Multihull Structure Thoughts

I made this very simple hinge for one of my tacking outrigger designs.

 

I would be inclined to explore building a hinge in composite based around a 100mm tube hinge maybe.

 

We have discussed the Tremolino trimaran before, but I found a really good build recently which shows the versatility of the design. There were basically 3 versions. A plywood one with hobie floats and aluminum cross beams, a fiberglass production version and a refined home build version with a longer waterline, increased rig, strip plank cedar ply build and larger floats. The version we will look at is the refined home build version.

The Tremolino is 23.5 x 18 foot with a weight between 1000 lbs to 1230 lbs depending on the materials and floats used in the build. The mast height depends on where it came from. Some people use 27.5 foot plus Hobie rigs others build wing masts as high as 32 foot. The sail area depends on the masts but is between 270 and 300 square foot. Draft is 4.5 foot when the daggerboard is down. The length to beam on the main hull is about 11 to 1 depending on the version.

The accommodation is limited being more of a camp cruiser. Narrow single berths and some storage space. The Tremolino can be disassembled for transport.

The build of “Blue Moon” was done by a first time builder who did an excellent job. The hulls are 9.5 mm western red cedar with 330 gsm glass cloth either side in epoxy. The float hulls were built on female mould stations 305 mm apart. The builders averaged six to ten strips per evening. After building the first set of ama halves, they reversed the molds to build the opposing, complementary ones. In contrast to the floats, the mainhull was built on a male mold setup. While the strips went on more easily than they did on the female molds of the floats, fairing was much harder. The cabin sides, foredeck, cockpit floor, and bulkheads are of okoume plywood. BLUE MOON’s cabintops are strip- built. The crossbeams were laid out on a strongback, which established bends in each one according to dimensions shown on the plans. This bending took the Douglas-fir almost to the breaking point—but Newick’s procedure worked well.

The performance is good, to very good. One owner reported “Quickest speed we have achieved is 16 kts on the boat that was in far from ideal conditions, loves to sit on 13-14 kts all day in fairly light wind, when the wind gets up and the waves build up it really knocks it round speed wise. We raced last weekend and had a fairly tight screecher run, about 12-13 kts of wind and the centre hull was gust kissing the water, leeward hull was nowhere near submerging.”

This is a classic fun tri that is still competitive if kept light. The jpegs is a combination of the original design and the refined version. The plans still appear to be available for $350 US.

 

A demountable system can be pretty simple if the tri is small enough. This is my 15' tri (Broomstick), with its welded crossbeam/cockpit assembly used as a base to support the hulls. I admit it was a bit of a hassle to assemble on the beach though, usually taking an hour or more to get ready.

 

The Mk 4 version (you have shown the study print for) was an updated all ply version with larger floats and rig options including a wing mast. I sailed on one of these with an 18 foot skiff rig on it. Very fast, very wet. very fun. There was a production folding version - the T Gull 23 that included bigger rig and 'New Moon' floats.



The ultimate version was the glass production T-gull 2300 very similar to the strip plank version but with hinged beams. IIRC these were developed by Dick Newick and John Olin but John passed away before many (any?) were built. There was an attempt (by a third party, not DN) to re-establish production, in the 200os, but the company failed. Shame. I wonder what happened to the molds? I recall reading somewhere that Newick was going to design a swing wing version for home builders, but this does not seem to have eventuated.

 

Sorry if I have done this tri before, I am trying to update the first page indexes to reflect the current 130 pages. The tri we are talking about is a very good home design and build day sailor. The trimaran is 19 x 19 foot with a weight of 670 lbs. The 26.25 foot rotating carbon wing mast carries 225 square foot of sail from a DM20. The mast is 180 x 74 mm with 2 mm solid carbon walls and a PVC carbon fibre on either side lateral web internally. After initial sailing the builder was thinking of adding 5 foot to the mast to increase the sail area to 300 square foot. The floats are Hobie Miracle 20 foot that have been lightened, made slightly higher and widen to have about 1800 lbs of buoyancy. The floats have the daggerboards and rudders.

The owner reports he got 10 to 15 knots of speed in initial trials and the tri was easy to control requiring little physical effort. The numbers of the 225 square foot rig indicate very good performance. A rig upgrade would increase the performance significantly.

The main hull build is 4 mm tortured ply with 300 gsm biaxal glass on either side in epoxy. There are some bulkheads and unidirectional carbon fibre as required for reinforcement. The cross beams are 80 mm diameter carbon fibre tube with 4 mm walls. There is additional unidirectional carbon fibre reinforcement on the top and bottom of the forward crossbeams. All carbon work was vacuumed bagged. The folding system is a single arm. With a tri this light it is practicable to be able to “person handle” the folding process.

The tri took about 2 years to do from design to on the water. This is a very well done project. The jpegs give the idea.

 

Oow look. Someone else who likes bridle mainsheets...

 

Thanks again for all of the input on trimaran folding systems. I modeled the folding system I was talking about until I was blue in the face and it just doesn't seem like it will work on a boat the size I'm thinking about (around 30 feet). I think I'm not the only one that never realized the importance of the secondary link in the Farrier system. The loads on the struts when folding would be enormous without the secondary link if the outrigger hull went out of plane. I'm doing a deep dive into swing wing geometry now.

 

Russell; is the purpose of fold up for trailering or marina berthing or ?
You mentioned being a cruiser and going for some volume so just curious what the list of requirements are for this boat.
Is demountable a better goal.
Might be time for it’s own thread.

 

One of the drawbacks to the swing wing design is many of the older boats that adopted this folding design do not meet legal towing width requirements necessitating disassembly and removal of the outer hulls. So the big benefit is fitting into smaller slips and navigating narrow inlets and channels when on water, and launching at narrow ramps. Another is that the bottom side of the hulls remain in the water, unlike the Farrier design which is disliked by people who slip their boats.

Does anyone know if the swing wing design allows for unfolding on trailer, or does the water need to support some of the load until locked?

One of the things I appreciate about the Farrier design is I am able to unfold the boat for maintenance and detailing on trailer.

There was someone I came across a while back that had designed a telescoping system using square tubing with rollers for smooth actuation, but I don’t remember where.

 

I live in a place with almost no natural harbors that is being taken over by millionaire refugees from California, so the only way I can afford a boat is if it's trailerable. The launch ramp in summer is over run with diesel monster trucks driven by entitled white men who have massive equipment to catch a tiny fish, so I like to limit my time at the ramp.
What I have been drawing is something like a pumped-up Adagio, but 30 feet.
Did you see the recent article about Adagio? Gougeon’s Everlasting Experiment https://www.sailingworld.com/story/sailboats/gougeons-everlasting-experiment/?fbclid=IwAR1QCVwz8Y7C8VnYr0JKEjcrdjoiFAJE2lufenjHT7G3h_oZLC-lAhnJFLM

 

If you look at the Horstman MT 26 the amas fold under the flare of the main hull . The MT 26 has a 16'6" beam , so I take it a 29' would need 18' to 19' . So why hot have an 18-19 ' alum . beam slide through an amas pocket , through the main hull , into the other amas pocket . Each amas could be slid to the main hull under the flare for transport and pined to the main hull , the 18-79 beam slid out of the hulls for transport . This might not work well in a marina , but it could be transported and I would think as long as the beam pockets are lined up , the alum. beam could be removed and installed without much problem .

 

Swing wings trimarans come in many formats from agricultural to elegant but they all depend on the same basic structure. A near vertical pin attached to the main hull a cross beam structure and a vertical pin attached to the float. The first jpeg of the Oceanbird 30 tri was a production boat in 1970, it displaced 10,000 lbs. It worked very well but was not elegant. The cross beam structure are galvanised mild steel. The cross arm top and bottom tubes are 60 mm diameter. The bearings for the X arm pins are conical to ensure a tight fit to minimise movement due to wave action. A later 26 x 21 foot Westall tri weighed 3100 lbs had a 600 mm long 75 mm stainless steel tube (300 mm exposed) vertically in the floats. The inner pins were 35 mm stainless steel bolt pins attached to the top and bottom main hull brackets which were at 380 mm centre lines apart.

Next was the Trikini series of trimarans. This guy built tris, in the 70’s and 80’s, from 18 to 35 foot with a lot with swing wings. The 30 foot Trikini PB was 30 x 20 foot weighing 4500 lbs and had upper and lower 125 x 75 mm aluminium tubes with water stays for additional support. The main hull had a 300 mm welded C section bracket for the top and bottom tubes. The C brackets are from 125 x 25 mm aluminium. A 25 mm stainless steel pivot bolt attaches the cross arm tubes. The float pivot bolt was 35 mm with similar C brackets on the inside of the float hull.

The Contour 30 weighs about 4000 lbs and has 25 mm stainless steel pins welded to stainless steel plates held in by 8 layers of unidirectional glass against a bulkhead. Water stays are 9 mm 1 x 19 mm stainless steel wire. Original cross arms were aluminium boxes but were later changed to carbon fibre tubes.

The Dragonfly is the most elegant. The Dragonfly 28 x 21 folds to 8.2 foot wide and weighs 4800 lbs. The inner pivot is a 225 x 15 mm stainless steel pin which pivots on 8 x 50 x 500 mm stainless steel chain plates bolted on the top and bottom of the glass carbon fibre cross beams.

The Kurt Hughes 31 foot swing wing weighs 2600 lbs and has a variation. The beams on the floats rotate around large diameter plastic rudder bushings for tugboats. That reduces the point loads. The connective beams are carbon fibre. Seastays are not needed so the ride is clean. The amas slide forward in the "in" position so the length overall when towing is not significantly increased.

Jim Artrim’s Erin 30 foot tri is attractive. His quote about swing wings is: “We spent countless hours analyzing different folding systems. In hindsight, the path seems simple. Vertical hinging methods, while I admire their ease of operation and clever structural geometry. Once horizontal hinging was settled on, the question was forward or aft? I liked forward folding immediately since it seemed better suited to resisting sailing loads. In the end, forward was the only way to nestle the hulls to a reasonable folded width – the relatively broad ama bows fitting in nicely beside the main hull bow; and alongside the bowsprit.”

The Magazzu tri has a “folding” swing wing which keeps the floats in the same relative position out or folded. Do not know details. Finally, the 23 foot home build folder is the simple timber version. It is similar to the Seaclipper 16, 20, 24 and DC 3 tris.

The jpegs give some idea. The above is a guide. Do not underestimate the point load forces on pins and especially the supporting brackets.

 

Part 2 swing wing tri jpegs

 

Thanks for the deep dive into the swing wing. I got far enough on the drawings to see that it can work for my application. It would take some compromise and paid engineering, but it could work. Why am I not excited about it? It looks a bit agricultural with the straight beams and what goes on at both ends of the beams and it adds 3 or 4 feet to the length of the boat when it's on a trailer. Still attracted to the Radikal system where the struts are just for folding. Found out yesterday that John Marples linked the struts on his Marples 26 with a tube (running fore & aft) to keep the struts from moving independently from each other. This would avoid the dreaded bow up or down issue when folding. It would still need the mast up for folding on the trailer.