For a 4-5 m boat choose the spritsail if you want the fewest parts, the lug if you will reef often and sail in changing wind, and the lateen only if you accept a long, awkward yard in exchange for the best upwind performance. Whichever you pick, begin with the small end of the 5-8 square meter range, because wind force on a sail rises with the square of wind speed and a sail is far easier to enlarge than to shrink.
Part of Small Sailboat Construction
A sailing rig is the mast, spars, sail and ropes that turn wind into boat speed; three traditional designs suit a small hull built with hand tools.
The Rig You Can Build Is Better Than The Rig You Admire
A sail does not care what it is called. What matters at the start is how many spars you must shape, how easily the area can be reduced when the wind rises, and how the rig behaves when you change course. The three rigs in the carrier answer those questions differently, and the table keeps the differences in one place.
| Rig | Spars beyond the mast | Reducing sail | Upwind | Main drawback |
|---|---|---|---|---|
| Spritsail | One (the sprit) | Poor; slackening the sprit only spills wind | Below the lateen | The sprit is a long thin pole working in compression |
| Lug | Yard, often a boom | Good; roll or tie down to reef points | Balance lug better than standing lug | Heavy yard overhead; on a standing lug the cloth can press on the mast on one tack |
| Lateen | One long yard | Poor | Best of the three | Yard must be swung around the mast when tacking |
Details are in Spritsail Rig, Lug Sail Rig and Lateen Sail.
What You Need
- A hull that can take a rig — a rowing hull with a keel or a flat bottom, 4-5 m long, plus a way to resist sideways slip; see Centerboard or Leeboard
- A mast roughly as long as the boat, 8-10 cm across at the base — see Mast Construction
- Cloth for 5-8 square meters — see Sail Materials
- Ropes for the sheet and halyard — see Running Rigging
Method: Choose The Rig In Four Questions
Step 1: Count the spars you can make. A spritsail needs one pole beyond the mast. A lug needs a yard, usually a boom as well. Poles that are long, straight and light are the scarce item, not cloth.
Step 2: Decide how you will shorten sail. If your coast or river has gusty afternoons, you want the lug, which reefs by rolling or tying the lower part of the sail down (about 30% of the area with reef points at roughly one third of the height, as the carrier gives).
Step 3: Decide how much upwind work you will do. A lateen points highest but costs you effort at every tack. A boat that mostly runs or reaches loses little with a spritsail.
Step 4: Cut the first sail small. Take 5 square meters, not 8. You can add a second panel later; you cannot take back a capsize.
Worked Example: What 6 Square Meters Asks Of The Crew
Wind pushes on a sail with a dynamic pressure q = ½ × ρ × v², where ρ is air density (1.225 kg/m³ at sea level, 15 °C) and v is speed in m/s. Take the top of Beaufort force 4 from Wind Speed Estimation:
- v = 28 km/h ÷ 3.6 = 7.78 m/s
- q = 0.5 × 1.225 × 7.78² = 37.1 N/m²
- On 6 m² of sail, force ≈ 37.1 × 6 = 222 N, taking a force coefficient of about 1 (an order-of-magnitude assumption, not a measured value for any sail)
At force 5 (38 km/h = 10.56 m/s) q is 68.2 N/m² and the force is 409 N, 1.84 times as much from a wind only 36% faster, because speed is squared. That is why a rig that feels docile in a gentle breeze can overpower a small boat inside a single step of the Beaufort scale. The heeling moment arithmetic is in Spritsail Rig.
Common Mistakes
- Fitting the largest sail the carrier allows — 8 square meters is a ceiling for a loaded, well-ballasted hull, not a starting point.
- Copying a rig because it looks fast — a lateen is fast only if the crew can swing the yard cleanly; an awkward tack in a gust is how boats get knocked down.
- Sailing a rowing hull with no board — without something under the hull the boat slides sideways instead of forward.
Safety
Wind force grows with the square of speed
A sail that holds a crew comfortably at 19 km/h delivers about 4 times the pressure at 38 km/h (the ratio is (38 ÷ 19)² = 4). Learn in light wind, stay near shore, wear a flotation device on the water rather than carrying it in the boat, and read Safety & Capsizing Recovery before the first outing.
What’s Next
- Learn next: Mast & Rigging — how the chosen rig is held up and controlled
- Combine with: Sail Making — turning the chosen shape into cloth