Multihull Structure Thoughts

Helmut Mueller wanted a 10 meter proa but decided to build a half displacement prototype to test the ideas and do some test sailing in the Greek islands. Oh, how hard life is. Helmut said it will be designed by people who have an understanding of proa’s so he employed John Dalziel for the concept, lines and layout, construction design and methods were done by Helmut Mueller. The sail plan, spars and carbon fiber specifications was done by aeronautical engineer Janusz Ostrowski. This proa is laid out along the general lines of the Kiribati proas, with the famous “Kiribati dimple” in the lee side, and a 40 mm lateral camber to the keel.

The proa is 25.4 x 17,7 foot with a displacement of 1,435 lbs fully loaded. The design weight distribution has the main hull carrying 75% and the ama 25% of the weight. The carbon fibre mast length is 26 foot and the carbon fibre boom/yard lengths are 27.5 foot with a single sail of 269 square foot. The main hull length to beam is 18.5 to 1. The ama is 16.4 x 1.2 foot. The draft is 1.6 foot. Non-steering daggerboards and slots are built into the hull at either end; these will take the strain off the helmsman when sailing downwind, and will also allow the boat to be balanced when the Western-style rigs are tested.

Helmut plans to use Gary Dierking’s bungee- assisted shunting system, and will test shunting using a free yard, a continuous shunting line, and if necessary, a full-length track-and-car system on deck. Spilling lines are used for sail control. The steering, is the tried-and-true long sweep. The sweep can be used on either side of the stern, though it was intend at first to use Gary Dierking’s system on the windward side. There is a lot of extra reinforcement in the ends, to allow testing of quarter-rudders or leeboards.

The construction of the hulls is plywood, timber stringers and frames. The spars are carbon fibre.

No performance or handling information is known, could anyone help please.

The limited jpegs give the idea.

 

Please view the Video provided by NICK12345 above. The information is well researched and reflects what can happen even in a new build. When resin infusion is not well done on a production boat we all need to worry. Also if a frame fractures away from the inner hull surface on a couple of occasions there needs to be questions asked and answered. The further into the video the more concerned I became.

 

Sundreamer is the iconic performance cruising cat designed by New Zealand artist David Barker, and built by David and Fiona Kay in 3 years 7 days a week on a New Zealand farm and launched in 1983. David is an artist first, boat designer second and after building a 40 foot light bridge deck cat, Sundancer, he then designed a 62 foot cat, Stratosphere, for Gordon Miller which was built under David’s supervision. The basic principles of Stratosphere were replicated in Sundreamer but in a slightly smaller and lighter package. David is a lateral logical thinker and could not afford an “expensive” cat built by others and reused the mould (yes, 1 mold generated 14 parts to build the boat) used to build Stratosphere.

Sundreamer is 57 x 28 foot with a weight of 10,700 lbs. The 60 foot mast carries 1070 square foot of sail in its basic rig. The length to beam of the hulls is 18.5 to 1. The draft ranges from 1.3 foot to 5.6 foot over the daggerboards. The tiller steered rudders are kickup. The power was in one hull is a 9.9 HP outboard. This is a sailing machine, the engine is rarely used.

And to the question of performance 26 knots peak, 22 knots averages for an hour and 10 plus knot averages for 24 hours. Yes, it can really sail and has raced successfully under its 3 owner who tend to keep Sundreamer for 10 years plus.

The accommodation is effectively 2 separate hulls, each hull has 3 single berths with 2 additional berths in the forward crossbeam tubes. There is a minimalist galley and toilet facility. There's no plumbing, but a chemical holding tank toilet is used when cruising with more delicate friends. There are only seven electrical switches, for dual logs, VHF transmitter, navigation lights, cabin Iights (concealed neon tubes). None of the owners have upgraded the accommodation finding this minimalist approach a benefit as maintenance is significantly reduced.

Now we get to the fun part. This cats hulls and decks are solid glass averaging 3.2 mm thick. This cat has been sailing for 41 years. Yes, this lightweight structure works very well. The fiberglass was a 6 oz CSM, 3 x 15 oz unidirectional fabrics (effectively a triaxle fabric before triaxle was available) with 18 oz kevlar on the flat and high stress area average thickness is 3.2 mm with 230 x 51 mm klegcell top hat stringers under bulkheads. The bulkheads are foam cored with unidirectionals at 45 degrees on both faces. The cross beam tubes are 2 foot in diameter with foam, unidirectional fabrics and kevlar. There is strengthening under the mast step. The hulls are angled in at the top to reduce the length of the crossbeams. The weight of the 57 foot Sundreamer was 20% less than the 62 foot Stratosphere.

The genius of this build is the majority of the components came from a simple half circle mold. The majority of Sundreamer was lifted from that mold, as were the underbodies, the side decks, and the blisters on either flank. There are 14 different applications of the same shape in Sundreamer, the pieces were simply assembled at the end of the construction process through the magic of fiberglass and kevlar.

If you read the attached PDF you will get the majority of the story but there will be another item tomorrow which will give greater detail. The jpegs give the idea of a spectacular sailing catamaran.

 

The second part of Sundreamer description. David Barker design approach appears to be get the basic concept correct developed the structure as he builds. He has the entire design in his head but details such as chain plates, rudder concepts, crossbeam details are sketched in a building log as he goes. The ideas are then thought about more and adjusted as required. I have done a small cat like this and unless you have a very clear picture of what you want it can lead to a lot of rework. David appears to have a very clear overall picture and only refined components as he went.

David wrote a log book of C3 (his 3rd cat design, Sundreamer) that showed his development of Sundreamers structure and build as he went along. It is not fully detailed but gives an insite into some of the decision on shape and EG mast support structures.

David and Fiona built a very successful light, fast, relatively cheap boat in a short period. If you want a floating apartment Sundreamer will be of no interest. If you want to cross oceans in sea going comfort with the speed to avoid storms study Sundreamer. It ranks along side boats like Adagio as a significant step forward in design and building of multihulls.

The C3 log book is below over 2 items.

 

Sundreamer log book part 2

 

Kalapuna is a 26.3 foot Pacific proa done by Othmar Karschulin. The design is a larger version of his P 5 proa he did several years before. The simple proa took a year to build in a small open air garden, a reaal backyard boat.

Kalapuna is 26.3 x 12.5 foot with a weight of about 500 lbs and a displacement with 2 crew of 900 lbs. The ama is 16.4 x 1 foot. The 23.3 foot GRP mast and two 23.4 foot carbon fibre spars carry a crab claw sail of 215 square foot. The sail area was later cut down to 193 square foot to make it easier to handle. The length to beam of the mainhull is 15 to 1 at the water line. The rudders/daggerboards are in slots in the hull at either end. The draft is 200 mm. Motive power initially is an oar but was changed to an outboard.

This is an open cockpit boat with storage areas at each end.

The construction is mainly 6 mm plywood with timber frames on plywood and 20 x 35 mm timber stringers. The hulls are covered with 200 gsm cloth in epoxy and reinforced on keels with one layer of 300 gsm fiberglass. Beams are also made from good quality plywood covered with 3 layers of 650 gsm uni-directional glass. The profile of the beams is a hollow box girder with ribs for stiffening of a box with a cross-section 140 x 75 mm. The beams are mounted on the hulls with rubber mounts. The beams were later reinforced with a fiberglass cover.

The platform between the hulls is 7.4 x 5 foot 6 mm plywood panels on either side of 60 mm thick construction foam to form a stiff base. After trials the mast base was moved from a hull gunnel onto a part of this panel. It needed to be stiff.

The mast is made in a mould of 3 layers of 300 gr glass and covered with 3 layers of 650 gr UD glass. Weight is about 22 lbs. Spars are made of 2 layers of 300 gr glass and covered with 3-4 layers of 150 gr UD carbon. Weight of each is about 8 lbs.

Performance according to Othmar is: “First sail trials shows, that the boat is well balanced, and the rudders are working properly. Shunting the “big” sail was a little problematic, and there I think about a rail guided yard for next season. Also a small outboard motor will be added for returning to port if no wind (paddling is possible, but very laborious).” The proa can sail at 8 knots in a 15 knot wind, but improvements in the rig and handling of the rig should improve the speed.

An interesting proa. The jpegs give the idea.

 

Hi New Zealand guys. Is Gary Baigent still with us and interested in multihulls. The last post I have seen is in 2023. I would like to DM him as another person is interested in contacting him about his knowledge of NZ multihull history. Oldmulti.

 

This is a story of determination. A NZ guy is retiring in a few years and said he would like to retire to a place with a sea view. So he designed a cruising houseboat that was coastal capable. Once he had done a few drawings, studied some naval architecture texts and was going to follow Lloyds building rules and regulations. He decided to build his dream. Only problem was the build site limitation. His garage and backyard. The garage is 16 x 10 foot and The houseboat catamaran is intended to be 66 foot long. Simple I will just build the hulls in 4 sections and glue the sections together. OK.

The houseboat cat is intended to be 66 x 28 foot with a weight of 85,000 lbs and a displacement of 101,000 lbs. The hull length to beam is 10.3 to 1. The hull is a chine shape with a small propeller tunnel in the hull aft. The beam at the water line is 6 foot. The underwing clearance is 4 foot. JIGSAW is intended powered by 2 diesels of between 120 and 150 HP and propelled by two 24" dia x 19" pitch propellors running on 1 3/4 inch stainless shafts housed in semi tunnels in the hull , the tube runs in a solid wood keel and is approx 5' long , main part of the tube is just over 3/8 " thick rolled biaxial and quadaxial fiberglass with the endpiece for the cutlass bearing enlargened to 5/8 ". JIGSAW is a houseboat and never meant to break any speed records , cruising at 6-7 knots and max at 9 knots was all that was originally intended.

The accommodation is just open cabin spaces. The intention is to fit the cat out with commercial household furniture to save the time of building a lot of integrated furniture structures. Any item of furniture will relatively light and bolted down.

Now the fun, the build. Design the hull to be built in 4 parts, measure very carefully so that the 4 parts will join together then start to build your frames. Pure wood open frames are made from 150 x 38 mm solid timber with 12 mm plywood at the joints, these allow for the open storage area's in the hulls. Next are plywood timber sheet frames , basically formed from a single 12mm sheet of Plywood with a solid Timber reinforcing structure made from 25mm thick Kauri. Finally there are bulkhead frames, a solid timber 38 mm thick reinforcing structure with both sides are covered in 18mm plywood,. These are the primary structural entities in the vessel and link from one hull , across the accommodation levels and back down to the other hull . Jigsaw has five such frames across her beam.

Once the frames are built and set up stringers are installed and 2 layers of 12 mm ply act as the hull skin. This is covered by a layer of 12 oz ( 400gsm ) biaxial cloth and West Epoxy Resin. The glass is doubled over the bottom and over the chines. Each hull section was meant to take 3 to 4 months to build with all 6 sections meant to take 3 years. The start date was in 2013 and by 2019 the 8 hull sections were completed. Also completed were the rudder tubes 10 mm solid glass walls and the rudders 10 mm solid glass skins as well as the fiberglass propeller shaft tubes.

The story ends here as the guy had to work on his house to sell the property to fund the next part of the build. I do not know what happened after this but Covid hit and life may have become difficult. All I can say this is a very large project being driven by a man who has a dream. He has already gone further than most people and I wish him success. The jpegs give the idea.

 

@oldmulti re your post above, I am reminded (in a way) of the power cat in the photos below which has been under construction here for the past 20 years or thereabouts.
Although the New Zealand cat in your photos is by far an infinitely better design - the builder of the cat here has just been winging it the whole way, and I have reservations about how much buoyancy these hulls have - especially as he wants to do party cruises with the boat, when he finally launches her.
I think he wants to be able to carry at least 100 fare paying passengers.....

The first photo is an aerial view, taken a few years ago, that I found online.
The next photo (P3300659) is one that I took 14 years ago.
Then a photo showing some steel transverse beams that were added in 2012 to try to improve her transverse strength. Up until this stage he was only relying on the timber beams (and the superstructure) to hold the hulls together.
And a stern view photo, taken a year later.
The final two photos were taken in September last year - she was originally set up parallel to the coast, but she is now resting on a pair of trailers, and she has been rotated so that she is at right angles to the sea now.
She has been fitted with a pair of 6 cylinder diesel engines on shaft drives with fabricated S/S 'P' brackets.
It will be interesting to see where she floats when she is eventually launched.

 

I think I have done this before but I find this tri interesting. The Windrider 17 was a follow on from the Windrider 16. The Windrider 17 has more space and displacement to allow it to be more of a fun day sailor and camp cruiser.

The Windrider 17 is 17.5 x 11.9 foot (foldable to 8.5 foot or less) and weighs 400 lbs. The claim is you can have up to 6 people onboard which means an all up displacement of about 1100 lbs. The cat sail mainsail is 96 square foot. You can have as an option a roller furling jib for extra performance. The draft is 1.5 foot over a fixed keel. The outboard power can be a 2,5 HP outboard or an electric trolling motor.

When Jim Brown designed of this tri in about 2000 it was more about sensible cruising tri than racing machine. The tri has 2 cockpits and such luxuries as pedal (foot) steering to allow you to drink your coffee as you sail. There is several storage spots to keep your beer and food in if required.

The fixed fin keel allows a fixed underslung rudder which again simplifies things. The folding system appears to be initially a sliding beam system but some owners store the floats separate from the main hull. I do not know if this allows a narrower boat for trailing. The claimed time for set up from a trailer is 20 minutes but owners report it takes about an hour if single handed.

The construction is roto molding or the main hull and floats. If this is done well you end up with a tough boat although it is a little heavier. The sliding crossbeam structure is bolted down to the main hull with the cross arms permanently attached to the floats.

There are many of these tris around and one entered the Race to Alaska in 2016, it took 15 days to do the 710 mile course as it was a light wind year and there was a fair bit of paddling. The 2 guys that were sailing the boat said if they had enough wind they thought they could have done the race in 10 days.

A tough practical tri for fun day sailing and camp cruising. The jpegs tell the story.

 

The following is about a plywood cruising catamaran that is designed specifically for home builders. The Easy series of cats, designed by Peter Snell, start at the 32 foot and go to 42 foot. Several of each model have been built and many have cruised for a long time over many miles. This item will be about the Easy 37 (same plans can do an Easy 10.5).

The Easy 37 is 36.1 x 19 foot with a weight of 8,800 lbs. The cutter rig has a 42 foot mast and carries a sail area of 834 square foot. The draft is 2.5 foot over the low aspect ratio keels. The underwing clearance is 2 foot. The power is optional but most have EG 2 x 10 HP high thrust outboards.

The accommodation is 2 double berths forward followed by the main bridgedeck cabin containing seating, table and navigation area. The galley is down in a hull. Aft beside the cockpit is a large toilet shower and optional storage on the opposite side.

The reason for this item is a set of plans have come up for sale with an excellent 1 to 10 model of the Easy 37. The detail you learn from this model is good.

The construction is plywood, timber and covered with fibreglass cloth and epoxy resin. The majority of the shell is 9 mm plywood and the main bulkheads are 9 mm ply timber (about 25 mm) reinforcing and 9 mm plywood. Hull bulkheads are 9 mm ply with 19 mm timber edging, The underwing is 12 mm plywood with six 60 x 40 mm external timber stringers, The curved forward underwing has 2 layers of 6 mm ply.

Owners of the Easy 37 report a simple to handle boat with good qualities when built to plan. The cat performs very well in winds up to 12 knots and sails well in stronger winds. This is a case of how much money a person is prepared to spend on the rig and sails. It has reasonable upwind capability but daggerboards would help.

The jpegs give the idea.

 

Patrick Balta is a French designer who has designed sailing and power multihulls and monohulls from 20 to 80 foot. A lot of his designs are done in plywood and timber and covered in glass and epoxy..He designs practical boats capable of being built by professionals and amateurs.

The boat we will feature today is a smaller version of a 80 foot power trimaran for home builders. The TRI 11 – Fishing is 36.1 x 18.5 foot with a displacement of 7900 lbs. The power is a 130 HP Diesel with a shaft drive. The request is for a “fishing motor”.

The accommodation has 3 berths, one per hull with the main hull also containing a galley, toilet and some seating. There is also holds for fish you catch etc. This is a practical not a luxury solution.

The TRI 11 has a 1000 litre fuel tank indicating it has a 1200 mile range and can cruise at upto 12 knots with peak speeds of 20 knots.

The construction is plywood, timber and covered with fiberglass biaxial cloths and epoxy.

Patrick does very well in designing good boays for the task intended. The jpegs are limited.

 

CATP is a charter catamaran designed by Patrick Balta for charter work. It again is a simple to construct, but very practical, sailing cat for its task. This cat was constructed by “Mayday” boats (a rename of the build company would be good) in plywwod, timber, glass over and epoxy to do charter work.

The CATAP is 49.4 x 25,6 foot with a displacement (not known but my guess) is about 20,000 lbs if it has 20 charter guests and 3 crew. The maximum load is listed as 13,300 lbs. The rig is fractional with a mast about 65 foot high. The sail area is unknown. The length to beam of the hulls is about 15 to 1. The draft over the fixed low aspect ratio keels is 3 foot. The underwing clearance is 3 foot. The cat is powered by two 29 HP inboard diesels.

The basic layout has a toilet in each hull, 2 berths, and a kitchen area. There is some seating available. There is spacious storage for safety equipment, personal effects and lazarette. The designer says a “shelter could be built on the bridgedeck if required.

The construction is as economical as possible. The hulls have a sharp “V” chines and a flat bottom. It couldn't r be simpler. The shapes can be developed for easy construction in plywood but the sides are slightly curved, this presents no difficulty and gives a less brutal appearance to the cat. Plywood is the best weight/ease of construction ratio, and has many advantages in this shape configuration. Similar sized cats have 12 mm plywood for decks and hull sides and 15 or 18 mm ply for hull bottoms. The bottom's may also be 12 mm with several layers of glass over to act as strengthening and additional protection. As you can see from the jpegs there is extensive framing and stringers to support the shells plywood skins. The crossbeams are box beams.

The performance is not mentioned but judging by the thin hulls and light weight I expect peak speeds of 20 knots plus with averages of 10 knots plus if required. This basic design has a lot of potential for a high speed cruiser if you don’t want to much accommodation.

The jpegs give the idea.

 

The following is a near 2 hour video of the October 2023 North West Multihull Association meeting. This is an important video. The meeting featured the issues with a F27 (and several other tri’s) main structural bulkhead failure and frames pulling away from the inner skin (about 5 minutes in is the first pictures). Also there is discussion on several other structural defects. Most of these problems appeared in the Race to Alaska 2023 after 3 days of upwind work. They go into an analysis of what happened and compare the plans to a F 22 which starts out being structurally stronger especially around the main cross beam bulk head. Also there is a comparison to the F 32 main bulkheads.\

The next boat discussed at about 22 minutes is an F9R that has a cracked ring frame. This is followed by a Corsair 880 tri, Team Tres Equis Race To Alaska “significant issues” for a 3 week old tri. The Tres Equis issues required an update to all Corsair 880 tris main structural bulkheads paid for by Corsair. There is also several other tris with bulkheads pulling away and other issues such as rudders, cassette boxes etc. There is a lot to learn.

One of the conclusions was the well built home built Farrier boats were actually stronger than production boats as the home built plans were designed to allow for home builder errors and therefore had occasionally stronger fabric layups etc. Also home builders did correct coves at bulkhead to hull joints whereas some production builders took short cuts to save time and money.

I think the video stand for itself and gives many learnings about possible weaknesses of production and home built tris.

The address of the NWMA is https://www.youtube.com/@NWMA and the specific video is the October 2023 meeting at

 

The following cat is an extension to Patrick Balta's design of CATP. The CAT20 is designed as a practical solution to charter work, but if you were creative could be developed into a simple high speed cruiser. But please remember, a 65 foot cat is still a large project even if it professionally built.

The CAT20 is 65.6 x 28.6 foot with a displacement of 27,000 lbs to 34,000 lbs depending on purpose and fitout. The cat can carry 35 guests plus crew. The 65 foot mast carries about 440 square foot in the solent jib and 915 square foot in the mainsail. The hull length to beam ratio is 16 to 1. The draft over the daggerboards is about 8 foot and the rudders are kickup, the result is the draft when all foils are up is less than 3 foot. The underwing clearance is 4 foot. The power is 2 x 75 HP inboard diesels.

The accommodation is not specified, but the hulls are 4.1 foot wide at the waterline and 5.9 foot at the gunnel which will allow double berth cabins, face to face seating and 2 sided galley areas etc. Think of it this way, this cat will have more useful internal space than a 63 foot Wharram Gaia.

The construction is as economical as possible. The hulls have a sharp chines and a flat bottom. It couldn't r be simpler. The shapes can be developed for easy construction in plywood but the sides are slightly curved, this presents no difficulty and gives a less brutal appearance to the cat. Plywood is the best weight/ease of construction ratio, and has many advantages in this shape configuration. Similar sized cats have 12 mm plywood for hull sides and 15 or 18 mm ply for hull bottoms. The hull skins are supported by an extensive framed plywood and timber bulkheads and timber stringers. The exterior surface is covered by fiberglass and epoxy. The crossbeams are box beams.

No performance figures and the rig is very conservative to suit the function of a charter cat, The same rig could be used for a true long distance cruiser and you will probably reach 20 knots in good winds and average 10 knots plus under reasonable conditions. The cat may need more sail area in light winds but thin hulls will help speed across the wind range.

Sorry about the limited jpegs but this is an initial design offering of a very good simple cat for charter or other purposes like a fast simple cruiser..