NEW! Scandinavian Cruiser 20 - Classic One-Design Day Boat

Recapture the essence of sailing!

 

 

Sailing means different things to different people.

 

Some people prefer to go cruising, alone, or with family and friends, and explore, relax and disconnect and enjoy the freedom of the sea.

 

To other people it is the challenge and excitement of racing that attracts them to sailing.

 

However, many people also get disillusioned with sailing. Some of the common reasons for this are the high cost, complexity and time involved, or uncomfortable, slow, and unattractive boats.

 

The idea behind Scandinavian Cruiser is to recapture the essence of sailing, by going back in time to a period a century ago when boats were considered truly beautiful, and sailing was a genteel, aspirational and romantic lifestyle.

 

 

 

Design concept

 

 

Scandinavian Cruiser combines the style and beauty of classic yachts with today’s modern lifestyle and the latest technologies.

 

Scandinavian Cruiser is designed for owners who want to recapture the essence of sailing, and for who style and great design is very important.

 

Stunningly beautiful design

 

Most people admire the sleek looks of the classic Skerry Cruisers (Square Meter Yachts). The design of Scandinavian Cruiser is admired equally by experienced sailors and landlubbers, giving the owner true pride of ownership.

 

High speed at all points of sail and wind conditions

 

Scandinavian Cruiser is faster than most other boats that appear to be much bigger. The light, long and sleek hull accelerates fast in even the lightest puff of wind, and the narrow bow cuts gracefully through the waves.

 

Superior maneuverability

 

Scandinavian Cruiser is an extremely pleasurable boat to sail because it heels over and accelerates gracefully and gradually, and the helmsman always has full control of the steering at any angle of heel.

 

Designed for today’s busy lifestyle

 

Considering the high demands on our free time, and the difficulty in finding sailing crew, Scandinavian Cruiser is designed for safe and easy single or short-handed sailing by one person, couples, small families and friends, for fair-weather day-sailing, shallow water anchoring, convenient trailering, and fast Corinthian club and one-design racing.

 

 

 

Features

 

 

•Ultra-light and strong E-glass, VE resin and Navicell Q60 core composite materials

•Rotating semi-unstayed tapered carbon wingmast

•Furling self-tacking jib and furling asymmetrical spinnaker

•Lifting carbon fiber keel strut with lead bulb and lifting carbon fiber rudder

•Stern sun deck

•Small cabin with entrance hatch

•Hiking straps and single trapeze belt

•20’ shipping container compatible

•Road trailer (optional)

 

 

 

Design brief

 

 

Scandinavian Cruiser is designed without regard for any handicap, class or measurement rules. The only design compromise is to design the fastest possible small day boat with the most stunningly beautiful classic yacht lines.

 

The two-sectioned mast and hull fit within a 20’ shipping container (up to 3 SC20’s in one 20’ container), and the boat is road-trailer legal.

 

Fast and easily driven hull, with wave-piercing bow, long and narrow water-line, low freeboards, and long bow and stern overhangs. The hull lines above the waterline are inspired by the classic Skerry Cruiser (Square Meter Yacht) lines.

 

Scandinavian Cruiser is designed with lifting keel and lifting rudder that can both be operated while sailing, thereby allowing access to shallow-water harbors, anchoring without swinging, and easy hauling, trailering, storage and container shipping.

 

The efficient keel & rudder are designed to achieve maximum speed and lift while maintaining the characteristics of the original Skerry Cruisers, such as a rudder that rarely stalls, a boat that does not easily drift sideways at low speed, a boat that is equally fast upwind and off the wind, and a stable boat that accelerates and heels over gradually without easily luffing up or spinning out.

 

The rotating carbon fiber wingmast is semi-unstayed, to achieve an uncluttered and modern look, as well as better safety and aerodynamic performance. The sails include a furling asymmetrical spinnaker, furling self-tacking jib with vertical battens, and full battened main.

 

The deck and cockpit layout is designed in classical lines with modern day boat functionality, including enough space for a small family. The halyard and trim line layout is designed for the boat to be sailed by one person, or raced by two people. The large cockpit has standing and seating space for up to 3 people, and the sun deck has sitting space for one person.

 

The hull and deck are constructed in VE resin, fiberglass and Navicel Q60 core composite, to achieve minimum weight and optimum performance.

 

The accommodations are carefully designed for convenient day-sailing, anchoring and socializing. The cabin offers storage space for cooler chests, sails, etc.

 

 

 

Free-standing and rotating wingmast

 

By Eric W. Sponberg, Naval Architect, PE (CT), CEng. (UK)

 

Beauty • Safety • Simplicity • Efficiency

 

Free-standing rigs are inherently more beautiful, safer, simpler, and more aerodynamically efficient than conventional rigs.

 

They are beautiful because of their sleek modern design and the absence of a myriad of standing rigging.

 

They are safer because stayed rigs are held up by multiple wires and spreaders, any one of which could fail or slip out and cause the rig to fall down. A free-standing mast is held up by just two parts—the deck and the heel fittings—so safety of the rig increases.

 

Free-standing rigs are more aerodynamically efficient because without wires, the sail-plan is no longer defined and confined by the triangular shape bounded by the backstay. The triangle is absolutely the worst possible plan-form shape that anyone could ever conceive of to be a lifting surface because of induced drag.

 

Induced drag is automatically created with lift. You can control it—make it bigger or smaller—but you can never get rid of it. Induced drag is a fact of life.

 

In any given aerofoil plan-form, the airflow on both sides of the surface are at different static pressures—high pressure to windward, low pressure to leeward—and they would really like to equalize. In a triangular plan-form, the airflow on the high pressure side gets a chance to equalize sooner, by virtue of the shape, than on a rectangular plan-form for example, by skewing up toward the tip and off the surface. This skewing of flow from the high pressure side, mixing with the flow on the low pressure side, creates a vortex off the tip. The bigger the skew, the bigger the vortex, and the greater the induced drag.

 

To reduce the vortex we can use a totally different shape for the plan-form, either elliptical or rectangular. The flow across an elliptical plan-form, as it turns out, has little tendency to twist off into a large vortex. In fact, the vortex is very small. A rectangular plan-form also has a pretty small tip vortex, and it can be made smaller, close to or better than that of an ellipse, if the tip of the sail is twisted to leeward. This is exactly how gaff rigs are shaped and why they are actually pretty efficient. It is also why we add roach to the leeches of mainsails—we are trying to approximate an elliptical or even a more rectangular, twisted, plan-form. You may have seen square-topped mainsails on modern multi-hulls and windsurfers. This is the reason—to reduce the tip vortex, and therefore the induced drag, to as small as possible. Less drag for the same amount of lift, or even greater lift, means more aerodynamic efficiency. More power is being devoted to making the craft move forward, not sideways.

 

The only reason we have triangular sail-plans is because we have wires that hold up the masts, and this necessarily makes sails triangular. And if you have wires in the way, you don’t want your sails to chafe on the wires, so we have triangular sails.

 

And the only reason we have wires in the rigs is because we are afflicted in modern sailboat design with arbitrary sailboat design rating rules that, for no good aerodynamic reasons, require the wires in the rigs. While many evolutionary changes have occurred in rig design over the years--most notably in new materials, first with metals, then with composites--standing rigging still remains steadfastly impacted inside the rating rules. And there is no relief in sight. Wires in the rig, and, therefore, triangularly shaped sails, are so inbred into our industry and our thinking that we blindly accept them without question.

 

It takes a bit of courage, I guess, to ask the question: “Why do we do this?” Well, sailors and designers are conservative people. There is no other explanation. The idea of a mast without wires is so foreign to most people that they just cannot fathom how a sailboat mast can stand up all by itself without something to hold it up.

Today, a Boeing 747 airliner at take-off weighs 875,000 pounds, carries 524 passengers, flies at 567 miles per hour more than 7 miles above the earth, and it does not have any wires holding the wings on!

 

Free-standing mast design and construction:

 

In engineering jargon, free-standing masts are called cantilevers. Stayed masts, on the other hand, are columns. Cantilevers bend, columns compress. The two behaviors are different, and so the structures are designed and built accordingly.

 

In a stayed rig, the boat heels due to wind pressure on the sails. Without wires holding up a normally skinny mast, the rig would fall over. But the wires hold the mast in place, pulling on the mast in tension and with their lower ends anchored into the deck and hull. This tension in the wires induces an equal and opposite compression load in the mast itself. The mast has to be big enough in cross-section with a thick enough wall so that it can handle the stress and not buckle.

 

In a free-standing rig, the wind pressure on the sails causes the mast to bend sideways and back. No wires support the mast, so the mast itself has to have a big enough cross-section and a thick enough wall to handle the load. This necessarily makes the mast bigger than its equivalent stayed counterpart.

 

And this is where carbon fiber plays such an important role. Carbon fiber laminates are about 60% of the weight of aluminum, the most common mast material, yet carbon is more than twice as strong. This makes carbon fiber a much more efficient material than aluminum when it comes to making sailboat masts (and other weight/strength sensitive structures, like airplanes).

 

The carbon fiber laminate is thicker at the base, where the load is greater, and tapers in thickness towards the top where the load goes to zero.

 

Wingmasts:

 

A wingmast is a mast shaped like a wing that is allowed to rotate. Wing shape and rotation further increase the efficiency of a free-standing rig. Unfortunately, mast rotation also falls victim to traditional rating rules—it is not allowed. This prohibition can be traced back to L. Francis Herreshoff, who had a patent on a rotating mast design, one of which he installed on an R class boat (Lwl = 20’) called Live Yankee in 1925. But when the regatta committee of the New York Yacht Club heard about this rig, it promptly passed a rule prohibiting “revolving masts, double luffed sails and similar contrivances.” This prohibition remains in current rating rules, and no changes to eliminate it are in sight. It really smacks of spite against a progressive designer and the yacht club’s desire to protect the status quo of the fleet at the time. But that was almost 80 years ago! It is truly amazing to me that such a prohibition has remained in place for so long.

 

However, in spite of the rules, rotating a stayed mast is difficult to say the least because the rigging wires simply get in the way. And actually, when sailing on the wind, stayed rigs are really very good. The airflow over a non-rotating mast attaches really well over the mast and mainsail. The power generated by a stayed rig on the wind and a free-standing wing-mast rig on the wind are pretty comparable. Two boats of the same type but with different rigs—stayed and un-stayed—do not have much advantage over each other—they sail about the same. The differences are really apparent when sailing off the wind. See the sketch below.

 

 

a. Stayed mast on the wind; b. Stayed mast off the wind;

c. Mast off the wind and rotated.

 

When sailing on the wind (a), the airflow on the back side of the mast is well-attached. Off the wind (b), the mainsail on a stayed rig sets off the side of the mast because the mast can’t rotate. The leading edge shape--the most important part of the rig for generating power--is awful. The airflow quickly separates off the mast. To recover some lift, the sail-maker has to build enough camber into the sail to fool the airflow into reattaching. Then, when you go even further downwind, you lose lift altogether and drag is the only component left to make you go. Most people will say that the more downwind you go, the more pure drag you want anyway, to push you downwind. They obviously have not felt the adrenaline rush of acceleration and speed caused by pure lift from a properly designed and rotated wingmast rig. Get rid of the wires, and full mast rotation is possible. Rotate the mast (c), and all the aerodynamics change. Even downwind--especially downwind--pure lift is much more powerful than pure drag. The boat is considerably faster because so much more power is harnessed from the wind. This has been proven a number of times in actual sailing trials between stayed rig boats and boats with free-standing, rotating masts. The free-standing rig boats just run away from their stayed counterparts when sailing off the wind.

 

Another benefit of eliminating the wires is that a boat is much more directionally stable and more resistant to gybing. A boat with a stayed rig can sail perhaps ten degrees by the lee before the mainsail gybes. If not properly controlled, the boom will swing violently to the other side and crash against the lower shroud, perhaps breaking the shroud or itself. The boat may also broach if the seas are running fairly high. If something breaks or the boat broaches, the boat is instantaneously in danger of losing its rig and getting rolled over.

 

On a boat with a free-standing rig, the boom can set way forward of abeam wing-and-wing. You can sail ninety degrees or more by the lee without gybing. If the boat starts to round up because of a hit by a wave or gust, the sails will naturally pull the bow back downwind. And even if the boat does gybe, what happens if the boom gets away from the crew? Nothing, because there is nothing to hit—if it is not there, it cannot break! The sails will stop in a luff position all by themselves. It is very unlikely that the boat will broach. When the other boats crash, this one just keeps on going.

 

For more detailed information on the topic of free-standing masts and wingmasts, please visit: www.sponbergyachtdesign.com/StateoftheArt.htm

 

 

 

 

History of the Skerry Cruisers (Square Meter Yachts)

 

 

The Swedish name Skärgårdskryssare means Shoal Cruiser, or phonetically translated Skerry Cruiser, referring to the protruding rocks off the coast of the Baltic Sea.

 

The rule of the Square Meter Yachts was applied by the Swedish Sailing Association in 1908 and revised in 1925. The rule applies to the sail area in square meters.

 

The original Skerry Cruiser designs were the most beautiful and fastest yachts in the world when they first came out in Sweden exactly 100 years ago.

 

The rule produced a classic elegant racing yacht with timeless beautiful and fast lines. With its slim and long hull the speed of these boats is remarkable. In light wind the friction in the water is kept to a minimum, while at increasing speed the overhang portions of the design increases the hull speed by stretching the waterline.

 

On the Swedish east-coast the Square Meter Yachts soon became popular. The small classes allowed more people to build boats, and the Square Meter Yacht became one of the first folk-boats.

 

Square Meter Yachts were required to provide basic living accommodations. Because these boats were raced in the ocean, it was important the designer created strong boats that could be sailed over distance. Even the small boats regularly crossed the open-sea stretches between the Scandinavian countries on the way to the international competitions; rather unusual for boats of that size those days.

 

Both the 30 and the 40 Square Meters were Olympic classes in the 1920 Olympics. The choice of Meter Rule boats for the war-time Olympics spelled the demise of an era. After the war, the International Rule favored by the USA ended the competition scene for the Square Meter boats.

 

The “grand old man” of American yachting, L. Francis Herreshoff, was one of the most vocal supporters of the Square Meter Yachts in the US. He bought one in Sweden and imported it to Marblehead, Massachusetts. He was convinced that these boats were bound to be the new Olympics class, and he judged them far better than both the European Meter class boats and the American R-class.

 

Mr. Herreshoff’s enthusiasm is a prime reason for the interest the Corinthian Club showed in the Square Meters. The class was introduced to the US in Marblehead, and the first races were organized by the Corinthian Club.

 

In 1928, Mr. Herreshoff designed Oriole II, a 30 square meter boat for one of his customers, Chandler Hovey's daughter Elizabeth, who admitted to having more fun with this boat than any other.

 

Another very important “ambassador” for this class of boats was Eric Lundberg of the Royal Swedish Yacht Club who, in August 1929, finished first in all races off the coast of Marblehead in the Swedish-German-American races. No other guest ever won all 11 races before.

 

By the end of the 1930s the class was so popular that there were 24 in the USA, 18 in England, 13 in Switzerland, 100 in Germany and 500 in Sweden. Today, more than 1200 boats of this type are built. They sail in the waters off Scandinavia, Germany, Switzerland, England, USA, and Australia.

 

 

 

Measurements

 

L.O.A. 19’3” (5.86 m)

Waterline length: 12’7” (3.84 m)

Beam 4’3” (1.30 m)

Freeboard height 1’2” (0.35 m)

Keel draft: 4’7” (1.40m)

Keel shoal draft: 1’2” (0.35m)

Rudder draft 2’4” (0.70m)

Rudder shoal draft 0 (0m)

Displacement: 0.34 ton (750 lbs)

Ballast: 0.17 ton (375 lbs)

Ballast %: 50%

Mast diameter at bottom3.39” (8.6 cm)

Mast diameter at top1.69” (4.3 cm)

Mast length23’0” (7.0 m)

Mainsail: 97 sqf (9 SQM)

Jib: 41 sqf (3.8 SQM)

Asymmetrical spinnaker: 172 sqf (16 SQM)

 

 

 

Detailed design specifications

 

 

Rig

 

The SC 20 is equipped with a sloop rig with that includes a main sail, jib, and asymmetrical spinnaker which are flown from a free-standing, rotating wing mast. Although the mast is designed for strength and stiffness to be completely free-standing, it nevertheless is equipped with running backstays which are used with the asymmetrical spinnaker to keep the mast from pumping. The running backstays may also be used with the jib to control the forestay sag, and in heavy wind conditions.

 

The mast is comprised of two equal length sections for easy transportation. The upper section is tapered. The mast is supported by two UHMW bearings, one mounted in the cabin roof, and one in the mast step.

The mast weight is only 7.1 kg (15.7 lbs) which means that it can be raised or removed by one person if it is not too windy.

 

Keel

 

The keel and bulb has a 1:5 purchase lifting tackle that allow it to be move up and down. Usually, the keel is lowered into position for the day’s sailing and is retracted only when entering shallow harbors or being maneuvered onto the trailer. However it is possible to lift the keel while sailing.

 

The keel blade is made of carbon fiber over a solid core made of high density closed cell foam. The blade aerofoil section is a modified GA(W) aerofoil of 10% thickness. The basic blade chord length is 26 cm (10”), therefore the blade width is 2.6 cm (1”).

 

The ballast bulb is an antimonial lead casting with a stainless steel armature built into it for affixing it to the keel blade. The bulb is called a Beavertail/Swallowtail bulb. The wide beavertail shape helps minimize the tip vortex by keeping the water flow running perpendicular to the span near the tip. The pointy swallowtail minimizes the vortices coming off the corners of what otherwise would be a square-tipped tail.

 

The keel slides up and down inside the keel casing which is made of composites and bonded into the boat. The top of the keel casing is situation 20cm (8”) above the water line to prevent sea water from coming into the cockpit while sailing.

 

Rudder

 

The rudder is a carbon fiber blade that is housed in a rotating composite drum that is supported in the hull by upper and lower UHMW bearings. Steering is by a tiller which is affixed to the drum. The rudder blade slides up and down by hand and is pinned in place at any of a number of discrete heights with a stainless steel locking pin.

 

The rudder blade is made of carbon fiber over foam core, molded in a female mold. The chord length is 13 cm (5”). The aerofoil section is, like the keel, a modified GA(W) aerofoil of 10% thickness, therefore its width is 1.3 cm (0.5”).

 

 

 

 

 

 

 

 

Done