Introduction
One of the defining characteristics of a catamaran is its immense beam. While this width provides incredible stability and living space, it fundamentally changes the geometry of the rigging and how the sails are trimmed. When designing a new headsail for a bluewater catamaran, two of the most critical factors we must consider are the sheeting angles and the clearance around the spreaders.
A poorly designed headsail on a catamaran will either chafe itself to death against the rig or fail to sheet in tight enough for upwind performance. At Kraken Sails, we engineer our headsails to work in harmony with the unique geometry of multihulls. In this post, we will explore the challenges of headsail sheeting and spreader clearance on catamarans and how to address them.
The Wide Beam Dilemma: Sheeting Angles
On a monohull, the genoa tracks are typically mounted close to the cabin top, allowing for a very narrow sheeting angle (often 10 to 12 degrees off the centerline). This narrow angle allows the boat to point high into the wind.
On a catamaran, the primary winches and genoa tracks are often located far outboard on the coachroof or even on the hulls themselves. This creates a much wider sheeting angle.
Overlapping vs. Non-Overlapping
If a catamaran uses a large, overlapping genoa (where the clew extends past the mast), the sail must be sheeted outside the shrouds. Because the shrouds are anchored far outboard on the hulls to support the mast without a backstay, the sheeting angle becomes very wide. This limits the catamaran’s ability to point as high as a monohull upwind.
To counter this, many modern catamarans utilize non-overlapping jibs (often self-tacking). Because the clew remains forward of the mast, the sail can be sheeted inside the shrouds, allowing for a tighter sheeting angle and better upwind pointing ability.
Flying Leads and Barber Haulers
To optimize the sheeting angle for different points of sail, bluewater cruisers often employ “flying leads” or “barber haulers.” These are secondary lines attached to the genoa sheet that allow you to pull the clew inboard (for better pointing upwind) or outboard (to open the slot when reaching). When designing a headsail, we must know exactly where your primary sheeting points are located to ensure the clew is cut at the correct height and angle.
The Danger Zone: Spreader Clearance
Because catamarans lack a permanent backstay, the mast is supported by heavily swept-back spreaders and shrouds. These swept-back spreaders are the mortal enemy of the headsail leech.
When sailing off the wind, you ease the headsail sheet, allowing the sail to travel forward and outward. On a catamaran, the leech of the sail will quickly come into contact with the swept-back spreaders. Over time, the constant rubbing and flogging against the spreader ends will chafe through the UV cover, the stitching, and eventually the sailcloth itself.
Measuring for Clearance
To design a headsail that minimizes chafe, we must accurately measure the spreader geometry. This involves measuring:
1. The height of each spreader from the deck.
2. The length of each spreader from the mast.
3. The angle at which the spreaders are swept back.
With this data, our 3D design software can simulate the sail flying on your specific rig. We can then adjust the roach profile (the curve of the leech) to ensure it clears the spreaders as much as possible when eased.
Mitigating Chafe
Even with a perfectly designed sail, some contact with the spreaders is inevitable when sailing deep downwind. To protect your investment, Kraken Sails incorporates heavy-duty chafe patches on the leech of the headsail exactly where it intersects with the spreaders. Furthermore, we highly recommend installing smooth, rounded spreader boots on your rig to eliminate sharp edges.
Conclusion
Designing a headsail for a catamaran is an exercise in 3D geometry. The wide sheeting angles and swept-back spreaders require careful measurement and precise engineering to ensure the sail performs well upwind without destroying itself downwind.
In our next post, we will turn our attention back to the mainsail, exploring the crucial concept of sail twist and how to control it using the mainsheet and traveler.
Kraken Sails – Engineered for the Ocean.