A lateen sail is a triangle laced to a long diagonal yard; it gives the best upwind performance of the simple rigs, but its yard is very long relative to a small boat and must be moved from one side of the mast to the other at every tack. In the 5.6 square meter example the yard is about 3.8 m on a 4.5 m boat, the sail’s centre sits only about 12% further from the waterline than a spritsail of the same area, and the real cost is the length of spar swinging overhead.
Part of Small Sailboat Construction
The lateen is a triangular sail on a long yard set obliquely to the mast, in use for millennia around the Mediterranean, the Indian Ocean and the Arab world.
The Long Yard Is The Price Of The Triangle
The carrier names two facts about the lateen: it points highest of the three simple rigs, and its long yard is unwieldy when tacking. The geometry explains both. A triangle with a 3.0 m foot and the same 5.6 m² of area as the spritsail example in Spritsail Rig must be tall:
- Area = ½ × foot × height, so height = 2 × 5.6 ÷ 3.0 = 3.73 m
- If the peak sits 0.8 m aft of the tack, the yard along the luff runs √(0.8² + 3.73²) = 3.81 m
- Against a 4.5 m boat that is 3.81 ÷ 4.5 = 85% of the hull length
A softwood yard of 3.81 m and 6 cm across weighs about π × 0.03² × 3.81 × 450 = 4.8 kg (450 kg/m³ is the midpoint of the 400-500 range for seasoned softwood in Logistics & Load Planning), and its forward end sits close to the bow while its tip reaches 3.7 m above the deck.
What You Need
- A long, straight yard, tapered toward the tip; the weight above matters, so use light wood
- A short mast with a block or rope strop at the top, on which the yard hangs at a balance point found by trial
- A halyard and a downhaul at the tack
- A sheet to the clew, and a boom only if you choose to add one
- Plenty of clear space in the boat to swing the yard
Method: Rig It And Practise The Tack On Land
Step 1: Lace the sail to the yard. The luff is the whole length of the yard; lace in short intervals so the cloth does not belly at the tack.
Step 2: Hang the yard at its balance point. Hoist with the bow into the wind and move the halyard position until the yard hangs steady at the angle you want, then lash the strop.
Step 3: Practise the tack on the beach. Stand where the helmsman will stand and move the yard through its full swing, with the boat pulled up and facing the wind. The yard must pass to the other side of the mast, and you must know where every rope goes while it does.
Step 4: Sail in light wind only. Make the first tacks in air no stronger than force 3 (12-19 km/h; see Wind Speed Estimation). Turn the bow through the wind slowly, ease the sheet as the sail goes slack, and do not wait for the cloth to fill again before the yard has crossed.
Step 5: Learn the recovery. If the boat stalls head to wind, push the tiller to one side and back the sail to turn the bow, or row it round; a boat caught head to wind with the yard half across is drifting backwards and is vulnerable.
Worked Example: The Heeling Arm
For the triangle the centroid lies one third of the way up, 3.73 ÷ 3 = 1.24 m above the foot, against 1.06 m for the trapezoid in Spritsail Rig. Adding the same 0.55 m from the waterline to the tack and down to the board gives an arm of about 1.79 m instead of 1.6 m. At the top of force 5 the force on 5.6 m² is about 382 N, so the moment is 382 × 1.79 = 684 N·m against 611 N·m for the sprit, a rise of 73 N·m or 12%. Lateen and sprit therefore ask nearly the same of the crew in a steady wind. The difference shows up when the yard is dropped, when it hits a swell, or when a wave strikes a boat with 3.7 m of spar above the deck.
Common Mistakes
- Choosing the lateen for its looks — the tack is the whole difficulty; if you rarely sail upwind, a simpler rig serves.
- Letting the sheet stay cleated through a tack — the sail cannot cross and the boat can be pinned head to wind.
- Stowing the yard loose — a long spar that slides off the boat is a hazard to anyone in the water.
Safety
A long yard swings across the boat
A 3.8 m yard at head height crosses the cockpit during the tack and, when a gust fills the sail, it moves quickly. Keep the crew low and to the side, never position a person in line with the yard, and do not attempt a tack in strong wind until you have done many in light air.
What’s Next
- Learn next: Tacking & Jibing — how any rig changes sides of the wind
- Combine with: Mast Construction — the short mast and strop that carry the yard