Make an oar from straight-grained spruce, ash or fir, with a round or oval shaft 4-5 cm across at the grip tapering to a flat, slightly cupped blade 12-15 cm wide and 50-60 cm long, and a length of about 2.2-2.5 m for a boat 1.2 m wide. The position of the oarlock along that length sets the lever ratio, from 2.29 to 1 with 0.7 m inboard to 4.75 to 1 with 0.4 m inboard, and the shaft is loaded most at the oarlock, where in the worked example it sees about 15.6 MPa.
Part of Canoe & Rowing Boat Construction
An oar is a lever and a paddle in one piece: a handle inside the boat, a shaft pivoting at the oarlock and a blade that pushes against the water.
The Oarlock Divides The Oar Into Two Levers
Length, weight and balance all matter, the carrier says: a good oar is a precision tool. The carrier’s rule for length is about 1.5 times the boat’s beam plus the distance from oarlock to the rower’s hands, and it gives the example of a boat 1.2 m wide with oarlocks at the gunwale taking oars of 2.2-2.5 m. Read literally, 1.5 × 1.2 = 1.8 m is the outboard part of the oar, and the inboard part is the remainder: 2.2 − 1.8 = 0.4 m up to 2.5 − 1.8 = 0.7 m. The carrier does not say how long the inboard part should be, so the ratio of outboard to inboard length is left open, and it matters.
The oar is a lever pivoting at the oarlock. Hand force acts on the short inboard arm and the water pushes on the long outboard arm. A longer outboard arm relative to inboard sweeps the blade further for each hand movement but means the hand has to push harder for the same blade force. For a rower this is the difference between a light and a heavy oar.
What You Need
- A billet or plank of spruce, ash or fir, straight-grained, light, strong and flexible (the carrier’s choice)
- A drawknife, spokeshave and plane (see Hand Tool Making)
- Sandpaper or scraping stones, and oil or varnish
- A bend-test rig as in Mast Construction
- A mark for the oarlock position
Method: Make And Check
Step 1: Choose the ratio. A rule of thumb, recalled from rowing practice and not from a source here, puts about one third of the oar’s length inboard, which gives a ratio of 2 to 1.
Step 2: Rough out the oar from the billet, shaft 4-5 cm across at the grip, tapering toward the blade.
Step 3: Shape the blade flat, 12-15 cm wide, 50-60 cm long, tapering to a thin edge, slightly concave on the power face.
Step 4: Balance it. Mark the oarlock position and balance the oar on a finger there. If the blade end is far heavier, the rower lifts it on every recovery; trim the blade or add weight in the handle.
Step 5: Test and finish. Bend-test an offcut of the same wood, sand smooth (splinters end rowing careers fast), and oil or varnish the whole oar.
Worked Example: Lever Ratios And Shaft Stress
For a 2.3 m oar, the outboard-to-inboard ratio at different oarlock positions:
| Inboard length | Outboard length | Ratio (out ÷ in) |
|---|---|---|
| 0.40 m | 1.90 m | 4.75 to 1 |
| 0.55 m | 1.75 m | 3.18 to 1 |
| 0.70 m | 1.60 m | 2.29 to 1 |
| 0.77 m (one third) | 1.53 m | 2.0 to 1 |
Take an assumed peak hand force of 200 N and 0.70 m inboard. The bending moment at the oarlock is 200 × 0.70 = 140 N·m. For a round shaft of 4.5 cm, section modulus π × 0.045³ ÷ 32 = 8.95 × 10⁻⁶ m³, so stress = 140 ÷ 8.95 × 10⁻⁶ = 15.6 MPa. At 5.0 cm, 140 ÷ 1.227 × 10⁻⁵ = 11.4 MPa. Against the illustrative 30.6 MPa offcut in Mast Construction (not a property of any species), the margin is 30.6 ÷ 15.6 = 2.0 at 4.5 cm and 30.6 ÷ 11.4 = 2.7 at 5 cm, so keep the shaft thick at the oarlock and measure your own wood.
Common Mistakes
- A thin shaft at the oarlock — stress goes with the inverse cube of diameter.
- A very long outboard length — it overloads the hands and the shaft.
- A heavy blade — the rower lifts it every stroke.
- Skipping the grain check — a short-grained shaft snaps.
Safety
A broken oar is a lever with a splintered end
An oar that breaks under load swings the handle into the rower’s chest or face. Check for cracks before each outing, and carry a spare.
What’s Next
- Learn next: Oarlocks & Thole Pins — the pivot the oar swings on
- Combine with: Rowing Technique — using the oar well