 12:42:43 · Wolfmann · CC BY-SA 4.0 · Commons ↗
A dugout is only as big as the biggest tree; a plank boat is as big as its builder can frame. Planks fastened to each other or to frames carried the trade of the Iron Age on rivers and coasts, and they are still the cheapest planked boats there are: FAO publishes flat-bottomed designs for fishing communities because a carpenter can build one after a few weeks' training. With planks come oars, which move a boat faster and for longer than paddles, and the sail, which is also what capsizes boats.
The shape of it
Choose the construction by tools and fastenings: sewn, clinker, carvel or flat-bottomed.
Pick timber that resists rot and shrinks little, and season it.
Fasten by rule: nails at least 1/7 of the plank's thickness across and 2.5 times it long, clenched across the grain.
Caulk every seam, and leave softwood planks room to swell.
Size the oars from the span between the oarlocks.
Add a sail only after the offset-load test, with the sheet always in hand.
Rate and mark the boat: its capacity and the water it is built for.
Four ways to join planks, in sectionFig 1
TimberMetalLoose fill / grain
Sewn and clinker boats join planks to each other; carvel and flat-bottomed boats join them to frames. FAO's nail rule for the flat bottom: at least 1/7 of the plank's thickness across and 2.5 × it long.
Oars sized from the span between the oarlocksFig 2
Timber
Inboard = half the span + 5 cm; oar = inboard × 25 ÷ 7. A span of 115 cm gives 62.5 cm inboard and a 2.23 m oar, and the handles just overlap.
Doing it, step by step
The summary above says what has to happen. This says how, with the numbers that decide whether it works.
1 — Four ways to join planks
Sewn: planks laid edge to edge and stitched with cord through holes along each edge, with a lath or a pad of moss over the seam inside. Needs no metal; the stitching is renewed as it rots.
Clinker (lapstrake): each plank overlaps the one below it and is riveted through the lap: a nail driven through, a washer (the rove) put over its point inside, and the point hammered over the rove. Light and strong; Nordic boats and Viking ships were built this way.
Carvel: planks laid edge to edge over frames, fastened to every frame with nails or wooden pegs (trenails), and the seams caulked. It needs heavy frames first, and it builds big ships (seagoing ships).
Flat-bottomed: straight planks for the sides on three or four frames, the bottom planked across and nailed up into a thickened lowest side plank. FAO calls it the simplest planked boat to build, and the cheapest.
A replica of the Gokstad Viking ship being built in Tønsberg, Norway, 2026: clinker planks overlapping, riveted through the laps and held by frames inside.TØNSBERG Norway 2026-06-10 SAGA GOKSTAD viking ship replica arkeologisk kopi bygging skrog clinker-built wooden hull akterstavn sternpost Vikingodden byggeplass building site IMG 6856 · 2026-06-10 12:42:43 · Wolfmann · CC BY-SA 4.0 · Commons ↗A plank hull being built shell-first in Malaysia, 2004: the planks are joined edge to edge before any frame goes in.Naga Pelangi building without frames · 2004-06-17 07:55:04 · Christoph Swoboda · CC BY-SA 3.0 · Commons ↗
✓ Check: You have chosen a construction, and you have the fastenings and caulking it needs before the first plank is cut.
2 — Timber that lasts
FAO's four tests for a boatbuilding timber:
Rot resistance first: rot, not wear, ends wooden boats in fresh water. Local builders and foresters know which species last; soak the rest in preservative or tar.
Stability: a timber that shrinks and swells opens its seams. Choose one that shrinks under 4 % across the grain from green to 15 % moisture; the best hardwoods shrink about 2 %.
Strength rises with weight: a heavier timber allows a slightly thinner plank.
Takes nails without splitting; pre-bore where it splits.
Season planks under cover with air between them, and keep them out of the sun, which splits the ends.
✓ Check: Every plank is of a durable, stable species, seasoned, and free of rot and of knots through its thickness.
3 — Fastenings by rule
Nail size (FAO): at least 1/7 of the plank's thickness across and at least 2.5 times it long: for 20 mm planks, 3 × 50 mm nails.
Pre-bore a hole slightly smaller than the nail wherever the wood splits.
Clench a nail that comes through: tap the point over, hold a dolly against the head, and drive the point back into the wood across the grain, never along it, which splits it.
Iron rusts. Forge nails of wrought iron and tar them; hot-dip galvanised nails last far longer; copper does not rust, and is worth its price only in salt water.
✓ Check: A test joint with your nails in your planks has been clenched without splitting, and pulls apart only by breaking the wood.
4 — Caulk the seams, and leave room to swell
Drive a strand of cotton (or oakum, moss or bark fibre) into each seam with a caulking iron, not a chisel or a screwdriver, and fill over it with pitch or bitumen (FAO).
Softwood bottoms: leave a gap the thickness of a hacksaw blade between planks. Fitted tight, pine swells in the water and buckles the bottom open along the chine. Stable hardwoods can be fitted tight inside, with a small caulking bevel outside.
A new wooden boat leaks until its planks swell: keep it wet, or sunk in shallow water, for a day before judging the seams.
Caulking a new plank boat in Malaysia, 2004: bark fibre laid along the seam between planks.Traditional Malay boat building - applying the caulking bark · 2004-05-30 01:18:45 · Christoph Swoboda · CC BY-SA 3.0 · Commons ↗
✓ Check: After a day afloat, the seams have stopped weeping.
5 — Oars by rule
Size the oars from the boat, not from the rower (Shaw & Tenney):
Span: measure between the centres of the two oarlocks.
Inboard (handle end to oarlock): half the span + 5 cm, so the handles just overlap.
Oar length = inboard × 25 ÷ 7: 7/25 of the oar inboard and 18/25 outboard, the rule in use since the 1850s. A span of 115 cm gives 62.5 cm inboard and a 2.23 m oar.
Thole pins — two wooden pegs in the gunwale, one each side of the oar — work as well as metal oarlocks.
A rowing skiff makes 5–7 km/h and a crew can keep it up for hours; see the boats guide.
✓ Check: The handles overlap by a few centimetres mid-stroke, and the blades bury fully without the rower reaching.
6 — The sail, and when a boat may carry one
Only after the offset-load test in the boats guide: the sail's push acts high up, and a gust heels the boat far more than the crew moving does.
A square sail on a yard drives the boat with the wind behind or on the side. It cannot sail closer than about 60° to the wind (Queen Anne's Revenge Project), so to go upwind, lower it and row.
Keep the sheet in hand, never made fast, so a gust can be let out of the sail at once; be ready to lower the yard.
Reef or lower early: at the first white horses, a small open boat is past its design category (force 4).
Leeway: a flat-bottomed boat has no keel and slides sideways; a leeboard or centreboard gives it the grip a keel would.
A Viking ship replica under a single square sail, Bergen, 2023: the sail drives it only with the wind behind or on the side.Storskarven viking ship in Bergen · 2023-09-17 14:51:30 · Marius Vassnes · CC BY-SA 4.0 · Commons ↗
✓ Check: The boat passed the offset-load test before the mast went in, and the crew has dropped the sail at a word on every point of sailing.
7 — Rate it and mark it
Capacity: length × beam ÷ 15, both in feet. FAO's 4.9 × 1.22 m flat-bottomed boat rates 4 people.
Side at that load: at least 0.2 × beam, which is 24 cm for 1.22 m (FAO).
Swamp test: a wooden boat full of water floats level (FAO).
Mark the capacity and the design category (D, sheltered water) inside the transom.
✓ Check: Capacity and category are cut into the transom, and the boat has passed all three tests loaded to them.
What it looks like
An old clinker-built boat hauled out on Gotland, 2014: each plank laps over the one below it.Båt Gnisvärd · 2014-03-30 15:42:28 · En-cas-de-soleil · CC BY-SA 4.0 · Commons ↗A clinker-built dinghy from above: bent frames inside the lapped planks, thwarts across, and a transom at the stern.Clinker built dinghy awaiting restoration · 2021-10-05 13:03:37 · ThoughtIdRetired · CC BY-SA 4.0 · Commons ↗A plank hull being built shell-first in Malaysia, 2004: the planks are joined edge to edge before any frame goes in.Naga Pelangi building without frames · 2004-06-17 07:55:04 · Christoph Swoboda · CC BY-SA 3.0 · Commons ↗Caulking a new plank boat in Malaysia, 2004: bark fibre laid along the seam between planks.Traditional Malay boat building - applying the caulking bark · 2004-05-30 01:18:45 · Christoph Swoboda · CC BY-SA 3.0 · Commons ↗A Viking ship replica under a single square sail, Bergen, 2023: the sail drives it only with the wind behind or on the side.Storskarven viking ship in Bergen · 2023-09-17 14:51:30 · Marius Vassnes · CC BY-SA 4.0 · Commons ↗
Reference sheets
One drawn sheet covering the whole subject at once — the breadth a photograph cannot give, bought at the cost of accuracy. Read them for range and vocabulary, never as the thing you identify from.
Building a wooden plank boatDesign, timber, tools and fasteners, seven stages from keel and frames to fittings, clinker, carvel, strip-plank and plywood hulls, sealing, fittings, safety checks, a finished 4.5 m example, and upkeep.Illustration, not a photograph.Its 4.5 × 1.4 m example is rated for too many people: the capacity rule gives 4, not 4–6 (how much it carries), and the load test decides. It is also an open boat for sheltered water (category D), not coastal. It builds frames first, the carvel order; a clinker boat is planked first and framed after. Epoxy, marine glue, screws and a power drill are modern: at this tier seams are caulked with cotton or oakum, and planks fastened with nails, rivets or trenails, as this step sets out. The lettering has typing errors (“shows shows”, “coastil”).Building a wooden plank boat · 2026-09-28 · Civilization101 Blueprint (AI-generated) · CC BY-SA 4.0
Build it
Dimensioned drawings, bills of materials and construction procedures for the things this step asks for.
What the record shows was done at this step, what to do instead at this tier, and the evidence. All of them: the better path.
Adopt earlier
A float for everyone aboard
What was done
Ships were required to carry a lifejacket for every person only from 1914, when the first SOLAS convention followed the Titanic; in small boats the float is still the thing most often left ashore.
Do instead
From the first plank boat, carry a float for every person aboard — cork, sealed gourds, closed containers or a rated lifejacket — and wear it on cold or rough water.
Evidence
Of the 556 people killed in US recreational boating in 2024, 76 % drowned, and 87 % of those whose flotation was recorded wore none (USCG). The 1914 convention required lifejackets for every person aboard (IMO).
Needs nothing that is not already in hand.
How this fails
Softwood bottom planks fitted tight, which swell and buckle the bottom open along the chine (FAO).
Nails too thin or too short for the plank, which pull through in the first seaway.
A sail on a boat that has not passed the stability test, or a sheet made fast so it cannot be let go.
Rot at the ends and under the floorboards, where fresh water lies.
A flat-bottomed boat taken out of sheltered water: it slams and drifts sideways (FAO).
How you know it worked
VerificationThe boat has passed the swamp test and the offset-load test, carried its rated load with the side clear by at least 0.2 × its beam, been rowed with oars sized by the 7/25 rule, and, if rigged, had its sail dropped at a word on every point of sailing.