Multihull Structure Thoughts

Vik 81 catamaran is a design by Eric Larouge. The bridge deck cat is 26.1 x 14.6 foot. The weight is 3500 lbs and the displacement is 5700 lbs. The 34.5 foot fixed aluminium or rotating wing mast that carries a 280 square foot mainsail (with 3 reefs), a 190 square foot jib (can be on a furler), 43 square foot storm jib and a 520 square foot spinnaker (1 oz). The boom is a 11 foot aluminium section The headstay and the majority of rigging is 6mm 1 x 19 stainless steel wire with the diamonds 5 mm 1 x 19 stainless steel wire. The hulls draw about 2.6 foot and have NACA low aspect keels and spade rudders. The length to beam on the hulls is about 8 to 1 with semicircular sections.

The Vik 81 design has adequate displacement and payload capacity to offers reasonable family comfort for serious coastal cruising. The central bridgedeck area has 5.1 foot headroom in the main cabin and accommodates a dinette which can be converted into a double bed. The hulls have 6.2 foot headroom and two extra berths, the galley and a serious bathroom.

The design can be built home built from 10 mm and 12 mm PVC 75 kg/sq mtr foam with biaxial cloths on either side in polyester or vinylester resin. There is also a strip plank cedar option available with biaxial fabrics and epoxy. In the home-built versions the bulkheads are plywood with 150 mm biaxial tapes with epoxy. The bridgedeck windows are 10 mm Perspex. The low aspect ratio keels are solid glass with a grounding shoe on the keel bottoms. The minimum anchor is a 28 lbs CQR with 65 foot of 8 mm chain and 65 foot of 14 mm nylon rode. At this size of cat two number 16 winches are required for halyards and sheets. Halyards and most ropes are 10 mm with 12 mm sheets.

This is a serious coastal cruiser that would make a good fun sailor. The jpegs give the idea.

 

Due to a “update to the internet” in 6 hours, I am doing tomorrows item tonight. The Vik 91 catamaran is a design by Eric Larouge and will be the last in this series as Eric has designed a 10, 11, 12, 13, 14 meter etc. All interesting fast cruising cats that have the same basic structures and concepts. Very good designs worthy of study at his web site: Erik Lerouge http://erik.lerouge.pagesperso-orange.fr/cat_9.htm

The Vik 91 bridge deck cat is 29.5 x 17.9 foot. The weight is 5,500 lbs and the displacement is 8,600 lbs. The fractional rig 38 foot fixed aluminium or rotating carbon fibre wing mast of 45 square foot that carries a 370 square foot mainsail (with 3 reefs), a 230 square foot jib (can be on a furler), 53 square foot storm jib and a 700 square foot spinnaker (1 oz). The boom is a 13.8 foot Park Avenue (wide boom for reefing and sailing efficency). The headstay and the majority of rigging is 8 mm 1 x 19 stainless steel wire or rod with the diamonds 7 mm 1 x 19 stainless steel wire. The hulls draw about 2.9 foot and have NACA low aspect keels and spade rudders. There is a daggerboard option. The length to beam on the hulls is about 8.5 to 1 with semicircular sections.

The Vik 91 design has adequate displacement and payload capacity to offers reasonable family comfort for serious cruising. The central bridgedeck area has 5.6 foot headroom in the main cabin and accommodates a dinette which can be converted into a double bed and a chart table. The hulls have 6.3 foot headroom with 2 double berths, the galley, a serious bathroom and an extra single berth if required.

The design can be built home built from 12 mm and 15 mm PVC 75 kg/sq mtr foam with biaxial cloths on either side in polyester or vinylester resin. One-off construction in foam sandwich on battened mould or using CORECELL foam strips set on templates. There is also a strip plank cedar option available with biaxial fabrics and epoxy. In the home-built versions the bulkheads are plywood with tapes are biaxial with epoxy. The windows are 10 mm Perspex. The low aspect ratio keels are solid glass with a grounding shoe on the keel bottoms. The minimum anchor is a 32 lbs CQR with 65 foot of 8 mm chain and 65 foot of 14 mm nylon rode. At this size of cat, number 40 winches are required for halyards and sheets. Halyards and most ropes are 10 mm with 12 mm sheets. The engine can be a 10 HP outboard as a minimum or two 2.8 KW electric inboards.

This is a serious cruiser capable offshore work that would make a good fun sailor. The jpegs give the idea.

 

Xcat is a 16.4 x 6.9 foot cat that weighs 121 lbs with no part weighing more than 39 lbs. the Xcat can carry 573 lbs. The mast is 15 foot high with a 60 square foot mainsail and a 36 square foot jib. The sails are 6 oz dacron. The jib is attached to a 2 part forward prodder and the rudder (partial daggerboard substitute) hangs off a 650 mm rear aluminum extension. This design is a bay or lake craft. But the Xcat has can be a row boat, SUP or a day sailing cat depending on the options you choose. The rowing option can be with you looking forward or aft depending on the option.

Now we get to the construction of the Xcat. Its being built in Germany which means it’s likely to be environmentally friendly and technically interesting. The Xcat is both. The hulls are HDPE skinned with EPP particle foam inside. The cross beams and mast support, net support, prodder and rudder support mechanisms in aluminum.

HDPE is high density polypropylene which can be purchased in sheet form and is lighter than plywood with a harder waterproof surface. Expanded polypropylene (EPP) is a soft-elastic to hard, closed-cell and thermoplastic foam. EPP foam has a high structural strength at low weight and combines several positive mechanical properties, such as very good energy absorption and high resilience. It has good chemical and water resistance.

Now I understand how the EPP core is formed with associated structural hardware posts to allow the assembly of the cat. It would be a full female mold. The part I am confused apart is how the HDPE skin goes on. Either it is a flat sheet that is “shrink wrapped” on or it may be roto molded on. Does anyone know?

Result is a very light strong hull structure that is very waterproof, knock resistance and only requires a wipe to keep clean and maintained. The aluminum structure is excellent in design to allow a very short assembly time. This is a genuine car topable cat or can be placed on a trailer. It appears to sail reasonably well, as well as row or use as a SUP.

The jpegs give an idea of the Xcat and its internal structure. Interesting.

 

Judging from the pictures on the website, the outer skin is rotomolded HD Polyethylene, and this (formed) skin is in one piece, folded over the inner foam and connected/closed at the keel and stems. Clever idea !
Cheers, Hans

 

On page 72 of this thread there was an article on Sardine run tri’s. A mention was made of the Sardine Run 23 which was designed by Allel BEHIDJ. The 23 is 23 x 17 foot but with Farrier type beams can fold to 7.9 foot. The 23 weighs 1120 lbs and displaces 2000 lbs at maximum displacement. The mast is a rotating 30 foot section (as a start, could be of a large Hobie cat mast) carrying the mainsail area of 236 square foot, a 107 square foot and 270 square foot gennaker. There is a 4 foot removable bow spirit option to fly an asymmetric spinnaker or code O.

The main hull has the daggerboard and kickup rudder. The draft is 1 foot to 4.5 foot. The main hull has aft a slight V shape with a tortured ply V forward section. The floats have a V bottoms. The reverse axe bow is as much fashion as it is functional.

The Sardine Run 23 is planned for the day or weekends in the San Francisco Bay Area and the Pacific Coast with a minimum of comfort for 3-4 people. That does not mean it will sleep 3 or 4 people. This tri has limited internal accommodation.

The construction is plywood, epoxy with Basalt glass joint tapes and some carbon fibre in the folding cross arm beam structure. The structural model used in the smaller 18 and 19 foot tri’s appear to be repeated in this boat with more sophisticated cross arm structures and associated bulkheads. The 4 jpegs give an overview of the design. The black seam tapes in the last jpeg are basalt cloth in epoxy, not carbon fibre.

This is a design that needs to seen on the water as I suspect it will be a good design based on the performance of the smaller 18 and 19 foot designs.

 

A Canadian Peter Walford home designed the following trimaran which he called W24 Pocket Cruiser. The W24 is 24 x 18.5 foot with sliding beams to allow a 10.5 foot beam for marina’s. The tri can be disassembled to 7.5 foot for road transport. The built weight was aimed at 1400 lbs. The 35 foot mast is capable of carrying 380 square foot of sail with a self-tacking jib. The main hull has a daggerboard and the rudder is a kickup on the stern. The length to beam on the main hull is 8 to 1.

Peter Walford has a lot of experience in tri sailing and wanted a tri suitable for the Pacific North West where he could go cruising for months in single digit temperatures. A 24 foot Farrier type tri was not going to have the accommodation or payload capacity to do a cruise like this for several crew. Peter wanted a center-cockpit, to allow the weight of crew, fuel and water to better distributed. Reefing is done on the mast using winches and sheet stoppers, without leaving the cockpit and without requiring turning blocks on the deck. A roller boom is specified for reefing. As there are no 24-foot center cockpit boats on the market except for the now out-of-production Newick T-Gull 23 is the only thing that came close, but it had almost no accommodations, payload capacity, or freeboard. The vintage Jim Brown 25 provided inspiration, but is dated in its rig and was demountable not foldable. Also the Brown 25 did not provide full headroom as required. So, Peter did his own design with cabins that have a much more useful configuration, with standing headroom in both cabins and greater interior volume.

So far, a good concept and reasonable design. This will not beat a F24 but it should sail well. Now we get to the construction. The jpegs give some detail. We start with the floats. They are cylinder molded (Kurt Hughes concept) with 2 layers of 3 mm plywood with 6 mm ply bulkheads with timber framing and a float deck of 8 mm PVC foam with 550 gsm biax on both sides.

The main hull sides and bottom are 6 mm ply with 8 mm PVC foam and fiberglass on outside to save doing any internal stringers etc and this will provide stiffer hull sections and insulation. The bulkheads are 6 and 9 mm plywood with timber framing on crossbeam bulkheads. The transom is 6 mm ply. Cockpit floors are 9 mm ply. The cabin tops are 3mm plywood skins, 8mm PVC foam sandwich, free of stringers and quick to finish while possessing a decent R-value. This build method is standard Kurt Hughes approach. The forward deck on the main hull is curved 3 mm ply with 8 mm PVC foam and fiberglass. The crossbeams are square tube sections of unknown dimensions for ease of sliding. Top brace is a 52 x 52 mm aluminum section with a 5 mm vectran waterstays. The crossbeams are held in place by 9 mm bolts.

I do not know if this tri is complete but I hope it will be sailing soon. The jpegs give the idea of a hopefully capable small cruiser.

 

I made my KHSD amas out of 4 mm plywood, and they have held up for 30 years, they don't see a ton of use but are really tough and well shaped, and they hold up well to very nasty outdoor storage. The 4mm is the offshore package, and it turned out to be lighter to make the deck of plywood than the alternative balsa core. Foam core would be lighter but not as stiff. The CM process does not yield better shape in these sections as post trim most of the heavily curved material gets trimmed off. You end up with a heavy part that may not even bend as deeply, and you waste a lot of time on making a mold and a vacuum bag setup. If the hull was to be CM, then you would have a worthwhile project, but the designer knows he won't get the desired displacement if he CMs a main hull for this project.

If you Stressform these amas, they can be made in about 20 hours, solo, if you already knew the drill. That would be completed to the point where the beams are being connected, and minus paint. You really can't beat Kurt's Stressform amas.

My 24 came out super light in all ply. But as nice a boat as my 24 is, there in nothing terribly usable about the interior, and I prefer the idea of a center cockpit. It sails nicely with 5 family members on it, but someone has to ride the bow to set the waterline. And center cockpits have all kinds of other advantages like more easily operated and sealed dagger board slots. I could never get the full length board in my boat, and under certain circumstance the slot can pump water into the cabin. Never happens when sailing. But a dagger in a center cockpit is a giant drainhole.

One nice thing about simple, penetrating, Al beams is that they can be easily adapted. You can have a boat and gradually add extra components over time and have a boat that is idea for canals, racing, overnight, and so forth. The parts are cheap to build and they can be mixed and matched as they accumulate over time.


Edit.

When I mentioned the waste of time in making a CM mold, I should say that the vac bag mold is a pretty small job. I don't remember exactly, but once the materials are assembled it is maybe an afternoon. I only meant that if you build it for the amas but did not need it for the main hull there would be a loss of efficiency due to the single use.

What can be a larger problem is space. I had a shop of 30 x 30 that had a corner office in it, and that space was about ideal for a 24 foot boat that had multiple parts, storage, and I had a 4x8 table that was very useful. But a lot of people have almost hull width spots to build their boat in, and that can lead to a real space crunch if you have some parts in production, a mold, and a scarphing area, etc...

 

Jim Brown wrote a book in 1982 which was titled “New working watercraft: a return to former capabilities” that not only shows a history of working sailing watercraft but also shows Jim Brown, John Marples and friends possible modern solutions to sailing working watercraft for many pacific islanders. This is a 33 meg PDF download that is 107 pages long but is very informative of constant chamber build techniques and designs. The download is available at https://core.ac.uk/download/pdf/235415098.pdf

Some of the designs shown (a few with details) in the PDF include the 82 foot Lazy Susan, 64 foot long range fishing catamaran, 62 foot “merchantman” tri built in the Guatemalan jungle, Chris White 52 foot cruising tri “Juniper”, Russell Browns 30 foot $1500 pacific proa that raced in the Caribbean, Constant Chamber 24 to 36 foot fishing trimaran that could be built in constant chamber wood, aluminum or foam glass and several versions of 20 to 30 foot sailing fishing proa’s. Also mentioned is John Marples “constant chamber 26 foot” tri.

This document will give an interesting view on how to build relatively cheap effective cats, tris and proas for fishing etc and options for cheap effective cruisers. The jpegs show some of the designs mentioned.

 

The Maine Cat 41 is a semi bridge deck cat produced by Dick Vermeulen’s Maine Cat operation starting in about 2003. The MC 41 is 41.5 x 23 foot that weighs in cruise mode 14,000 lbs with a displacement of 19,200 lbs. The 54 foot aluminium mast that has a high-roach “pin head” main is 715 square feet, a 281-square-foot self-tacking jib, screecher of 575 square foot and an asymmetrical spinnaker of 1200 square foot. Custom chain plates ½” thick of 316 stainless steel thru-bolted through solid fiberglass mounted externally at the major bulkhead. Total of four (4) Lewmar AST size 50 two speed self-tailing winches. One (1) AST 50 to be electric (starboard forward) for the main halyard, screacher furler, reef lines and the topping lift.

The wing deck clearance is 2.7 foot. The hull length to beam is 10.5 to 1. Single or twin daggerboards (depending on the production date) are 12% NACA foil sections with solid foam coring. The cat draws 7 foot with boards down and the rudders draw 2.5 foot. The rudders are balanced fixed, under-body 12% foil rudders with 1-1/2″ diameter solid 316L stainless steel shafts and high density coring.

The Maine Cat 41 is for sailors looking for a good performance cruising catamaran that has good sailing qualities. The Maine Cat 41 is small enough to be handled by one person and larger enough to take offshore in safety and comfort. The accommodation plan starts with the cockpit which measures 15.5 by 11.5 foot createing a central social and sail control area. Below decks is accommodations for six adults with ample space for the galley with a refrigerator, freezer, four burner propane stove/oven combination and microwave. The port hull includes a queen size berth, full bath and a private cabin with comfortable forward berth. The entire starboard hull is devoted to the master stateroom. A queen size amidships berth is a mirror image of the port berth with ample storage. The large master bath has a separate enclosed shower. There is also a huge private single berth in the forward part of the hull near a large office area for chart work and storage.

The Maine Cat 41 hull laminate is built up using vacuum bagged vinylester resin with 450 gram CSM followed by a sewn quadraxial 3508 (1130 gsm quad 225 csm) cloth over a 18 mm Corecell. The internal layup is quadraxial 2608 cloth (841 gsm quad 225 csm). 18 mm Corecell is laid up throughout the topsides except in the bows where, Vermeulen says, the shape forces laminators to use solid material. The hulls are then reinforced with a “keel” of unidirectional fibers on the centerline. The flat expanse of bridge deck gets 25 mm Corecell for added stiffness with the same glass layup as the hulls. The hull-to-deck joint is a ship-lap (85 mm overlap) that is bonded with urethane adhesive-sealant and fiberglassed on the interior with 1708 (550 gsm triax with 225 CSM) triaxial tape. Faired bow and stern to a seamless finish, the exterior seam is covered with a rigid vinyl rubrail with a protective stainless steel insert. The hull deck layup is not mentioned but I suspect would be the same as the hull topsides. “Smoked” acrylic windows are 9 mm thick outboard on port and starboard deckhouses.

Primary ground tackle includes bow roller with 50 lbs Delta anchor with 100 feet of 8 mm High Tensile chain and 150 feet of 16 mm nylon 8-plait rode. Rode leads to below-decks Lewmar V-3 gypsy-capstan electric windlass with up and down controls on deck and remote switch at helm console. Second bow roller with Fortress FX-37 and 20’ of 8 mm chain and 150’ of 16 mm nylon 3-strand rode provided on port side of centerline plank for back up.

Owners have said their best reported average speeds ranged from 11 knots to 14 knots over 48 hours, with a EG a Gulf Stream boost. The boat is close-winded her designer claims with the cat tacking (with no reluctance) through 90 degrees in eight knots of true wind and smooth water on one test sail. The designers claim a top speed of 18 knots. An owner had lived aboard the MC 41 for over two years before trading it in on a later model Maine Cat 38 (will discuss tomorrow). The reason was he wanted a lighter, easier to handle cat (shorter mast less sail) that has similar or better performance.

This is a good performance catamaran that has realistic accommodation for extended cruising. At least 20 were built. The jpegs give the idea.

 

The Maine Cat 38 is a semi bridge deck cat produced by Dick Vermeulen’s (who designs the boats) Maine Cat operation starting in about 2017. The MC 38 is 38 x 21 foot that weighs 8,200 lbs with a displacement of 12,400 lbs. The 49 foot Selden aluminium mast that has a high-roach main of 568 square feet, a 227-square-foot self-tacking jib, screecher of 523 square foot and a 810 square foot spinnaker. The length to beam of the hulls when loaded for cruising is 11.5 to 1, when empty is 12 to 1. The underwing clearance is 2.5 foot. The nicely radiused chine and “shoulders” are designed to provide almost 6 feet at the maximum beam of each hull. The chine is over 12 inches above the DWL and will provide very little resistance or interference. It’s also provides additional buoyancy for loaded-up live aboard cruisers in large seas. With the 2 high aspect ratio 12 % NACA composite daggerboards allow higher pointing angles and less drag off the wind, the boat draws 6.5 foot. The underslung spade rudders draw 2.75 foot. It has two 10 HP outboard engines.

The aim of the design of Maine Cat 38 is a lightweight, high performance cat that is simple to sail and maintain. The open bridge deck offers better visibility, better looking and great air flow. Flared hulls provide interior volume. Headroom is between 6.25 to 6.9 foot with painted headliners. Berths for up to five, 2 queen berths aft in each hull that are 5 x 6.6 foot. Large single in port hull forward is 4.1 foot wide at the head by 6.6 foot long. All cushions below decks (total 3 pieces) are 125 mm thick medium-density foam.

The build is interesting. The MC 41 mentioned yesterday weighed 14,000 lbs, the MC 38 is only 3 foot shorter but weighs 8,200 lbs. That is because Dick Vermeulen developed the MC 38 structure a lot. EG All possible structural components have thermo-forming Core-Cell PH core which adds less resin than conventional PVC cores. Thermo-formed Core-Cell PH cores are heated to 165 degrees Fahrenheit in an infrared oven to seamlessly bend around curves and corners without kerfs, cuts or slices which soak up additional resin in a conventional build. Next the hulls are moulded in female moulds with vinylester which is resin infusion with triaxial and quadraxail E-glass knit fabrics. All interior bulkheads are resin infused Core-Cell foam cored painted finish. The hull to deck joints bonded with Plexus structural adhesive and thru-bolted hull to deck joint glassed on interior with 1708 biaxial tapes multiple layers and with a PVC rub rail with stainless steel insert cap exterior. The finished boat is 2 hulls and deck units, a bridge deck platform and cross beam bulkheads.

Vermeulen saw the structural approach at Maine builders Hodgdon Yachts (builders of the 100 foot Comanche monohull racer) and Lyman-Morse, then developed the build technique with Gurit Composites. The use of a thermo-formed Core-Cell PH core, along with the hull and deck layups being infused with 100 percent vinylester resin allows Vermeulen to reduce the weight of the excess resin found in a typical PVC core as well as allow a tighter, more accurate fit of the laminates as a whole. “It’s ridiculous,” Vermeulen said. “When we built the first 38 hull, with three bulkheads in it, but 38 feet long, 6 feet wide and 6 feet of depth, it weighed 426 pounds. I could lift the hull out of the cradles.” The result is a lightweight structure that allows the boat to offer improved performance but also allowed Vermeulen to specify a smaller, easier-to-handle rig and equipment.

A test sail of the Maine Cat 38 on Miami’s Biscayne Bay had a 9 to 14 knots breeze. With a true wind speed of 12 knots, they notched 7.8 knots under working sail alone with the true wind just aft of abeam. Moments later a 14-knot gust immediately popped us over 8. In the light chop, the boat’s motion was easy and predictable, thanks in no small part to the boat’s fine entry. Later as the wind dropped to around 9 knots, they hardened to a 35 degree apparent wind angle, where the boat moved along at around 5.5 knots. The boat went to windward “as well as a monohull”. Later, on a delivery off New Jersey, with the wind aft and blowing in the 20s, the boat maxed out at 16.4 knots and kept up a steady Speed Over Ground of 11-14 knots under jib and reefed main.

I now think you can understand why the MC 41 owner sold the cat and purchased a MC 38. He got the same to better performance in a cat that has a smaller rig, lower sail loads requiring smaller equipment and is easier to handle. EG The MC 38 winches are AST size 46 two speed self-tailing winches, the MC 41 winches are AST size 50 two speed self-tailing winches. EG 2 the MC 38 has a Rocna 45 lbs anchor with 80 foot of 8 mm chain versus the MC 41 needs a 50 lbs anchor and 100 foot of 8 mm chain. Doesn’t sound that much different but the weight difference is over 100 lbs.

The jpegs give the idea.

 

Today we will look at an interesting tri built by the France Play Boat shipyard in 1996 with the central hull designed by Eric Magre and floats designed by Philippe Rivière. The “Sirrus 26” is 26.3 x 18 foot (can be disassembled to 8 foot for transport). The tri’s weight is 3,300 lbs. The 40 foot fixed aluminium fractionally rigged mast has a 325 square foot mainsail, a 130 square foot jib, a 430 square foot genoa and a 755 square foot spinnaker. The main hull has a cedar epoxy pivoting centre board and a kick up spade rudder to allow a 1 foot draft if required. The main hull is 8 foot wide at the gunnel with a guestimate waterline length to beam on the main hull of 6 to 1. The floats are the same length as the main hull and have 300% buoyancy (approx. 10,000 lbs).

The accommodation in this tri is good with a double berth aft, single berth forward, loo area, dinette and small galley area. The main hull has full headroom at the galley. You could do short offshore cruises in this tri and is certified for up to 120 miles between ports and 60 miles offshore in Europe. In the USA or Australia, I am sure you could sail it further offshore but Europe likes to keep their citizens really safe.

The central hull, 8 foot wide, without a step, is built in western red cedar strip-planking which was assembled on a male mold and the WRC strips are glued one by one with epoxy. They are light, naturally rot-proof, very resistant to compression, and impregnated with epoxy. The inner and outer skins are fiberglass - epoxy. This method of construction provides excellent longitudinal and local rigidity, combined with resistance to puncturing. A foam crash box is in the bow. The bulkheads are plywood with timber surrounds. The floats are solid polyester fiberglass with 2 watertight plywood bulkheads at the float mounting points. The 2 epoxy wood cross arms, front and rear, are in one piece, are set in grooves on the deck with just one bolt on each edge, and their ends are nested in 45 degree wells crossing the floats. The rigidity of the cross arms is ensured by tie rods connecting each end of the arm to the central hull, via oversized chain plates. The boat can therefore be dismantled for transported on the road, but is not foldable afloat. The deck and the coach roof are in epoxy laminated plywood.

The performance is claimed “to be high and the handling at sea remarkable”. The performance would be good with the sail area and mast height. In smaller tris the main hull length to beam is not such an impediment as when the tri is powered up the main hull lifts up and if the hull shape is good the length to beam becomes EG 8 to 1. As long as you have a good float design (in this case it is good) you are basically sailing on the float. Fat main hulls don’t work as well on larger tris as they do not lift their main hulls as much.

A very nice design. The jpegs give the idea.

 

The Dragonfly 14 is designed and built by Lance McIntosh of South Africa. He was inspired by the Weta trimaran and wanted an improved version with a narrower main hull than the Weta. The length is 14 x about 11 foot. Weight unknown. The mast section and sails can be from a Sonnet dinghy (SA 14 mono dingy). The mast is 18.4 foot mast fractional rig with a mainsail of 89 square foot and a jib of 33 square foot. Also, there can be a screecher furled from the bowsprit. The original boat had a Sonnet rig then had upgraded new sails.

The construction is fiberglass/epoxy sandwich laminates inside and out with 4mm marine plywood bracing in the initial build. He opted to build full GRP molds for the tri after, enabling multiple construction, rather than a one-off boat. Full plugs were shaped using a combination of polyurethane foam and wood from which he has made gel-coat GRP molds. The amas’ are foam glass.

The aka beams and mast are anodized aluminum. Inboard ends of the ama tubes fit into fairly burly sockets in the hull. Use of aluminum tubing keeps the costs down, with but a slight weight penalty over all-carbon parts.

This boat uses a centre board for ease of use. Likewise, the rudder is a flip-up style unit that eliminates the problems of hitting underwater objects.

The performance of the tri has been described as very good. I can accept this but remember this is only a 14 foot boat. In SA there are areas that have 20 to 30 knot winds on a regular basis, which means this tri should be reasonably strong and capable of handling stronger winds.

The jpegs give the idea of the building of the molds and the boats concept and sailing.

 

On page 40 and 54 of this tread I spoke about John Westell trimarans. He designed the 30 foot Ocean Bird folding trimaran in the mid 60’s. The tri that proceeded Ocean Bird was Matamona, which I have been looking for details of for a while and found the information on a Russian web site. Matamona is 40 x 28 foot and can fold to 17 foot. The tri weighed 14,700 lbs. The 43 foot aluminium mast carried a mast head sloop sail area of 950 square foot. The main hull length to beam is 5.9 to 1, the float length to beam is 11 to 1. The floats are submersible with about 100% of displacement. The centre board draft is 5.9 foot when down.

On a test the tri performed OK. “In fresh wind and strong waves, the trimaran quickly loses speed. In a light winds of about 8 knots, the trimaran moves at about the same speed. This speed is also the average on long cruising trips. The tack angle in light wind is 100 degrees between tacks. The highest speed achieved was 13 knots with a wind speed of 20 knots at about 70 degrees off in a seaway. This tri was raced in an early Round Britain and Ireland race and had a cross beam failure off Scotland.

The main hull and floats of the trimaran are solid fiberglass (floats are foam filled). The cross arms are steel tubing with steel support brackets and pins. The main hull has a narrow waterline, but has a 11.2 foot wide hull at deck level for internal volume and also this reduces the length of the steel truss cross arms minimising bending loads. When the cross arms are in sailing position they are fastened with cables. A 40 foot NZ folding tri “Majando” was the same displacement and about the same beam had very similar steel tubes cross arms structures broke (read tear) a 9 mm steel support bracket. The folding concept works well on the 30 foot Ocean Bird tri.

The jpegs give the idea and sorry about the quality as they came from a 1966 uploaded article. The Russian web site also provided some other interesting designs over the next few days. They range from a “creative” education to some very sane designs.

 

I have a 40 years experience on Trimarans, ranging from 15' beach tris (strike 15), 23 ft tremolino, Strike 20, to 33' racing cruiser (Twiggy) and I have capsised only one time in 40 years. Aside the performance which favours beach cats the probematic of small size beach trimarans is capsize.
Having also owned (since 1972 !) Hobie 14, 16, Tornados, Prindle, A cats, F20, Paper Tiger, I have capsised fequently on Small cats. If well fitted (tight masts and hulls are mandatory !) , they are easily and quickly righted by their crew.
In the case of small tris in the 14 to 15 ft they are fitted with low volume floats which most of time preclude lateral capsize as the small volume outrigger is competely depressed and allows the sails to spill the wind before complete capsize. This property makes capsize less fequent than similar size cats and as they are more comfortable , attractive to elderly sailors. However the complete capsize may still occure in strong wind on pichpoling mode (in my case only one time in seven year use of my strike 15, with 30kts wind !).
In this case the capsize results in complete thurtle and the only solution is to flood² either outriger allowing the mast to stay at 90° to vertical and the crew to complete righting using a line accross the upper outrigger. Then it is mandatory to quickly swim to the stem and turn the boat to present the flooded outrigger to windward, unless the boat will flip again. This procedure is tiring, time consuming an need a good training.
My conclusion is a caveat : less frequent casize may give excessive confidence in small tris high wind capabilty to their owners (as myself !). In the case of capsize, they are much more difficult to recover than small cats especially when single crewed.
2 : Like Wetas, my Strike 15 is equipped with an inspection port in each outrigger transom, to allow flooding, which takes a non negligible time.

 

Today we start Russia week with a cat called “Myth” launched in 1984. The cat is 34 x 17.7 foot with 4 foot wide hulls. The cat weighs 4400 lbs and carries 2 Pyramid rigs on 2 masts. The masts are 37 foot steel water/gas pipes with a diameter of 130 mm and a wall thickness of 4.5 mm. The foremast is secured by two forestays and two shrouds, the mainmast - by two backstays and two shrouds. The masts are interconnected by a cable between them. All standing rigging, made of 8mm steel cable, is attached to the tops of the masts. Rotating "carousels" (spreaders for base of sails) for the pyramid rigs are mounted on each mast, which are metal structures, consisting of four pipes-spreaders with a diameter of 40 mm, four top ties from a steel 10-mm bar the length of each tie is adjustable. Wooden 12 foot booms with a diameter of 100 mm are attached to the sail foot and tangs welded to the ends of the spreaders which can rotate. The sails are isosceles triangles with the length of the front and back leech 32.3 foot each, the ail foot is 11.5 foot. Each sail is 190 square foot (4 sails = 760 square foot in total). A well designed Pyramid rig has very low sheet loads as it is a “balanced rig” with some sail area in front of the mast.

The hull draft is 2 foot with rudders on the sterns of the hulls. The hull shape of “Myth” is experimental at best. It takes simple asymmetry to the extreme. This is a high wetted surface design with minimal foils for lateral resistance. The length to beam ratio is about 16 to 1.

Watertight bulkheads divide each hull into three compartments. In the port hull there are three cabins with four berths, in the starboard hull there are two cabins with three berths, a storage room and a loo. Each cabin has a porthole and 6 foot headroom. The is also a temporary collapsible deck cabin if required.

Now we get to the structure. As with all Russian home build designs, they build with what is available and what they can afford. Most of the designs have reasonable structures but they may not be the best way to build a design. The “Myth” is built from ply and timber. The hulls ply is five-layer 6 mm plywood. Frames are made of 40 X 60 mm pine, stringers are 30 X 60 mm pine. Outside, the hulls are covered with epoxy resin fiberglass. Eight transverse pine cross beams with a cross section of 100 X 60 mm support the bridge deck which is made of 10 mm plywood was laid on the beams. At the bottom, steel strips with a cross section of 3 X 30 mm are fixed to beams crosswise. The masts are supported by pine beams with a cross section of 160 X 80 mm which have 20 mm steel rod dolphin strikers below.

The performance of Myth is considered good. In local racing it points about 45 to 50 degrees to the wind which is poorer than most of the local monohull sloop rigs. Once on a fine reach to running it performs better than most sloop rigs due to the ability to adjust the rig angle to the wind direction. The speeds in local racing in 20 knots of wind is about 12 knots. The cat tracks very well and can tack without problems. A British magazine tested 2 Prout Quest 31’s, one with a sloop rig, the other with a single pyramid rig and found similar up wind downwind results. Pyrmid rigs work well in light to moderate conditions but become more difficult in higher wind conditions due to difficulty in reefing and the “reefed” sails unbalancing the rig.

An interesting concept which shows Russian creativity. The jpegs give the idea.