Elegance is a major preoccupation for the top brass at Nautor and when they began to design their new flagship Swan 108, one of the project’s primary objectives was to produce the most beautiful maxi Swan to date

Like every new model we produce, throughout the design and build process we spend a great deal of time looking at data, drawings and renderings and the Swan 108 was no exception. But when she came out of the mould for the first time we knew we had something special,’ says Nautor Group CEO Giovanni Pomati.

It is difficult to think of a time when the Finnish builders haven’t been busy, but in recent years and despite the recent global challenges, the rate of production has ramped up with new models streaming into a comprehensive range that is constantly evolving. Naturally, evolution is no accident for a company that has been producing luxury offshore yachts for 57 years, neither is their reputation for leading by example. But the need to produce elegant yachts has been an underlying constant as well throughout this time.

The sailplan is designed to be flexible with a large fore-triangle that enables owners to choose from a wide range of headsail configurations with up to four stays so the total sail area can be split into easily managed proportions

‘As a company we are obsessed with being as modern as possible,’ continues Pomati. ‘Along with our reputation for producing beautiful yachts, which we clearly want to maintain, it’s a fast-moving world and looking old is not an option. Elegance is in Swan’s DNA and when it came to creating the 108 one of our primary goals was to produce the most beautiful blue water maxi Swan to date.’

An ambitious goal perhaps, but with the success of the Swan 98, 115 and 120 the company had the enviable advantage of considerable experience in this area. The superyacht arena has been particularly successful for Nautor and this provided a key datum for their thinking when they were creating the 108.

‘Each of the boats in the group played an important part in the development of the 108,’ Pomati continues. ‘Aside from being a great looking boat and a good performer, the 98 brought Swan back into the superyacht world with maxis that were not aimed solely at racing but were focused on performance cruising.

A long, fully integrated bowsprit provides plenty of separation between an A-sail or code sail and the furled genoa while keeping the anchor well clear of the plumb bow

‘The four 115s that we built made it clear that it was possible to combine all of our previous experience with custom construction as they represented different approaches. Two of them, Solleone and Shamanna, were cruising yachts and represent milestones for Swan, while the other two, Highland Fling and Odin, were successful racing boats.

‘So, what we learned from the 115s and the 98s was that it was possible to take some of the key production elements and combine them with a custom build. This saved a great deal of time and expense and yet still allowed busy and active owners to take delivery of their perfect boat without the extra costs, complexity and longer time frames that are sometimes involved in a fully custom boat. ‘That was one of our starting points for the 108, another was to create a completely new and up-to-date hull shape.’

With these two key goals in mind and given that appearance was high on the list, it was perhaps inevitable that one of the central players in the international design team would be Germán Frers. Highly regarded as having created some of the most striking boats in the world, his team’s involvement provided a guarantee of good looks. Add to this Lucio Micheletti’s expertise in exterior design and Misa Poggi’s acknowledged talent for interior design and it’s hard to see this as anything other than a dream team.

‘As we worked through the early design concepts it became clear that the 108 provides a great deal of versatility when it comes to the interior configuration. An example of this is the ability to have crew accommodation aft for up to five people, along with a large owner’s cabin forward without compromising the space amidships that’s required for a spacious saloon and well-proportioned guest accommodation.

The new OverShadow is an inboard-powered GT version of the successful Swan Shadow with more accommodation

OverShadow

Entering the ruthlessly competitive power boat market was something that Swan thought long and hard about. It was clear that while they knew they could build a power boat to the same exceptionally high standards as the sailing yachts in their range, there had to be a very good reason for them to do so.

Originally the idea was to create a tender for their superyachts, to provide owners with a 360-degree experience. Swan Shadow was the result and once launched it attracted a great deal of interest. With its ability to explore bays and ports that are not easily accessible to a big yacht, it was clear that Swan Shadow could deliver a broad range of benefits while looking completely at ease with the Swan family style.

Since its launch, its success has led the Nautor Swan team to develop OverShadow, the next generation of inboard engine, gran tourismo configuration with more accommodation below decks and a capacity for longer trips.

Outside, the flush deck offers great liveability with an outside wet bar and galley plus a two-metre-long sunbed with a wide dining area around them.

The full, closed bow creates more space below deck, where OverShadow offers two alternative layouts: a double bed or a twin bed configuration where both options offer a larger and better appointed heads compartment than their predecessor.

Using the same successful and efficient hull shape as Shadow, the Swan OverShadow will be unveiled at Cannes Yachting Festival this summer

‘Interestingly, among the people that are looking currently at the 108, all are focused on blue water cruising around the world, no one is looking at the grand prix racing scene. Having said that, superyacht regattas are frequently part of the planning for those who are mainly focused on cruising. This also says a great deal about why we were keen to create a modern hull shape with good performance while still tapping into the elements that make for a comfortable long-distance cruiser.’

The option for a lifting keel is another example of this dual thinking as a practical solution for owners who seek to combine the benefits of a long-legged global cruiser with a superyacht that can enjoy the best harbours and anchorages in the world.

‘The option for a lifting keel is one that is being asked for more and more,’ Pomati continues. ‘It’s a little bit like carbon masts were a few years ago. Back then carbon masts were an option, today they are standard aboard this size of boat and I see lifting keels going much the same way.

‘The use of stern thrusters is another example. Where once they were considered a plus, now they are a regular part of the specifications for many Swan owners.’

Flush teak decks are an important part of Swan’s brand heritage. Some things never change

The sailplan is another area where the 108 has been designed to be able to cater for a wide range of tastes. From in-boom furling to more racing-oriented squaretopped mainsails, the new Swan Maxi can cater for a range of rig options. The ample foretriangle provides a similar scope for a variety of headsail configurations where up to four stays can break down the total sail area into easily managed proportions that allow simple and effective gear changes.

The 108’s deck layout is deceptively smart. Clean, uncluttered and elegant, this is also a layout that combines practicality with comfort. Twin wheels and pedestals are positioned close to the control lines while the ample guest cockpit amidships is not only in the most secure area of the boat but can be configured in a variety of ways.

The aft deck also has plenty of space for lounging and sunbathing, while the spacious fold-down bathing platform has already been nicknamed the terrace by the sea.

Below deck, the wide variety of colour schemes ranges from timeless classic through traditional navy and wine colours, the mood of which is called Wine Cowes. Each of these helps to show off the subtly different approach that Nautor has adopted, which began with the development of the innovative Swan 120.

‘We spent a great deal of time ensuring that the saloon accommodation gives the feel of a high-end apartment where you feel in touch with the outside world,’ he continues. ‘But while contemporary looks are very much in evidence with the 108, modern thinking for systems behind the scenes has been just as important.

The first Swan 108 has a 100% genoa on a single forestay and four sets of swept-back spreaders on its carbon mast

‘The move towards hybrid systems has seen a focus on achieving a greater capacity for the hotel loads,’ Pomati says. ‘Silent running at night is important to our clients but the demands are extending into daytime activities too where operating the boat, the air conditioning and cooking facilities without running the generator is a familiar objective for many.

‘From here the second goal is to include motoring without noise, while the third phase is to achieve a large proportion of this through hydrogeneration while sailing.’

The bottom line is that while family looks are important in a brand and a range that has been famous for its appearance, it is clear that evolution continues to be a crucially important part of the development of any new Swan. And here the 108 looks set to be one of Nautor’s finest.

Click here for more information on Nautor Swan »

After building successful one-off prototypes for the AC40 and HSV chase boat, McConaghy has now put both of them into production

After the Kiwis’ impressive America’s Cup win in Bermuda back in 2017 few could have predicted how big the changes were going to be in both the Cup world and the broader reaches of the sport. McConaghy Boats have been in grand prix racing a long time; they’ve been at the leading edge of raceboat construction and have claimed many manufacturing milestones from the first prepreg laminate in a boat to the first prepreg Nomex cored maxi. But not even they had any inkling of what was going to be on their shop floor six years later. No one did.

The hydrogen-powered chase boat (HSV) that McConaghy has now begun to manufacture for the AC teams and other customers is in many ways more technically advanced than the AC40s

Yet, to be building 12 (and very possibly more) of the most advanced and certainly the quickest foiling monohull one designs in the world is an example of just how far the racing world has come with the AC40s.

Since taking delivery, Cup teams have been hitting speeds well in excess of 50kts during training. Few predicted that either, and few dare to guess what they might achieve when the pressure of racing for real comes to bear. But if that isn’t enough to illustrate just how advanced this new breed of boats is, try taking a look below decks.

The AC40 may have a rig and a soft sail and look much like a raceboat from the outside, but inside you might as well be looking at the inner workings of an Airbus passenger jet with its mass of hydraulic pipework, manifolds and electronics. An AC40 is a machine in every respect.

‘A lot of what we do is not very conventional, we've always been in the esoteric racing world, so building the AC40s was not a leap,’ says McConaghy CEO Mark Evans. ‘But if you compare what we’re doing with conventional yacht building, what we are producing with the Cup boats is like a Formula 1 Ferrari or fighter jet, where every single ply, every single core is designed to a certain length in a certain direction so they can operate in tightly defined load paths. So it's a very, A very technical boat and the build tolerances are to points of a millimetre.

‘There is no getting away from the fact that they are very complex systems and it's because of the close partnership between us and Emirates Team New Zealand that we're able to achieve this. They've supported us very well and given us good drawings and good procedures of how to put these yachts together. ‘Every single carbon fibre bracket, every hose length, every piece of wire has been measured in a 3D model by the Team New Zealand designers and comes to us in a kit. Basically, we set the mockup of all the hydraulics on the factory floor and because we have all the bracketry put on the boat before the equipment arrives. We just pick up the hydraulics system and install it in the boat – everything fits the way it should.

The ETNZ-designed and McConaghy-built AC chase boats are capable of carrying six people including the driver plus 250kg of additional payload, as required by the Cup protocol

‘The result is that when they are completed in the yard – and we finish an AC40 every five weeks – these yachts are fully fired up and fully commissioned, sitting in our factory ready to ship out to the teams.’

Even more surprising, however, is that opposite the AC40 production line in McConaghy’s facility in Zhuhai, China lies an even more advanced foiling machine that is also a spin-off from the Kiwis’ foiling Cup vision: the hydrogen-powered chase boat.

Those who have closely followed the development of the Cup over the last year will know that Emirates Team New Zealand launched the prototype and were delighted at how well it worked straight out of the box. This was just as well because under the terms of the Protocol for the 37th America’s Cup, every Cup team has to have at least one, “hydrogen powered vessel (“HSV”) at the Match Venue to support its on-water race operations”.

Unless the teams want to go down their own route of development, the New Zealanders’ prototype is the answer and it's easy to see why they might opt for this McConaghy-built machine as the design brief is pretty demanding.

Under the terms of the Protocol the boat needs to be at least 10m long, have a top speed of least 50kts and be capable of cruising under hydrogen fuel cell power alone. The HSV has to be fully on its foils at 24kts and have a range of 75 miles at an average speed of 25kts, which well exceeds two back-to-back AC75 races.

On top of that, the chase boat needs to be capable of carrying six people including the driver plus 250kg of additional payload. And that’s just the headline specification. The reality of creating a hydrofoiling chase boat takes designers into challenging territory when it comes to getting cooling water back into the system. Naturally this is not a new problem, many hydrofoiling powerboats have had to deal with this over the years. But the difference with the HSV is that the foils and structures have to be slender to achieve the required levels of performance and efficiency.

Following up on its HSV chase boats, McConaghy is now working on a 13m version with a cabriolet roof and bimini

‘The gearboxes, the propeller and the shaft are all custom built in-house here in Zhuhai,’ Evans continues. ‘We're using bevel gears from different gearboxes and modifying those as well. The engineering is pretty complex as we have hydraulics running down the carbon fibre front foil struts and then water going up the struts to service multiple functions. One is to lubricate the propeller shaft that's running down the vertical and keeping the bearings lubricated, another is for the heat exchangers in the boat for the motor, the batteries and other items like the air conditioning. There's a lot happening.

‘There are two water pick-ups because you have port and starboard propulsion systems on board which are running from two fuel cells that are 80-kilowatt each.’

‘We have orders from two of the teams and also we're building some of the event boats,’ he continues. ‘So we have of a total of six hydrogen chase boats that we're manufacturing at present.’

But even at this extreme end of the scale there’s more that McConaghy is working on.

‘We're doing a 13m version of the HSV and that's going to be a VIP style of boat with a really nice interior. It’s called Chase Zero and we've made a couple of alterations to improve the styling as well, such as having a cabriolet roof, a wraparound screen and a bimini. We’ve also extended the forward screen so that it is lower at the front and we have incorporated carbon compression tubes for the structure to help free up the visibility forwards.

A total of six hydrogen-powered foiling chase boats were on the production line in McConaghy’s Zhuhai facility as this issue of Seahorse went to press

‘The control system uses carbon fibre steering wheel control at the main console, alongside the navigational equipment, VHF, AIS, and system monitoring displays. We are also looking at producing a 12-seater version of the Chase Zero that could be either a private boat or a commercial version aimed at high-speed ferries.

‘The commercial aspect of this is really interesting. Everybody is looking at green alternatives, whether it's full electric, hydrogen or another means of propulsion. In my opinion, hydrogen is one of the best ways to go.’

All of which makes for a fascinating discussion around the detailed renderings that have been produced for the Chase Zero. But what makes this project and McConaghy’s plans all the more striking is that all of it is far from the kite flying exercise that it could so easily be. Instead, as the AC40 production line rolls into double figures, so the build of the HSVs and Chase Zero are already under way.

In just five years since the Kiwis won the Cup and changed the rules, no one was expecting this.

Click here for more information on McConaghy Boats »

The German shipyard YYachts launches a rather different new project together with Cossutti Yacht Design – the 23-metre long daysailer Y75... Inspired by

YYachts presents a solution to challenges faced by the sailing yacht industry – the Y Breeze 75 daysailer. This innovative vessel combines the elegance of a sailing yacht with the convenience of a powerboat. Its key features include sporty performance, a luxurious interior, advanced technology and sharing possibilities. A wide range of customisable options ensure a unique sailing experience.

Inspired by motor yacht designs, the hinged aft quarters of the Y Breeze 75 can fold down flush with the main deck sole

YYachts carefully selected the name Breeze for this exceptional boat to emphasise that it goes beyond being just a new model. Instead, it represents a new concept that revolutionises how people experience and connect with the sea.

The naval architecture and the exterior design are made in collaboration with Cossutti Yacht Design. The YB75 is claimed to be the first sailing yacht with fold-down bulwarks to create a large aft deck to increase comfort at anchor. The exterior impresses with clean lines and gives the YB75 a sporty character. Michael Schmidt, founder of YYachts, says: ‘YB75 is a yacht that is simply meant to be fun under sail and at anchor - we designed her so that our customers can simply concentrate on their leisure time.’

The YB75 has a three-cabin, three-heads interior styled by Wendover Studio

Developed in collaboration with Wendover Studio, the interior style is designed to guarantee an inviting, practical and elegant atmosphere. Materials are appropriately used, carefully detailed and coordinated to represent today’s luxury style. People expect to feel at home of course, so the style can be customised following clients’ preferences. Co-founder of the studio is Gabriel Chipperfield, no less than the son of star architect David Chipperfield who was responsible for the interior of the very first YYacht.

Racing with small crew
The stern platform of the YB75 folds out, making access to the water much easier than on many yachts. To enjoy the cockpit, the YB75 offers a galley coming up from the deck. It’s equipped with a sink, two fridges (one for drinks/one for food) and a barbecue grill. The entire deck is designed as a safe walkaround, with no steps in between. In order to be able to head for shallower anchorages, the telescopic keel can reduce the draught to 2.5m. Fenders are deployed via a special system and stowed on board to save space.

A large stern platform for boarding and bathing, high cockpit coamings and twin helms set amidships to leave the aft deck clear

On the lower deck there will be a flexible layout with a saloon and different configurations for the guest cabin (daybed, two single beds or one double). A playroom for kids can also be installed. To enjoy the Mediterranean summer, the YB75 offers different options of sunbeds: stand-alone sunbeds or a box with built-in gimbaled sunbeds.

A good handicap makes the YB75 interesting for racing with a small crew (max six) and water ballast ensures high stability (big sailplan for performance). The naval architect considered the major wind configuration in the most popular Mediterranean areas – the rating, in comparison with other boats looks very favourable. The YB75 is also extremely easy to sail. There are pushbuttons for the mainsail and self-tacking jib and furlers for code zero and gennaker.

Cossutti explains…

The design of the YBreeze 75 is truly unique. In her simplicity we've managed to incorporate a complete walk-around deck, a “hidden” coachroof, a social area with sofa and dining table and a huge lounge area with a beach club at the stern.

The style of the boat is defined by the port and starboard sheer lines that run all along the hull and meet at the stem, which is neither vertical nor reverse, it is just the arched Y-Yachts style.

A hidden bar and galley unit pops up from the cockpit sole at the touch of a button

The nature of the bulwark makes it possible to integrate two folding terraces which, together with the bathing platform, create a unique access to the sea, all surrounded by couches and sunbeds to enjoy the sea. Thanks to the generous toy garage it is possible to enjoy the sea from every perspective with space for a jet-ski, SeaBobs, paddleboards and lots of other equipment to support every passion.

The spatial equations between the exterior and interior spaces have been redefined to enhance life on deck, making her the best place to enjoy Mediterranean living. The central cockpit galley creates the right atmosphere to bring people together and have fun at sunset.

On the other hand the interiors, designed by Wendover's partners, can fit every need. The boat has a three-cabin and three-heads layout with a galley and saloon, plus the option of a multi-purpose children's playroom and crew cabin.

We have studied the weather conditions of the main sailing events in the Mediterranean over the past year and have tailored the hull lines for medium to low wind speeds, resulting in a hull shape with a low wetted area and narrow width, which contributes to the overall slenderness of the design.

The boat has been designed to be easy to sail, even with a reduced crew. She offers a basic sail package consisting of square-top main, large self-tacking jib and code zero, to which a gennaker can be also added if needed for race purposes. All sail control lines are led to the pit winches, which are easy to operate without disturbing the guests on board. The lifting keel, together with the double rudder, is the perfect equipment to reach almost any place without losing the pleasure of a real sailing session, but it is also possible to choose a fixed, high-performance 4.2m keel. All in all, we think that the YB75 fits perfectly into the YYachts motto: look good, sail easy!

Ocean friendly construction
The shipyard’s carbon footprint is constantly being reduced. YYachts reviews all processes in order to produce boats as climate-neutrally as possible. For the YB75, they only use wood and panels that interior outfitters of larger mega yachts provide as surplus. For the construction of the yacht, the shipyard will use sustainable epoxy and numerous eco-friendly products and materials. The hull will be laminated in a female mould to achieve the shape defined by the naval architect and reduce to a minimum the fairing and the related additional weight. To achieve a maximum strength/light displacement ratio, the hull is made in a sandwich construction with Corecell M foam. The hull outer and inner skin and the inner structure will be built exclusively in carbon for maximum stiffness and weight saving. The fibres will be impregnated with a high-performance epoxy laminating system and post-cured at a high temperature to exploit the fibre properties to the maximum. All bulkheads and internal structures are made in carbon/ epoxy sandwich, vacuum consolidated. The epoxy is sustainable and fire resistant. For more strength and better load distribution there are additional carbon fibre reinforcements around doors, cutouts and cable penetrations.

Cossutti’s first design for YYachts has a fine entry with an arched bow profile, jib and code furlers on the stemhead, broad aft quarters and bulwarks all round at the same height as the coachroof

Always available
All YBreeze 75s will be delivered in sailing spots in Spain, France and Italy with a dedicated captain. Owners can also share the boat in this area and, using an app, they can book it. This feature, included in the price, will allow owners to always find the boat ready before their arrival. The sharing service can also be arranged on demand via the YYachts organisation.

Michael Schmidt says: ‘My credo has always been to reduce yachts to what is necessary without neglecting comfort. With the Y75, we have now developed a concept that even aligns the use of the yacht with this principle. This will also appeal to younger customers who are growing up with the sharing economy.‘

Technical Data

(approximate measurements)

Length overall	22,86 m
Beam	5,6m
Draught (standard, fixed keel)	4,2m
Draught (optional, fixed keel)	3,5 m
Draught (optional, telescopic keel)	4m to 2.5m
Displacement	26.5 tonnes
Water ballast (optional)	1 tonne on each side
Propulsion	1x NANNI 120hp (80kW)
Hotel batteries	24 V DC, 800Ah
Mainsail	190 sqm
Jib	125 sqm
Gennaker	460 sqm
Code zero	240 sqm
Naval architect	Cossutti Yacht Design and YYachts
Exterior design	Cossutti Yacht Design, YYachts Design Studio
Interior design	Studio Wendover – Gabriel Chipperfield, YYachts Design Studio
Shipyard	YYachts/MS Yachtbau

Click here for more information on YYachts »

A-sail design principles are often misunderstood. Top sailmakers explain…

To explain the thinking that goes into designing asymmetrical spinnakers, we interviewed three sail designers from UK Sailmakers: lead designer Pat Considine, UK Sailmakers Chicago; Geoff Bishop, UK Sailmakers Fremantle, and Stuart Dahlgren, UK Sailmakers Northwest - Sidney, BC. Their thoughts on spinnaker design fell into two buckets.
1. The boat itself
Type of boat - high-performance, displacement, one-design.
Exact measurements - pin-to-pin halyard length, sheeting position, etc.
2. The type of sailing to be done
IRC, ORC, offshore, coastal, onedesign, professional vs. Corinthian.

Key data points
When designing an asymmetrical spinnaker, a designer will focus on three primary data points:
1. The point-to-point distance between where the spinnaker will be tacked (on a sprit or a lowered pole) and the max height for the halyard.
2. The mid-girth (SMG) luff to leech measurement, expressed as a percentage of the foot length.
3. The trim position for the clew in terms of height off the deck and where the sheet will lead.

Pat Considine explains: ‘A symmetrical spinnaker is probably the easiest sail to design. It has no twist and both sides are the same. An asymmetrical spinnaker on the other hand is challenging to design because the luff is free flying, there’s twist in the leech and there are many other things to consider.’

Our sailmaker panel agreed that once the boat characteristics and racing plans are known, additional pre-design considerations include:

• The performance characteristics of the boat such as polars, reaching/running angles and so on
• The other spinnakers in the inventory: can this new sail have a narrow range or should it be all-purpose?
• Rating system to be sailed, optimisation for IRC, ORC, etc
• Budget: Yes, there is less expensive nylon and more expensive nylon. With spinnakers you get what you pay for
• The skill of the owner: experienced sailors (helm and trimmers) will not need as forgiving a spinnaker as less experienced sailors.

Geoff Bishop adds: ‘Once you get a good sail design and you know the boat’s measurements, you pretty much stick with it. That said, the critical thing for me is getting the luff length and the mid-girth ratio right.

‘Start with the straight-line measurement from the tack to the max hoist position (straight line), the tack point to the sheeting position, plus the sheeting position to the max hoist position. It’s critical to get those measurements right because every percent of difference in mid-girth in relation to the foot and luff length changes performance and ratings.’

A running sail could have a 105% mid-girth (SMG) of the foot length (SF) and a luff length longer than the straight-line measurement. Conversely, a reaching sail will have a smaller SMG in relation to the foot length as well as a shorter luff.

Above: the seven key sail measurement points for an asymmetric spinnaker. It’s crucial to understand how these parameters affect a sail’s performance when asking a sailmaker to design a new A-sail.

Luff length
The luff length helps to determine the projection of the sail. For windward/leeward racing, mostly in displacement boats, the goal is to soak for VMG. For that you want a luff that is longer than the pin-to-pin measurement; this creates positive luff curve allowing the sail to project to windward further so you can sail deeper on those shorter round-thebuoys races. If a spinnaker luff keeps collapsing when properly trimmed, the entry is probably too flat. One of your tools is the tackline: if it has been eased to allow more projection, pull it back down to help round the entry, making it easier to trim.

To design a good A-sail, the entry must be deep enough to support the luff round and allow the luff to curl without collapsing. Consider a heavy J1 jib. To sail that J1 upwind in a groove, you need curvature in the luff so the telltales work. Reachers (A1, A3, A5) will be designed flatter and straighter in the aft section to avoid the sail getting overpowered too quickly. Runners (A2, A4) tend to have deeper, rounder aft sections.

For running asyms, the luff length can range from 105-112% of the pin-to-pin measurement. 112% would be for a boat like a J/120 where projection is important. The longer luff helps to increase projection when sailing at the deeper angles.

Tweakers are another tool that can be used to improve your sail’s performance. As the sheet is eased the active tweaker should be tensioned, effectively moving the sheet lead forward, this controls twist and allows the designed depth to be maintained, so that the head doesn’t flip open as the sail is eased.

All these contributing factors that make displacement boats’ VMG quick downwind are your enemies when sailing a performance boat offshore in waves. Unlike displacement boats, performance boats generate tremendous amounts of apparent wind. With the apparent wind angle rarely aft of 110 degrees, the helmsperson will drive down to surf waves then turn up to regain speed and height. Displacement boats also may surf down a wave moving the apparent wind forward but when they put the bow up to dig out of the trough, they won’t respond as quickly. Also, the apparent wind shifts relatively more than on a performance boat.

Offshore and coastal running sails generally have the same depth, but what differs would be the luff length defining the luff round, and the overall projection of the luff. This is achieved by designing the sail’s optimal flying shape and then engineering the panel layout to handle the loads and maintain stability.

Sailing in waves you “drive” the boat more aggressively moving the apparent wind more dynamically. If conditions allow the boat to be stable, it’s great to have a super long luff; but when the boat starts to move around under the sail, oscillation increases as do the chances of collapse or wrapping the sail around the forestay. There is also the physical limitation on how long the crew can keep up aggressively trimming the sheet in a distance race.

Because of the relatively smaller shifts in apparent wind angle in performance boats, their offshore spinnakers are cut flatter with a tighter luff. This design will be more resistant to collapsing from a serpentine steering pattern through waves. By adjusting the tackline you have more range with this sail.

Mid-girth measurement (SMG)
A big difference between one-design or coastal and offshore spinnakers is the mid-girth measurement (SMG). Offshore, where you typically sail at higher wind angles, your asym’s SMG is likely to be narrower depending on whether it is an A1, A3 or A5. Coastal or one-design spinnakers, used more for VMG running (A2 and A4) will have a wider SMG, as you’re looking to soak deeper. This wider SMG design will allow the sail to rotate out in front and to windward further in the VMG soak mode.

Below: an asymmetric spinnaker rotates as the sheet is eased. A wider SMG (mid-girth measurement) allows it to rotate further in front and to windward, which is ideal for inshore racing in a displacement boat. Sails for offshore use and for fast planing boats tend to have a narrower SMG which is more efficient at tighter wind angles

Sheeting position/leech length
The leech in an offshore asymmetric isn’t much different than a coastal or one-design sail, yet it’s still critical to get the clew height and sheeting angle right. The amount of fullness in the back end comes down to the type of spinnaker it is. Reachers are flatter in their aft sections so that you don’t get overpowered as quickly. Runners’ leech sections tend to be rounder, generating more power.

Pat Considine continues: ‘With our computer design software it’s very easy for us to change the depth of the sail but it’s important that you understand the corner-to-corner loads. Someone may be looking to save time and money by designing an asym with fewer panels but that’s no good because of the bias loads going across the panels. Designing a sail to have more panels that are narrower will result in a structurally stronger sail. We orient panels so the warp and fill yarns reflect the load paths of the sail. We also specify heavier fabric with narrower panels in luff, where most of the load is.’

Tweaking the leech shape
As the true wind angles being sailed change, you will want to control the leech shape and sheeting angle of the sail. Attaching a tweaker to the sheet allows you to raise or lower the sheeting angle and optimize the twist and exit angle of the sail.

Geoff Bishop notes: ‘With our running sails, if you’re in eight knots with a 150-degree target angle, we’d put on a little tweaker. But if we had to head up to 140 degrees to gain speed, we’d release the tweaker. We constantly play the tweaker up and down to optimise leech shape and control twist.’

Overtightening the tweaker will close the leech and prevent it from exhausting properly. To sail deeper angles, ease the sheet so the sail rotates forward and tension the tweaker to control twist.

Summary
Taking the time to understand the boat and the manner of sailing it will do is critical to designing and building an asymmetrical spinnaker that will help you win races. After that, it’s up to you to properly adjust and set the spinnaker so it will match the design’s optimal flying shape.

If you are looking for a new asymmetrical spinnaker for your boat, don’t just take what you’re given. Ask questions about the key measurement points of the sail, understand the performance differences of various options and then practice to sail it effectively. If you do this, you’ll be able to sail with confidence.

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