Multihull Structure Thoughts

Discussion in 'Multihulls' started by oldmulti, May 27, 2019.

  1. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    You want a F22 tri but the realities of a spouse who wants an upgraded bathroom etc mean you do not to have the time or money to get your dream, so what does a person do? He did not need accommodation and was set on a day boat to race. Maybe he could build a small tri that will be fast and fun. OK, let’s see what is possible. Are there is a cheap Hobie 20 cat that could provide the rig and hulls for the floats. All we need is to build the main hull and crossbeams. Good idea, let’s get started, it will be finished in a few months. The tri was finished 7 months later which is very good.

    The tri is named “Mama Cocha” (translates to God of the Sea) and is 20.3 x 15 foot and a weight of approximately 420 lbs for the Hobie plus about 350 lbs for the main hull and beams for a total of 770 lbs. A Hobie 20 rig has a 30 foot rotating aluminum mast with a 195 square foot mainsail, a 55 square foot jib, a second jib of 77 square foot and a 226 square foot asymmetric spinnaker. The daggerboards and rudders are the standard Hobie 20 foils.

    The main hull was designed by a European guy and is a flat bottom plywood structure that has strong points for the folding system, a large open cockpit and a small stowage area forward for safety gear, lunch etc forward. The main hull is constructed of 6mm ply/epoxy composite with 7 ply bulkheads and timber stringer, gunnels and chines. The hull is covered with 200 gsm e-glass cloth in epoxy with an additional tape layer at chine and gunnel joints. The bench seats are foam glass to minimize weight.

    The crossbeam structure uses a variation of the Farrier type system. The beams are 100 x 3 mm aluminum tubes with an aluminum doubler bar screwed to the beam from the lower control arm connection point to the float. The lower control is a “ladder” welded item with strong connection points on the main hull and crossbeam. A second flat bar upper control arm is attached to the main hull and crossbeam. This approach has the same functionality of the Farrier system but much easier to make. It is basically all aluminum and stainless steel bolts. Please study the jpegs for more detail. This is good and only cost $900 (2013) to do the welding etc of the crossarm parts.

    So how did the tri work out? It performs well across the wind range and on all directions. Some quotes “In 15 knot winds, the tri was not under pressure during the gusts, there was plenty more capacity in the floats, they seemed to get down to their rocker line and that was about it. The main hull sailed flat up to about 7 to 8 knots.” And “In the gusts going to windward we managed 9 knots and we managed that a few times. The boat felt great at all speeds to windward and at 9 knots it did not seemed pushed but I don’t think it would have gone much faster had we tried in that breeze. Happy to do those speeds hard on the wind with a good angle of about 45deg. The sail home was different, breeze gusting to 15knts and on a beam reach and varying around this angle of sailing. We hit 13 knots a few times and 14 knots once.”

    The builder learnt a few lessons from the build which he passed on.

    Measure twice and cut once. This saved me more than once. Read everything twice especially if you have never built a boat before, like me.

    After you put the building frame down, mark it or better still fix it down to the slab or ground, you “will” knock it out of alignment.

    If you make a mistake and end up with 2 lines marked on a piece of ply, cross the wrong one out because the next day you won’t remember which is the correct line.

    Soaking out the epoxy externally. I read the best way to do this was to use a foam roller and do it wet on wet. Well it left a lot of sanding, at least 8 hours with a good orbital sander so I tested a bit by using the foam roller but using a painters technique of brushing it out while still wet. That made a huge difference.

    In hindsight I would look into using foam sandwich panels instead of ply. It might save a lot of work doing the framing. Maybe use a system the same as Team Scarab use.

    Painting and fairing: It is true that a paint job is 90% prep and 10% application of paint. I spent a lot of time doing the prep and still could have spent another 4 full days. Even then I don’t think it would be perfect. Your choice do extensive preparation, otherwise be happy and go sailing quicker, like me.

    This is a nice fun boat that wins the occasional local race beating 26 foot trailer sailor’s and comes close to a local F 22 performance in some races. A good build. The jpegs give the idea.
     

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  2. SolGato
    Joined: May 2019
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    SolGato Senior Member

    I wonder how the builder of the above Tri decided on the geometry and angle of the floats as they appear to have a more significant bow up attitude compared to most designs.

    From the performance report it seems to all work well, but something about the bow up float angle of the floats and bow down angle of the main hull has me wondering if it would perform even better or perhaps worse if the geometry was more parallel.

    I remember @revintage had asked about this when he was trying to determine how to best setup his Tri.

    From my experience with my Hobie Getaway hulls under electric propulsion, I have found that the boat moves more efficiently through the water when the hulls are trimmed down and able to slice through the water with some of the bow edge instead of the water hitting up under and against the belly of the hulls. Different scenario being motor powered, but it’s easy to notice the increase in speed and smoother handling with less power consumption thanks to the BMV and shunt reporting in real time and the affects of trimming the bow up and down.

    Based on the photos of the Tri above under sail power it appears that the main hull may be doing that job and that the outer floats remain pretty high. The builder also mentions heeling angle at speed and that the floats seem to have a good amount of reserve buoyancy which might be a factor of the geometry.

    I’m not knocking the build, just curious about the design geometry.

    When I used to sail my Farrier Tramp single hand with lots of gear up front, it had a very bow down attitude that made the boat track really well while reducing hobby horsing allowing me to better point windward provided of course there wasn’t any swell big enough to roll up over the bow and turn the cockpit into a foot bath!

    And while on the topic of float size and reserve buoyancy, I guess these guys never got the message that big floats and Burmuda rigs are all the rage these days :D

    Sure looks like fun!




     
  3. revintage
    Joined: Nov 2016
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    revintage Senior Member

    Thanks oldmulti for the in depth info about Mama Cocha. Have read about it before, found it interesting, but have not seen as many images. I didn´t react to the bow up configuration until SolGato mentioned it and referred to my build. It is not much needed to get a decent bow down. I ended up with 1.6 degree, which is what you get when lifting the rear beam 6cm wrt the main beam when they are 220cm apart. In this case the front beam is lifted 5 cm and the rear 11cm above deck. Took this image today and will begin with the shallow cockpit tomorrow.
    down.jpeg
     
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  4. oldmulti
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    oldmulti Senior Member

    Revintage. The other jpegs I did not post of Mama Cocha.
     

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  5. revintage
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    revintage Senior Member

  6. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    The Seaquest 46 hybrid catamaran is a new design by Shaun Carkeek and is built by Mike Eaton in Dubai where his shipyard has been based for 20 years. The Seaquest is a high performance sailing cruising catamaran with hybrid power. The Seaquest is 46 x 24.6 foot with weight of 18,400 lbs. The 60 foot fixed aluminium or carbon mast carries a 770 square foot mainsail, a self tacking jib, a 645 square foot headsail and a 1,720 square foot spinnaker. Spectra soft standing rigging and soft shackles are used throughout. The length to beam on the hulls is about 10 to 1. The draft varies from 4 foot to 8.3 foot over the curved daggerboards which help lift the bows at speed. The underwing clearance is 2.4 foot. The engine power is 2 Oceanvolt 15.1 kW (2×20 HP) electric motors with a support diesel generator and 3KW solar panel capacity on the coach roof. Standard battery capacity provides a range of 80 nm on a single charge.

    Accommodation includes three or four cabins with queen size berths, although due to the slim hulls here’s not enough floor space to do walk-around beds. The bridgedeck accommodation is spacious with a large galley, navigation and entertainment area and seating. There is a large door to a cockpit which can add to the saloon area. The helming position is on a raised bench in the main cockpit with a hatch to get a helming view. The powerful sail plan is set up to be handled, with electric winches, mainsheet, traveler and furlers (including Code 0) all available. From what I have seen so far there needs to be some clarification of the helming sail handling position.

    The build of the Seaquest is basically foam glass with carbon fibre reinforcement. Hulls are constructed with vacuum infused E-glass with a high-density foam core and extra multidirectional E-glass below the waterline. Carbon fibre frames running across the bridge deck supporting foam cored bulkheads linking both hulls. Externally visible frames and structure finished in gel coat. The mast is also stepped on the roof to minimise noise of halyards etc getting into the saloon. The cabin roof structure is reinforced to take the mast loads. The decks are vacuum infused E-glass with high-density foam core on all flat sections. Extra E-glass for all high loaded areas.

    No performance numbers beyond the designers estimates which said 200 mile days in reasonable conditions with quote “When fully powered up and actively sailed in performance mode, about 360 miles in a day should be easily achieved.” Translation peaks of over 20 knots and averages of up to 15 knots. Realism says when short handed cruising 8 to 10 knot averages are more likely in good conditions.

    The jpegs are a few concept images and of the build process. Good cruising concept of which several have been sold prior to launch of the first cat.
     

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  7. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    A short one about 1 persons experiment of how to get a cheap tri that will get a sail on it in the future. It started with a 12 foot canoe that was a little unstable for even paddling. He lives in an area that has alligators and was a little nervous about getting to close to the local wild life. So he decide to stabilise the canoe to provide some peace of mind. He read about the Sahili Ngalawa canoes and thought how he could do a similar thing. The canoe is 12 foot with 9.5 foot long outriggers. The weight is unknown. The rig is yet to be developed.

    The following approach will work with up to 15 foot canoes. The floats in this case are a 9.5 foot epoxy/EPS windsurfer board cut lengthwise down the centre stringer line. This creates a “thick” float with the centre stringer for crossbeam attachment and the edge of the board providing a good shape for travelling through water. The next requirement was that the tri had to be trailable. That required a variable beam. The ngalawa style tris have a simple multiple part wooden cross beams with ropes lashing the parts together.

    The designer builder decided to update the materials to aluminium tapes etc. Result, a combination of parts that allowed a variable beam depending on circumstances. At time the floats can be folded in for trailing, other times fully out for stabilisation or partially folded in to provide more buoyancy to carry a slightly heavier load. The floats shape also provides the opportunity to provide “planning” lift at speed if a rig or outboard motor is fitted.

    I suspect the jpegs will provide more information than words from here. The first jpeg is of a Sahili Ngalawa canoe, the rest are of the build. One jpeg has a red box on it, you will find a friendly local reviewing lunch options.
     

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  8. oldmulti
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    oldmulti Senior Member

    When you’re sailing you want to have confidence that your boat is up to the task. Most home builders trust the designer to specify the correct materials and the designers hopes that the builder is capable of using those materials correctly to build the design. As a result the designer often puts in very large safety factors to protect the designer from claims of a faulty design when the builder uses the wrong materials, incorrect material handling or building procedures or changes the design without getting the designers approval.

    So, what do good professional manufactures do? The get the best designers they can, get engineers to verify calculations, get quality assurance certificates from material manufacturers and train their build teams in manufacturing processes. But then some do a final step. Destruction testing of a manufactured part to see if all the design, materials and most importantly, product build processes, have worked.

    Below are jpegs of destruction testing of the Corsair 880 crossarm. Be very glad this testing is done because you and I are safer because of this sort of testing. The Corsair 880 displaces about 3,600 lbs and when loaded displaces about 4,500 lbs. The test rig was set up and with a load cell at the very end of the crossarm the crossarm was loaded up to over 6700 lbs before the crossarm failed. That means the entire tri could land on the bow of a float with just the forward cross arm attached and the crossarm would not break. That means with 2 cross arms the Corsair 880 has a “real safety factor” of over 3 times (sorry for the loose language). And please notice the top and bottom parts of the crossarm are breaking apart, there was no failure of the top and bottom carbon flanges.

    Also Corsair try to continuously improve the product and production techniques. The deck mould you see in a jpeg originally was designed to be an e-glass foam structure, then with the introduction of resin infusion and up to 20% of carbon fibre into the structure there is a 7% weight reduction with a stronger, stiffer final product being achieved. Using these materials in production resulted in a more consistent weight and structural results for a given part.

    If you can afford it and you are unsure about a part or the build of a part, be prepared to load test the part. You don’t need to load test it to destruction but load test it to a realistic load number. I have seen on 1 occasion a very surprised builder when he got a heavy friend stand on a crossbeam he had just built out of timber for a cat, it cracked, there appeared to be a faulty glue line. Testing is good.

    The jpegs give an idea of the story.
     

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  9. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Many thanks to the moderator for upgrading the thread index on the first page of this thread. The index now covers entries from page 1 to page 212. The first part of the index is for general interest items (those with a 1 in front) after that the index first number is the length of a boat. Hope this helps.
     
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  10. Boat Design Net Moderator
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    Boat Design Net Moderator Moderator

    Thanks for your very interesting posts!
     
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  11. revintage
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    revintage Senior Member

    Great index, will be useful. This is a multihull bible!
     
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  12. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Kurt Hughes designs boats that people ask him to and others based on a long experience of what works in the real world. He also does something that some other designers don not, he really engineers a design. If he doesn’t know he contacts his network to solve a problem before the design is built. The only problem Kurt has many home builders and some professionals that do not build a boat as designed. Enough, back to today’s design.

    This is a high performance open bridgedeck cruiser catamaran. The cat is 49 x 30.7 foot with a weight of 11,280 lbs and a displacement of 17,650 lbs. The 70 foot (carbon fibre) mast carries a 922 square foot mainsail, a 311 square foot self tacking jib, a 619 square foot genoa and a 988 square foot screecher. In a world of 50,000 lbs 50 foot cats, these numbers alone should tell you this is a performance vessel. The length to beam is about 11 to 1. The draft ranges from 1.7 foot to 9 foot over the daggerboards. The rudders are kickup on the sterns. The engines are outboards on a kickup frame on the stern that completely lift the outboards out of the water and move the weight forward into a semi protected environment. It is a good idea. An interesting feature is the cat “parts” are designed to be demountable for transport and remote assembly.

    The first version is an open day-deck, with 3 staterooms for 6 people below. There are 2 toilets and a navigation area. There is also a galley and seating area. The cockpit area is vast. There is also a second version which has a bridgedeck cabin that will increase the internal space but this cat does not have the payload capacity to fill every corner with all mod cons. If you need vast luxury accommodation with air conditioning etc look at other Hughes more cruising orientated designs.

    This composite cruising catamaran is designed to be light and easily driven. The hulls are foam, e-glass and the crossbeams and strong points are carbon fiber. Kurt uses EG Dyeema rigging, carbon fiber chainplates, foam glass boards etc. Building a light weight cat requires all aspects to be built light, not just the hull layup.

    No performance numbers but my simple calculator says peaks of over 20 knots, 350 mile days in ideal conditions and up to 15 knot averages. Real world experience says to me you could have a reefed main and the self tacking jib up and, in this cat, could still run rings around a Lagoon in 10 to 15 knot winds. I regard this as real cruising, being reefed down and still going fast without having to care about altering rig until 25 knot plus winds arrive.

    The jpegs give the idea.
     

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  13. oldmulti
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    oldmulti Senior Member

    A wave-powered hybrid trimaran was completed in Aklan, Philippines. The Department of Science and Technology (DOST) Secretary said it is “environment-friendly, safe and unsinkable.” Sorry, I do not know any dimension of this vessel beyond it is large and the ship's structure is made of steel. The fast hybrid trimaran can carry 100 passengers, 4 vans and up to 15 motorcycles and was built by Metallica Shipyard, Aklan State University with the Maritime Industry Authority. “This is a hybrid so when it operates it will use wave energy, which will reduce the requirement for fuel.” The ship’s “independent multi-engine technology (diesel and electric power) has a 3000 hp drive shaft engine combined with a wave energy device that’s capable of generating up to 300kw/h of energy. “Our analyses revealed that a trimarans improved hydrodynamics over a monohull and can ensure fuel savings of as much as 40 per cent. We therefore expect the propulsion arrangement to enable the ferry to comply with EU Stage V regulations.”

    Waves are energy-dense with power densities of 40 to 70 KW per metre. If you can convert even part of that energy into useable power it will add considerable to the tris fuel economy. But converting the high-force, low-speed motion of waves in an efficient way can be a challenge. “There may be many sources of loss along the way, from friction in the hydraulic systems to heat in the electrical generator.” The engineering challenge that remains is to minimise these losses. Another hurdle would be designing a wave energy converter small enough for the ship’s dimensions. “Wave energy converters generally develop more power the larger they are, but on a boat there are size and weight limitations.” Engineer Jonathan Salvador, owner of Metallica Shipyard, this would be the first hybrid trimaran that is partly powered by ocean waves. “We’ll be the first to use wave energy for a trimaran,” he said. “What we are doing now is a prototype.”

    The hybrid trimaran, is environment-friendly. Its use of wave energy double action hydraulic pumps, which will be integrated in the outriggers of the hybrid craft generate the electricity. “The mechanical movements in the pumps will be converted to electrical energy that can be used to provide additional power to the vessel,” a DOST release said. “The more waves that the vessel encounters, more power will be produced. This technology is expected to improve the vessel’s energy efficiency, making it not only cost-efficient, but also environment-friendly.” And because the vessel is fast-sailing, it can transport passengers in half the time a normal monohull ferries takes.

    The DOST is hoping that the hybrid trimaran will be able to change the roll-on roll-off (RORO) shipping industry. Ocean waves are among the cleanest renewable sources of energy. It is utilized by devices or machinery that captures the natural movement of the ocean to generate power.

    The jpegs give some of the idea. Notice the floats are only attached at a couple of points which allows them to move independently from the main hull. Result the float movement supplies “power” to hydraulic cylinders that drive electric generators that assist in powering the trimaran. Solar panels are not the only way to generate electric power for a boat. The ultimate aim is to run the ship on wave generated electricity in a seaway and only run the main engine in port and in light wind no wave conditions. Hope it works.
     

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  14. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Sometimes my sanity is challenged, I ran across these 2 power boats and said why? The first is how not to go fishing, why 9 x 25 HP outboards to do the job of 1 x 225 HP outboard. The second is a drug smuggling boat that was designed for pure speed with 8 x 250 HP, above 60 knots and it carried 16,000 liters of fuel (plus a ton of drugs) for its one unsuccessful run to the USA.
     

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  15. Robert Biegler
    Joined: Jun 2017
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    Location: Trondheim

    Robert Biegler Senior Member

    It has two strakes, a short one at about the waterline and a long one nearly at the bottom. Does anyone know what they are for?
     
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