Multihull Structure Thoughts

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

  1. oldmulti
    Joined: May 2019
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    Location: australia

    oldmulti Senior Member

    Historical Multihulls thread has just produced some very interesting photo’s of the original Cliffhanger cruiser racer tri by Lex Nicol. I spoke of Cliffhanger (Ben Bolt) on the first page of this thread. Sorry for repeating some information. The tri is 42 x 28 foot displacing 7000 lbs carrying 900 square foot of sail. The main hull has an aluminium tube space frame around the gunnels and along the keel and stem. When the hull was built and the internal frame attached glass was wrapped around the tubes which then "shrank" fit the hull tubes to the tubes. All rigging loads were basically taken by the perimeter tubes allowing the hulls just to deal with water forces. The tubes are 100 x 3 mm 5083 H32 (high strength aircraft grade). The 3 cross beams were also 100 mm tubes for the top and bottom trusses with 50 x 4 mm tubes acting as truss frames. The inner ends of the cross beams where they leave the main hull are 1 meter high, the outer end of the cross beams where they enter the float are 400 mm high. This boat has done thousands of miles of racing and cruising and looks as good as new but the cross arms need constant inspection for stress cracks as they have had to do some minor repairs on them over time.

    The main and float hulls were constructed from 200 gsm kevlar 12 mm airex foam 200 gsm kevlar (doubled outside on main hull bottom to waterline). The decks were 330 gsm cloth, 300 gsm cloth 12 mm airex foam 200 gsm kevlar on the inside. The BH's were foam glass. The dagger board was aluminium with a 25 mm leading edge tube, 3 mm aluminium walls second vertical tube 75% aft of cord and some shaping bulkheads at stress points and to handle uphaul and down haul.

    The tri is now doing the Queensland coast as a live aboard cruiser under a new owner and his family after a mild refit. The aluminium crossarms had some strengthening done a few years back due to cracks in some of the welds but the same basic structure has lasted over 30 years, some of it very hard racing. If well conceived, multi’s can be built very lightly and if well maintained, be very effective long term cruiser racers.
     

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  2. catsketcher
    Joined: Mar 2006
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    Location: Australia

    catsketcher Senior Member

    Cliffhanger is now in Lake Mac - I buzzed the owner in a light day when she went near my mooring. He has put new sails on her and removed the front daggerboard. She looks good.
     
  3. oldmulti
    Joined: May 2019
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    Location: australia

    oldmulti Senior Member

    A Russian man wanted a version of “Miss Cindy”. Miss Cindy is an ocean crossing 16.25 foot cat designed, built and sailed by Tony Bigras from Canada. The Russian cat is a 16.25 x 10 foot cat that displaces 1320 lbs. (Miss Cindy fully loaded was 1100 lbs).

    The Russian tried to get a bit more stability with slightly more beam (10 foot versus Miss Cindy's 8.5 foot) and putting the hulls further apart (hull centre lines 7.6 foot versus Miss Cindy's 5.8 foot). Result is the Russian cat has 30% more stability for a given displacement than Miss Cindy. The Russian cat has a length to beam of 10:1, Miss Cindy has a length to beam of 13:1. The hull shapes between the two cats are similar. The Russian also wanted more deck space and put more accommodation in the hulls which also slightly lowered the centre of gravity of the cat. The maximum hull width is 2.5 foot at the gunnel with 3 foot headroom.

    So, what sort of performance would you get from the Russian cat? If we again use Miss Cindy’s sail area and a similar displacement the performance would be very close. Miss Cindy top speed was 15 knots, averaged between 3 and 7 knots under sail with a longest day run of about 130 miles. Miss Cindy sailed up to 200 miles offshore, crossing up to 430 miles of open water in 4 days and completed over 4000 miles of sailing. If you are well setup, choose your weather well and have a lot of sailing experience it is possible to sail a small boat a long way. But these cats do have limits, please do not try and cross the North Atlantic in boats like this, choose the Gulf of Mexico or the Pacific during the non cyclone/hurricane season.

    This boat could be built with 6 mm ply over the majority of the hull and deck with 9 mm plywood keel plates and bridge deck bottom. The rig was going to be from a “beach cat“ but the design would be easy to convert to a bi-plane lug rig the same as Miss Cindy.

    An interesting fun design. The first jpegs are of the Russian design, the final jpegs are of Miss Cindy.
     

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    Last edited: May 22, 2020 at 7:43 PM
  4. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    The Class 4 design is basically a development of Erik LaRouge 46 foot cat range built by a Latvian company O-Yachts. Erik LaRouge has had over 500 of his designs built and sailed globally and Erik really knows how to design and structurally specify a fast yacht. The Class 4 is a 46 x 25 foot with a shell weight of 11600 lbs a float weight of 13900 lbs with rig, interior, deck gear etc and a maximum displacement of 18400 lbs with crew, water, food etc onboard. The mast is 62 foot high with a mainsail of 870 square foot, jib of 470 square foot and a genoa of 800 square foot of sail area. The rig plan is in the jpegs. The hull length to beam is 11:1 when loaded and the cat has large low aspect ratio keels for upwind work.

    This cat is fast for a fast and easy to sail being able to achieve 250miles/day in comfort. In the 2014 ARC Class 4 “Ena” sailed over 4000 miles going upwind 25% faster than wind from 3 to 9 knots real wind. Then when wind is about 10 to 15 knots, the Class 4 did over 10kts. At 20/25kts the boat will go 14 to 19 knots with reduced sails area and perfectly balanced. The maximum speed reached was 27 knots.

    The Class 4 is a fast yacht with a light displacement of 6700kg thanks to the composite material and build. Build method is a 100% infused sandwich composite in female moulds for the hulls and decks from eglass and vinylester. There is a 2 layer Kevlar shield from the bow to keel/dagger wet area. There is carbon fibre in beams and high strength areas such as a the front and central beam, bowpole, mast pilar, pilar beam and aft beam. The bulkheads, beams and much of the interior furniture is also infused.

    The yard also assembles by hand all composite panels that are not structural. This way, they become structural after hand lamination. The process represents hundreds of labour hours. Sofa, kitchen, stairs, floor, bed, are structural and will not produce a single “sound” when the boat is sailing as they are an important component of the cat’s structure.

    This is a good fast design that appears to well built. An interesting design. PS I do not know if Erik has retired as I could not find his web site, in France they have a rule that if a yacht designer is no longer active, they cannot advertise or sell boat plans.
     

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  5. Dolfiman
    Joined: Aug 2017
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    Location: France

    Dolfiman Senior Member

    It is Lerouge, not Larouge, started his career in 1976 and still in activity :
    Erik Lerouge http://erik.lerouge.pagesperso-orange.fr/catamaran.htm

    PS : Erik Le Rouge (=The Red, due the colour of his hairs and beard) is also the name of a famous viking, he installed the first colony in Greenland by years ~ 1000, Greenland so named by him because of the favorable climate in those days (already a climate change!) and also to attract more settlers.
     

  6. oldmulti
    Joined: May 2019
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    Location: australia

    oldmulti Senior Member

    VMG design submitted the following visions for the Volvo In-Port Series. They were inspired by the famous D35 cats used in Swiss lake racing. They kept thinking if the Volvo and Swiss Lake circuits could race with the same platform. So, they proposed two designs, one that matched the Swiss Lake circuit and another that answered the Volvo tender. Design 1 is for the Volvo circuit requirements. Design 2 is for a “improved Volvo approach” with an eye on the second need of the very specific wind conditions on Lake Geneva.

    VMG 35 Design Proposal 1:
    This 35′ feet flying catamaran that includes all the latest features. This catamaran is a “limited risk project” and is an evolution of the current trend of foiling catamarans. This boat can race in either of the following mode: Non Foiling or Foiling. Therefore, this boat is somehow a “3 in 1” boat that is compliant with the specificity of being a full foiling boat on short In-Port Series, an exciting one design boat for long distance racing and a boat that can deal with very light winds encountered on some lakes.

    Design 1: 35.5 x 23.25 foot (total length with prodder 38.8 foot). Displacement (weight) 2000 lbs with an upwind sail area of 915 square foot including the wing mast. The cat is constructed of Carbon – Nomex – Epoxy.

    VMG 35 Design Proposal 2:
    The second project is the result of a brand new approach to the concept of foiling multihull. The concept is the foils are the central piece of the boat. This 39‘ catamaran is light and efficient with a twin rig with soft wing sails. The hulls are only to maintain the boat afloat when not foiling. The overall flight stability is clearly enhanced as the distance between the main foil and the rudder is at a maximum.

    Design 2: 38.8 x 27.85 foot. Displacement (weight) 1680 lbs with an upwind sail area of 970 square foot including the wing masts. The cat is constructed of Carbon – Nomex – Epoxy.

    These designs were done in 2017 and were not selected by Volvo but are interesting. Design 1 jpegs first. Design 2 with twin rigs second.
     

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