Hollow a dugout by one of two methods, often combined: burn small controlled fires on the surface to be hollowed, protecting the rest with clay or wet mud, and scrape out the char with an adze, shell or metal tool, repeating for days to weeks; or saw cross-cuts every 10-15 cm to the target depth, split out the wood between them with a chisel or axe, and smooth with an adze. Aim for a wall of 3-5 cm, and check it by drilling gauge holes from the outside to a depth that equals your target thickness.
Part of Coracle & Small Watercraft
Hollowing is removing the wood from a log’s interior, by fire and scraping or by cutting and splitting, until a canoe-shaped shell with thin, even walls remains.
Thin Is Light, Thick Is Safe; The Gauge Holes Settle It
The carrier gives a target wall thickness of 3-5 cm: thinner is lighter but weaker, and too thick makes the canoe too heavy to handle. It suggests checking thickness often by drilling test holes from outside. A hole is a gauge: its depth from the outside is the wall thickness you will leave; when your hollowing reaches the bottom of the hole you stop in that spot. Many such holes in a pattern let you work to a known thickness everywhere without guessing. Plug each hole afterwards with a tapered wooden peg set in pitch.
Fire and scrape. Split the log in half lengthwise, or flatten one side to make the opening. Build small controlled fires on the surface to be hollowed, using clay or wet mud to protect the areas you want to keep; scrape out the charred wood with a stone adze, shell or metal tool; repeat. The carrier calls it slow (days to weeks) but needing minimal tools.
Adze and axe. Mark the outline of the hollow on the top; make cross-cuts with a saw every 10-15 cm to the desired depth; split out the wood between the cuts with a chisel or axe; smooth the interior with an adze.
What You Need
- The rough log, supported and wedged so it cannot roll
- For fire: clay or mud, water, firewood, and a scraping tool; for the other method: saw, chisel, axe, adze
- A drill and bit for gauge holes (see Drill and Auger) with a depth mark
- Tapered pegs and pitch to plug the holes
- Water and a helper whenever a fire is lit
Method: Hollow To A Gauge
Step 1: Mark the outline of the opening and the wall thickness.
Step 2: Drill gauge holes from the outside at intervals, each to the depth you want to leave as wall.
Step 3: Remove the wood by your chosen method, working evenly and keeping the ends thick until last.
Step 4: Stop at each gauge hole when the interior reaches it.
Step 5: Plug, smooth and seal, and let the canoe dry slowly (see Wood Seasoning).
Worked Example: Cuts And A Mass Check
A hollow 2.8 m long (3.5 m log with 0.35 m left solid at each end, an assumed layout) needs 2.8 ÷ 0.15 = 18.7, so 19 cross-cuts at 15 cm spacing, up to 2.8 ÷ 0.10 = 28 at 10 cm. Gauge-hole depth for a 4 cm wall is 4 cm; the full-length shell volume is 0.123 m³ (from Dugout Canoe). Weigh the canoe as a final check: at 450 kg/m³ the shell should be near 55 kg, but green wood at 800-1,000 kg/m³ gives 0.123 × 800 = 98 kg to 0.123 × 1,000 = 123 kg. A hull that weighs far more than that still has material to remove, or the ends are too heavy; one that weighs far less has thin walls.
Common Mistakes
- Hollowing without gauge holes — you cannot see a wall from inside.
- Burning unprotected edges — clay or mud shields what must remain.
- Letting the ends dry fast — the log cracks from the ends; keep them sealed and drying slowly.
- Leaving a fire unattended — see below.
Safety
Fire in a log, smoke and edge tools
Embers can run along cracks in the wood and reignite after you leave. Keep water and wet clay at hand, never leave a fire unattended, keep clear of drifting smoke, and let the char cool fully. An adze swings toward your shins: wear stout boots, keep the log blocked, and stand so a glancing blow goes into the log.
What’s Next
- Learn next: Shaping for Stability — the form of the hull
- Combine with: Boat Sealing — sealing cracks and the plugged holes