Multihull Structure Thoughts

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

  1. brian eiland
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    brian eiland Senior Member

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  2. brian eiland
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    brian eiland Senior Member

    I just saw a reference to this vessel about a week ago, and I was going to ask you about it, when suddenly I went to page 28 and found this posting of yours.

    Very interesting vessel, particularly the mast construction.

    Is there any more info available on the power system? I believe i saw where it uses electric outboards, but I am woundering how they get the power down to the props,...and if they are retractable??
     
    Last edited: Apr 4, 2020
  3. bajansailor
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    bajansailor Marine Surveyor

    Thank you Brian for reminding me about this post by Oldmulti re the Conser 47.
    Re Ron in Barbados, here is a link to Ron's cat 'Wasn't Me'.

    BARBADOS AHOY - Wasnt Me http://www.barbadosahoy.com/wasntme.htm
     
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  4. brian eiland
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    brian eiland Senior Member

    I was very much interested in that Solidary Cat design as well,... I posted this back in 2012, but I think all the links are dead now,...
    Post your design ideas https://www.boatdesign.net/threads/post-your-design-ideas.37103/page-8#post-562566
     
  5. oldmulti
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    oldmulti Senior Member

    A request for more Chris White information has led to the next design. A performance cruising cat of 40.3 x 18.8 foot displacing 11,000 lbs. The Low Aspect Ratio fin keels draw 3 foot and the forward freeboard is 5 foot. Now we come to the rig. The rig is claimed to be “A super easy to sail MastFoil (US patent) design. Layout features all controls led to cockpit for easy short handed sailing. No mainsail to hoist, reef and furl!” The rig is self-tacking and all sail controls are led to the cockpit.

    The sailplan composed of two roller furling, self tending, jibs supported by two 40 foot high MastFoils which are carbon fiber small rotating wingsail masts. This sailpan has been proven in 11 larger cats sailing approximately 100,000 miles. The MastFoil rig is all vacuum bagged carbon fiber/epoxy, built by Alwoplast. Reefing lines and furling are led to cockpit. Standing Rigging: All 1x19 SS wire, Running Rigging: Spectra double braid Jib halyards and Reacher Halyard, Sta-Set low stretch Dacron sheets and control lines. Jib Roller Furling: Harken roller furler with reefing line led to cockpit mounted clutch adjacent to winch. Sails Ullman Sails, Fiberpath Carbon/Vectran Laminate 2016 Harken Mk4 furlers Ullman Code 0 on bowsprit with Harken furling system.

    To quote Chris White: “Our experience to date with the MastFoil rig is that the windward sailing performance is about equal to a conventional sloop rig. A Computational Fluid Dynamics study by Doyle Sails CFD comparing a conventional rig and MastFoil rig in the new Atlantic 47 catamaran indicates a 1% performance difference, essentially no difference. Given the ease of handling and versatility of the MastFoil rig I gladly accept a moderate reduction in predicted aerodynamic performance. The ease of handling means the Mastfoil can be "dialed up and down" so quickly that the MastFoil is likely to be faster when actually sailing. This will be especially true when sailing shorthanded, where crew delays in responding to wind changes account for HUGE variation in performance. Make the rig easy to sail well and it will be sailed better.” At anchor, with the aft MastFoil locked on center, the boat will ride head to wind, eliminating the need to rig an anchor bridle.

    Construction: Hulls are epoxy composite with carbon fiber skin outside, white cedar core and high strength S-glass inside for a clear finish. Decks are constructed from foam cored carbon fiber/epoxy laminate cored. All exterior surfaces are painted with AwlGrip™ polyurethane coating. Rudder blades are fiberglass composite, high performance hydrofoil section with solid Aquamet 19 rudder stocks turning in low friction bushings. The build jpegs give an idea of the structure.

    In order to keep the profile low, and preserve underwing clearance, the standing headroom of the MF40 is located in the hulls where it is most needed - in the galley, the head, and the hull adjacent to the Queen size double berths amidships. The deckhouse consists primarily of the settee in the main cabin where people are sitting or lying down most of the time. The deck house height is low enough to not obstruct forward visibility from the cockpit. Cockpit: 14’ wide by 8’ long, 11' bench seat and cushions with stowage below.

    Propulsion Twin Yanmar 3YM20 (20 HP) diesel saildrive engines High output (115 amp) alternator on both engines. Propellers are bronze geared folding type by Flex-O-Fold. The range under power is 400 plus miles. Electrical: (3) Solar Panels, 100 watt output each, with deep cycle gel AGM 150 amp hour capacity each. Ground Tackle 35 lb. Delta anchors, each with 200’ ¼”chain. 22 lb Danforth , 50’ chain 150’ nylon Maxwell Anchor Windlass.

    This is a light fast boat built with strong lightweight materials, resulting in lighter hull and deck laminates and better performance under both sail and power. An interesting cat and rig.
     

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  6. oldmulti
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    oldmulti Senior Member

    Brian. From my understanding the Eagle 53 currently has 3 engines. A YANMAR 3YM30AF-C 29 HP probably to drive the electric system which drives winches etc and two 70 HP S.D.25 Diesels probably to drive the boat. It also has a 1596 Watt, 24V SOLAR SYSTEM and LITHIUM ION BATTERY BANK. The owner wants to change the boat to an all electric drive system etc.
     
  7. Russell Brown
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    Russell Brown Senior Member

    The construction photos of the Chris White cat are really informative. What a clean design and build.
    I just saw Chris for the first time in 30 some years. He's still switched on for sure.

    Brian, there's an article in Pro Boat about Eagle and I'm sure there's something about it on the Bieker Boats website.
     
  8. brian eiland
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    brian eiland Senior Member

  9. brian eiland
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    brian eiland Senior Member

    I just recently got referred back to some older issues of ProBoat that had stacked up unread on my shelf,...And I found that article on Eagle. ...VERY INTERESTING rig design there. I'm sure Chris White has taken notice of it.
    1) 'cable rigging all the way to the very top (only 3), attached to a swiveling cap that would allow the wing mast to rotate a full 360 degrees'
    2) the very rigid carbon fiber, foil leading-edge mast section that accepts big compression loads without addition of spreaders, etc. "The solid D-shaped leading edge of the foil acts as the mast that holds up the entire rig, while the trailing edge is covered in a fitted cloth cover..."

    I also found them using a 'central protuberance, called the pod, beneath the bridge. Almost hidden, it runs lengthwise down the center of the tunnel between the hulls to form a robust structural girder that suggest a vestigial third hull. It obviously supports the bridge deck, ' but it also adds fore-aft rigidity for the rig loads.

    I called my central protuberance a nacelle. I've been promoting this idea for YEARS now


    Forgot where those many images of my central nacelle sketches were?
     
  10. brian eiland
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    brian eiland Senior Member

    Sail Loading on Rig, Rig Loading on Vessel

    Vessel Substructure to Support Rigging Loads


    The Boat ‘Is’ the Structure

    Who would have ever dreamed that a lake sailing, ultra light-weight, racing catamaran would encounter, and be capable of sustaining rigging loads comparable to those of an America’s Cup boat??

    From a recent article in Seahorse magazine, “Alinghi, Birth of a Crazy Boat”, this paragraph emerges, “The boat ‘is’ the structure. These boats are now so complex, and the loads so high, that structural aspects take on a particular high importance: imagine that on a 1.2 ton boat you can reach 23.7 tons of mast compression…levels seen on an IACC design weighing over 24 tons! Also one cable in the substructure is sized at 56 tons…it is amazing that such light boats can produce such enormous loads.” (let alone absorb them, BE)
    Alinghi Catamaran
    http://www.boatdesign.net/forums/showpost.php?p=98787&postcount=39
    ….attached PDF

    The point is ‘the boat is, or should be, designed as a structure’ to carry the rigging loads. In far too many cases with production vessels and custom vessels this is not the case. Most are concerned with a maximization of the interior layout, and bulkhead placements are supplemental to this interior layout configuration. Yes, care is taken with the placement of the mast and the need to support the compression loads of the mast, but seldom are the shrouds and stays tied to a 'designed substructure’ of the vessel…they are simply and traditionally attached to the outer hull skins and ends of the vessel’s shell.

    This ‘flaw’ can be even more of a problem with a multihull vessel. The catamaran platform lacks the ‘backbone’ structure of the traditional keeled monohull, or central hull structure of the trimaran. Yet seldom is there any serious thought given to some sort of supplemental frame structure in these vessels. No wonder we see so much headstay sag. No wonder these boats can not carry a nice masthead genoa. Added to this equation, the shrouds are attached at a ‘shallow angle’ (half that of the forestay), so their aft-pulling capability is limited by both this shallow angle and the 3 point (tri-angled) configuration. Then at their point of attachment to hull sides (skins) there is likely no firm bulkhead backing, just skin. The shell of the hull is being asked to absorb the load, which it does in a ‘forgiving manner’ resulting in more forestay sag. It’s no wonder these vessels can’t carry a decent size headsail.

    Now some would say this is not important, just utilize a fractional rig and smaller headsails. Rather interestingly this same Seahorse article discusses the preferred selection of multiple headsails and overlapping foresails for this optimized race boat. Naturally I found this observation rather interesting due to my preference for headsails, but I won’t rehash those arguments here, just reference a few subject threads I’ve contributed to these discussions. **see below

    From another portion of the Seahorse article, “Alinhgi, Structural design:
    The below-deck cable and beam truss structure is clearly visible in these two pictures, tying in the torsional loads that cause conventional cats to twist under sailing loads. The first boat sported a full carbon truss/tie rod structure on the centerline, looking somewhat like one side of a mast. This takes the place of a trimaran’s main hull, to carry the very high fore-and-aft loads generated by the forestay, mast and mainsheet.”


    I have suggested such a fore-to-aft truss member be incorporated in the central wave splitting nacelle structure on my cruising designs:
    A Longitudinal Beam & Headsails/Headstay Load http://boatdesign.net/forums/showpost.php?p=111971&postcount=71
    …excerpt..“Imagine a flat, on edge, mounted down the centerline on the underside of the bridge-deck. This flat plate will act as a rib to strengthen the fore-to-aft rigidity of the vessel. If a tow-bundle of hi-tech fiber was laid along the bottom edge of this flat plate, the rigidity could be even greater, akin to a bottom truss structure”…(or one side of a mast).

    Back to the Sea Horse article,"On Alinghi the concept was taken an important step further. The aft portion of the central longitudinal truss member was divided into two separate members that ‘Y’ out to the stern beam. This completely solves the Achilles’ heel of catamarans, which is torsional deformation of the platform. Alinghi’s windward hull trims down by less than one-degree compared to the leeward hull at maximum load.
    Finite element analysis and a specially written truss-analysis program were used to calculate the loads on every structural member and optimize their stretch behavior under all conceivable loading conditions as some of these loads reach 40 tons."


    This torsional deformation subject matter is certainly an important one, not only in race boats, but cruising ones as well. It can prevent us from carrying our sailing rig in a most efficient manner, and it can rack a boat to a slow death.

    The big Polish RACE catamaran "Warta Polpharma" added a cross X bracing of hi-modulus cable between the inner corners of its fore-beam and aft-beam in an attempt to stiffen itself in torsion and racking.

    "Team Adventure" was also contemplating the same arrangement (in fact I believe they did such an installation right after the finish of the RACE in preparation for a trans-Atlantic speed run). Of course these are non-bridgedeck cats.

    Solid bridgedeck designs that we find with cruising cats are advantaged over the trampoline cats with respect to this cross-brace stiffening. But particular attention must be paid to the ‘flat-plate nature’ of most bridgedecks, and their construction composition, and their positive attachment to the main crossbeams in order that they are utilized most effectively.

    Many cats are seen to have basically a flat bridgedeck structure with some attached fore-to-aft stiffening beam/ribs on the bottom side. These attached beams/ribs do act to cut down the unsupported panel size and give a stiffer walking deck to the saloon, but they only act in a small manner to prevent the bridgedeck from bending fore-to-aft. And they don’t contribute to the athwartships or diagonal bending problems at all. If we give a little camber shape and/or add a corrugated channel shape to the flat panel deck we improve things a little bit further.

    Athwartships bending is a most serious concern as our rig’s shrouds are always acting to bend our vessel up in half around the mastbase pushing down. In open-deck cats the stiff crossbeams along with their dolphin strikers and gull strikers resist these bending loads. In our cruising cats it’s the main bulkheads we rely on to do this job. But so often we see vessels with less than desirable bulkhead arrangements. I believe it is very important that their be a minimum of two major bulkheads, one fore, one aft, and that akin to the open-deck boats these two bulkheads must be continuous across the whole beam of the vessel. And these bulkheads need some ‘beef’ rather than just be made of some ‘flat sheet’ of ¾ or 1 inch plywood or the sort. What’s wrong with a good stiff 2 - 5 inch thick panel of hi-tech sandwich cored material. Now you have a ‘bulk’head! Make sure you have a good bond between this super bulkhead and your bridgedeck and you are on your way to a stiff boat. Throw in a couple of ‘diagonals’ of hi-tech yarn (possible buried within the other structures, skins, and panels of the boat) to triangulate things.

    Now you’ve got a stiffer boat and some good substructure to mount your sailing rig to.
     
    Last edited: Apr 6, 2020
  11. oldmulti
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    oldmulti Senior Member

    A few extra jpegs from Chris Whites 40 foot mast foil cats. I forgot to mention the basic sail area of the cat's 2 headsails is 700 square foot. Another White tri in an hour or so.
     

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  12. oldmulti
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    oldmulti Senior Member

    The Chris White 39 trimaran is 39.75 x 28.3 foot weighing 7800 lbs with a 50 foot aluminium mast with a 550 square foot mainsail and 330 square foot jib. The tri has a small stub keel and a daggerboard. The floats are removable for overland transport.

    The tri was designed and built in 1995. Construction is epoxy composite, cedar core with unidirectional glass/epoxy skins. The engine is under the cockpit a Yanmar 3GM30 (27HP) Diesel Fresh cooled with a Martec folding prop. The ground tackle is a 33lb Bruce anchor, 20’ 3/8 chain, and 5/8 nylon rode.

    The Chris White 39 is a high-performance, comfortable cruising trimaran for two to four people. Designed to be owner-built, she is dismountable for easy highway transport from one cruising ground to another. The fractional rig has been set up for short handed sailing, with all controls leading to the cockpit. Performance is high on all points of sail due to an efficient underbody configuration and sail plan. This is a light and fast with a clean, liveable interior. She is very fast, seaworthy and easily handled and has sailed at 17kts the length of Biscayne Bay.

    Chris doesn’t sell this design any more but it looks a good fun boat. The jpegs give the idea.
     

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  13. Russell Brown
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    Russell Brown Senior Member

    That's a boat I could see myself owning. The ability to take it apart is such a necessity for low-budget people like me and it's a good looking boat.
     
  14. brian eiland
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    brian eiland Senior Member

    New Shallow Draft Weekender for Budget Minded Boaters

    This concept to design a new vessel was re-energized when I saw the vessel design that was being sold to Jimmy Buffett, an infamous 'flats fishing guy'. Why would he be buying a vessel with a sizable draft that would likely preclude his shallow water preferences. There were a number of other faults I found with that design,...faults in terms of a vessel for him, not necessarily faults with the design itself.

    Jimmy Buffett just bought a New Sail/Gamefishing Boat,...motorsailer https://www.boatdesign.net/threads/jimmy-buffett-just-bought-a-new-sail-gamefishing-boat-motorsailer.54630/



    There were a few other ideas languishing in my head. First off my experiences with other such multihulls including the Stiletto 30's, the Louisiane 37, the Firefly 26, etc...
    Multihull Concept http://www.runningtideyachts.com/multihull/


    Then a catamaran I spotted over in Thailand that I termed a Weekender/Picnic boat,..
    Weekender/Picnic PowerCat https://www.boatdesign.net/threads/weekender-picnic-powercat.33751/



    I started collecting up other ideas that might be incorporated into this new design. Then suddenly I just got burned out on boating subjects. Friends asked me how I could continue with these ideas of doing another boat project after what I had gone thru with a previous project that took me into bankruptcy. I finally agreed with them, and went off onto other subjects (such as marriage to a Thai woman, temporary move to Thailand, then move to Florida, another hobby, etc, etc).


    A couple of recent events have re-sparked my interest in looking at this subject again. I believe when we get out of this newest recession brought on by this virus situation, that some folks will still be longing for a boat. I believe that some just might be attracted to a shallow water capable, economical in purchase price and operation, weekender, might just be the ticket.


    So I'm going to document some of the options for this new design on likely one of those subject threads I mentioned above. I likely will make some similar postings on other forums, as I find that some talented participants often don't crossover to different forums. Maybe change that subject thread title to 'Weekender/Picnic Boat',...that could include both power and sail or combo. Or perhaps a title like I gave this posting??


    I think this fellow OldMulti would be an excellent source of construction specs, and ideas as well. He appears to have a GREAT ability to assemble & compile images and specs. I'd certain welcome his participation.
     

  15. oldmulti
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    oldmulti Senior Member

    There is a certain type of boat that frustrates the hell out of me. They are smaller simple tri’s like the Seaclipper 28 by John Marples and the Explorer 34 done by Chris White in the early 1980’s. Both are simple, easy to construct tri’s that sail very well from reports (I have sailed on a SC 28) BUT they have accommodation for one or 2 really good friends. This is the type of boat that Catsketcher has problems with also, the light long lean “cruising” boat where you buy all the things you would need to build and fit out a 28 or 34 footer but end up with accommodation of a 23 foot cat. Sorry about that. Both of the tri’s are excellent ocean capable boats, that as I said, sail very well.

    The Explorer 34 is 34 x 24.3 foot weighing between 3200 to 3800 lbs depending on construction and capable of carrying 1200 lbs to 1500 lbs of payload. It carrys a 360 square foot in main with a 205 square foot jib and up to 800 square foot with genoa’s etc. The mast is 40 foot aluminium tube carrying the fractional rig. The main hull is 9:1 and the basic boat has a Bruce number of 1.52. This is a potentially a very quick boat if it has a good rig on it. The engine can be an outboard or EG Westerbeke 12hp inboard.

    The 34 is built with constant camber (variation of double diagonal ply). The hulls are 3 layers of 3 mm western Red Cedar or ply with minimal stringers as it uses the internal furniture EG shelves, bunks, seats, floors, cockpit etc act as the support structure. The bulkheads are 9 mm ply that are filleted and taped to the hulls. The gunnels are 75 x 19 mm. The cross beam tubes are aluminium 250 mm outside diameter. The floats are bolted to the cross beam and the beams are held in place by 2 shear pins. The tri can be disassembled for transport. The original 34 was built in 8 months part time. A well organised builder who had a good simple design to build.

    As you can see from the jpegs this is a simple boat that will serve you well if you have simple cruising requirements.
     

    Attached Files:

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