Multihull Structure Thoughts

SMG Multihull has produced an interesting proa that can be converted to a trimaran or vica versa. The main hull length is 14.75 foot. If its in proa mode its beam is 9.75 foot and weighs 215 lbs, if it’s a trimaran its beam is 12.15 foot and weighs 260 lbs. The 23.4 foot mast carries a 94 square foot mainsail, a 29 square foot jib and a 107 square foot screecher.

The boat came in 5 versions depending on need. 2 Proa’s. NINJA PRO standard tacking proa ready to sail, without bow sprit or screecher and a total sail area of 122 square foot. Next is the NINJA PRO plus a tacking proa ready to sail, with Carbon bow sprit and screecher and a rig of 230 square foot.

3 Trimarans. The NINJA SPIDER resort trimaran is ready to sail with Dacron sails with jib on roller furler and a 122 square foot rig. The NINJA SPIDER plus trimaran ready to sail, North Sail sails with Carbon bow sprit and screecher with a sail area of 230 square foot. The NINJA SPIDER R trimaran ready to sail with North Sails sails, carbon bow sprit and screecher, Ronstan racing hardware and extra Carbon reinforcing in the beams and 230 square foot rig.

NINJA PRO is a fast tacking proa which was inspired by Polynesian proas. The Ninja version big advantage compared to her historical parent is It tacks like a sailing dinghy. The advantage is the Carbon mast is fitted on the main hull and there is only one rudder and dagger board needed the proa can be build lighter and easier tacking performance compared to sport catamarans.

NINJA SPIDER is a modern designed trimaran. With its chines on the hulls and relatively wide beam the big advantage of the Ninja SPIDER compared to the Ninja PRO is the well balanced stability given with the second outrigger hull.

Both versions of the Ninja has no boom and provides more safety during sailing and jibeing.

The boat is built from vinylester, eglass, foam and some carbon fibre reinforcement in the beams and other area’s. The mast is carbon fibre. The entire boats female molds and tooling cost 80,000 euro.

The proa and trimaran could sail very well but was a commercial failure resulting in the sale of the molds and tooling for 30,000 euro. The concept is interesting for a person wanting to learn about some fun boats.

 

If it doesn't shunt it is a outrigger.

 

A short one. CLC John Harris is a good thinker and develops many ideas, some of which evolve into production. I found a diagram of a possible trimaran done by John. I don’t think it is a standard design but it looks very good and could be the basis of a home built design. The tri is 15.75 x 11.75 foot with a displacement of 575 lbs. The rig would likely be a second hand Hobie 14 or 16. As with the majority of John work it would be plywood with in this diagram aluminium cross beams.

After this drawing was publicized the next development that went into “production” was the CLC Outrigger Junior. A 15.5 x 12 foot with a weight of 260 lbs and a displacement of 700 lbs. The outrigger has a sail area of 165 square foot. Again, it is a plywood design with timber cross arms. This boat cold easily be turned into a trimaran with an additional hull and modified cross arms.

I don’t know if one CLC design inspired the other, but you could do a home built version of the Ninja proa tri (outrigger) and have some real fun on you local lakes or bays.

 

The following is a very fast, fun one design trimaran with no internal accommodation. The Diamond 24 is 23.75 x 18.5 foot that weighs 1165 lbs and can “carry” in racing 625 lbs. It carries a carbon wing mast that is 210 mm x 100 mm by 37.75 foot long. The mainsail is 259 square foot with a 16:1 rope control, a self tacking jib of 97 square foot and the gennaker is 398 square foot. The mainsail and jib are black aramid with the Gennaker a laminated polyester. It has textile side stays (Etai câble inox) and a wire forestay. The boom is a 60 mm diameter 10.1 foot long carbon fibre tube. Sail handling is easy as well, the jib and gennaker are on Karver KF2 furlers, and the mainsail on a conventional halyard with clutch at the mast base.

The dagger board is 6.5 foot with a 350 mm chord (5.25 foot draft). The float transom hung rudders kick up and it has a central hull daggerboard to simplify building and reduce weight. The foils are e glass sandwich with pvc foam and carbon unidirectional reinforcements and epoxy resin with a gelcoat finish.

The structure of the tri is all resin infusion with the central hull and floats in e glass sandwich with pvc foam with polyester resin and gelcoat finish. There is selected carbon unidirectional epoxy reinforcements in some areas. The beams are e glass, pvc foam sandwich with carbon unidirectional reinforcements with epoxy resin and gelcoat finishes.

The tri is a stiff and rigid platform because non folding beams guarantee a diagonally stiff boat. The beams are bolted by 4 bolts to the main hull and have a mechanism of cone inserts and sockets in the floats keeping it simple during assembly disassembly for transport. The set up time is about the same as a F18 according to one test report.

The performance of the Diamond 24 is good, it can sail at 14 knots upwind and 30 downwind if you are brave enough. There is a global racing series with a lot of high profile skippers using the tri as training boats.

But as per usual there is always a guy who wants to “hot up” his boat for more speed. So he got a standard Diamond 24, rebuilt the floats and added float based lifting foils to make it faster. After a couple of sets of foils and some fine tuning this modified 24 could sail very well on foils in all conditions. The guy then said it seems to work so I will build a bigger version, OK. The bigger version is 100 x 69 foot and is crossing oceans foiling at absurd speeds. The guy’s name François Gabart who is backed by a company MACIF. To quote François “The M24 is a live training platform. It is important to spend time at sea during the winter, especially on a boat whose behaviour is as close as possible to the trimaran, because we set her up that way. It allows me to experiment a few things at the helm and with trimmings, and even to try things that I wouldn't dare to do on the big boat."

 

The Diam 24 concept is due to a small boatyard, ADH Inotec / Director Vianney Ancelin with the help of architect VPLP.
The feat of ADH Inotec • Diam 24 one design https://www.diam24onedesign.com/en/the-feat-of-adh-inotec/
Since its selection in 2015 for the "Tour de France à la voile" , this small racing tri play a similar role as the Figaro 3 for the monohull, i.e. a low budget platform for the junior division to form the future champions of the major offshore league (Route du Rhum, Vendée Globe, ...)
Diam 24 one design - Dare to speed • Diam 24 one design https://www.diam24onedesign.com/en/diam-24-od/

 

The Shuttleworth 35 is a 35 x 23.3 foot weighing 5200 lbs displacing 7900 lbs carrying a 45 foot mast, aluminium, with double spreaders, cutter rigged with stay sail, running back stays and standing rigging of 1 x 19 SS wire, head stay and cap shrouds are 3/8” Dyform. The sails are 340 square foot full-batten main, 400 square foot Genoa, 390 square foot drifter, 280 square foot lapper, 190 square foot yankee, 135 square foot stay sail, 40 square foot storm stay sail and a 1200 square foot spinnaker. The hulls length to beam is 10:1 when at full displacement. The John Shuttleworth designed catamaran has round bilges and dagger board in each hull. Flush decks and open cockpit aft with companionway hatches that allows steps down to cabin areas in each hull.

This design has had several boats built which have crossed the Atlantic and a large part of the Pacific. This design performance is impressive. The Shuttleworth 35, “Malihini”, in a race from Honolulu to Kauai averaged 12 knots for the 120 mile course. Once out of the lee of Oahu it had several periods of 20-plus-knot boat speed and a few brief periods of 24 knots of boat speed. “Malihini” on a trip from Nawiliwili (Hawaii) to Los Angeles, which is often upwind, covered 2,965 miles in just under 19 days, averaging 156 miles/day. The best day’s run was 250 miles with the worst day’s run of 69 miles and had five days over 200 miles. On the return trip from L.A. “Malihini” covered 2,775 miles in 15 days, averaging almost 185 miles/day. The best day’s run was only 205 miles. The worst day’s run was 161 miles with only two days with over 200 miles.

The construction is all foam core, epoxy/vacuum bagged construction. The hulls are a composite of 2 layers of 660 gsm uni-E-glass at 45 degrees, 15 mm PVC 8 lbs Divinicell foam, 792 gsm B-glass, all epoxy resin and vacuum bagged. Bulkheads are 12 mm Divinicell foam with 2 layers of 495 gsm uni-“E” glass on each face and epoxy resin, 100 mm tabbings between bulkheads and hull. Each hull has 6 watertight bulkheads. Decking is E-glass/epoxy, foam core, vacuum bagged. Awlgrip LP paint and non-skid. Composite chain-plates with foam e-glass carbon rudders/post, foam glass/ carbon dagger-boards and carbon fibre main beam top and bottom flanges. The twin balanced spade rudders is kick-up and steering in tiller across cockpit connected with tiller bar. Finished in Awlgrip.

The engine is a Yamaha 9.9 high thrust outboard, the engine is mounted on a HD sled faring which is retractable.

This design is a very quick effective cruiser that has a proven track record. It needs to be built well and light but the reward is real ocean crossing performance. Shuttleworth has upgraded the design recently to a reverse bow 37 footer in the final jpegs. An extra 5 foot of waterline and taller rig/bigger rig will ensure more performance. Fun.

 

The following is about storm conditions and cheap drogues that may help you. If you are in a storm a drogue can help you survive by controllably slowing or “stopping” the boat in a storm tossed sea. You can sail a cat or tri in 50 knots plus of winds if you have an alert crew, but the reality of cruising is you have limited crew who do not “have to be” at a location at a given time. The cruising boat doesn’t need to be driven hard and a sensible seaman will just want to controllably minimise the boats movement and let the crew just rest until the storm passes. There are many drogue options available, each have different characteristics and are suitable for different conditions and boat types.

Jpeg 1 and 2 are The Gale Rider web netting type when appropriate sized and set off the bow can “stop” the boat and hold it head to the waves. This is when you can get rest whilst the storm blows itself out. The Gale Rider can be brought commercially or home made from webbing. One guy went to a car wrecker and cut out car seat belts and sewed them together with a wire ring around the top.

The next is a para drag type system. Literally a correctly sized parachute that is set of the bow and can stop the boat until the storm is over. Again commercially available but second hand old style military cargo parachutes have been used successfully. Parachutes can have shocks go through to the system as a boat is eg going down the face of a wave while the parachute is in a different wave allowing the line to go slack.

But I give a BIG warning about these two types of sea anchors, if you are lazy about pulling them in after a storm and there are big seas around they can kill you. Why? A parachute sea anchor that is not streaming near the surface do to wind pressure, can drop vertically below your boat and not allow the bow to rise to an oncoming sea. Instant wave impact to your topsides and windows. Not good.

The next is the JSD system (Jordan Series Drogue). It is a series of small (150 mm diameter) cones (up to 160 depending on boat type and size) that are attached to a line from the stern of a boat. With the JSD you should be able to better control your boat speed and angle to the following seas. Controlling your boat speed and angle is what heavy weather seamanship is all about. Broaching a multihull is not good especially a low buoyancy float trimaran.

You can home build a JSD system and there are 3 jpegs sowing the concepts. The following web site has an excellent description of how to make your own JSD system. Instructions to make your own JSD device are in a PDF at http://www.napmarine.com/wp-content/uploads/2013/12/JSD.pdf

Next is the “seabrake” system sold in Australia which is a cone shaped drogue device. Again it is set from the stern to slow the oat down. I have not included a jpeg because although I have used one in one storm, it is effective, the seabrake depends on a very specific design and shape to work. Not easy to replicate by a home builder.

Next are a couple of home made approaches for use in minor storms to slow the boat down. Cut down used car tires or wooden creations that can slow the boat from the stern. Both are cheap and simple but they are heavier than the fabric based drogue solutions. The final 2 jpegs are examples of the tire or wooden solution.

The drogue at the end of the line is only half the solution. The real trick with drogues are the lines and shackles connecting the drogue to the boat. The lines need to be strong and have a least some portion that can stretch a bit to absorb shocks. Nearly all drogue devices spin when deployed so the shackles need to allow rotation. Recovery lines need to be thought about as if a drogue spins it can twist a recovery line in the system making the drogue ineffective or very difficult to recover. The boat needs several VERY strong line anchoring points forward and aft on the boat without any deck gear in the way that may cause chafing on the drogue deployment lines.

Even if you do short offshore trips, please plan for the worst and have at least a simple drogue drag solution available just in case. The only time I had to use a drogue was on a 150 mile “short” trip short handed. A front came through from the wrong direction and I had some small rudder problems. The boat needed to be slowed to fix the rudder. You can use eg anchor lines, chain even an anchor in extreme conditions but a proper drogue will control the situation better. There is a 4 meg coastguard report on drogue devices.

Also the following Practical Sailor site has an article on Drogues at Sea Anchors & Drogues - Practical Sailor https://www.practical-sailor.com/sails-rigging-deckgear/sea-anchors-drogues

 

I'm a bit late to the party. It's an amazing thread thanks oldmulti!
But please accept a photo of one of the first boats mentioned here. Devils 3.
My father bought her from col Fraser (?) In the very early 80s and sailed her out of Bowen for many years.

 

Thanks for your contribution Ian. When I saw and raced against Devils 3 it was a very fast boat. How did you find it's sailing capability and did it require much maintenance over your fathers ownership?

 

I was only a young fella, but I suspect we never pushed her too hard. We were always competitive but not overtly dominant with the locals. I remember we entered one of the early Hamilton island races and watched slack jawed while Riverside Oaks started emptying the cushions out of her to drop weight! Can't recall any significant maintenance issues. Certainly not with the aluminium frame or skin. In hind sight I liked her layout. Wide cockpit and 2x 3/4 wing berths half under the cockpit. Have not seen it anywhere else. I'll ask dad if he recalls any issues with her.

 

The following is the story of the development of an ancient canoe replica. It gives a lot of hints about the evolution of cat design. This comes from the Polynesian Society.

What were the design features of the ancient double-hulled voyaging canoes (vaka taurua)? What features would form the design of a replica to be called “Hokule'a”. Kenneth Emory and friend went through all designs of canoes recorded in early drawings and other evidence to get features of the hull design and sail plan. The design had a waterline length of 55 to 60 feet to handle the swells yet recover easily in the troughs, and Emory found that this could be taken as an average for the length of canoes used in the 18th and 19th centuries for long distance voyaging in the Tuamotus and Tahitian islands. Canoes of far greater length would put great stress on the lashings.

Kino (Hull): Hulls were carved from logs wherever timber of sufficient size was found. The depth of a hull might be increased by adding one or two courses of boards (strakes) fitted and lashed above the hull's upper edges (gunwales). On atolls where large timber was not available for dugout hulls, the use of gunwale strakes was transformed into a method of building entire hulls "plank-built" over a dugout keel piece, with ribs and thwarts inserted to strengthen the planking.

All hull and sail design features must be compromises. Where paddling was the primary power mode with sail as auxiliary power, round-bottomed hulls were favored for their maneuverability; but where sailing was the primary purpose, hulls were deeper or had a greater amount of "V" shape along the keel for better tracking through the water. Such hulls are less maneuverable but offer lateral resistance to the water, reducing leeway. A rounded "V" hull, with the sides swelling outward in convex curvature, is also stronger than a flat-sided "V" hull because it adds the strength of an arch against the impact of waves. Longitudinal curves below the waterline are smooth-flowing from bow to stern, creating a gentle entry at the bow and an equally gentle departure at the stern-features necessary for a "soft" ride and maximum hull speed. In these curves there are no abrupt breaks-no "chisel" bows to snag the water and make steering difficult, no abrupt departure at the stern which creates turbulence. For best speed the hull curves are faired out as much as possible (canoe builders knew how to use a flexible fairing strip to check their hull curves), with no hollows or flat areas to cause turbulence.

The volume of Polynesian hulls aft of the midsection is slightly greater than the volume forward of the midsection. This extra flotation aft offsets the tendency of canoes to "squat" at the stern when under a hard press of sail.

Because double canoes are held together by rope lashings, the hulls must be assembled closer together than the hulls of modern catamarans. This narrows the space through which water must pass between the hulls. To avoid excessive turbulence between the hulls, the greater volume aft of the midsection should be obtained by greater hull depth, rather than increasing hull width.

Pe'a (Sails): The first preliminary drawing for Hokule'a (1973) featured triangular sails carried with the peak of the triangle downward and mounted on straight spars, a design which by its simplicity and wide distribution seemed to be the most ancient form. This sail plan was modified later in 1975 and again in 1976 with a curved boom to more closely resemble the Hawaiian sails at the time of European contact. However, experiments in 1991 and subsequent voyages have demonstrated that the simple triangular sail carried on straight spars is no less efficient; moreover, it is easier to furl and handle on deck when the rig is dropped to ride out bad weather.

Iako (Connecting Cross-beams): A true replication of an ancient canoe should have crossbeams shaped from straight poles-the method most widely distributed. The arched crossbeam is a feature of the classical Hawaiian double canoe, invented only four centuries ago by the designer Kanuha in the time of Keawe.4 In a quartering sea the hulls of a double canoe will work against each other. By inter-connecting the crossbeams with diagonal bracings of strong rope, this motion can be restrained, adding very little weight to the vessel. While most cross-beams were lashed to the gunwales, the connection of the two hulls could be strengthened by two or more lower crossbeams let through the hulls.

Hokule'a is a slower sailer. Assembled with cordage, it lacks the rigidity of modern multihulls, and the hulls must be closer together to reduce stress on the cross-beams. Assembly by lashings seems to offer one advantage. As noted on the replica Hokule'a, the cross-beam lashings absorb much of the shock of waves that beat against the hulls, a pounding that is transmitted throughout a modern vessel.

Mast steps: Wind pressure on the sail drives the mast downward. Such pressure should not be borne by only one crossbeam. The masts may be stepped upon strong longitudinal beams (kua), each distributing the downward thrust over a least three crossbeams. Once the optimum center of effort is found by experimentally moving the masts forward or aft over these steps, additional crossbeams may be added under those points.

Steering: The idea of steering a sixty-foot multihull without a rudder has intrigued conventional yachtsmen on their first sails aboard Hokule'a. On a downwind course the steering paddle is handled in the manner of a rudder, and long sweeps were used on some Polynesian canoes. On any other tack, however, the steering paddle is held against the lee side of the hull near the stern. The pressure of the water against the blade helps hold it fast, and very little effort is required to hold a heavy steering paddle in place. A slight twisting pressure to hold the leading edge of the blade firmly against the hull prevents the flow of water from getting under the blade and kicking it away. For this reason, steering paddles were often carved flat on the side held against the hull, and concave on the other.

Steering with the Sails: On long reaches, steering paddles may not be needed at all; the canoe can be rigged to steer itself by sails alone. The aftersail is eased out slightly more than the foresail. As the canoe rounds up into the wind, the aftersail luffs and loses power. Pressure on the foresail now causes the vessel to turn off the wind a few degrees. The aftersail is again presented to the wind; it fills, and the vessel begins another slight turn to windward. Sawing slightly into the wind and off the wind, the canoe will steer itself on a close reach for hours.

Leeboards: The use of leeboards to diminish leeway and help a vessel without a keel go to windward was a Chinese invention which never got to Polynesia, but the same effect was accomplished, when required, by a row of men holding paddles against the lee side of a hull. This takes practice, but it can add ten degrees to a canoe's windward performance.

 

On page 28 number 408 of this thread we mentioned the Eagle 53. The Eagle 53 is 54 x 28 foot weighing 13200 lbs and displaces 16,600 lbs with a maximum displacement of 22,000 lbs. The 78 foot high modulus rotating carbon fiber Hybrid Wing mast with Carbon shrouds that has 1290 square foot main, a 580 square foot jib and a 1480 square foot screecher. The reason for this addition is the finding of more detailed diagrams and drawings of the Eagle 53. We find the hull shape basically semi circular underwater with a length to beam of 15:1 when sailing fast and not foiling.

Her construction is lightweight prepreg epoxy carbon-fiber skins over honeycomb and foam cores, with very specific layup schedules and lots of unidirectional carbon reinforcements, which, according to structural analysis, are arranged to parallel the load paths. All components were vacuum-bagged and post-cured in an oven. Some parts were autoclaved. Eagle’s overall configuration exemplify the designers (Bieker’s) approach. The foils are Pre-preg carbon daggerboard C Foils and Pre-preg carbon T rudders.

When the Eagle 53 is showing off her C-foiling in more wind, she can skip along at boat speeds in the 30s with one hull flying high and the other is still partially in the water. To fully foil the boat is going to need T-foils and automated ride control that will allow amateurs to successfully take the helm at 30 knots, and safely depower the boat when conditions become excessive. According to the design brief, such foils should make the Eagle 53 fly flat with all foils in the water and all hulls out, with boat control at speeds approaching 40 knots. Got a bit of money? This would be a weapon in local racing.

 

The plans for the following 5 meter (16.3 foot) proa are available at 5 m Proa building plan for free https://www.multihull.de/proa/p5/p5gb.htm

The conception of the P5 is a light car toppable proa for 1 to 2 sailors. Both hulls are multi chine designed for plywood/epoxy (stich&glue) building. The total weight should be 170 lbs.

The main hull has three parts: lee side plank, upper windward side plank and chine plank. Every plank could made from mirrored halfs from 4mm plywood. Next step is to glue a stringer (20x20mm) along the upper edge of the lee side plank (may be a second one into the middle) and of the upper luff plank for fitting the decks later. Another stringer should fixed at the below edge of the upper side plank. For more planking stability, use a keel batten (20x20 mm) as backbone.

First put the lee side plank into the support, then the keel and the chine plank. Then stich all together with copper wire. If all is perfect aligned, glue it together with epoxy putty/glue. After the glue has dried strengthen the keel section and the connection of the luff side planks with stripes of 200 gr fibre glass.

Construct the deep V float from 2 sheets of 4 mm plywood joining them at the bottom with epoxy putty/glue.

The cross arms are 50 to 60 mm aluminum tube. Scaffold tubing would be good. The rig yards etc were initially bamboo but were converted to old windsurfer masts as they were easier to obtain and lighter. Fine demonstrated is this rig at the homepage of Gary Dierking or in the Gibbons-Special at multihull.de. This Gibbons/Dierking rig has a simpler handling than Crab Claw rig sails. A fun boat.

 

The following is about the evolution of design thought. Schionning designs commercial life started with a very cute 930 (30.5 x 19.5 foot) flat panel bridge deck cat that could be built in plywood or other materials. The boat performed well, had reasonable accommodation and was easy enough to build. But as per usual there was a demand for a “higher performance” more “yachty” type boat with slightly more accommodation (mainly higher bridge deck cab of 5. 25 foot). Result is the featured Cosmos 930. It is 30.5 x 19.5 foot weighing 2700 lbs and displacing 5900 lbs. It carries a fractional rig with a 39.5 foot aluminium mast with a 350 square foot mainsail and 200 square foot fore triangle. The length to beam of the hulls is 12:1.

The second main difference is the construction technique. The original boat was flat panel, the Cosmos 930 is strip plank Western Red Cedar. The 12 mm WRC had about 446 gsm 45/45 e glass on either side in epoxy. Some boats were done with 400 gsm 45/45 on outside and 200 gsm uni on the inside. The main cross beam were timber framed plywood web faces with unidirectional e glass top and bottom flanges. The rear beam is similar. The remaining bulkheads were plywood. Redrueben, who posts on this thread, once commented that commercial builders of WRC strip planks use a lot of “fast build” approaches. Most amateur builders do it strip by strip gluing each one. Commercial builder just layup the majority of strips then apply a layer of epoxy to fill the WRC surface and fill the gaps between the strips at the same time. He says you can build a strip plank hull fairly fast. Some of the later Cosmos 930’s were built in corecell foam glass with triaxle cloth on either side. The beams and bulkheads were also mainly foam glass.

At about the same time a simpler build version was requested and the Wilderness 930 was born. The Wilderness is a multi chine flat panel build with mainly 13 mm duflex balsa panels. The panels are put in female frames and taped together then have an additional layer of glass over the outside and inside. The bulkheads and cross beams are again duflex with some having e glass unidirectional initially then carbon fibre glass around the edges to provide strength.

The requests came for bigger cats with more accommodation. Schionning learnt more about the design and build techniques required to build a good fast boat and eventually dropped the Cosmos and Wilderness series. Now Schionning does not provide designs less than 40 foot long and the majority are only provided with a kit for simplicity of building. The current Arrow and G Force series are good designs but they need to built to the design weigh as they are often high to very high performance cats that only allow a minimum of overloading.

Schionning web site is http://www.schionningdesigns.com.au/sailing-designs

The first jpegs are the Cosmos 930, the last 3 jpegs are of the Wilderness 930 “Wasabi”.

 

The Arrow 40 is a Schionning designed bridgedeck performance cruising cat that is 39.3 x 21 foot that displaces 11200 lbs and carries 1130 square foot sail area. The masts can be aluminium or a wing mast of carbon fibre and dyneema shrouds . The underwater sections are multi chine not round bilge. Does it have an effect on the performance? Richard woods says a good set of foils are more important to performance than chine hulls. Jeff Schionning gives an estimate of 20+ knots top speed. With 14.5:1 hulls, reasonable rig and a light weight its performance has proven to be good. One owner found on his first sail in 15 to 20 knot winds. “For two hours the speedo didn´t fall below 10 knots, mostly staying at around 11 with max 12.5 knots without pushing it, Wild Thing sails so well! From my last cat with fixed keels I was used to tacking angles of 120 deg. Wild Thing tacks well below 100 degrees! The wind dropped to 12 knots we were going 7-8 knots upwind at a TWA 45 deg. For me this might have been the most revealing moment of the weekend. Never worry about going upwind again!” This design has topped 20 knots and can do 250 mile days in tradewind sailing.

The Arrow 40 design is a 100% flat panel construction which keeps the building process fast and simple. The design is based around you purchasing a kit for the hull shell, then if you want purchase additional kits for the interior fit out. The 16 mm duflex balsa panels with 150 kg/qm end grain balsa core and 600 gsm glass on each face provide the base of the hull shell, deck and superstructure kit. Some bulkheads are 16 mm duflex panels with some 25 mm duflex balsa panels for the underwing and some main bulkheads. The kit panels are cut out and panels are glued together at EG chines. The hull panels are put in female mould frames then taped at seams. Next step, glassing the hull with 2 layers of 450 g/m2 Double Bias E-Glass, one layer up to WL, second layer up to WL +100 (inside) and WL + 500 (outside). The main cross beam bulkheads are then placed in position and glassed in. The underwing is completed and the interior kit of 16 Panels of 60 kg/cubic meter PVC foam core or Featherlite Interior Honeycomb core of 16mm with 600 gsm faces. This saves a lot of weight while still being strong and rigid. All panels are now glued and all parts are cut and glassed in. Arrow cats depend on the internal structure to stiffen the shell structure. The deck is then placed on. The gap between the kit panels were a maximum of 2 mm, very good.

The build time should have totaled 3500 hours but a builder took longer. The reason why can be explained by some of the timings: joining the panels and cutting the tabs – 170 hours, preparing the building site – 20 hours, building the starboard hull – 270 hours, building the port hull – 200 hours, inserting the main bulkheads and the bridgedeck – 130 hours, cabin top assembly – 60 hours etc. This boat was built in a professional boat yard with all the tools and facilities necessary for the building process are available. For example, the setup of the strongback only took minutes because there was one there already. A home builder would take longer in setup time, tool acquisition, shed establishment etc.

This is a fast, sensible design for a home builder that would be a good cruiser.The blog for this builder is … catbuildingblog.com http://www.catbuildingblog.com/