SAILING SMART

How to Upgrade the Sails on Your Multihull

Modern design and fabric can really add to you multihulls sailing performance by Brian Hancock

MULTIHULLS, BY THEIR VERY NATURE ARE A

cruiser’s cruising boat. They are spacious, they don’t tip (much), they have a shallow draft and they are relatively fast. What’s not to like? It’s not surprising then how cutting-edge multihulls have become when it comes to innovation and their embrace of new technology, especially when it comes to sails.

The first experience most multihull sailors have with sails are the standard crosscut Dacron sails that come with most production multihulls. They may be practical, but they are not very exciting and cheap construction and price take precedent over durability and performance. Usually the main is pinhead, meaning that there is an acute angle at the head of the sail and it does not incorporate a large roach or, as is increasingly popular, a square or a round head. Same too with headsails. They are usually unimaginative triangular sails there to suffice the requirements of a new owner being sold a boat.

Multihulls are unique in that they are rigged in a tri-pod configuration, that is there is a headstay and two shrouds. The shrouds are attached as far outboard as possible, and aft of the mast so that there is no need for conventional spreaders. The tri-pod rig configuration supports the mast. This configuration has one big advantage and one, well not so great drawback. With just three pieces of rigging supporting the mast there is no need for a backstay meaning that you can create just about any kind of mainsail that you like. There is no backstay to obstruct things when you need to tack. The drawback, however, is that because the shrouds are so far outboard you can’t have any kind of overlapping headsail. This is not really a bad thing because most multihulls are mainsail driven, meaning that the principal sail is the main and the headsail is there to provide a little extra sail area and to provide a bit of ‘slot effect’ when sailing to windward.

MAINSAILS So, let’s see what we can do with the main. You can add as much roach as you like. This increases sail area while still having a fairly manageable sail. You can, if you like, make the sail square-headed, meaning that the top of the sail, rather than being pinhead, is square, or at a right angle to the mast. This provides an overall better sail profile but it comes with a couple of issues. One of the issues is the compression load on the “gaff” batten, the one that is angled to support the square head. Because of it’s configuration the “gaff” batten has to deal with much more compression than the other battens but this can be managed with a sturdy car on the inboard end, preferably one that runs on some kind of bearing system, either balls or rollers.

The other issue is that with the gaff batten in place you can’t furl the sail flat on top of the boom. This batten, rather than being parallel with the boom, is at an angle. In order for it to lay flat the headboard needs to be released from the headboard car. On a small boat where you can easily reach the headboard this is not really a problem but on a larger boat you may need to rig a bosun chair and get hoisted to detach the headboard. This is obviously a lot more work.

There is a system where the main halyard is deadended at the headboard and runs over a sheave that is part of the headboard car and loops back through the headboard. When the halyard is tightened it pulls the headboard into a slot on the headboard car. When it’s released the headboard falls away from the headboard car and can then lay flat.

Having a mainsail-driven boat is not a bad thing, especially one with a large roach. Your sail designer will design a certain amount of ‘twist’ into the sail. Twist is the amount a sail opens up to the wind angle the higher up the sail you go. Twist is necessary because the wind flow across the sail is effected by friction caused at the lower end by the wind passing over the deck and superstructure. You can also add twist by bringing the mainsail traveler up to windward and easing the main sheet. This puts you in a controlling position when it comes to balancing the overall sail plan as the conditions vary.

I would suggest contacting the designer of your multihull before going too crazy adding sail area either in the form of a larger roach or a square head. Boats are designed to be balanced with the center of effort of the sail plan specifically placed to provide the best performance. If you arbitrarily add sail area you may add unwanted weather helm to your boat.

HEADSAILS Headsails on a multihull are pretty much a second thought. They are restricted in size because of the wide shroud base that restricts overlapping sails. Many are fractionally rigged which also reduces the size of the sail. Having said that, I suggest that you try and make the most of it by adding battens to the sail. These battens can be parallel to the headstay so that when the jib is rolled up the battens will not be an issue. By adding battens you are able to fill the foretriangle and improve the ‘slot effect’ between the headsail and mainsail.

These are two very good and quite simple improvements over the standard production sails that come with a new multihull. You will definitely see an increase in performance.

SAIL CLOTH You can add additional performance by upgrading the fabric and engineering of your sails. Cross cut Dacron has worked for decades but a tri-radial laminate is a much better way to build sails. The laminate, which incorporates mylar there to counter off threadline stretch, can be used to build radial sails. Not only does the laminate have better strength and stretch characteristics than Dacron, you can place a heavier fabric

in the high load areas like the leech and foot and a lighter fabric through the body of the sail where the load is greatly reduced.

Many multihull sailors are opting for membrane sails. This type of engineering, once limited to racing sailors with deep pockets, has become increasingly popular with cruisers mostly because the price has dropped significantly and the engineering results in significantly better sails. With a membrane sail the sail and the fabric are made at the same time. There is usually a substrate upon which fibers are laid. Each individual fiber is placed precisely along the anticipated load path in the sail. The fibers can vary with more exotic yarns being placed in the high load areas and less exotic yarns in the body of the sail and along the luff which do not see the same kind of loads. External taffetas can be added to give the sail some grunt and to protect the delicate loadbearing fibers. This is optional but recommended especially if you plan to sail in the tropics. The taffetas can be treated with UV inhibitors. One of the beauties of multihulls lies in their simplicity and frankly you can go far and wide with a full or partially fully battened main, a solid jib on a furler, and some kind of reaching and/or downwind sail. The reaching sail can be made of either nylon, which has served the purpose for decades, or something a bit more exotic like a laminate or membrane. The more money you invest in fibers and engineering, the more performance you will see from your sails. I like to say that you should measure the length of the life of a sail by how long it holds its shape and not just by how long it holds together. If you go for a good quality laminate or even a membrane, the sail will hold it’s shape longer than a standard cross-cut dacron sail - but of course it will cost more. An investment in fabric and engineering up front will pay dividends down the road.

Brian Hancock is the principal designer at Great Circle Sails. He has many tens of thousands of miles offshore under his keel and makes his home in Marblehead, Mass.