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

    The following 21 foot trimaran is a design proposal from Richard Fraser from Fraseraerospace.. Richard has built a Piver Mariner 25 trimaran (story over 6 pages at: Richards_Arthur_Piver_Mariner_25ft_Trimaran https://fraseraerotechnologycompany.com/Richards_Arthur_Piver_Mariner_25ft_Trimaran.html )

    The proposed trimaran is 21 x 13.3 foot with folding floats that will reduce the beam to 8.5 foot. The weight is unknown but a guess of about 1500 lbs and a displacement of about 2200 lbs. The 30 foot mast will carry about 200 square foot of mainsail and 130 square foot mainsail. The main hull will be round bilge, float shape is unknown.

    The concept model for the 21 foot ocean sailing, 2- place wood and fiberglass trimaran day sailor with forward cubby for one person to get out of bad weather. The tri has a very comfortable cockpit area for beach camping as well.

    Richard runs an aircraft business and as a result understands design and light weight build techniques. The real boats construction would be the latest in simple cold molded construction techniques with epoxy and mahogany strip veneer composite construction. This technique lends itself very well to wooden aircraft construction and is extremely easy and forgiving to the beginner who wants to build a light, very stiff and strong craft. Epoxy used is the West System. The hull thickness would be 6 mm with frames/bulkheads and ribs but very few stringers.

    Floats (amas) would fold down for trailering and the mast is self-rotating. Safety netting would be between the main hull seating and each ama. Forward netting can be optional as this has turned out very beneficial in previous trimarans.

    An interesting concept which I hope was built. The limited jpegs give the idea. There is some development in the jpegs as you will see in the rigs size and main shape.
     

    Attached Files:

  2. oldmulti
    Joined: May 2019
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    Location: australia

    oldmulti Senior Member

    The Threefold 6 is designed by Dudley Dix to be a safe and lively trimaran to sail singlehanded or with a crew and can be used as a day sailor or comfortable gunkhole cruiser. The Threefold 6 is 19.66 x 16.25 foot in sailing format with a dock beam of 10.9 foot and a trailing beam of 8 foot. The weight is 990 lbs. The 27.5 foot mast (could be a Hobie mast) has a mainsail sail area is 152 square foot and the genoa is 113 square foot. The length to beam of the main hull is 5.5 to 1 on the 18.33 LWL. The draft is 0.66 or 2 foot.

    The accommodation is simple with 2 wing berths, a forward berth, a small galley and a small seat area. It has 4.5 foot of head room but with the moving hatch it will allow 6 foot headroom at the galley when open. Simple and effective accommodation for 2 people for short cruises.

    The performance of the Threefold 6 is best described by Oleg Zelinskiy built in Russia. “In November 2008 he went out in extreme storm conditions to test his boat. With winds of 15-22m/s (30-40 knots) and gusting to 32m/s (65 knots), they sailed with storm jib and deeply reefed main. He reports that she handled perfectly, even with seas washing over the deck through to the cockpit. She achieved speeds of 15-17 knots and was responsive and under full control at all times. He says that stability was perfect and there was no hint of the boat ploughing in. Oleg is very satisfied with his testing of the boat in storm conditions.” And “In September 2009 Oleg reported that in 15-25 knots of wind he and one other crew had sailed 15 miles in one hour, with speeds sometimes exceeding 20 knots.”

    This would indicate Dudley Dix has designed a good sailing vessel and he has some brave clients willing to test their boats capability to the limits.

    The tris construction is plywood, timber and an aluminium cross beam structure. The materials list is as follows:

    MARINE PLYWOOD 1,22x2,44m (4'x8') (preferably Gaboon or Okoume plywood)
    4.5mm (3/16") - 11 sheets (use 4mm if 4.5mm is not available)
    6mm (1/4") - 14 sheets and 9mm (3/8") - 3 sheets

    CEDAR or similar, selected, free of knots, shakes fractures etc
    15x30mm (5/8"x1 1/4") - stringers, framing - 80m (262')
    15x40mm (5/8"x1 1/2") - beams, framing - 20m (66')
    20x20mm (3/4"x3/4") - framing - 94m (308')
    20x30mm (3/4"x1 1/4") - framing, tiller - 67m (220')
    20x40mm (3/4"x1 1/2") - framing - 70m (230')
    20x50mm (3/4"x2") - keelson, sole bearers - 9m (30')
    20x60mm (3/4"x2 3/8") - framing, sole bearers - 4m (14')
    20x200mm (3/4"x8") - companion ladder - 1m (4')
    25x50mm (1"x2") - beams, posts - 9m (30')
    30x30mm (1 1/4"x1 1/4") - sheerclamps - 10m (33')
    30x40mm (1 1/4"x1 1/2") - framing - 6m(20')
    50x50mm (2"x2") - stem, beams - 3m (10')

    This is a relatively easy to build small cruising tri that can sail well and is trailable (with a bit of effort). The jpegs give the idea.
     

    Attached Files:

    Last edited: Nov 26, 2021 at 10:32 PM
  3. Slingshot
    Joined: Aug 2019
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    Location: South pacific

    Slingshot Junior Member

    Good day Old multi.

    I searched the index and did not see any info regarding the Bazapi 50. Do you by chance have any info on the material used for construction and technique of these cats?
    thanks

    All the best
     
  4. oldmulti
    Joined: May 2019
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    Location: australia

    oldmulti Senior Member

    Slingshot. More information please on the Bazapi 50 cat as I do not know the cat. Eg who is producing or designed it. i can possible follow up from there.
     
  5. Slingshot
    Joined: Aug 2019
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    Location: South pacific

    Slingshot Junior Member

    The Brazapi is a Eric Lerouge design that was produced in Belgium. I have seen info on Eric’s site in the past but never a mention of the resin or core used to build the hulls.
     
  6. oldmulti
    Joined: May 2019
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    Location: australia

    oldmulti Senior Member

    Slingshot. They talk about the Brazapi 50 and a 51 which were custom builds. The 50 was Foam epoxy glass with kevlar reinforcements and an EG can be found at Brazapi 50 https://www.36degrees.nz/yacht-boat-sales-auckland-new-zealand/boat/brazapi-2
    Next have a look at Eric web site at the 15 meter range and you will find its heritage. Eric design structures are similar across his range. the web site is Erik Lerouge http://erik.lerouge.pagesperso-orange.fr/cat_15.htm
    Finally I have a book Eric wrote in french describing how to build foam glass boats where he describes the build of his cats and mono's. I will find the title tomorrow. hope this helps.
     
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  7. oldmulti
    Joined: May 2019
    Posts: 1,514
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    Location: australia

    oldmulti Senior Member

    Slingshot. The book is by Erik Lerounge and is titled "Materiaux Composites" It was produced by HS 30 Loisirs Nautiques. The book is no longer produced but was written in 1991. presse 50143 issn o47 5017 I cannot even find a second hand version. But it is worth a try. It describes composite construction and in a few chapters mentions cross beam structures for open wing deck and full bridge deck cats. Maybe someone has it around.
     
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  8. Slingshot
    Joined: Aug 2019
    Posts: 25
    Likes: 4, Points: 3
    Location: South pacific

    Slingshot Junior Member

    Thanks for the search Multi. I will have a look for the book.
    Cheers
     
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