Multihull Structure Thoughts

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

  1. catsketcher
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    catsketcher Senior Member

    Wow, that is a lot of thought into everything, even the mast crane is clever.
     
  2. oldmulti
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    oldmulti Senior Member

    Tiki 8 meter is a “production” foam glass version of Wharrams Tiki 26 that has slight differences. The Tiki 8 meter is 26.25 x 14.25 foot weighing 1650 lbs displacing 3300 lbs carrying a wing sail rig of 300 square foot. The hulls are 3.75 foot wide and have 4.33 foot of headroom. Waterline length is 22.33 foot.

    The Tiki 8m has 2 berths a minimal galley and loo area with a versatile flexible deck tent/ all weather sailing dodger to at-anchor windbreak and decktent/cabin, giving double berth and wide living space that connects both hull cabins.

    Using state of the art moulding techniques for the Tiki 8m they were able to design a new curved hull shape, with more internal room and more hydrodynamic efficiency than the previous 26-27 footers. The 27 foot Tane/ Tanenui and Tiki 26 (1100 plus plans of these three designs sold) have crossed oceans.

    The new TIKI 8m is built in composite fiberglass. Hulls, decks and beams are constructed using biaxial fiberglass cloth with vinylester resin, sandwiching a foam core, which results in a stiff, strong and lightweight structure. The hull halves are a gelcoat, 225 csm mat, 1708 biax in vinylester, 9 mm divinycell, 225 csm mat, 108 biax. Hull halves are joined at the keel line by 5 layers of 1708 biax. The deck is gelcoat, 225 csm mat, 108 biax, 9 mm divinycell, 225 csm mat and 108 biax. 1708 fiberglass is 560 gsm 45/45 biax with a 225 csm backing material "stitched on" and 108 fiberglass is a 500 gsm biax cloth. The cross beams on the original 8 meter were “divinycell, carbon fibre, uni directional glass and CSM”. The beams are tied on to the hulls with 6 wraps regular polyester stayset. The internal “furniture support structure” is a fiberglass moulded tray that slots into the hulls.

    An alternative cross beam structure could be a set of carbon fibre cross beams from C-Tech New Zealand ordered by a British guy. The mast beam was 158 x 122 mm inside diameter with a 3.9 mm wall thickness. In the centre of the beam at the mast point there was an additional 9 layers of 200 gsm carbon cloth up to 1 meter long on the top (and bottom) of the beam for additional reinforcing. Inside the beam under the mast is a 40 mm carbon fibre tube to separate the faces. The ends of the beams at the hull attachment points were reinforced with extra carbon fibre wraps. The mast beam can take 40,000 lbs of down thrust with 8 mm of deflection. The rear beam was 158 x 122 mm with 3.3 mm walls. The owner wanted this size of beams but C-Tech said the beams could have been 138 x 94 mm of the same build and be strong enough.

    Another alternative cross beams are offered by Wharram for the Tane/Tanenui Tiki 26 shown in the last jpeg.
     

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  3. trip the light fandango
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    trip the light fandango Senior Member

    I really like the hinges on the hatches they're simple and practical, it seems a bit like they have stuck with some of the design for trademark wharram luddite reasons, yet the boom sweeps the deck like a performance cat, lowering centre of effort etc,, safer...[bring your helmet] The bow gives up comfort and hull speed to ride over a submerged container. The twin side stays pass the windows, it has hard corners although it is made of glass and foam. It seems mostly massively strong and should outlast all previous wharrams, being made of , narrow your lids , spit at the ground, plastic composite.. It is impressive and remarkable from this novice backyarders perspective... an enigma..
     
  4. oldmulti
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    oldmulti Senior Member

    The claimed largest Pacific Proa in the world is a 71' 0" x 37.75 foot vessel designed and built by Yvette Ini Wijnen in Australia in 2009. It displaces 20,000 lbs and is capable of carrying up to 60,000 lbs according to the sales doco but only 20,000 lbs additional load according to the initial build site. The wood composite 140 square foot Wing mast is 70 foot high with 1400 to 1800 square foot (depending on sail choice) of sail supported by Dyneema synthetic standing rigging and 2 x soft furling units. The main support for the mast is a tension/compression rod that goes from deck to mast spreader height combined with the fore and aft roller furling jibs. The main hull is a flat dory bottom and is capable of a maximum speed under sail of 20 knots with a cruise speed of 12 to 15 knots under good conditions.

    Gaiasdream is a 71 foot Pacific Proa which follows the same principals and design as the traditional proa. It was initially designed for transporting cargo and with a circumnavigation in mind. She is controlled by dual rudders and helms on the main hull. This allows the vessel to 'shunt' (tack) by reversing direction. Gaiasdream carries dual Raymarine autopilots, wind and navigation instrumentation. The single engine 50 hp Nissan DT 27.

    The Bridge Deck houses a Captain's cabin with additional double cabin sleeping quarters fore and aft in the main hull. Multiple pipe costs can sleep several more crew or be replaced with cargo (such as food or building supplies and tools suitable for outer island communities of the Pacific). Cabins 3 x Double, 1 x twin pipe cot bunks, 1 x double bunk in workshop compartment. Pipe cot compartments are also intended to stow cargo.

    Gaiasdream was built from Plantation pine using the West system. Hull materials is Ply/Ply-Glass Queensland Pine with ply bulkheads and stringers. Deck material on the wing deck to support the additional cargo load is Queensland Plantation Pine (32mm thick) with a 12 mm GRP outer layer. We come to the interesting part. This boat is built with Plantation Pine and pine ply which is not known as a general use boat building timber. It would have required gallons (litres) of West to seal it properly and will require continuous maintenance to seal any damaged parts of the proa. The timber dimensions in this boat are big which compensates for the big timber knots and lower quality plywood used as shown in the jpegs. This Proa has sailed and is large enough to be sailed relatively safely because of its size. The Pacific Proa is one of the few multihull types where size has advantages.

    The jpegs give the idea. All this could be yours for $79,000 as it is for sale. Found his build web site. Inigo Wijnen/pictures of Gaia's Dream http://www.pacificproa.nl/picture.htm
     

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    Last edited: May 11, 2020
  5. Eric ruttan
    Joined: Jul 2018
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    Eric ruttan Junior Member

    Is this it?
    Gaiasdream – Yvette Wijnen http://iniwijnen.com/gaiasdream/ 4 pages of build
     
  6. oldmulti
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    oldmulti Senior Member

    Eric we both hit web sites at the same time with different addresses. Thanks for your effort.
     
  7. Eric ruttan
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    Eric ruttan Junior Member

    Hahaha well done. Also, thanks for all of this
     
  8. catsketcher
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    catsketcher Senior Member

    Old multi - the ply is Austral (IIRC) and I have built 3 boats out of the timber - 2 Austral and 1 Brimsply. They all use Hoop Pine. Hoop Pine will rot (a few years in the tropics) on the side of a hill in the Whitsundays but is looking great on my 20 years since launched 38ft Chamberlin. I have removed two patches where I was really dumb and did not epoxy a screw hole. Apart from that it is great. You just have to be sensible.

    I have found no real difference in epoxy soak between Hoop pine ply and anything else I have borrowed of bought in ply - the Hoop Pine ply is lovely ply and being plantation, it means that you are not destroying rainforests so you get better karma.

    Hoop pine AA or AB is a world away from the cheap and very nasty stuff you get from regular and knotty Radiata plywood. Plywood is a great material and gets a bad rap from those who don't use it properly. It is tough and when looked after stands up to the loads of a boat really well. In all the many kilometres of jigsaw cuts I have made in Austral and Brims ply, I have found the interior quality to be very good. Hoop pine ply - it's great stuff when used well.

    As an aside I have never seen Gaia's dream move. She looks like she hasn't moved much and I doubt whether many other people will be interested in her. I find her very interesting but is not the type of boat you could take away for an afternoon spin on your own.
     
  9. oldmulti
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    oldmulti Senior Member

    Ekolokat 33 and 34 are very similar cats designed by Nicolas Gruet of NG yacht design based in Tahiti.

    The 33 cat is 32.3 x 19.5 foot weighing 3350 lbs and carrying a 460 square foot main and a 205 square foot jib for a total of 665 square foot of sail. There is a 420 square foot Code 0. This version is built in plywood timber epoxy with glass covering and some Kevlar. Thanks to its construction in plywood-epoxy, from developable panels, including the mast and forward crossbeam, this version can easily be built by an amateur. It is built upright in a female basket mould. The structure's lightness means that a modest sail area is all that is needed for a high level of performance. The build time estimate is 1350 hours (I suspect it will take more).

    The 34 cat is 33.3 x 20.5 foot weighing 3700 lbs with a 45 foot high mast and 705 square foot of sail area. A 667 square foot gennaker and a 1000 square foot spinnaker. This version is built by vacuum bagged, infused vinylester resin on glassed foam sandwich core. Kevlar and optional carbon fibre reinforcements locally where required to keep building costs down.

    Both versions have the same narrow width hulls at waterline and a chine flat adding volume to the hull higher up. The plywood version has a single joint chine, the foam version has a small step chine in the hull above the waterline. The chine also acts as an efficient spray deflector. The predicted speed is between 15 and 20 knots, probably more with an experienced crew and optional high performance rig. Both versions have dagger boards but the plywood version can have fixed keels with a 3.25 foot draft.

    Interior layout of both versions is basically the same and comprises 3 large double berths 2 metres long by 1.5 metres wide and a large head/shower compartment. In the warm climate version, a large outdoor galley and dining unit seats 6 adults, the bathing platform on the rear of each hull plus the trampoline provide plenty of space for games and relaxing. An optional cold climate hard top covers the galley and dining area.

    Both models have double outboards (9.9 HP outboards) on either a drop down system under the wing deck or in a well system with trapdoors to close the motor well when the motors are raised. The motors are as efficient as inboards but the weight and low cost are in favour of this new system.

    These boats look like fast fun minimal cruiser that you choose the material you build in. Good looking design that should meet its performance expectations.
     

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    Last edited: May 12, 2020
  10. jamez
    Joined: Feb 2007
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    jamez Senior Member

    Interesting boat. I see there is a production version too (pic) . One of these has been for sale for a while on various brokerages, like a lot of boats ATM.
    tropical_cruise_34_01.jpg
     
  11. oldmulti
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    oldmulti Senior Member

    This is a story about a Tiki 21 which is 21 x 12 foot with 600 lbs build weight and load capacity of 800 to 1000 lbs. The hulls are 3 foot wide at the gunnels. It has a 23 foot mast with a “wing sail” 140 square foot main and 80 square foot headsail. These boats sail reasonably well and one has circumnavigated (Cooking Fat).

    We are going to focus on the (re)construction of an original boat and the consequences of “improving” on the design. The first version of this Tiki 21 was purchased 2nd hand but had build problems which resulted in a total rebuild of the Tiki 21 virtually from scratch. New hulls, beams, rudders modified rig etc. The guy had the plans for the 21 so built to the cat to original size and shape.

    Now the structure. The keel design was 15 mm ply, he used 18 mm ply. Hardwood was used instead of softwood in a lot of areas eg Keel line. The ply hull sides remained at 6 mm ply but the gunnels stringers were meant to be 12 mm thick softwood but were made in 18 mm thick hardwood. The bulkheads remained 6 mm ply. The diagonal internal stringers in the hulls were built to plan. Filleting and glassing of keel lines and bulkhead joints were generous and there is glass over many fillets that were not specified in the plans. The deck has square deck stringers are double the size required. They were specified to be triangular and of smaller dimensions in the plans. Most of the deck hull ply was 6 mm but many hatches were 9 mm ply not 6 mm ply. Many hatch surrounds timbers were larger than specified. The hull external glassing was heavier than specified in the plan in many areas. Additional timbers were added in some areas for additional functions. Internally instead of 6 mm bunk boards 9 mm boards were inserted. Result the hulls are supposed to weigh 175 lbs each but each hull weighed 335 lbs so each hull was 160 lbs overweight.

    Next came the cross beams which were built to plan size 100 x 19 mm top and bottom flanges on a 15 mm plywood web. The top and bottom flanges timbers were meant to be Douglas Fir or Spruce but were built of Ash hardwood. The bridge deck panels were meant to be 6 mm ply but were built in 9 mm ply. The rudders were thicker than specified. The mast section was 20 foot but to get the required 23 foot height timber inserts were built into the top and bottom of the aluminium tube to extend its length. The result of all this is a weight of 372 lbs for all these components, the plans specified 250 lbs.

    Now I understand why the builder wanted a little bit extra strength and substituted materials eg hardwood for softwood if he could not easily obtain the plan specified materials, but there is a price. The “price” is both in dollar cost and in weight. The Tiki 21 total boat was meant to weigh 600 lbs but this version ended up weighing 1000 lbs.

    Designers design boat structures for a set of requirements and if your needs suit those requirements then build according to the plan, both parties will be happy. But if you are a 300 lbs guy and you want a long term cruiser, you may find eg a Tiki 21 does not really suit your needs. Please do not “strengthen” a light weight boat to make it “safer or stronger” as this may effect its performance and sailing capability lowering your safety factors etc. Trust your designer and build accordingly. If you want to build in heavier materials, fine, just design the cat for the extra weight. If you want to maintain the performance you will need more sail area, stronger rigs, crossarms etc.

    The jpegs are just some of the following web site Sitemap https://www.monarisa.org/sitemap/ PS There are many good build tips and ideas in this and his trailer design for the 21 is good.
     

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    Last edited: May 14, 2020
  12. trip the light fandango
    Joined: Apr 2018
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    trip the light fandango Senior Member

    I've found that people over 110kgs 250lbs are more likely to bend ally tube if they slip a little and land in the middle of the say an 8ft ,2metre length.
    I suspect many small multis and yachts in general may not cater for the big people that well. It is an extra factor to consider when they're a fresh deckhand,.. movable ballast can be a real nuisance..Ha. "You can get in there"? yes ,and always hold on to something would you and stay low when we're underway..sheesh. They can be so handy on land, pushing ,lifting, etc..ha.
     
  13. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    The Tiki 38 is one of Wharrams more popular designs. Its 38 x 20.33 foot with a 31.5 foot waterline. It weighs 7200 lbs and displaces 11000 lbs carrying a schooner wing sail rig with 32 foot wooden masts. The mast options are 150 x 3.5 mm aluminium tubes, a 140 x 4 mm aluminium tubes or in timber 150 mm diameter with 25 mm walls. The mainsail is 225 square foot, the fore sail is 222 square foot and the jib is 140 square foot. The spinnaker is 536 square foot and if a staysail is carried 140 square foot. The hulls at light displacement has 12:1 length to beam. Tiki 38’s have travelled far and wide and are very capable of crossing any ocean. Pilgrim, a Tiki 38, crossed the Atlantic from New York to the South of France in 2011 in 31 days for the 4500 nautical miles at an average speed of 6 knots. They frequently sailed at 14 knots and their top speed was 16.6 knots. (Remember the Pahi 63 averaged less than 6 knots on ocean passages).

    The structure of Tiki 38’s are plywood with timber framing and supports etc. A lot of epoxy and filleting material is used with glass epoxy used to tape parts together. The lower and upper hull skin is 9 mm plywood. Bulkheads in the lower hull are 9 mm ply and the keel is 18 mm plywood. The lower hulls/keel are bogged together with glass biax tapes inside and out. The upper hull has 12 mm plywood bulkheads. Stringers are 45 x 19 mm on the flat against the hull sides. The decks are 9 mm with under deck stringers notched on the bulkheads. The 3 main cross beams have a centre I beam plywood web of 2 layers of 18 mm ply with a top and bottom flange of 140 x 70 mm timber. In each corner of the web flange interface is a 56 x 85 mm triangular support timber. There are many support “bulkhead” timbers between the top and bottom flanges. The Tiki 38 three I-shaped beams are lashed to the hulls in twelve places. Four lashings per beam, one inside and outside each hull. These lashings have to be stretched tight, really tight, as if they were set like concrete. Wharram recommends 6 wraps of 8mm polyester (Dacron) braid. It takes a lot of effort to get the last bit of stretch out of 8mm Dacron braid. The aft beam is a 140 x 4 mm aluminium tube.

    One interesting aspect of the Wharram designs is the wind vane designed by Henneke Boon. It is a horizontal-axis vane and trim tab self-steering system. The system is home-built and simple. According to one skipper (Luckyfish) “It performed flawlessly from Cape Town up to Namibia, then over 6,000 miles across the Atlantic. The boat barely strays more than 5 degrees from her course, often less. It requires no electricity, has no proprietary drive belts, worm screws or electronics to fail and only requires a wind of 5 knots or so to become active.” Luckyfish in severe weather, on a lee-shore, a sailor’s nightmare, carries a 16’ foot diameter Fiorentino sea anchor which is attached by a bridle attached to two 30cm x 18mm S/S eyebolts, through-bolted and epoxied to gussets bonded to hull stringers.

    Tiki 38 can be powered by twin high-thrust 9.9HP Yamaha long-shaft outboards. The engines can be mounted on retractable sleds.

    Tiki 38’s are a popular size for serious cruising and many have been built. They are large enough to have really useable accommodation including real double berths and proper dinette and galley arrangements and carrying a reasonable amount of stores etc. One of Wharrams and Hennke Boons better designs.
     

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  14. cavalier mk2
    Joined: Mar 2010
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    cavalier mk2 Senior Member

    Isn't it Hanneke old boy ?
     

  15. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    We spoke of the Hanneke Boon (sorry about yesterday misspelling) Wharram wind vane and its effectiveness. The following diagram came from Kaimu Wharram Catamaran. The picture is a scan of a sketch downloaded years ago from the internet. It is a rough drawing of the Wharram windvane by Hanneke Boon with a few dimensions and some description of materials.

    The 2 jpegs after is of the Wharram windvane in operation. The windvane itself is a piece of plywood held in place by a bungee cord to a frame shaped like the letter H. The frame can tip back and forth on an axis angled 20 degrees from horizontal, angled away from the wind. One leg of the H has a counterweight which is adjustable to make the windvane balanced just slightly in favour of the weight, i.e., the vane will tend to revert to a vertical position. The frame also has an anchor point for the control lines, which pass over a large sheave on the axis. The size of the sheave is given as 100mm in the drawing (next time).

    The axis is mounted in a pair of vertical supports, maybe 25 x 100 mm timber sections, and they are mounted on a round plate. The plate can turn around a vertical pipe, about one foot long and about 50 mm in diameter. This pipe is glued into another plate, fixed, which is the base of the whole apparatus. A simple clamp of a wood block with a screw is used to clamp the round plate to the base. The control lines pass down the vertical pipe to a pair of sheaves that are fixed in the bottom of the pipe side by side. The pathway of the control lines is restricted by moulded epoxy filler so that they can't jump the sheaves. The lines can then control a trim tab shaft that is attached to a trim tab attached to the main rudders. The only problem is how to fit the trim tabs to the rudders and running of the control lines. The size of the trim tab versus the rudder depends on the design and boat. Some boats like Jim Browns Searunners had about 17% of the underwater rudder area in the trim tabs. Wharram groups suggest about 20%. A case of tuning the trim tab size required to suit the efficiency and type of rudder used.

    Now wind vanes can be home built but they must have low friction bearings, large sheaves, low stretch control lines and well built structures to handle the constant workloads. Windvanes are suitable for heavier cruising boats as they respond more slowly to speed variations. Light boats tend to accelerate and slow more rapidly causing greater than required steering adjustments making them better suited to electronic self steering gear.

    Wind vanes also have a “wind range” eg they rarely work effectively below 5 knots of wind speed and in high squally wind speeds they are less useful. But they are very useful in Trade wind or consistent wind conditions etc. Many wind vane controlled Wharrams and Searunners have circumnavigated. The following e-book may also be very useful. Either the attached PDF or available at https://windpilot.com/n/pdf/bookeng.pdf Also there is a section in the Searunner Construction Manual on windvanes which give some details of the construction.
     

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    Last edited: May 15, 2020
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