Multihull Structure Thoughts

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

  1. oldmulti
    Joined: May 2019
    Posts: 1,004
    Likes: 504, Points: 113
    Location: australia

    oldmulti Senior Member

    The following is more about the materials used to build the boats, not the boats themselves. Whilst looking for Basalt fabric information I suspected that it could be used in strip plank WRC construction. I then ran across the Fipofix company and its test boats. The first is a dual transatlantic crossing 16 x 7.5 foot monohull that weighs 1075 lbs and has a 400 lbs keel on 6 foot canting bulb keel. The carbon fibre mast carries a 173 square foot mainsail, 32 square foot jib, 139 square foot genoa and a 280 square foot Gennaker. The boat has twin rudders and a forward centreboard. This boat did a 10,000 miles dual transatlantic crossing in 133 days in 2014.

    So you didn’t think you could afford an ocean crossing cruiser? Here it is with a small limitation, the amount of room inside but you cannot have everything. But back to the structure.

    The boat is a basalt fabric skin on either side of a balsa core. Fipofix pitches Basalt fabrics as a viable and cost-effective alternative to known composite materials, not just for boatbuilding but also for wind turbines, fishing gear and surfboards. Basalt fabrics are also used in crash boxes, chain plates, rudderstocks and as reinforcements to bulkheads and keelsons. Fixpro say Basalt fabrics can be used on most core materials and in conjunction with most resins being stronger and lighter than e fiberglass composites and offer more longevity.

    After the 16 foot boat completed the transatlantic sailing, Norbert Sedlacek set a new task for himself, a 60 foot mono to sail 34,000 miles alone, without stopovers, departing from Les Sables d'Olonne via the Northwest Passage, two passages through Cape Horn and all the major southern capes, before returning to the Vendée. Equivalent to one and a half times the Vendée Globe, with sailing in both poles, this course corresponds to the Austrian skipper's sailing philosophy: robust boats that can face all conditions.

    The architect Vincent Le Bailly and his team designed the 60 x 19 foot monohull that weighs 21000 lbs and has a double bottom forward with big frames and stringers to “bounce” of small growlers. The boat carries a 1800 square foot main and 4300 square foot gennaker. The 60 foot monohulls had to take into account the significant risks of impact with growlers in the far North. For that, the ultra-light design of the current IMOCA could not satisfy them as the carbon fibre construction shatters if hit hard enough. So, they opted for a composite construction in balsa - volcanic fibre sandwich which is more forgiving. The choice of materials is guided by the impact resistance, impact damage is lower, both for balsa compared to PVC foams and for Basalt fabrics compared to carbon or glass. The structural grid has also been optimised with more watertight compartments to ensure the skipper's safety in the event of flooding.

    Finally, the Fast 435 catamaran featured on page 22 of this thread has a hull with a 700 gsm bi-directional basalt is used as the outside skin, then a layer of 20 mil (40 mil is used on the roof) AFC47 Divinycell structural foam is placed onto the layer. The foam is superior to core balsa which is traditionally used in light weight boats because it is lighter, will not absorb water, cannot rot and requires less resin to assemble. Twaron is used on the inside of the hulls as an extra impact protection barrier; it has over 8 times the strength of glass against impact and is light weight. Twaron aramid and Carbon Additional Twaron aramid and Carbon are used throughout the boat where extra strength is required such as in the bulkheads, modules (mast support), daggerboards, rudders and winch stands. Entire structural components (hull and deck molds) are vacuum bagged for 24 hours for the infusion of epoxy resin. After the boat is complete it is baked for 8 hours at 80 degrees centigrade to ensure everything is cured.

    The jpegs are of the 16 footer and 60 footer with the last of the Fast 435.
     

    Attached Files:

  2. bucfan
    Joined: Oct 2020
    Posts: 3
    Likes: 0, Points: 1
    Location: coffs harbour

    bucfan New Member

    Oldmulti, do you have any information/images of a completed scarab 32 trimaran? After reading your advice regarding this model I have checked it out but can’t find a completed one. Any information would be greatly appreciated.cheers
     
  3. oldmulti
    Joined: May 2019
    Posts: 1,004
    Likes: 504, Points: 113
    Location: australia

    oldmulti Senior Member

    bucfan. The first Scarab 32 is not launched yet and is being completed by the designer. His history of 100's of launched tri's of many sizes indicated than the Scarab 32 will do what it is designed to do. That is , be a good high performance cruiser that will match if not exceed the performance of a Bucc 33. There are some attached jpegs and the following 2 links you may have looked at. The links are:
    Building the Scarab 32 folding trimaran http://www.teamscarab.com.au/Scarab%2032/Build.html
    Building a Scarab 32 Cruiser. http://www.yendys.com.au/Scarab32/Build.html
     

    Attached Files:

  4. catsketcher
    Joined: Mar 2006
    Posts: 1,298
    Likes: 143, Points: 63, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    Thanks Oldmulti about the basalt.
    Bucfan - I just went sailing on my first Scarab on the weekend and whilst it was a nice sailing boat, I think it would be harder to build than round bilge foam version like a Farrier. Chines are right royal buggers. Get a tight one out by less than a mill and you can see it wander. On my cat the only thing that worries me about the build is the chine - it does wander around a bit. I hide it with the rubbing strake. On my little cats I round the buggers as much as possible. Designers like Schionning and Oram go to huge trouble to put chines below the waterline. Strip foam is so easy and both methods need fairing so I don't get why you would go chined although I note that the 32 has far fewer chines than her older sisters.
     
  5. oldmulti
    Joined: May 2019
    Posts: 1,004
    Likes: 504, Points: 113
    Location: australia

    oldmulti Senior Member

    Catsketcher commented on chines being a problem to fair well and round bilge is ultimately easier to build. In principle I agree. But the is one large problem. I have built chine and round bilge boats in both foam and composite. I can assure you a round bilge foam glass boat built over a male mould is a pain in the behind to fair and finish well. You need to fair the male mould which has to be strong enough not to move around as you do the rest of the build. Then you have to fair the foam after cutting it or heat bending it to shape. The you either have to do a really good glassing job on top of fabrics which have minimal amount of overlaps. That means buying fabrics which have the correct fibre orientation that can be run from the bow to the stern. Then you start with the bog and fairing. Once faired you take the hull of the mould the glass the interior of the hull trying again not create too many overlaps as fairing on the inside of a partially completed boat is a bigger pain. Then you get your eg 2 hulls and start to glass bulkheads on the inside creating more opportunity to practice you fairing skills.

    To get around the fairing problem professional builders use female moulds, gel coats, a lot of vacuum bagging and/or resin infusion. They literally build cats in half the time because they minimise the fairing required.

    Home builders usually build a design once so the effort of building a complex female mould is “not” worth it. So designers have come up with a variety of solutions. Derek Kelsall suggests large foam glass panels done on a flat table then bending and cutting the panels to form a round bilge hull shape. Yes you save a lot of fairing but you also create a lot of fairing at the cuts to distort the panels and reinforce the joins. Kelsall tries to keep these cuts underwater but after speaking to a few people who have done a Kelsall you either love the approach or hate it as it has some variables in shaping which are hard to resolve. Next approach is done by many which is create foam glass flat panels and the built a “chine” hull. This has the benefit of controlling the hull shape but has the big disadvantage of having to fair the fiberglass taping used to connect the chines. You either need to keep as many chines as possible under the waterline or do very accurate chines to make it look good. Then you have to fair the chines accurately to minimise any visual imperfections. This is what I call the half way house in boat building terms. Even professional builders get annoyed at this method. Venom a 42 foot carbon fibre tri was built flat panels. The very experienced builder said he would have preferred to build it as a foam unit then do a final carbon fibre layup. He thinks the tri’s weight and faring issues would have been less.

    The final approach (beyond paying someone else to build the boat) is to build a simple female mould EG Denny’s Intelligent Infusion approach that allows you to build a basic female mould then do vacuum bagging ad/or resin infusion to produce a hull that is almost pre faired with continuous fabric glass layup. This method produces the lightest strongest hull structure in probably shortest time. A variation of this method is to produce a female round bilge mould from the waterline down. Manufacture the hull bottom. Then have flat panels for the topside sides, decks and bulkheads.

    Fairing is a pain, good fairing is a monument to someone skills, patience and technique. Use good long boards, some of the fancy large fairing power tools that can be home built and have a supply of friends. It all helps.

    The following pages have good ideas. Sanding Tricks of the Trade https://www.epoxyworks.com/index.php/sanding-tricks-of-the-trade/

    Building a cat https://buildacat.com/cool%20tools%20.html
    Building a cat https://buildacat.com/bbsplit-sander.html
     

    Attached Files:

  6. Scuff
    Joined: Nov 2016
    Posts: 77
    Likes: 6, Points: 8, Legacy Rep: 10
    Location: Richmond VA

    Scuff Junior Member

    I'm almost finished with my first hull in a trimaran build using a male mold and foam/glass. I completely agree on the multiple fairing operations needed. I learned some hard (and time consuming) lessons. I think the next two will require much less fairing as a result.

    For the female mold approach don't you still bear the burden of fairing the mold as well as fairing the finished product?

    This is one of the best reads on multihulls! Thanks for expending the effort.
     
  7. waynemarlow
    Joined: Nov 2006
    Posts: 419
    Likes: 39, Points: 28, Legacy Rep: 134
    Location: UK

    waynemarlow Senior Member

    The easiest way almost certainly for building 1 offs is to follow the Farrier build method of female sort of mould using a stongback and ribs with cheap longitudinal stringers in between. Two of us built the CNC cut frame in less that 1/2 a day and were able to insert the required foam panels the following day, once we realised how to work the foam with heat guns ( only rarely needed ) and how to pull the foam to the stringer ( screws from the stringer side or there are number of building fixtures made of plastic that are used to pull things to a frame ) there was almost no fairing.
     

    Attached Files:

    CocoonCruisers likes this.
  8. waynemarlow
    Joined: Nov 2006
    Posts: 419
    Likes: 39, Points: 28, Legacy Rep: 134
    Location: UK

    waynemarlow Senior Member

    Just another couple of photos of that build, it was taking about 4 days for each side of the 20 ft central hull to have it foamed, carbon and glass laid up and the inner ring beams and associated ribs and strengthening areas put in. We had the whole central hull joined and the outer layers on in about 10 working days. At that point you think you are nearly there but in fact you are just starting.
     

    Attached Files:

    CocoonCruisers and Corley like this.
  9. catsketcher
    Joined: Mar 2006
    Posts: 1,298
    Likes: 143, Points: 63, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    I think Wayne is onto something there. I built my cedar cat on the typical male mould and had the problem of fairing with no interior laminate on, which was okay still. But when we did the Farrier method - nice. We kept all our datum marks, all of the interior laminates and half bulkheads went in first. Then when we pulled the super stiff hull half out of the mould we stuck it on the mirror image one (we had prepared earlier) and faired away. (The moulds themselves were highly accurate because we used mylar prints of computer faired plans)

    For my foam folding cat I made the hull pan out of vertical strip foam. Then I installed all of the interior laminate, bulkheads, even the centreboard case, floors and interior before I put the cabin sides on. Then after the whole thing was bombproof it came out of the mould and was faired.

    And I rounded those bloody chines.

    As for fairing - fairing is pretty fast away from edges. Rocking on your feet with a longboard in your hands, on a hull you can roll around is pretty nice to do. Getting anywhere near an edge and things slow to a crawl. Fairing a round bilge hull can be done by a blind man - your longboard speaks to you with the way it moves. Edges - they are always ready to have too much taken off. If the chines are underwater, then chines are great, if they are above - they slow composite building down.

    Chines are relics from plywood days. My little cats have foam and ply in them so they have some chines in the ply construction. To better fair a chine we would use a chine log, a nice piece of timber that runs the length of the chine and is planed down with correct bevels. But I tend to use double bias instead of chine logs so the thin ply can wobble. I ended up screwing lots of fair timber to the ply edges to produce fair curves before gluing - doing the same job as a chine log. Of course Duflex and premade foam panels are stiffer and fairer than ply.

    And don't worry about filler on the boat. In her 2o years of life I have been happy to have 2-3mm of filler all over my cat's hull, it adds a layer to the laminate from water ingress and if the dinghy or sailboard knock her, she has a slightly sacrificial layer before the vital hull laminate.
     
  10. oldmulti
    Joined: May 2019
    Posts: 1,004
    Likes: 504, Points: 113
    Location: australia

    oldmulti Senior Member

    Excess 11 is a new cat from Excess (Groupe Beneteau). Beneteau Groupe’s Bruno Belmont says “With the Excess range, Bénéteau aims to fill the gap left between the comfortable cruising catamarans of the Lagoon or Fountaine Pajot brands and high-performance cruising catamarans such as Gunboat or Outremer.” Interesting claim.

    The Excess 11 is 37.1 x 21.6 foot that weighs 19875 lbs. The fixed aluminum mast carries 590 square foot mainsail, a 237 jib and a 581 square foot gennaker. The cat has low aspect ratio keels and spade rudders and draws 3.75 foot.

    So, lets compare it the sort of boat its replacing. The Lagoon 380 was produced from 1999 to 2008 with 550 of them manufactured. The Lagoon 380 is 37.9 x 21.5 foot and weighs 16005 lbs with an aluminium mast. It has a 560 square foot mainsail, 325 square foot jib and 570 square foot gennaker. The cat has low aspect ratio keels and spade rudders and draws 3.75 foot. VPLP designed both the Excess and the Lagoon 380.

    Look at the numbers of both designs, very similar size, same mast length, similar overall sail area but with one big difference, the Excess 11 is 24% heavier than the Lagoon 380. I am sure the hull shape of the Excess 11, being designed 20 years later with high volume of the forward hull sections to provides a damping effect on pitching and improves performance, is better than the Lagoon 380. But the Excess 11 additional 24% of weight is a negative on performance. One hopes the rig/sail improvements of the Excess 11 can compensate for the weight gain.

    So where is the weight gain. The Lagoon 380 has a solid up to 12 mm thick solid fiberglass below the waterline the foam or balsa glass above the waterline. To save weight, the Excess 11 structures include more vacuum infused components than any previous multihull that Beneteau Groupe has built, with sandwich construction throughout, above and below the waterline. The weight of interior furniture is reduced by 30 to 50 per cent by building it as integrated modules rather than individual pieces. The Excess 11 weight saving even goes to Signature textile lifelines, Dyneema steering cables and Titanium coated aluminum stanchions and cleats.

    The wingdeck length is shorter on the Excess 11 than the Lagoon 380 but the chines on the topsides of the Excess 11 hulls allow the beam to flare out and increase the internal volume without a “significant impact” on performance. If you look at the jpegs of the accommodation you may get a hint of the extra weight. The aft double berths measure 6.5 x 6.5 foot. The biggest berth on the Lagoon 380 was 5.1 foot wide. The bulge in the topsides of the Excess 11 are to fit the wide berths etc in the hulls. In short there is a lot of extra surface area both internally and externally in the Excess 11. Surface area adds weight. Modern inconveniences also add weight. Result, the Excess 11 may have lighter build specifications with more modern fabrics and build methods but because these is “additional internal volume” puts the weight back on.

    We also have other not so obvious compromises. The mast of the Excess 11 and lagoon 380 are on the main mast bulkhead in front of the main cabin. The Lagoon series of cats moved the mast aft to the center of the main cabin. Moving the mast backwards offers a gain in performance due to the mast being nearer to the center of gravity allowing reduced pitching and makes it easier to install a self-tacking jib with a good surface area. But on a catamaran, it requires a reinforced structure under the underwing and main cabin to support the compression forces. While a mast installed in front of the deckhouse is placed on the front beam, without the need for additional weighty reinforcements in the saloon underwing and cabin.

    Again, the accommodation and weight considerations effect sailing performance options. But the most interesting statements are: "The idea is to turn off your engine at 5 knots of wind and be able to sail at the same speed or even faster than the speed of the wind." details Alexandre Dauberville. And “There are no daggerboards because they require a bit more knowledge,” Bruno Belmont says. “You need to be a good sailor to use them properly, or there is a risk of either capsize or breaking them.”

    This is a good cat with a lot of accommodation for its size. It will be a commercial success for those who want good accommodation and some performance. I just wonder if 6.5 foot wide berths are worth the weight gain. The first 2 jpegs are of the Lagoon 380, the third jpegs shows the evolution of the mast movements in the Lagoon series. The rest are of the Excess 11.
     

    Attached Files:

    Last edited: Oct 15, 2020
    CocoonCruisers likes this.
  11. redreuben
    Joined: Jan 2009
    Posts: 1,726
    Likes: 98, Points: 48, Legacy Rep: 349
    Location: Beaconsfield Western Australia

    redreuben redreuben

    Chines are a relic of plywood but many materials come as sheet stock, a quick female mould can be made of glossy melamine which can give you a pretty impressive finish, its also a useful method to create interior furniture components.
    There are 2 methods you can use on chines/corners, radius them in the mould with plasticine or builders bog (polyester car body filler) to a radius your cloth can follow. Or, leave them sharp and apply a "wet' radius of bundled uni before you put your cloth down. Obviously its not a wet radius if infusing but fills the space regardless.
    Fairing I use the notched trowel method, much faster. I'm not a fan of machine tools for fairing apart from the initial knockdown, in my experience the only thing they do faster is make mistakes. However I'm sure some of the more modern tools may have changed that. Torture boards and guide coat are the best methods
     
  12. jamez
    Joined: Feb 2007
    Posts: 506
    Likes: 28, Points: 28, Legacy Rep: 231
    Location: Auckland, New Zealand

    jamez Senior Member

    It seems appropriately named. I can't help thinking the sailing ability described is a tad optimistic.
     
  13. oldmulti
    Joined: May 2019
    Posts: 1,004
    Likes: 504, Points: 113
    Location: australia

    oldmulti Senior Member

    On page 21, 66 and 88 I have written about Minimus 11, an open deck design catamaran that is 23.75 x 13.3 foot which is about as small as one can go in an ocean-crossing multihull with enough weight-carrying capacity for a crew of two, around 1200 pounds of crew, gear and provisions for 4 to 6 weeks at sea. Minimus 11 has 4 masts (2 mounted on each hull) and uncambered junk sails. This cat is intended (and will be) an ocean crosser not a day sailor.

    The materials we're using in the dory flat bottom hulls of Minimus II are 1/2" MDO plywood throughout with 25 x 50 mm lumber for chine and sheer stringers. 50 x 50 mm lumber is used for bulkhead reinforcement and deck beams. Raka epoxy with medium hardener and epoxy additives, wood flour, chopped fiberglass and microballoons.

    Why the ongoing interest? This man has done many ocean miles in a 23’ Wharram cat from Mexico to Hawaii, a 20’ monohull from Seattle to southern Mexico and most recently, a 25’ monohull (Minimus) from California to Tahiti. The owner is an original thinker who is willing to design and build his ideas and then sail them many ocean miles. Have no illusions when he says he has built an offshore cruiser, he is serious about crossing oceans.

    The latest sailing trial update gives us all something to think about. EG This cat is capable of ocean crossing can self steer downwind without any "self steering device" assistance. It can self steer on a reach using its own rig and a simple block and tackle arrangement. The simple drogue system it uses can slow the boat down very well in rough weather. And finally, he has an AIS system for locating other vessels within 15 miles of his vessel for under $100 US. The second sailing trial update is available at Second Sea Trials https://www.omick.net/adventure/minimus_ii/sea_trials/second_sea_trials_september_2020.html

    On the above web address there are 4 video’s of the cat self steering and the arrangements. They are short but informative.

    This is the very opposite of the Excess 11. Minimus will transport its crew across an ocean with minimal effort and expense but without standing headroom and only single bunks. The Excess 11 will transport you across an ocean with a lot of effort and expense but you will have standing headroom and big double bunks. Finally, I am sure the cost of just one of the Excess 11 headsails will buy you all the materials, rig, sails and motor power for a complete Minimus 11.

    In short, Minimus 11 is an excellent vessel for those who don’t have much money but want to have a big adventure and really see the world.
     

    Attached Files:

  14. skyl4rk
    Joined: Aug 2006
    Posts: 44
    Likes: 8, Points: 8, Legacy Rep: 21
    Location: Lake Michigan

    skyl4rk Junior Member

    Does that sound like an accurate capacity target of 1200 pounds per person for long distance cruising?
     

  15. oldmulti
    Joined: May 2019
    Posts: 1,004
    Likes: 504, Points: 113
    Location: australia

    oldmulti Senior Member

    The exact quote of the owner is: “She's an open deck design, 23' 9" long with a 13' 4" beam, which is about as small as one can go in an ocean-crossing multihull with enough weight-carrying capacity for a crew of two. Her carrying capacity is around 1200 pounds, which is what we figure for ourselves, gear and provisions for 4 to 6 weeks at sea.”

    How realistic is it? Water 4 lbs/person/day, 2 lbs of food/person/day and 2 people 300 lbs including some clothes etc. That equals for 6 weeks 804 lbs. The other gear on board would be EG outboard 40 lbs, fuel 20 lbs, battery 40 lbs, anchor gear chain and drogue 130 lbs, ropes and spare ropes tools etc 100 lbs. Internal galley gear stove dishes buckets etc 60 lbs plus a few luxuries like books, cushions, flexible solar panel 100 lbs. This adds up to 1300 lbs for 6 weeks for 2 people. Cooking Fat, a Wharram 21, sailed around the world with about the same load. Kliss a 22 foot trimaran sailed the Atlantic with about the same load.

    Please do not be confused by boats designed to handle people who have dally showers, start an engine in under 10 knots of wind. These boats also have 4 people, 2 windsurfers, 2 dinghies, three 60 lbs anchors and a 100 meters of chain and 200 meters of rope, plus batteries to power TV’s, internet, air conditioning, washing machines etc. These boats need 6,000 to 10,000 lbs payload capacity to handle what they consider a “normal cruising lifestyle”.

    Minimus 11 works at an entirely different end to the scale. Its load capacity is based on what 2 people need to live for a few weeks and very little more. These people have done bicycle trips from Arizona to Oregon, kayaked from Vancouver Island to Alaska etc. They know what they personally need to travel long distances over extended periods. They can teach a lot of people what is really required if you wish to travel far on very little income and using a minimum of resources.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.