Multihull Sails For Catamarans And Trimarans 
Your source for racing and cruising catamaran and trimaran sails

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Sails for Cruising Catamarans (and Trimarans)

Cruising Sails

Modern cruising catamarans have very unique requirements for sails. Because of the wide beams, and moderate displacements, these boats can carry full sail much longer than their mono hull counterparts.

Often it is difficult to determine the time to reef as modern catamarans, with their high stability, do not heel or even feel over powered until the breeze becomes quite high.

This imposes very high loads on the sails, requiring strong materials and constructions.

Most manufacturers supply recommendations for various wind speeds to reef the mains and roll in reefs in the furling genoas. Of course, these will be on the conservative side for liability reasons.

Also, for liability reasons, most production cats will come with rigs and sails on the conservative side.

This will leave the owners wishing for more power in less than moderate winds or when sailing on low angles.

We at Calvert Sails have worked closely with boat owners for many years building quality, custom, after market sails. Our objective has been to improve performance and durability over the stock sails sold with most production multihulls.

Much research has been done to determine the optimum sail designs, sail cuts, and materials to obtain improved performance in all conditions as well as extended life.

Here are our thoughts on these design and construction parameters, as well as sail selection, for short handed cruisers.

Design concepts;

From over two decades of designing multihull sails that have won scores of US and Caribbean regattas, we, at Calvert Sails, have been trend setters, pioneering materials and sail designs that out perform the competition.

With this vast knowledge, gained on the race courses, we are able to apply this thinking to performance cruising multihulls sails.

Knowledge of Cruising;

For 35 years, Dave Calvert has worked closely with owners of cruising multihulls, listening to their comments and what they want in sails to go the distance. He has personally owned a long line of boats, the latest being performance cruising catamarans during the last 12 years. He has logged over 60,000 miles cruising, racing, and setting world records offshore.

Dave and wife Trish, currently sail their Belize 43 catamaran between Florida and the Caribbean averaging 4,000 to 5,000 miles annually.

His boats have always been test beds using the latest sail designs and constructions, to accurately discuss these design and construction improvements with first hand experence.

Mainsail construction, roach profiles, reefing systems, furling/reefing genoa features, and various off wind sail options, are all part of this ongoing testing.

The Sails


Most stock production mainsails are made with economy in mind. Dacron cloth, few full battens, and reduced roach, are common features in "OEM" sails.

Our first question to potential buyers is, "What kind of sailing do you have in mind?" We than determine if the intended use for the boat will be inshore or offshore cruising, as well as the regions of sailing. Also, "where is the performance lacking", is asked. We strive to improve performance on each sail in the inventory. One of the most important objectives is, maintaining the designed sail shape. We call this the "Performance Life of the sail". This is the length of time the sail will be used before the designed shape is lost. Cloth too stretchy or under speced for the application is one of the main contributors of sail shape becoming too full or the draft moving too far aft.

Sails are only as good as their construction and materials used.

Engineering sail constructions, based on the boats and their intended use, are all important.

We design the main sail's 3 dimensional shape, and leech profile to optimize performance all around.Than, the number and stiffness of the full battens are chosen to complement this designed shape.

Also of main concern, is the number, position, and construction of reefs.

Final construction features like corner patch design, size of rings, batten pocket reinforcements and chaff protection, luff hardware and reinforcements, leech line size and exits, tell tails and their positions as well as sail covers and lazy jacks are all well thought out. All of our sails are custom designed to meet the criteria of the owners requirments.


Most jibs and genoas today are on furlers. These furling sails must also be properly thought out for their intended uses. In most cases, these working headsails need to be treated like the mainsails they will be used with. This includes similar sail construction and materials. The typical cruising jib or genoa will be used in extreme conditions. These will be used full size when the main sail will have one or even two reefs. Than the furling headsails will be furled part way as a reef and continue to endure up to storm force winds.

Because of this, these sails must be built to withstand extreme conditions and maintain good sail shape even when rolled up part way.

Of foremost importance is the initial designed shape. Cruising headsails must perform in little breeze up to strong winds, complementing the mainsail during all of this. There has always been concerns on keeping furling sails from becoming overly full when reefed. Foam luff pads, foam strips, and a series of sewn in ropes, can work well to keep an efficient sail shape when partially rolled.

To compliment this, "reef patches" should be used. These run down the leech, from the head, and along the foot, from the tack, to the maximum recommended reef positions. These reef strips add extra layers of reinforcement to the high loaded areas of the "new" head and tack, when the sail is reefed.

Screachers, Code 0, and Spinnakers;

I won't take long for new boat owners to see the value of after market light air and off wind sails. When sailing along nicely in a fresh breeze, than, steering down to a broad reach, this will be realized.

The typical response may be to change to the "iron genoa" or reliable diesels! Very high hours on most cruising catamaran diesels attest to this. Why not add another sail to eliminate much of this engine use and increase sailing pleasure? Here are the three most recommended sails for this, and descriptions of each.

Screachers, are commonly designed to tack to a bow sprit and fit within the shrouds to enable them to be sheeted in close for sailing upwind in light air. These sails offer much better performance than the stock jibs or genoas in light conditions. The construction for good screachers must be strong. Use of low stretch materials and a radial cut, are needed to maintain the designed sail shape in apparent wind max limits of around 18 kt.

Because of their larger size, compared to the standard headsails, they also can be powerful reaching sails. When used on a furler, it becomes an easy task to simply roll up the working headsail, and unroll the screacher, or vice versa.

On these loose luff, furling sails, we use Kevlar or Vectran anti twist luff ropes that are adjustable internally, at the tacks. This "anti twist" construction of these luff ropes help to furl these sails without use of foils or wire luffs. Also, of importence is the UV strips. Most cruisers will want to leave the screachers furled on the bow sprits for long lengths of time.

To avoid damage from the sun's UV rays, protective UV strips need to be sewn to the leech and foots of all furled sails. We often will use light weight dacron UV material for these light screachers. The heavy Sunbrella material, as used on the working furling headsails, will be too much weight on leeches of light screachers.

Screachers can also be used "wing n wing", without the mainsail, for sailing straight downwind.

Because these sails have a foot length short enough to sheet inside the shrouds, the sail area will not be as large as the Code 0 or Asymmetrical Spinnakers. If more sail area is needed, consideration should be given to a Code 0 or spinnaker. One of these sails can be used in place of the screacher, if a three sail inventory is desired, or used in addition to the screacher.

Code 0 sails have evolved from narrow, flat spinnakers, to triangular, loose luff sails with low stretch luff ropes. The size of these sails are between the screachers and the asymmetrical spinnakers.

The modern code 0 is often constructed with purpose designed materials called Code 0 cloths.

This cloth is much stronger and lower stretch than the best of the nylons. The weights are also light but, these cloths are laminates with a taffeta on one side, a strong warp fiber, (often an Aramid like Kevlar and Technora), and a light mylar film on the other side. The construction is designed to have a "soft hand". This allows the material to be rolled, folded, and even stuffed into a bag.

Cloth weights range from 1.7 oz. up to 4.25 oz,with up to 9,000 DPI of Kevlar or Technora in the warp, the main load bearing fibers.

Code 0 material, in the higher weights, can also be used very successfully on screachers up to moderate size catamarans.

Code 0 sails typically use the spinnaker points of attachment. To set this up properly, a bow sprit is needed. The sail then tacks to the end of the bow sprit, runs outside the shrouds, and sheets to the spinnaker blocks aft. This allows the Code 0 to have a much longer foot than the screacher, giving an increase in sail area. Apparent wind angles will be lower than the screachers, because of the wider sheeting angles, but the increase of area will give more power when sailing on broad reaches. A properly set up Code 0, will work well close reaching in light air, but not go upwind.

For best results, the Code 0 halyard, as well as the Screacher halyard, should be a 2 to 1. This allows for higher luff tension and reduces loads at the bottom rope clutch and winch.

To obtain and maintain, the Code 0 and screacher's designed shape, a very tight luff is needed.

Because of this, we also use an adjustable Kevlar or Vectran anti twist luff rope in the luffs of these sails. Even using low stretch luff ropes, there may be times the luff rope stretches enough to transfer too much tension to the sailcloth at the luff. Using the internal luff rope tensioning system will bring the high luff loads back to the luff rope.

On the boats, the 2 to 1 halyards should also be made of a very low stretch material like Kevlar, Technora, or Vectran. This works with the sail's Kevlar luff rope to maintain luff tension.

It can be easy to under estimate the loads from these sails on most multihulls. When the luff of the screacher, or even the Code 0, are properly tensioned, the forestay will become a bit loose. This indicates that the luff of the sail, the halyard, and the bow sprit, are taking forestay type loads!

Proper attention should also be given to the construction and attachment of the bow sprits.

Contact the boat builder for advice on attachment points for the whisker stays to the bows.

Often these will need to be positioned low, just above the waterline, with strong backing plates.

Spinnakers can be designed as symmetrical and asymmetrical in shape. We have made multihull sails our specialty and feel the best all around multihull spinnakers are asymmetrical. These have a draft forward designed shape, unlike the symmetrically round shape of the symmetrical spinnakers.

Because of this, we will concentrate our discussion on the multihull designed asymmetrical spinnakers.

Spinnakers are typically much larger than both the screacher and Code 0. Both the luff and leech will often have considerable convex curves greatly increasing the total sail area over a triangular sail of the same dimensions.

Cruising catamaran spinnakers can be rigged with a bow sprit or with blocks on the ends of the two bows. This system eliminates the need to set up a bow sprit if the boat does not have one.

However, we do recommend setting up a bow sprit if there are plans for a screacher or code 0 in the future.

Multihull spinnakers and quite different than those built for similar sized mono hulls.

When shopping for a catamaran (or trimaran) spinnaker, best to go to companies well acquainted with multihulls and their unique requirements.

Once again, these sails must be designed and built for the higher loads of stable boats, that do not heel.

Cloth weight in the 1.5 to 2.2 oz range are normal even for the smaller boats. On moderate size multis and up, extra wide luff, leech, and foot tapes should be used as well as extra tapes, sewn flat on all three sides. Lines in all three sides and large patches are also required. Count on getting stuck with the spinnaker up above the recommended wind range on occasion. Also, asymmetrical spinnakers, with flatter, draft forward shapes, can be used closer to the wind to extend their range. These close reaches dramatically increase loads on the sail and hardware.

We design and build multihull spinnakers as true multihull sails. The designed shape gives good performance on a wider range of sailing angles. The construction is engineered taking into account the higher loads sometimes experienced when sailing beyond the recommended wind strengths.

We can offer advice on the best ways to set up and use asymmetrical spinnakers rigged on bow sprits or tacked to the two bows.

A "must" for handling spinnakers short handed are spinnaker sleeves, like the ones built by ATN. These simply cover the spinnaker from the head down to the clew, in a long "sleeve".

The end result is a sausage type package, that can be raised with the halyard and deployed by pulling an internal line, bringing the entire sleeve to the head of the sail.

To douse, this is done in reverse.

More on this and other techniques in our section on "Catamaran Tuning"

Please give us a call for any sail, hardware, canvas, or rigging needs. We can offer consulting and package deals on sails and any hardware needed at very attractive prices.

"Before and After"

The dacron 44 ft cat main photo on the top left shows a very full, stretched out shape, not good for sailing upwind. This photo is in light winds and will look much worse when the winds are close to the reefing point.

The new Triradial cut Hydra Net 43 ft cat main photo shows the shape needed for good upwind sailing and, with this material and cut, will retain this nice designed shape in a wide range of conditions.

Used Dacron 44 ft cat main

New triradial Hydra Net cat main