A small sailboat’s rudder is a flat wooden blade 20-30 cm wide and 40-60 cm deep, shaped with a rounded leading edge and a tapered trailing edge, fixed to a vertical stock that hangs from pintles and gudgeons on the transom and is turned by a horizontal tiller. Push the tiller left to turn right; set the two fittings as far apart as the stock allows, because wide spacing shrinks the load on each (about 146 N on the lower one instead of 292 N when they are half as far apart in the worked example).
Part of Small Sailboat Construction
A rudder is the blade at the stern that steers the boat, turned by a tiller, a handle, and hinged on pintles and gudgeons.
The Rudder Is A Small Wing With A Hinge
The rudder blade deflects the water flowing past it, and the sideways force it creates turns the boat. Its leading edge is rounded and its trailing edge is tapered, which makes the water flow smoothly and keeps the blade from stalling. The blade is attached to the stock, a vertical post, which carries the load to the hull through two hinge fittings: pintles (pins) fixed to the stock and gudgeons (sockets) fixed to the transom. The tiller is a handle extending forward from the top of the stock, so the helmsman, sitting forward of it, steers by pushing it sideways: tiller left, bow right.
What You Need
- Blade wood: a straight-grained plank, tough and resistant to splitting
- A stock: a post of strong wood, or the blade itself extended upward
- Pintles and gudgeons, salvaged from an old boat or forged from iron strap; in a pinch, rope loops (the carrier notes that works but limits the turning angle)
- A tiller: a stout stick, long enough for leverage
- Fasteners large enough to stay put in the transom (see Riveting and Lacing for ways to hold wood to wood)
Method: Build And Mount
Step 1: Shape the blade. Plane the leading edge to a rounded shape and the trailing edge to a thin taper, making the cross-section an airfoil (see Plane Building for the tool).
Step 2: Attach the stock with through-fastenings, a stack of glued boards, or one piece of wood, and check that the blade is straight when viewed along the stock.
Step 3: Fit the pintles to the stock as far apart as the length allows and the gudgeons to the transom at matching heights. The lower pintle should be below the waterline at all times.
Step 4: Fit the tiller to the top of the stock, long enough to reach the helmsman’s hand, with a notch or pin to prevent it from sliding off.
Step 5: Fit a lifting line and a stop so the blade can be raised in shallows and cannot lift out of its fittings by itself.
Worked Example: Loads On The Fittings And The Hand
Take a blade 25 cm wide and 50 cm deep, the middle of the carrier’s ranges (20-30 cm wide, 40-60 cm deep): area 0.25 × 0.50 = 0.125 m². At 2 m/s the dynamic pressure is ½ × 1,000 × 2² = 2,000 N/m², and with an assumed lift coefficient of 0.5 (an illustrative value, not a measured one), the side force is 2,000 × 0.125 × 0.5 = 125 N.
If the force acts 0.35 m below the upper gudgeon and the fittings are 0.30 m apart, moments about the upper fitting give a lower-fitting load of 125 × 0.35 ÷ 0.30 = 146 N. If the fittings are only 0.15 m apart, half the spacing, the load is 125 × 0.35 ÷ 0.15 = 292 N, twice as large. Wider spacing is the cheapest way to cut load on the transom. The same lever law applies to the tiller: if the rudder needs a 15 N·m torque at the stock (assumed), the hand force on a 0.5 m tiller is 15 ÷ 0.5 = 30 N, and on a 1.0 m tiller 15 ÷ 1.0 = 15 N.
Common Mistakes
- Fittings too close together — they loosen quickly and wear the transom.
- A thick, square-edged blade — it stalls, drags, and steers poorly.
- A rudder that cannot be lifted — it breaks on the first grounding.
- A tiller too short to hold in a gust — see the lever calculation.
Safety
Losing the rudder means losing control
Carry a spare rudder or a steering oar, and rig a lanyard so a rudder that lifts out cannot float away. If the rudder fails, row or paddle; do not try to steer under sail with the sheet alone in a rising wind.
What’s Next
- Learn next: Basic Sailing Skills — using the steering you have built
- Combine with: Centerboard or Leeboard — the balance between board and rudder