MULTIHULL ENTHUSIAST New Sails for Your Multihull

New Sails for Your Multihull

Here are your best options for a new mainsail, headsail and downwind sails

by Brian Hancock

I KNOW THAT I MIGHT BE STATING THE OBVIOUS here but while multihulls and monohulls are both boats, they are very different not only in the number of hulls, but in so many other ways including the way that their sails are designed and engineered. There are two big contributing factors; rig configuration and the fact that multihulls are considerably more stable than monohulls meaning that the loads placed on the sails are significantly increased. If you are out sailing your monohull and the breeze increases you quickly find yourself rail down and chucking in a reef or two. If you are out sailing your catamaran, it’s much harder to tell if you need to reef. The boat barely heels and as such the loads go directly onto the sails and rigging. So, let’s take a look at how sails for multihulls are different and things to keep in mind when ordering new sails from your sailmaker.

Rig engineering is in large part a factor of beam. On a monohull beam is limited and the rig needs to be supported by a number of spreaders and in some cases an inner forestay and running backstays. Most modern multihulls have what’s called a tripod configuration. A forestay and twin shrouds that are all the way outboard and quite far aft. Because of the angle that the shrouds connect with the mast they offer much more support to the mast. This much simpler rig opens up some interesting possibilities for sail designers, most important of which is that there is no backstay. No backstay means no worries about roach size. There is nothing for the sail to get hooked up on, so the possibilities are endless.

MAINSAILS

Many, if not all new multihulls come with some kind of square head main. It’s a very efficient sail plan. Think about a wing on an airplane. They would never be triangular in shape because it’s inefficient. The part of the wing closer to the

tip will barely be able to generate lift so airplane wings are almost rectangular. Same with a conventional main that is constricted by the backstay. It’s almost triangular and the top quarter is not contributing much. Add a square head and suddenly you have a much more efficient profile. The top of the sail is not only generating lift going upwind, but projecting sail area when sailing downwind. It’s a nice look and an efficient shape but it comes with some inconveniences. To support the square head there is a diagonal batten placed at 45 degrees, or some variation thereof, where it can be the most effective in supporting the square head. All well and good until it comes time to drop the sail. The regular battens lie flat against the boom and stack neatly. The 45-degree batten is obviously unable to lay flat. There is a solution. You can add a quick release pin to the headboard and by disconnecting the sail from the headboard the batten can then be laid flat on the boom. This is OK if the headboard and headboard carriage is within easy reach but, if not, it can be a challenge at the end of a long day sailing.

There are some workarounds to this. I have seen setups where there are two rings added to the headboard car.

Instead of a regular headboard on the main there is a ring. The halyard, usually a two-to-one, is attached to the ring on the head of the sail. Then there is a separate line that dead-ends on the lower ring on the headboard car and is led through the headboard ring and then the upper ring on the headboard car and back down to the deck. Once the sail is hoisted you can tighten the line. This will pull the headboard toward to the headboard car. The beauty of this system is that when you lower the sail you release the headboard line and this in turn allows the top angled batten to lay flat against all the other battens. It’s a pretty nifty way to go, but also just one more thing that could go wrong. There are definitely some advantages to having a more rectangular mainsail profile but as noted the square head can present some challenges. There is an alternative and that’s an elliptical head on the sail. This offers the advantage of the extra sail area without the associated batten issues. Instead of an angled batten there to support the square head you can instead have a series of parallel battens spaced quite closely together. They will support the elliptical head just fine and you won’t have any issue with the battens lying flat against the boom when the sail is lowered. There is one more specific advantage to a square or elliptical head and that’s that the top of the sail will twist open when a gust of wind hits. This helps prevent the boat from becoming overpowered and reduces strain on the sails and rigging.

Mainsail shape is also an interesting

topic. In general, multihull sails are much flatter than monohull sails. You don’t need all that extra power - read camber - to drag around all that lead found hanging under monohulls. Plus, multihulls are fast, their speed coming from the extra sail area and high righting moment. The faster the boat, the flatter the sail. Many sail designers think that the maximum depth of the sail needs to be quite far forward and this may be true if the mast is a wing mast that is able to rotate and is used as part of the overall sail profile. If it’s a standard mast the maximum depth can be roughly in the middle of the sail.

CORNERS AND BATTENS In terms of engineering, corner reinforcement as well as reef patches need to be oversize because of the high righting moment of multihulls and the additional strain that places on the sails. The patches should have multiple layers and the rings reinforced with heavy webbing, preferably Spectra. Because the shrouds are quite far aft when you are running downwind the sail, especially the battens, will chafe against the rigging so make sure that your sailmaker reinforces those areas.

Batten configuration is always a contentious subject among most sailors. Many prefer all full-length battens. For my part I prefer two full length battens up high and standard-length battens through the reef area. The full length

battens up high lends stability to the fabric and makes the sail more manageable when using with some kind of lazy jack system. Leaving them out down low gives you much more control over sail shape. If you have full length battens down low their stiffness usually dictates the overall shape of the sail. Fewer battens also means a lighter sail which is easier to hoist and to handle.

HEADSAILS

Headsail configurations differ depending on how the boat designer has set up the deck hardware. Some multihulls just have a non-overlapping headsail that is either set on an athwartship track where it can be self-tacking, or two regular tracks port and starboard mounted on the cabintop. For the latter configuration you can have a larger headsail. Because the shrouds are quite far aft the headsail can overlap the mast quite a bit thereby gaining some sail area. Self-tacking nonoverlapping jibs can be quite skinny and tall with the top half of the sail not doing much. Vertical battens in the leech can help regain some sail area.

The same engineering applies to headsails as it does to the main. Large reinforcement patches and webbed clew ring. If the sail is set on a furling unit the head and tack will be soft webbing loops but they, too, need to be adequately strong and out of Spectra preferably. UV protection along the leech and foot is a must if the sail is going to remain on the furler, and a foam luff really does help take some of the shape out of the sail when reefed, which in turn allows you to sail closer to the wind.

DOWNWIND SAILS Most modern multihulls come with a bow sprit and this opens up many possibilities for downwind sails. Some sailors still like to sail with an asymmetrical spinnaker set either on a top down furler or doused with a sock, but increasingly sailors are choosing a Code 0 type sail for their convenience. These sails are set on a line drive furler with an anti-torque cable in the luff of the sail. They can be as large or as small as you like and will be used in an apparent wind angle of around 40 degrees to around 140 degrees depending on the boat design. The nice thing about this is that the sail can be quickly and easily doused with the line drive furler. You can even run the furling line all the way back to the cockpit making it a very easy sail to deploy when needed. I don’t recommend any kind of UV strip on these sails. They are easy to lower and stow and that’s recommended, but if you want to leave the sail permanently set then I recommend a sleeve with a zipper that can be hoisted over the sail when at the dock or at anchor.

There are still some sailors who prefer a symmetrical spinnaker set conventionally with a spinnaker pole. If you are planning a long offshore passage in the Trade Winds where the wind can be predictably from

astern, a symmetrical spinnaker is a great option. Sure it’s a hassle to set the sail but once it’s up and drawing you don’t need to do much and you can effortlessly sail some deep downwind angles.

SAIL CLOTH

For many decades, Dacron was the chosen fabric for the main and jib and nylon for downwind sails, but that’s changing. There are some affordable laminates that can be used for the main and jib and these offer some real advantages. With a laminate you can make radial sails placing a heavier fabric in the high load areas like the leech and foot and a lighter fabric through the body of the sail. The result is a much lighter sail with the same strength and stretch resistance as an equivalent Dacron sail.

There has also recently been an increase in the number of membrane sails used on multihulls. Membranes used to be for racing sailors only and they were expensive, but that is now changing. One advantage cost wise is that with a membrane you make both the fabric and the sail at the same time. A stringing machine strings the sail placing fibers precisely along the anticipated load paths in the sail. It’s a very efficient way of engineering a sail. The membrane panels are then vacuum bagged to seal the different layers together and the panels are then assembled. There is no need to import fabric made in a different country only to build the sail and then ship it out. With membranes you only need to import rolls of fiber. Membrane sails are significantly lighter than equivalent Dacron or laminate sails and lighter sails are easier to set and trim and easier to handle. They also take up less space down below should they need to be stowed.

Same thing applies to Code 0 fabric. Because nylon stretches the range of a nylon sail both in terms of wind range and wind angle is limited. Code 0’s have become so important on multihulls that building them out of a light laminate is the way to go despite the additional expense. A laminate Code 0 will have a much broader wind range as well as wind angle.

Sails, like most things boat related, are a fine balance between performance and budget. Spend a little more on fabric and engineering up front and you will be rewarded down the road when the sails hold their shape over a longer period of time. On the other hand, Dacron has been the go-to fabric for decades and has served sailors well.

Brian Hancock is the founder and principal designer at Great Circle Sails in Marblehead. MA. He has completed multiple circumnavigations and has built sails for a wide range of racers and cruisers. Check out his website at greatcirclesails.com.