Multihull Structure Thoughts

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

  1. oldmulti
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    oldmulti Senior Member

    Neil. The 25 x 18 foot tri Free Spirit may have been inspired by the Crowther 24 but it appears to be a home design. The hulls appear to be round bilge, it has a kickup centreboard and the EG float to cross beam connections are different etc. The majority of the vessel appears to be foam glass. The cross beams being aluminium and 38 plus years old would need to looked at very closely. Fatigue from constantly working is real problem in older boats and this guy has sailed many miles. The rig would also need a real inspection with some wires and some sails may need replacing. For $10,000 it could be a good deal, but understand how to inspect foam glass for soundness and potential water intrusion. It appears to sail well for a weight of 2400 lbs and a displacement of 3000 lbs.

    On to today’s short one. The Multi 50 was a design proposal for a 50 foot racing trimaran by OwenClarkeDesign. The sponsorship funding fell though and the tri was not built. The only 2 jpegs available is the concept of the trimaran and a structural diagram that may be of interest.

    The main hull structure has a variety of glass inside and outside a 25 mm foam core. The basic glass inside and outside is Gruit SE84 xe603 which is a 603 gsm prepreg biaxial e-glass with a 49% resin ratio that can be cured between 80 to 120 centigrade. There is additional reinforcement inside and outside especially forward and between the cross beams. There are also additional tapes at the main hull gunnels and keel lines. Most of the latest 50 foot racing tri’s are built using resin infused or prepeg carbon fibre structures which can be made slightly lighter.

    Please study the jpeg diagram and expand its size to look at the detail, there is a lot of information in it. Included is the Gruit product catalogue that gives details of some of the fiberglass fabrics used in the structure and their building specifications.
     

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  2. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Thoughts on the Free Spirit video. A 25 foot tri crossing an ocean is a brave move. Its not because of the boat but the limitations of small boats on big oceans. I have spoken at length with a guy who crossed the Pacific on a 22 foot mono and a couple who came from Canada to Australia in an 18 foot mono with a child. Both said its was a good experience but they had the same issues. Weather windows were really important, they did not sail when there was a chance of rough weather and even then they were caught out. Secondly the space and load limitations meant a series of short hops to get supplies and save the relationship. These boats were not fast and 100 mile days were "very good". Both said they wanted to go cruising again but on a bigger boat maybe 25 foot plus.

    Multihulls have space and load limitations if they perform reasonably well. Do not underestimate the loads required even for 1 person. Free Spirit required 600 lbs of gear and crew for a hopefully 14 day trip. The journey took 28 days due to a broken backstay. The weather was threatening but was mostly downwind and kind. Had the weather gotten really rough and upwind it may have taken longer. You can only take so much water and food before the overload becomes dangerous. Small multi's can have real space issues, yes I know a Tiki 21 has circled the globe and a 16 foot cat has taken 2 brothers across the Atlantic but these are tuff guys. The brothers had sailed a 21 foot proa and a 14 foot mono across the Atlantic before and they refused to sail the 16 foot cat after they reached the Caribbean because it was "to small" to live on.

    Small boats are good to handle at sea due to small sails and ease of handling but they require more attention especially at night in rough weather. They tire you out faster than big boats due to constant movement and needing to be aware of the weather and adjusting sails etc to suit conditions. Also smaller multihulls need to be handled well when you are side on in wave conditions especially tri's.

    Finally, you and your boat may have sailed for 30 years along coasts and around bays but please understand being really offshore at night in strong winds when you are tired is a whole different ball game. Wharram spoke of Sea Shock, this is when people are truly out of site of land and more importantly any viable help if they have a real problem. Some people literally cannot do it and only realize this after there first attempted transocean sail. Also just because your multi has been reliable for 30 years does not mean its in ocean crossing condition. Check everything especially rigs, sails, equipment and your navigation skills. Electronics and water don't mix well and are you capable of living without your satnav? What if hatches leak in big seas, can you easily get to safety equipment in an emergency etc.

    Ocean sailing is fun if you are well prepared in any size of boat but understand your limitations and how react under stress.
     
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  3. oldmulti
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    oldmulti Senior Member

    “Slime” is one of 4 Bladerunner catamarans I am aware of. Each has the same base hull shape but have variations in the final execution. EG Afterburner started out as a 44 foot cat then ended up in California extended to 52 foot for Bill Gibbs to terrorise the locals. Limelight remained closest to the original design and then came Slime in 1987. In 2016 Slime was reengineered (wing deck pods, carbon cross beams and a lot of detail added) and is a semi open bridge deck cat that is 44 x 28.9 foot with a weight of 7,000 lbs. The alloy fixed mast is rigged with Dynema shrouds, forestay and inners. The original rig had 1,040 square foot of sail but was increased with a larger mainsail, Number 2 headsail and self tacking number 1 with a reef line in it. The hulls have a length to beam of about 14 to1. The draft is 400 mm with boards up and 7 foot with boards down. The single outboard power is 25 HP with a 9 knot cruise speed and a maximum of 11 knots.

    Now let’s clarify one thing. This is a fast cruiser with a double berth partially in a pod and a single berth forward in each hull. There is a galley, some seating and a bucket toilet. There is 6.5 foot headroom in most of the interior. Good, now let’s talk about performance. A tester found “At speed she’s wet to leeward and the odd slap creeps along the windward hull. But that’s to be expected at 24 knots. She claws upwind happily at 16 knots, pointing higher than many monohulls thanks to her slim hulls, tight headsail angles and large centreboards. The speed becomes an illusion. As Hughes (the owner) observed, with us boiling along at 20 knots: “This is her most comfortable cruising speed.” And it was. The boat was flat, stable, and the twin wakes streaming out the back were the only visceral sensation of the speed.” OK. 20 knots is Slimes most comfortable “cruising speed”? I need to adjust my definition of a sailing cruiser.

    So, what is the construction of Bladerunner catamarans? Afterburner has 200 gsm carbon fibre, 300 gsm 80/20 e-glass on the outside 10 mm western red cedar strip planking and 200 gsm Kevlar on the inside with an additional 300 gsm kevlar underwater, all in epoxy. Limelight has 200 gsm carbon fibre, 285 gsm 80/20 e-glass on the outside 10 mm western red cedar strip planking and 380 gsm biax inside with foam ring frames covered with biax cloth and carbon fibre caps every 800 mm thru out hull. The bulkheads are 4 and 6 mm ply. Some cross beams on Limelight and Afterburner are aluminium. The main beams are carbon fibre. On Slime all beams are custom John Hughes design and build in carbon fibre epoxy vacuum bagged. The prodder and boom C-Spar Carbon carbon fibre.

    On Slime a lot of the detail structure is also carbon fibre including things like hatch hinges etc. John Hughes the owner did a major rework in 2016 to reshape above the gunnel and a lot of refined detail on Slime. The rudder detail is spectacular as are covered rope lines, effective turning blocks, traveller arrangements etc. Slime is a very well thought out cat that is easy to handle and sail with just 2 people.

    The jpegs give the idea of this very fast “cruiser”. It was recently sold for $275,000, someone else is going to have serious fun.
     

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  4. redreuben
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    redreuben redreuben

    I see Tennantdesign has closed their webpage ?
     
  5. oldmulti
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    oldmulti Senior Member

    Agreed, I could not find any reference to Tennant design either beyond a company claiming to have the archives but they did not show any reference to them. Can our NZ friends give us any insites as Tennant designs are still competitive.
     
  6. trip the light fandango
    Joined: Apr 2018
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    trip the light fandango Senior Member

    An amazing rudder pintle hand hold stairs gudgeon arrangement. , wow. thanks oldmulti
     
  7. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    The next 2 days we will talk about 1 tri with a couple of variations. The company and boat names will be confusing but we are talking about the same tri. The Hudson Airplay Raw trimaran is 30.1 x 22.6 foot (folded 8.2 foot) The dry weight is 2,965 lbs. The 41 foot rotating carbon mast carries a 406 square foot mainsail, 230 square foot jib, 423 square foot Code 0 and a 968 square foot spinnaker. The draft over the hull is 1.5 foot. The outboard is 9 HP.

    Now a short discussion on the design. Tony Grainger worked with Corsair Trimarans. At that stage, Corsair were looking to replace their existing C31 with a new model. Two years of work between the Corsair factory and Grainger Designs resulted in a corporate decision to "not go ahead". So, Tony Grainger scooped up the last two years of his life into his arms and walked away. Then Hudson yachts approached Tony Grainger for trimaran designed as a production boat to fill a gap in the production boat market. The Airplay trimaran was born from previous unused design work. We made an agreement to put the concept into production starting with the RAW30 trimaran. A second version called the Sport (same dimensions as above) but with an aft cabin was developed.

    2 jpegs give an idea of the hull shape. It has flat bottoms on the main hull and parts of the float bottoms. The flat bottom of the Airplay Series is as flat as a water ski and works in a similar fashion. The faster you go the more it 'lifts' and you go faster. Flat on the main hull also means it stays upright when you are on the beach. NOTE: the rocker profile on the main hull really kicks up in the back of the boat. This shape sucks the transom of the boat down a bit when you're running fast. As it 'sucks' it down, the front of the boat can lift so that it's easier to drive downwind fast.

    Raw’s accommodation is reasonable with a “double berth”? forward and single settee berths in the main cabin and an aft berth under the cockpit. In an initial version there was a slide out galley from under the cockpit seat. We will talk about the aft cabin version tomorrow.

    The initial Raw tris were built in infused carbon fibre. The folding system is classic Farrier but with shape and structural improvements. The build jpegs give some idea of the structural cross beam arrangements.

    The performance of the RAW 30 is very good. Reports include. “We had 12-15 knots of breeze when we headed out, sailed from Raffles Marina. Upwind the boat tacks easily, and we saw 12-13 knots of boat speed. Setting the kite is simple with the top down furling, and gybing is easy as long as the trimmers time the ease/trim correctly, just like any big asymmetric kite. We saw around 17-19 knots downwind, but we were using a gps app on a tablet for speed. Got to helm for a while both up and down, and the helm is very light upwind. Downwind she accelerates easily.” Also “The boat was nice a steady and would do 14-16 knots fairly easily in the 10-12 knot breeze.” Translation it can go faster than windspeed in light to moderate conditions and has peaked at 20 knots. Fast enough for most.

    The jpegs today are of Raw sailing and parts of the build. The hull shape is in the first 2 jpegs (first jpeg is Raw blown over at dock in 40 knot winds). Tomorrow more about the “fast cruise” version.
     

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  8. Greg Martell
    Joined: Apr 2022
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    Greg Martell Junior Member

    Hello there! Just letting you know that I built the main hull sections for Crazy Train (Fusion X) using 6mm Red Meranti exterior grade plywood and glassed them with a 430g E glass double bias finished with a 200g boat cloth.

    As mentioned, the plywood was exterior grade. Back in the early 2000's, in New Zealand we could buy very good quality exterior grade product made by the same manufactures of BS1088 stock (not any more). It was quite common to get oversize 3 ply sheets (1500mm x 3000mm), and these were used for the sections from transom to just forward of the fore beam. The structure forward of this was fashioned from solid blocks of foam and glassed with 1200g of E glass.

    The hulls were filled and faired using West Systems Microlight.

    Typically with larger stress form structures, you can develop hollow forward sections in the topsides. These were faired out using Microlight.

    The 1500mm wide sheets of ply set the limits of the hull panels. The rounded gunnels / sheer was built onto the ply edge and 'lifted' the line a bit.

    The transom, foredeck and cockpit sole were all laminated on the same mould using 3 x 3mm ply.

    The cabin tops are a ply foam ply sandwich using bs1088 1.8mm gaboon plywood with a 6mm 100kg pvc foam core, and glassed with a 290g boat cloth.

    There are 3 stringers per side.

    The foils were all E glass female moulded as halves and joined together with a secondary bond.

    I managed to loose written details and images during a move, but am currently trying to locate hard drive back ups of images... will let you know if I find them.

    Let me know if you have any questions... happy to help.

    Cheers
    Greg
     
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  9. Greg Martell
    Joined: Apr 2022
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    Greg Martell Junior Member

    Hello Russell... As I have mentioned above, I built the hulls for Crazy Train (Fusion X) using 6mm Red Meranti Exterior Grade ply. It had a 3 ply layup, not the more common 5 ply that comes with 6mm BS1088 stock. Let me know if you have any other questions... Happy to help! Cheers. Greg.
     
  10. Greg Martell
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    Greg Martell Junior Member

    I was responsible for building Cat2Fold here in New Zealand. Happy to chat about the boat and its design. Cheers. Greg.
     
  11. oldmulti
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    oldmulti Senior Member

    Greg Martell. My apologies for incorrect information and thank you for the correction. I am getting worried about my information sources. The advantage of 6 mm 3 ply is that 65% of the grain is running fore and aft and it can be folded more easily. Am I correct about Crazytrain beams aluminum and also have you any idea of Crazytrain weight or displacement?
     
  12. Greg Martell
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    Greg Martell Junior Member

    Yes the beams are aluminium. I don't recall the section details. I did weigh the hulls individually at undercoat stage but again don't recall the weights. I lost a bunch of written information and images during a move. Cheers.
     
  13. Russell Brown
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    Russell Brown Senior Member

    Hello Greg,
    Thanks so much for posting and clearing up the plywood thickness. I think that high-grade, 3-ply, 6mm plywood may be a thing of the past. I live near a major plywood distributor and they say no.
    The article that Oldmulti posted a link to on the John Tetzlaff 8.5 cat Attitude says that it was built with 4 mm. Do you think that can be so? I sent an e-mail to John, but nothing back yet.
    I'm on the fence about proceeding with this book about tortured plywood because I've had such a steep learning curve, but I have come so far on it. All of the design, modeling, lofting full size, etc is done and has good photos. I thought my hulls would go to the dump at one stage, so hard to recommend a process so challenging. If I can come up with more data and photos, I will probably proceed. It would be a digital download e-book and probably cost about 5 bucks.
     
  14. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Part 2 of the Hudson Airplay Raw Sport trimaran. The Raw Sport trimaran is a fast cruiser and is 30.1 x 22.6 foot (folded 8.2 foot) The dry weight is 2,965 lbs. The 41 foot rotating carbon mast carries a 406 square foot mainsail, 230 square foot jib, 423 square foot Code 0 and a 968 square foot spinnaker. The draft over the hull is 1.5 foot. The outboard is 9 HP. I suspect the dry weight of the sport is higher as it has additional internal accommodation and is built mainly from e-glass not carbon fibre.

    One thing about trailing a tri this big is a warning from Tony Grainger “Keep in mind that even at 41 foot and carbon construction the mast can be a handful to raise and lower if you are going to be trailering often”. Wise words, as there was one person said the tri and 2400 lbs trailer, at launch weighed, 7000 lbs implying a displacement of 4,600 lbs fully loaded for a sailing. Plausible. Trailing around a 30 foot long, 7,000 lbs boat with a 41 foot mast on top is not simple task even if it can be launched easily. But putting up a 41 foot mast in any form of wind is hard. You need to be well practiced and have some help. And yes, a RAW 30 tri was blown over (when folded) at the mooring in 40 knot winds and I have found that it has occurred to some other folding tris. When strong winds are predicted either have the mast down, leave the boat at full width or have the folded boat has the mast left up tied down very well.

    The Sports accommodation has a full galley down one side of the main cabin leaving only one settee berth and table on the other side. There is also an aft cabin option which allows a roomer berth aft with sitting headroom. The internal furniture and fittings are very light with veneer finishes on light panels. “Doors” are fabric etc. Every attempt to reduce weight is done.

    The Sport and Sport+, are for those who want a very well behaved trimaran that provides enough comforts to ensure that cruising weekends are a reality whilst maintaining emphasis on high cruising performance. The performance may be slightly slower than the lighter carbon fibre RAW 30 but I think you will still be doing wind speed up to 15 knots of wind if you have good sails.

    The Sport version is cheaper due to the hulls and deck being foam and resin infused biax e-glass. The cross beams are still carbon fibre as is the mast if required.

    . The jpegs are of the interior, trailing, moored and some sailing shots. A very well thought out and developed trimaran that really can perform as exemplified by its performance in Asian racing.
     

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  15. Greg Martell
    Joined: Apr 2022
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    Greg Martell Junior Member

    Hello Russell... Yes, John did use 4mm Gaboon on Attitude as well as other cats he designed and built.

    It was a step learning curve for me as well. After building the initial very small hull model I then built a couple of 2.4m / 8ft models to see how things scaled. It was a BIG leap to then commit to the full size hulls. It definitely at times felt like a bit of a dark art! I was mostly happy with the Crazy Train hulls but would not do another standard stress form hull that big again. I think there are ways to tweak the process for better results. I am currently having a discussion with a current client who wants a 10m electric power cat and is open to having stress form/tortured ply hulls. We will see.

    Not sure how much of an interruption or distraction putting the book together is for you, but there is not very much recent info around on the subject. It would be great to see your process and outcomes! I would buy your book!

    Would love to stay in touch so let me know where I can follow your progress! Let me know if I can help in any way! Cheers Greg.
     
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