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Downwind Sailing Perfected with Quantum Sails Ireland

1st June 2021
A fisheye lens view of a new Carbon M6 Mainsail and S2 spinnaker on Emmet Sheridan's Dufour 45 Blaoga on Dublin Bay
A fisheye lens view of a new Carbon M6 Mainsail and S2 spinnaker on Emmet Sheridan's Dufour 45 Blaoga on Dublin Bay

Mark Mansfield of Quantum Sails Ireland on the factors to consider when building a downwind inventory

Quantum's speciality line of high-performing downwind reaching and running sails are versatile, easy to trim, and tailored to the unique characteristics of your boat and your type of sailing. They're designed with the goal of helping you get the most out of your experience and your time on the water.


Sometimes referred to as "code zeros" or "code sails," the category of reaching sails gets confusing quickly as the term can apply to a broad range of sails. To simplify and clear up any confusion, Quantum developed its line of reaching sails around the target apparent wind angles. After all, this is how we actually sail! Our three sail options are defined by possible apparent wind angle and overall optimum range. Each reaching sail line is available with a traditional torsional cable or as an XC cableless sail with a structured luff.


More than four years ago, racing sail designers began experimenting with ways to remove the traditional torsion cable used in the luff to not only enable furling reaching sails but also to reduce headstay sag and achieve superior performance in a wider range of angles. Quantum led the way in structured luff or cableless technology with the successful Maxi 72 class. This technology has been refined and enhanced to make it accessible to racers and cruisers alike. While not practical for all downwind sails, Quantum's XC structured luff technology and designs are great for reaching applications like the AWA 40, 60, and 80, and are available in membrane or tri-radial construction to meet the needs of any sailor.

Click here to learn more about our XC reaching sails.


Quantum's XC reaching sails have more luff projection to weather and more twist (five to 10 degrees) compared to traditional reaching sails and other cable-less designs on the market. The superior performance is a result of a straighter, more stable leech and a flatter exit, both contributing to an increase in drive in all conditions but not overpowering the boat in heavy-air reaching. And because there is less surplus material along the leech, there is less backwinding of the mainsail, which creates less drag when sailing close to the wind.

Running sails


Downwind sails fall into two categories: reaching and running. For broad angles, Quantum's line of spinnakers fits the bill. Quantum's A3 is an all-purpose asymmetrical spinnaker and covers the mid-range, while the A2 is designed specifically for broad-reaching and running performance. 


Understandably, sail size is a critical design feature. The optimum foot length for any downwind sail is a function of aspect ratio or the height (luff) versus width (foot). When too tall and skinny, the sail won't be stable. Too wide and short, and the sail will not twist properly to achieve the right flying shape. No matter what type of downwind sail you are building, you have to start with the correct aspect ratio for the boat's rig proportions. This is what dictates size. The next consideration is the girth of the sail halfway up; this is known as the mid-girth. The smaller the mid-girth, the more genoa-like the sail becomes and more capable at closer apparent wind angles. Bigger mid-girths equal wider apparent wind angles. At the small end of the spectrum, genoa will have a mid-girth of around 50%; at the top end, a running asymmetrical spinnaker will have a mid-girth of over 100%. Quantum's AWA 40, 60, and 80 cover everything in between.
Overall depth is another important variable. A flatter sail means closer apparent wind angles and a fuller sail means broader angles. As a sail gets wider mid-girth, additional depth is necessary to support the area so that the sail will hold its shape and not just flap at the edges.

An A4 Spinnaker on the J/109 Something Else last week when winning DBSC's Class One Training Race An A4 Spinnaker on the J/109 Something Else last week when winning DBSC's Class One Training Race

The final variable to consider is the amount of area outside the straight-line luff and leech. For close apparent wind angles, the luff will be straight and any additional girth will be in the back end. As you design for wider apparent wind angles, this balance gradually changes, with more of the sail's width shifted to the front end. A running sail has a significant amount of area forward of the straight-line luff. When the sheet is eased, this area moves past the centerline and projects to windward. This is what allows the sail to perform in broad apparent wind angles.



Bottom-up furling systems work the same way as conventional headsail roller furling systems. The tack is fixed to the drum at the bottom. As the drum turns, the track winds around the cable or the structured part of the luff instead of an aluminum foil. The sail furls from bottom to top. Bottom-up units are a perfect option for the genoa-like AWA 40 and 60 reaching sails, as the top of the sail is not too wide. The mid-girth should be around 50% and generally no larger than 60-65%.


As downwind sails get bigger and the mid-girth increases, it becomes harder to get the top of the sail to furl if you start from the bottom. With top-down furlers, the head is attached directly to the swivel, and the tack is secured to a free-rotating fitting on the drum. As the furling line is pulled, the tack lags behind and the sail furls from the head to the tack, capturing the hard-to-furl top sections first.


No matter how well the furling system works, there are still limits. Full size broad-reaching and running spinnakers have mid-girths of as much as 100% and are very deep. Even with a top-down further, these can be problematic to furl. As a rough guideline, if the mid- girth is over 88-90% of the foot length, all bets are off—it might furl, it might not. As a result, a spinnaker sock is the better, more reliable option. In fact, it is also a good option for any full size asymmetrical spinnakers, even if you do have the ability to furl it. Also in the plus column for spinnaker socks, they are more cost-effective.



For more traditional asymmetrical spinnaker sails such as the A3 and A2, nylon continues to be the best material, but it is not necessarily the best choice for the new generation of specialized reaching sails. In order to handle higher loads at closer apparent wind angles, a stronger material is needed. The best material choice is based on boat size, righting moment, and target apparent wind angle. In some cases, the best option could be as simple as a heavier nylon or polyester spinnaker cloth, but often a composite material with more strength and durability is the better choice. Quantum's proprietary Fusion M™ tri-radial construction process is used to create the ultimate custom structure for membrane reaching sails. Quantum collaborated with industry leaders to develop a range of composite materials specifically for high load reaching sail applications.


A boat's design has a big impact on which downwind sail option is right for each sailor. For more traditional cruising boats with large foretriangles and overlapping headsails, reaching angles are well served by a large genoa. An A2 or A3 rounds out your sail inventory to cover the broader angles. Conversely, modern boat designs tend toward small foretriangles with non-overlapping jibs. These smaller headsails lack the punch of their larger genoa cousins when it comes to reaching. AWA 40, 60, or 80 reaching sails fill this gap. Some other questions to address when determining your boat's best sail options: Is there a bowsprit? Is the boat a multihull? Where are you sailing? How fit and enthusiastic is your crew? Quantum's experts can help you sort these and other questions to make sure you get the perfect downwind sail option for you and your goals.



Even underway, it's always preferable and recommended to lower and properly pack and store downwind sails whenever they're not in use or won't be used for an extended period of time. Most of the time, a properly furled and protected downwind sail can be safely left hoisted and ready to go, assuming the conditions are relatively benign. However, if it gets windy, it's best to take down furled downwind sails. Unlike a furled working headsail, a furled downwind sail is not supported by a fixed furling system and can easily start to unfurl in strong winds. Aside from not using a UV cover, leaving a furled downwind sail up is the fastest way to shorten your sail's lifespan − or flat-out ruin it. No matter the conditions, at the dock or mooring, Quantum recommends never leaving the boat with a freestanding furled downwind sail aloft!
Check out Quantum's Onboard Sail Care video series for more tips on protecting your sails.

For quotes or queries, contact

Mark Mansfield: [email protected] Tel 087 250 6838
Yannick Lemonnier: [email protected] Tel: 087 628 9854

Published in Quantum Sails

Quantum Ireland is very happy to discuss individual requirements with owners.

We offer a full-service loft at Oranmore in County Galway to look after all our new and existing clients.

Please contact us for advice and quotes

Mark Mansfield: [email protected] Tel  087 2506838

Yannick Lemonnier: [email protected] Tel: 087 628 9854

About Quantum Sails & West Sails Ireland 

The sail loft is owned and managed by Yannick Lemonnier, a former professional sailor. Opened since Jan 2011, West Sails joined forces with Quantum Sails in 2013.

Prior to coming to Ireland, Yannick worked in La Rochelle with a leading French sailmaker and he is trained in the most modern high tech CAD-based systems and software. Yannick understands sail design and has the experience and expertise to advise you on all of your needs.

In 2020, Irish Olympic helmsman, professional sailor and coach Mark Mansfield joined the loft as a sales agent.

Website: Quantum Sails and FaceBook page Team

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