A catamaran sailing on an open body of water on a sunny day

Choosing Downwind and Light Air Headsails

Fountaine-PajotLearning Center

Concerning downwind and light air sail choices, there are many factors at play and special considerations for cruising catamarans:

  1. How will you be using your boat?
  2. How many additional sails will you have in your inventory to cover the downwind gamut of situations from close reaching to broader reaching and variable wind conditions?
  3. Which choice will you make in reference to sail handling equipment, furlers, snuffers, and deck hardware?

While we’re talking primarily about catamarans, the same discussion applies to today’s modern monohull:

Employing a true downwind headsail might make sense for extremely long voyages and trade-wind sailing where you might leave the main down entirely to prevent chaffing. Perhaps also because of its relatively inefficient contribution to downwind performance. A more knowledgeable, experienced skipper might want to explore the advantages of considering his polars and VMG (Velocity Made Good) optimization instead of immediately assuming he needs to undergo the expense in dollars and space of adding another sail– while considering his choices for downwind and light air sailing.

We have a number of ways to create more forward fairleads for the Genoa to help prevent twisting of the upper sections of the sail with the associated degradation of performance that results from this. We can enhance off-wind and light air performance with this approach with very little investment.

Try this approach first before investing in any additional inventory. This approach primarily involves a second set of outboard sheets. I’ll show you how I actually employ a boom vang I make up for this purpose. It works perfectly using the outboard, mid-sheet cleat as the outboard anchoring point so you don’t need to have the expense of another set of winches for this secondary, outboard sheet.

Of course, if you’ve been talked into getting a boat with a small headsail, you don’t have this option. You’ll have to have two headsails just to cover the normal wind and sailing angle ranges–a real expense and inconvenience. What we’re talking about here is a modest overlapping, all-purpose, reefable genoa such as is standard on Fountaine Pajot’s boats.

By nature, catamarans are designed to sail from reach to reach, and not dead downwind. This is true of America’s Cup catamarans, but also of the new generation of America’s Cup monohulls; you don’t need to be on foils to take advantage of the lessons and enhancement to multi-purpose, reaching sails. Catamarans simply have much better VMG results when not sailed dead downwind. This shallower downwind angle also mitigates the downwind chaffing of the main on the shrouds, which can be further helped with padding on the spreaders and sacrificial chaffing patches on the main. Chaffing is due to the nature of the rig with no back-stay and more swept-back shrouds – the main, simply, cannot be let out as far without coming into contact with the aft shrouds and, potentially, breaking the typical full-length battens. But off-wind performance is also affected by the configuration of the hulls and keels; shallow keels with a wider chord are incorporated for maximum cruising versatility. It may be a trade-off, but this is a good one!

At the end of the day, trying to force the catamaran to sail in a zone that doesn’t suit its configuration results in poorer performance. Reach up, jibe, and the downwind VMG will be similar to a monohull with a more conventional mast sailing a deeper downwind angle. Catamarans simply have excellent reaching performance (as shown on the polars) that will reward you for adjusting your sailing strategy to take advantage of what, often, amounts to up to a 20% or better passage making speed, on average, compared to a monohull. At our commissioning meeting while your boat is on order, we include a discussion with a sail-maker for those more interested in enhancing passage speeds and downwind, light-air performance.

Most people don’t realize that by optimizing VMG you may sail slightly more distance, faster, and beat the traditional monohull sailor trying to point as high as possible, or sail more directly downwind. Anyone who has raced sailboats has enormous respect and appreciation for this “VMG” fact of life.

Downwind and light-air sails enhancements:

  1. For passage-making downwind, a symmetrical spinnaker may be considered in some cases with either an appropriate sheeted in main or with a dropped mainsail.
  2. Then there are a host of sails that better match the polars for efficient catamaran reaching and off-wind sailing. Generally, if the mainsail is up you’re most often reaching!
  3. The off-wind sail choice diagram illustrates some of the choices that we typically review with the sail-maker. The choices often come down to expense, storage, expertise, and priorities.  Note that the orange filled portion of the diagram is an asymmetrical spinnaker.

This may be one of the best, most versatile choices. It can come with a top-down furler or a snuffer to make it easy for short-handed sailing. Different sailmakers may have their individual names for this sail. North Sails, for instance, calls the most popular iteration the “G Zero Gennaker”.  This is the most popular, versatile, all-purpose sail for multihulls.

Getting more technical with North’s technical paper. Download the paper here.

Bowsprit, or no bowsprit–that is the question.

If you’re going for maximum performance, the bowsprit extends the reach and increases the size of whatever downwind sail you choose. This is mostly important for very light air–under 8K or so conditions. So if you’re cruising more casually, not needed. If your boat is in a charter fleet, this introduces a possible extra challenge when docking.

I often recommend to my less experienced customers, who plan to charter at least for a while, to forgo the bowsprit initially, knowing that the bowsprit is literally a carbon fiber, bolt-on option which can easily be installed later. After getting a year or two’s experience under your belt, you might want to consider this option, and order your light air, downwind sail then.

But first, make what you already have better with simple adjustments:

Before investing more money, you can greatly enhance the performance of an overlapping genoa.

I make up a traditional rope boom vang with two simple modifications. On the jam cleat (lower) end, I add a 4′, or so, line and make a large loop, big enough to attach to the center deck cleat on the boat. On the other end, a fairly large SS hook.

Before I go off on a reach I engage the hook in the clew of the Genoa, put in enough slack to put the loop on the center cleat, and then lead the free end from the jam cleat back to the cockpit. As your sailing angle increases, off the wind, you let out the inboard sheet normally. But now, instead of having the Genoa twist off more and more becoming less efficient as you let it out… You take in on the new, outboard sheet lead proportionately as you let off the inboard lead sheet. Generally, adjusting the tension between these two sheeting angles will result in obtaining an ideal shape for the genoa with just the right amount of twist. Your performance will noticeably improve.

A couple of notes:

  1. You will need a surprisingly long line for this vang. If you have a 4 part purchase with, say, 3/8″ line, you will probably need at least 50-60′ of line for the vang to accommodate the multiple blocks and lead back to the cockpit.
  2. Having a lower block with built-in jam cleat that has an adjustable exit angle makes this set-up even more versatile.
  3. I carry the pictured vang in my “To-Go” bag so that when I am out on someone else’s boat, or a charter so that I have the ability to enjoy the fun of having a well-trimmed genoa on any boat I’m enjoying. Meanwhile, my cruising friends are sailing with a twisted off, luffing, and much less efficient headsail.

Let’s examine polars and VMG:

The concept is easy. Choose your sails based on your practical sailing style with consideration for optimizing performance. With the choice of the right sail that suits your realistic expectations for 90% of the time:

Imagine you point your boat dead into the wind. What’s your speed? If you said “0” you’re right–not a trick question. As you bear away and adjust your sails to the wind, and as you increase your angle away from the direction of the wind towards your boat, your speed picks up until it peaks out somewhere in the reaching range – look at the polar. Then, as you continue to turn more downwind, the speed goes down again. At least in part, because as you go downwind your boat speed in effect reduces the apparent wind speed that the boat feels, so with less power you go slower. Please note that the polars for all of our Fountaine Pajot’s are in our printed or electronic brochure.

Everything changes proportionately with higher wind speed, so polars need to show performance at different wind speeds as in the example. Now, we can improve the performance throughout the range by employing bigger or more efficient sails for the conditions. While this skews the results some, the basic premise remains – that is unless we’re talking about foiling boats! Your maximum speed is going to be on a reach as you can see by the polar curve in this example.

The reality is we tack upwind. We don’t sail directly into the wind to achieve the maximum speed as you can see by the polars. But, what many don’t realize is that the same thing happens downwind. Dead-downwind is the slowest speed. The optimum is on a reach so we reach and then jibe to the opposite reach to optimize our VMG. The fastest approach to our upwind or downwind destination is not a straight line, but rather takes into account the optimum speed for the particular boat and point of sail as shown by the polars for your boat, wind speed, and sail combinations. (The next step in the learning process is to learn how to combine your knowledge of optimized sail angle VMG with wind changes and overall VMG over the entire course or passage–this is where the rewards really show up in much better passage times).

Generally, for racing boats, you have a complete set of polars for different incremental wind speeds and sail combinations. Seldom is this information available for cruising boats, but if you can get the basic polars, you’re much closer to understanding your boat’s performance capability. You can have fun plotting your own enhancements to your set of polars. Some of the new electronics have the capability of helping by providing the calculated function VMG on the fly!


Choose your light air downwind sail for the way you will be sailing 90% of the time. Unless you have an unlimited budget, this probably means one multi-purpose sail. Getting it right, beats doing it over every time!

For most clients, the asymmetrical spinnaker with appropriate gear and, if budget allows, a top-down furler would seem to be the best choice. Atlantic Cruising Yachts specializes in custom commissioning. This includes calling in the best consultants and working with them to get the right gear installed. We work with virtually all major sailmakers and can recommend one for your sailing style.

For further reference

  1. A great article with an overview on downwind sails from Cruising World.
  2. An article about trimming off-wind and light air sails from North Sails.

Eric  Smith, Senior Sales Consultant, Partner410-703-5655
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