Introduction
Ordering a new set of sails is an exciting milestone for any bluewater cruiser. However, before the first panel of cloth is cut, precise measurements must be taken. While the basic principles of measuring a sail (Luff, Leech, and Foot) apply to all boats, catamarans present a unique set of challenges that can easily trip up an unwary owner.
At Kraken Sails, we know that a millimeter off on paper can translate to a sail that doesn’t fit on the boat. Catamarans feature wide beams, massive cabin tops, rigid biminis, and complex sheeting angles that must all be accounted for in the design phase. In this post, we will guide you through the specific nuances of measuring a large cruising catamaran for new sails.
The Standard Rig Dimensions: P, E, I, and J
Before measuring for specific sails, you must understand the four primary rig dimensions of your boat:
- P (Mainsail Luff): The maximum hoist of the mainsail, measured from the top of the boom to the highest point the halyard can pull the headboard.
- E (Mainsail Foot): The maximum length of the mainsail foot, measured along the boom from the mast to the outhaul maximum position.
- I (Foretriangle Height): The height from the deck to the point where the forestay attaches to the mast.
- J (Foretriangle Base): The distance from the front of the mast at deck level to the forestay attachment point on the deck or bowsprit.
While you can often find these numbers in your boat’s manual or the ORC database, never trust them blindly. Rigs are often modified, and factory specifications can vary. Always physically measure your own boat.
The Catamaran Mainsail: Boom Angle and Clearance
The most common mistake when measuring a catamaran mainsail is failing to account for the boom angle and the massive structures beneath it.
The Cabin Top and Bimini
Unlike monohulls, where the boom often sweeps low over a relatively flat cockpit, catamaran booms are usually mounted high to clear a large, rigid bimini or a raised helm station. When measuring the leech length (the back edge of the sail), you must ensure that the boom will not strike the bimini when the sail is fully hoisted and sheeted in tight.
The Boom Angle
The angle of the boom relative to the mast is critical. If you measure the leech too long, the boom will droop down at the aft end, potentially hitting the bimini or restricting headroom. Conversely, if you measure it too short, the boom will point skyward, making it impossible to apply proper leech tension and ruining the sail’s aerodynamic shape.
To measure this correctly, you must use the main halyard to hoist a tape measure to the top of the mast track. Then, fix the boom at the exact angle you want it to sit when sailing (usually 90 degrees to the mast, or slightly angled up to clear a bimini). Measure the straight-line distance from the top of the halyard to the clew outhaul attachment on the boom. This is your maximum leech length.
The Catamaran Headsail: Clew Height and Visibility
Measuring a headsail on a catamaran also requires careful consideration of the boat’s geometry.
Clew Height
On a monohull, racers often want a “deck-sweeping” genoa to maximize sail area and efficiency. On a cruising catamaran, a deck-sweeper is a liability. It will constantly chafe on the lifelines, scoop up solid water when plunging into a wave, and completely obscure the helmsman’s forward visibility.
When measuring the luff and leech of your new headsail, you must calculate a clew height that allows the sail to clear the lifelines and provides a clear line of sight from the helm station. This is usually achieved by raising the tack attachment point on the furler or designing the sail with a higher cut clew.
The Furling System
Most bluewater catamarans use roller furling headsails. You must measure the exact length of the foil extrusion, not just the forestay. The sail’s luff must be short enough to allow the halyard swivel to tension the luff without bottoming out on the top of the foil.
The Importance of Professional Guidance
Measuring a large catamaran is a two-person job that requires patience and precision. A mistake here can result in a costly refit.
At Kraken Sails, we provide detailed, step-by-step measurement forms specific to catamarans. Furthermore, we always review your measurements against our extensive database of boat models to flag any anomalies. If you are unsure about a measurement, take photos of the hardware and the rig—a picture is often worth a thousand numbers to a sail designer.
In our next post, we will delve deeper into the complexities of the catamaran headsail, specifically focusing on sheeting angles and spreader clearance.
Kraken Sails – Engineered for the Ocean.