Multihull Structure Thoughts

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

  1. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    This will be first of 2 items on this design. The first will describe the cruising catamaran and the second item will show build photo’s and some construction detail. The cruising catamaran is the BOHEME 43 which is designed by Gerard Danson as an evolution of the Outremer 43. This model is designed for home or one off construction. The BOHEME 43 is 43 x 21.65 foot with a dry weight of 18600 lbs or 46 x 23.65 foot with a dry weight of 21,000 lbs. Depending on which option you choose. The 46 foot version carries a fixed 60 foot carbon fibre mast with a 730 square foot mainsail, 280 square foot self tacking jib, 107 square foot storm jib and 1170 square foot asymmetric spinnaker. The rigging is Dynex dux 13 mm (Precourt dead eyes) fore stay and 12 mm stainless steel. The length to beam is about 10.5 to 1. The draft with low aspect ratio keels is 4.6 foot or with optional daggerboards between 3 foot to 8.4 foot. The cat can be powered by two 30 HP diesel inboards.

    The cats performance is good, especially with the daggerboard version. The cat can average 200 plus mile days and peak at around 20 knots. The fin keel version can also go upwind very well. With the self tacking jib on a curved track going upwind is relatively simple.

    The base design has 2 double berth cabins and full toilet in each hull. There is an option of 3 double cabins with a workshop if you intend to do serious cruising. The main cabin has a full settee, navigation area and extensive galley. The galley has a large doorway and opening window facing the cockpit to give the impression of a larger space. Steering is done from the cockpit on a raised seating area.

    The cat is constructed from plywood, timber and fiberglass in epoxy. All timber and ply has “West” type system applied. The 46 foot version shown here was started in 2005 and finished in 2015. More details tomorrow. The jpegs are mainly of the 46 foot version.
     

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  2. revintage
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    revintage Senior Member

    Just found Corleys thread, where he rebuilds a Kraken 25 with paulownia planking. Impressive but surely time consuming. Like it though and I´m using it for my hydrofoil cores being built now.
     
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  3. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    The BOHEME 43 which is designed by Gerard Danson as an evolution of the Outremer 43. This model is designed for home or one off construction. The BOHEME 43 is 43 x 21.65 foot with a dry weight of 18600 lbs or 46 x 23.65 foot with a dry weight of 21,000 lbs depending on which option you choose. The rig is 1010 square foot of main and fore triangle. You can have dagger boards or fin keels.

    Now we start on the construction. This is a plywood and timber structure of full West epoxy construction. The unusual part is the round bottom approach. The hull basic structure is a flat bottom box which then has a series of half circle ply bulkheads positioned on it. The gaps between the ply bulkheads on the bottom are then filled with Styrofoam slabs that are sanded to a smooth hull shape. Over this basic shape is e-glass fabrics in epoxy to form the hull bottom. In the jpegs there is a low aspect ratio keel on the hulls which goes from the ply box section to the exposed part of the keel. I have no problems with a ply timber cat especially when fully West system BUT I do have a problem with using Styrofoam as a structural component. Even high density Styrofoam can breakdown over time especially if its surface is damaged by EG running into a floating log. Airex, Corecell etc have much high resistance to vibration, impact resistance and generally have better water resistance. Airex, Corecell etc foams also have stronger shear capability. If you are doing a bay or limited coastal multi that you can maintain regularly, fine use the technique, but it would not be my preferred approach for an offshore multi.

    Back to the BOHEME basic structure. The hulls have 12 mm ply sides and bottoms over 4 stringer, chine and gunnel strips per side. The hulls with the shaped Styrofoam is covered with 1040 gsm quad fabric and a surface glass covering all in epoxy. There is a frame or bulkhead about every 3 foot. The decks are 10 mm plywood with deck beam and stringer support covered with 2 layers of 300 gsm roving fabric protects the plywood in the hull, deck and lockers. Seats etc. have a 300 gsm glass layer with an epoxy covering. The underwing is 15 mm plywood with framing support. The cross beam bulkheads are probably 15 mm (guess) with timber support framing. The timber is mainly Mahogany for the structure. The deck cabin has multiple layers of 5 mm ply to form its shape with timber framing. There are some 22 mm plywood components.

    The jpeg cat has been very well built over the 10 years of construction but was built by a small team. The basic boat materials, engines and some equipment cost 90,000 Euros not including labor, shed rental, build equipment and the rig. This is a substantial investment in time and money to achieve a dream. The 46 is for sale at $375,000 US dollars or (327,000 Euro). The jpegs give the idea.
     

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  4. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    A short one for East Coast Australians. The 21/22 Jaques Harve double handed transat was shown on 73 TV on Friday morning 4/2/22. It was an hour long and hopefully is on channel 7 catchup facility. The shots of the tris and monos sailing were good. The winning Ultims did a 9000 mile course at an average of 24 knots, the 50 foot tris averaged 17.5 knots over a 6000 mile course, the IMOCA foiling 60 foot mono's averaged 15 knots over the 6000 miles and the 40 foot monohull class averaged 10 knots over a 4000 mile course. Modern racing mono's have very full bows to try and create as much stability as possible trying to imitate a catamaran type stability in a wide monohull. interesting how the wide bow mono's go through a seaway. Also foils are becoming much more reliable. Seeing the 60 foot monohulls and 100 foot tri completely flying with only 2 crew is interesting.

    Also revintage, paulownia for strip work and planking is a nice material. If you have a good source of the material you will not be unhappy.
     
  5. guzzis3
    Joined: Nov 2009
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    guzzis3 Senior Member

    OM: I tried to look back at the thread index yesterday. I may have missed it due to my poor sight. Have you looked at the larger, now withdrawn, Woods cats or the Waller CC40 ?

    I ask because so many boats in that 40+ size range are full bridgedeck cabin designs. The boats mentioned are variations on this, with the Woods "cuddy cabin", open deck or the Waller open back "shelter" ? on the bridgedeck. I suppose that's the market but it's nice to see something a bit different. You can find an old version of the RW website here:

    over 40' Catamarans by Woods Designs https://www.sailingcatamarans.com/40ft.htm
     
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  6. peterAustralia
    Joined: Mar 2006
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    Location: Melbourne Australia

    peterAustralia Senior Member

    Sniper Outrigger Sailing Canoe
    Length.: 6.15 m
    Wide: 3.3 m
    Sail area:9 m2
    Slenderness ratio :1:20
    Weight:115 kg
    Mast length:6 m
    Performance:Broad reach 13 knots in 18 knots wind,10 knots knots up wind
    Paddle speed:4-5 knots
    Engine:Outboard 5hp 14 knots
    Capacity:2 persons
    No.of 3 separeted flotation chamber
    Stayless free rotating mast ,vertical battens,Dacron 5 Oz Ullman sails
    Fiberglass NACA leeboard and folding rudder
    Rudder steering pedals for easy paddle
    2x1.2 m trampoline
    3 water tight plastic enclosere for storage of camping tools
    Telescopic tiller
    CE Catagory "C"
    Fiberglass Polyester hulls
    My name is Bahadir Egi,retired Elec.Eng.I am designing small sailing boats( www.yelkensever.com ) and selling them also.
    Sniper is Outrigger Sailing Canoe which is designed 13 years ego,no.of 15 Sniper is on the water.
    Rotating boomless sail is so easy to use,she can sail 13 knots broadreach.

    mmmm.jpg
     
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  7. Hell_Bent
    Joined: Sep 2021
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    Location: Vancouver BC, Canada

    Hell_Bent Junior Member

    Those little outriggers are neat, and this is one of the nicest I've seen. I'm following the design of a different custom one over on SA and we were having a conversation on the backup floatation on the stub akas which would be to leeward on the proa tack. It's a good idea, but I think I would have put a bit more effort into the shaping of the backup float, as that flat face is the kind of thing that would readily slam into a wave in the kind of conditions where the reserve would be needed. Still an excellent little boat and hey, theres quite a few out there so I guess it works fine.
     
  8. peterAustralia
    Joined: Mar 2006
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    peterAustralia Senior Member

    the backup float is called a safety ama. Yes, you are probably right, a little shaping of the bow for it might have been a good idea. A relatively easy modification. One surprise to me was 14 knots on 5hp,, gee
     
  9. Hell_Bent
    Joined: Sep 2021
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    Location: Vancouver BC, Canada

    Hell_Bent Junior Member

    Right thanks. For whatever reason I just couldn't find the words for that.
     
  10. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Guzzis3, I will look at the Coral Cove 40 and Meander over the next few days. But a few trivial things today to clean up some stuff.

    We looked at the Kelsall KSS X-Kat 26. The 26 is 26.2 x 14 foot (or this version 16 foot) with a displacement of 3150 lbs. The sail area of the mainsail is 247 or 280 square foot with a jib of or 120 or 140 square foot depending on the mast height chosen. The draft is 2 foot over the low aspect ratio keels. I have found a more detailed study plan shown below. The hull length to beam is 8.6 to 1 and the mast height is 32.8 foot. The draft is 2.25 foot over the fixed fin keels. The hull width at the gunnel is 4 foot and at the waterline is 3.1 foot which means the double berths are 3.2 foot wide. I personally think that is a single berth but I have been spoilt for luxury with 4.5 foot wide berth for most of my sailing.

    Next is a “design concept” I have seen from Reefscape Marine. The MAX 30 ST jpegs show a new trailable folding tri they are promoting. I know very little beyond its length of 30 foot. Reefscape has produced other multihulls to a high standard of finish so hopefully this will match it. Web address: https://www.reefscapemarine.com.au/boat-models/max30st-sailing-trimaran/

    The final jpeg is the Vector 24 catamaran which is designed by Viktor Brejcha, a Czechoslovakian. This 24 x 13 foot open bridge deck catamaran is designed to be fast, easy to build, transportable and a fun cat is for lakes and coast sailing. The displacement is 2550 lbs. The hulls will be foam glass and the cross beams carbon fibre for lightness to allow disassembly for trailing. Some hull accommodation for bunks and storage. No further details.

    Tomorrow will be about a 30 foot South African cruising catamaran, then we will do Woods 40 foot Meander.
     

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  11. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    The following cruising catamaran designed by Rajen Naidu and was built in South Africa by Rayvin Yachts on a production basis. The Rayvin 30 is 30 x 18 foot with a weight of 5500 lbs and a displacement between 8,000 lbs and 9,000 lbs depending on the level of equipment, engines etc. The 38 foot aluminium mast carries a fractional rig of 610 square foot. The draft is 3.3 foot over the low aspect ratio keels. The rudders are underslung spades. The hull length to beam is about 9 to 1. The engines vary but several have two 18HP diesels which when cruising at about 6 to 7 knots consume 1 litre per hour per engine.

    The reason this cat was designed and built by Rajen Naidu was the desire to have a 30 foot ocean cruising catamaran. The problem being a husband and wife team with two young children, they found that any cat over 30 foot was a handful for them but small manageable boats were too cramped and hardly performed under sail. Result, Rajen designed the Rayvin 30. The Rayvin has 3 double berths and a full toilet cabin in the hulls. The main cabin has a galley, settee and navigation area. Some Rayvin 30’s had a galley in the hulls. Most areas including the main cabin have 5.9 foot plus headroom. There is sensible storage space with lockers with sliding doors etc. You can even have a real cat claiming your double berth cabin as an option. The cockpit is relatively large.

    The capability of this cat is the real issue. To quote an owner “The Rayvin 30 is living proof that even a small cat can be a true bluewater boat; seaworthy and ready for the challenges of an ocean adventure. The owner reports she holds 40 degrees to the wind in flat water, 50 to 60 degrees in rough water. She has sailed in 50 to 60 knot winds without any difficulties.” There are Rayvin 30’s in South Africa, Australia, USA, the Med with other owners reporting upwind capability in strong winds and averages of 6 to 9 knots with peak speeds of 15 to 18 knots when not overloaded with cruising gear. These boats are real ocean crossers if sailed sensibly by good often short handed crew.

    The construction of the Rayvin 30 varies. Some were built in infused vinylester and Balsa. But several hulls had e-glass + Balsa core sandwich composite with epoxy resin with Kevlar/Carbon fibre under the waterline and up the bows. The deck material is glass + Balsa core sandwich composite - epoxy resin. Bulkheads and main beams etc are epoxy glass balsa sandwich. Balsa below the waterline is not my preferred material but if is done with epoxy and well done it will be strong and should last well. The first boats were built about 2005 and production appears to have stopped in about 2015.

    This is a good example of a small cat that is ocean capable and can handle difficult conditions. Rajen Naidu has designed an excellent solution for people who want to really cruise without pay for a 40 foot plus cat that starts to require a crew to help them cross an ocean. The jpegs give the idea.
     

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    Last edited: Feb 7, 2022
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  12. bajansailor
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    bajansailor Marine Surveyor

  13. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Today we start our review of 40 foot open wing deck cruising cats. The first cat we will look at is Woods Meander. A 40 x 22.6 foot cruising cat that weighs 7,850 lbs and displaces 13.450 lbs. The 45 foot fixed aluminium mast carries 750 square foot of sail in its cutter rig. The length to beam on the hulls is 12 to 1. The draft over the daggerboards ranges from 2.2 foot to 6 foot. Engines suggested is two 9.9 HP outboards.

    The accommodation is hull based with 3 double bunks and 2 singles. A galley and table arrangement are in one hull. Loo in the other hull. There is a very large cockpit for easy sail handling. A Pod cockpit cover has been built on a few Meanders.

    The structure can be sheet ply or grp flat panel deep V hulls or strip plank cedar or foam glass deep V or rounded V hulls. Today we will stay with the sheet plywood version although in design updates Mr Woods preferred the strip plank or foam version which we will deal with tomorrow.

    The hulls are 9 mm ply for hull sides, 12 mm ply for keel panels. There are 75 x 25 mm stringers and bulkheads are 9 mm plywood with 50 x 25 mm framing support. The decks are 9 mm plywood with deck beams and stringers. The bridge deck panels are 9 mm plywood with timber framing support. The cross beams are wooden box beams with a 12 mm plywood web 50 x 50 mm top bottom flange, 12 mm ply web with 75 x 50 mm top and bottom flange, 12 mm ply web with 50 x 50 mm top and bottom flanges then the final 12 mm ply web. The entire hull deck and beam structure is West epoxy saturation with e-glass on exterior surfaces. The internal floors bunk 9 mm ply with 6 mm furniture with 25 x 25 mm internal framing. External rubbing stakes are 75 x 25 mm hardwoods.

    The entire structure can be built in separate components of EG hulls, cross beams, deck platform etc and then moved next to water for final assembly. Woods suggests the boat be rigidly locked together for the best long term results. Many of these boats have been built and some have done long distance sailing. This is an old design which has a fine ended hull shape which may impact pitching. Richard Woods originally worked with Wharram for a short time which appears to have influenced some of his original designs. These cats are good load carriers and are faster than Wharrams of the same length but there are faster modern designs.

    The jpegs give the idea of the Meander. Tomorrow we will focus on the strip plank cedar and foam version of the Meander.
     

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    Last edited: Feb 8, 2022
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  14. SolGato
    Joined: May 2019
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    Location: Kauai

    SolGato Senior Member

    I came across this photo of a catamaran, perhaps someone can identify it?

    I think the deck/cabin layout is interesting. It looks to have nice wide flat deck surfaces either side of mast, bunks in the side wings of the bridge with a center cabin pod, all in an effort to reduce windage and increase performance, or maybe it’s just a custom conversion.


    1B4F8DC7-E8E5-43AD-BC09-5CF2D46CF0F8.jpeg
     

  15. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Solgato. I cannot find the exact detail but this was a french transportable cat. How? It was about 28 foot long and the entire bridgedeck section for the full beam could be lifted and turned sideways to be put on top of the hulls for transport to get it under 8 foot. A few were built. The main cabin had a double berth either side of a settee with a table. I think the company was Advetura but am unsure. Hope this helps but some of our french readers may be able to give a better guide.
     
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