Multihull Structure Thoughts

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

  1. brian eiland
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    brian eiland Senior Member

    KETCH RIG ATTRIBUTES
    To those cruising sailors that have had the pleasure of utilizing a ketch rig, I do not think I need to sell them on the concept. In fact I think most of them would join me in the praise of this rig configuration. Besides the full sail configuration, they are happy to be sailed under genoa/mizzen, with the mainsail stowed or reefed, and under mainsail alone, or with a combo of genoa, mizzen staysail and mizzen sail. This is a balanced and very versatile cruising rig.

    Of course they do require two masts and correspondingly some extra amount of rigging.

    Could I add a mizzen sail onto my double-headsail configuration and come up with a ketch style rig?? Wow, I believe so!! I could even term it a ‘single-masted ketch’ !. The idea was born.:idea:

    There is another big plus for a ketch rig on a multihull. The overall center of effort, CE, is lowered by a considerable amount compared to the sloop rig, and particularly the fractional sloop rig. Have a look at the illustrations below, and the illustration I will be providing for a big tri project I was consulting on. The rig heights can be a good 25% lower, and the overturning moments considerably reduced.

    The overall sail area could even be increased on this lower aspect ratio rig. Besides, too much emphasis has been placed on hi-aspect ratio sailplans that are really only good for windward work. Marchaj, et al, have shown the virtues of low-aspect ratio sails for off-wind sailing….often two times more efficient!!

    Same sail are on these 3 illustrations

    [​IMG] [​IMG] [​IMG]
     
  2. oldmulti
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    oldmulti Senior Member

    Brian. I don't care what sort of rig a person uses to drive their boat, what I have been talking about so far is efficiency. I have sailed on and against Shotover, I can assure you it would be faster upwind and close reaching with a different rig. But if we are purely talking cruising and usability, I will be addressing this in my next post. Cruising is not about the ultimate efficiency but all round usability. But there is one major consideration when discussing a cruiser, how much they choose their weather windows and how much they use an engine. Some cruiser avoid going to windward so they dont "need" the ultimate in performance. Other cruisers only sail at a maximum of 8 knots for comfort even though their boats are capable of more.

    In the 2 previous posts I was discussing the difference in efficiency. The performance of the same length boat with the same sail area but with differing rig configurations can be as much 50 %. If the hulls and foils are inefficient as a well a moderate rig the inefficient boat will only sail at half the speed of a good design with an efficient rig. If you want any proof, put a Lagoon 40 against a Schoinning or Grainger 40 footer over a 200 mile trianglar course and see the results. More to come.
     
  3. brian eiland
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    brian eiland Senior Member

    I ran across this posting I had made under that aftmast discussion,,,,


    Headsails for Offshore passagemaking


     
  4. brian eiland
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    brian eiland Senior Member

    Another posting of mine I ran across this evening. My friends name was Randy West, and he was now the owner of the infamous catamaran 'Ppalu'. Regrettably he past away a few years ago, RIP Randy.

    Sailing Challenge

    I recently caught up with an old friend who skippered Olaf Harken's unusual vessel Procyon for its first few years. I showed him a model of my 'single-masted ketch' concept, and then just the other day I sent him a copy of this 'sailing challenge' I had issued to a few naysayers in the past.



    You know I can still imagine sailing a big 65-foot catamaran with this mastaft (single-masted ketch) rig right off the mooring, and back to the mooring, without the engine, by myself, with so little effort that I might take it out having only a few spare hours to kill, or for just a carefree daysail.

    I wouldn’t have to uncover any sails, nor recover them when I returned to port. I'd likely start out with just unrolling that central 'mainstaysail' then add in more sail area as needed.

    I would be less concerned with reefing by myself if the wind were to really come up. If I were short-handed at sea, I would have many of the benefits of a ketch rig, without the necessity of slab reefing the main and mizzen sails of the traditional ketch rig. I'd be in a constant state of helm balance as I could tweak the mizzen sail for that.

    That about sums it up. I would like a 65 foot cat that I could take sailing by myself, and that might even be easier than a beach cat. Try hoisting a full batten mainsail on a 65 footer by yourself, or even a 40 footer. Most folks over 50 will have second thoughts, or will just unfurl the jib and forget about hoisting that traditional MAIN sail.

    I'm 65 (now 73), and I could sail this 65 foot cat by myself with this aft mast rig. And with the balance and low power afforded by the smaller 'mainstaysail' I could sail this vessel right off the mooring or maybe right off a side-to-dock slip.



    Here's a challenge Mr Naysayer..... Le Mans start. I'll be out sailing before you get the covers off your mainsail, and when we return for the day, I'll be at the bar sipping on a Margarita watching you put away your vessel for the day.



    Randy sent me a reply that next morning...
    ...reminds me of Procyon,....we would have her sailing before the crew could put away the fenders
     
  5. catsketcher
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    catsketcher Senior Member

    Okay I'll bite Brian

    The loads involved in hoisting a main are sizable but not magnitudes higher than winching in a large genoa. You raise the main once in a sail, but you may tack ten or twenty times. Then the object is to reduce overall energy use. In this case, the larger mainsail and smaller genoa boat is easier to sail than the mainless rig with its large and high sheet load genoa. A main does not have to be trimmed greatly every tack.

    Personally I want a boat that can day sail, live aboard long term. sail to windward, blast on a reach and is within my budget. A large cat is too much for my wallet so hoisting a medium sized main on a 38 footer is easy enough and the boat is easy to sail once moving. So my boat is easier to sail than a large genoa cat, because it has a mainsail driven fractional rig.

    Add in the fact that this is the fastest rig as well and the fractional rig owner may be minutes slower to start sailing, but will tack faster and get to the destination faster, with a more balanced boat, on a boat with better resale, and be packed away before the harder to tack and trim and slower cat has entered the anchorage. The rig is lighter, more efficient, cheaper, because it is not custom and requires smaller deck gear, and the planform and sail effiicieny is higher allowing a smaller and cheaper rig - the boat pitches less and the motion is more comfortable - for the same length.

    A genoa based rig is okay. John Hitch used one on X It. BUt he actually got out of the sailing game after this cat as the loads were very high. Great boat, sailed fast, but the loads were quite enormous.

    Catamaran set to become 'torque' of the town after repower installation - Power Equipment https://www.powerequipment.com.au/catamaran-set-to-become-torque-of-the-town-after-repower-installation/
     
  6. brian eiland
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    brian eiland Senior Member

  7. brian eiland
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    brian eiland Senior Member

    Center Nacelle Backbone, Centerboard Mounting
    Just happened across this better image,...
    [​IMG]
     
  8. brian eiland
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    brian eiland Senior Member

    @ Catsketcher
    I am glad you have conquered your mainsail rig, but there are many that are uncomfortable with theirs, even in relatively smaller cats. Here are a few I documented over on that other subject thread:
    Aftmast rigs??? https://www.boatdesign.net/threads/aftmast-rigs.623/page-67#post-782369

    Aftmast rigs??? https://www.boatdesign.net/threads/aftmast-rigs.623/page-67#post-782876

    Aftmast rigs??? https://www.boatdesign.net/threads/aftmast-rigs.623/page-67#post-782901

    Aftmast rigs??? https://www.boatdesign.net/threads/aftmast-rigs.623/page-67#post-785658
    https://www.boatdesign.net/threads/aftmast-rigs.623/page-67#post-782903


    Did you take notice that both my inner 'main-staysail' and mizzen are both self-tacking? Only my genoa has to be brought over and re-sheeted. One nice electric/hydraulic winch could make relatively little work of this.
     
  9. Xpert
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    Xpert Junior Member

    Hopefully is the correct thread,

    Did anybody try to laminate carbon fiber with honeycomb for catamaran hulls structure? is it a good or bad idea?
    I'm experimenting with some samples at the moment and the results look promising.

    Attached Carbon fiber vs Fiberglass at same size 90gr vs 120gr ( two layers 300gr + 15mm honey comb core two layers 300gr)
     

    Attached Files:

  10. catsketcher
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    catsketcher Senior Member

    Looks like a nice job, is that Nidaplast you are using, a plastic honeycomb. A couple of people in Australia have built boats using the Nida or Polycore plastic honeycomb. I have used it sometimes too - I have just made a cab for the back of my utility car with it. It is okay to work with but I prefer foam, but foam is more expensive. Edging the honeycomb is harder than foam or balsa core.

    The concern I would have is flexibility in the panel. If you are testing the panels, you could make up some with foam and balsa and check for stiffness. I have read that the plastic honeycomb produces a more flexible panel that foam or balsa would. I would say that is due to the increased flexibility in the core which I would agree with. There was a cat built out of it (with an aft mast rig too Brain) and IIRC it was a bit floppy.

    You can read about it in this slighly crazy magazine

    TCP A 36 PG 1 - The Coastal Passage Home Page https://www.yumpu.com/en/document/read/30618326/tcp-a-36-pg-1-the-coastal-passage-home-page

    Building a cat https://buildacat.com/lyra2.html

    cheers

    Phil
     
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  11. oldmulti
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    oldmulti Senior Member

    Xpert. Yes there are many racing multihulls that have a carbon fiber honeycomb core including boats (Orange 2) that have circled the globe. The upside is this combination is light weight and is strong if designed and used correctly. Notice I said race boats here, that are not mistreated by running onto beaches, banging into wharf's etc. BUT there are downsides that need to be considered.

    Number one. If you are doing a cruising boat (I have seen your thread and will assume we are talking of the 9 meter cat) a thin skin will not handle knocks or dings well. Every time you approach a wharf or sail in coastal waters that have junk, weather bouys, tree branches, semi submerged containers etc you are at risk. Cruising boats that have thin structurally strong skins that can be pierced very easily. If a thin skin honeycomb core is pierced it lets in water, it is a real problem. Its not without reason that Catalacs had 8 to 10 mm thick solid skins. Lagoon 38 have up to 12 mm solid skins. Real world says about 1.5 mm minimum of some form of glass/carbon on outside of a foam or wood core on the external underwater parts of your hull give you some form of knock resistance in the real world.

    If the carbon fibre honeycomb core is not built well, thin skins can be permeable (let moisture in). Even if it is well built and suitably painted, movement can let moisture/vapor through a thin skin. I have watched to owner of a 44 foot serious racing monohull slowly peel back parts of the inner skin of his boats and found water in many parts of the core. The outer and inner skin looked good and no one could figure out how the water got there, the best guess was water vapor or migration.

    The type and size of honeycomb cells is important in both construction and use. If you are using vacuum pressure to apply the skins an incorrect core can distort around the edges of each sheet an around tighter bends. Some honeycomb core carbon fibre skin combinations are too stiff in real world use. A series of 60 foot ocean racing tris in the early 2000's were breaking forward wing components because the carbon fibre honeycomb structures were to stiff and cracking in an area that was required to be flexible. Orange 2 also had problems in its forward wing area.

    The thinner and lighter the skins are, the better your design knowledge of the dynamic movement of your hull structure needs to be. All multi's are flexible, some are more rigid than others but when the rig is loaded up in a seaway these boats flex. This is getting to FEA stuff. As you lighten the structure the less margin of error you have. I have seen a light foam glass boat that was literally torn apart when a minor crack developed into a split hull in rough seas.

    I have no problems with using carbon fibre in boat building. I have some problems with using honeycomb cores in cruising boats in hulls, foam or wood cores are better. Decks or cabin structures with honeycomb cores are OK. I also have problems with very thin "structurally OK" skins on a cruising boat. In the real world of the cruising boat you are proposing an e-glass skin on a foam core would be easier to build, more knock resistant and would probably only add 20 % more hull shell weight (it still will weight half of a Catalac 9 meter structure). Your proposed payload capacity will only be marginally cut.

    Finally if your aim at weight reduction is improved performance there are many ways to improve performance beyond weight reduction. A decent set of foils (eg dagger boards) will give you an EG 5% increase immediately. A good hull shape lowering the wetted surface and improving the length to beam ratio ratio will give you another EG 5% gain. Put a good rig on the boat and you get another EG 5% gain. Yes reduced hull weight helps, but if the reduced weight is going into an increased payload without other changes you are back to the same staring point of performance as a heavier hull with less payload. Have fun in the design process, there are many people who will give advice.
     
    Last edited: Jun 24, 2020
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  12. oldmulti
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    oldmulti Senior Member

    This part of the rig series is about useability. Now I will define “cruising”. It can range from an occasional light hearted day race to extended offshore sailing. The major criteria here is that you are not required to be at a given location travelling a specific course in the shortest possible time. Cruising is about choosing you weather window, powering the boat up to the point you are comfortable with and adjusting the course to suit your sailing needs. Cruisers can be caught in difficult conditions on a lee shore and will need an efficient boat to get to safety but under most conditions a easily handled useable rig is the aim. There are several ways to get a useable effective (less than optimum efficiency but still good) rig.

    Option 1. Have a rig that either has a sail up or down. Minimal sail changes or reefing. Example are James Wharram wingsail ketch rig cats. They have a ketch rig with one or 2 headsails. To reef for higher wind speeds, you just completely drop EG a headsail or a mizzen. Reduced sail area, if winds are stronger drop the main and mizzen and run under a small jib. Simple, effective and relatively easy to adjust to increasing wind speed. PS one warning dropping a “wing mainsail” or eg a Freedom 40 mainsail that wraps around a mast is not simple if the sail is loaded up. The friction between the sail cloth and the mast can be large! Brian mast aft rig on wire stays uses the same general idea. Both ideas are useful when you don’t care about the “optimum speed” across the wind speed range.

    Option 2. This is used in EG several Newick designs (White Wings is one EG). Basically have a ketch rig with free standing masts. The free standing mast can roll the mainsail around the mast to “reef” the sail. This allows you to fine tune the sail area to the wind speed but again requires a good sail maker who understands the mast bend and the sail shape of the sail partially reefed.

    Option 3. Have a roller reefing (on boom or in mast) mainsail and headsails that are on roller furling gear. If the jib can be self tacking the better. This is all possible. This allows a very adjustable rig to suit the windspeed conditions BUT you must have good furling and reefing gear. If a furling system goes wrong you can have a very big to life threatening problem on your hands.

    Option 4. Chris whites mast foil rig we have spoken about in a recent post. Very effective and simple to use.

    Option 5. Have a conventional fractional rig with small headsails and large main. If the jib can be self tacking the boat is easy to sail under most conditions. In increasing wind, you have 3 big reefs in the mainsail. Now your deck and reefing gear needs to be very good, well sorted, permanently fully set up and you have practiced using it. The reason for the big reefs is you only want to do a manual reef occasionally as it can be hard work. Aerorigs are a variation of this approach. Aerorigs are more powerful than the same sized sloop rig and can be tuned to wind angle better than a fixed sloop, but when it comes to reefing they have the same issues as a conventional sloop rig.

    Option 6. Use an alternative rig type. EG Conventional junk rigs or improved camber or split junk rigs have been used on multihulls. Lug rigs can be used etc. As for the efficiency of these rigs you would be surprised. The problem is that some of these rigs (mainly the Junk rig variations) are very easy to use and reef. Lug or Crab claw sails which are according to Gifford university studies are more efficient than conventional sloop rigs, but can be a real problem to use. So, we will stay with Junk rig variations. Now to eliminate one issue, you do not have to place a freestanding mast/rig on a hull. The can be stood on a wingdeck of a cat as long as there is at least 10% of the mast length supported by a cabin/wing structure. Kurt Hughes, John Shuttleworth (50 foot plus cats) have done several cats with centrally mounted freestanding masts on a cat wing decks with strengthened cabin roofs and cross arm structures. See previous posts on this thread.

    In short there are many ways to rig a cat/tri to have reasonable efficiency and easy use for cruising. Again, this is getting to long more tomorrow. The jpegs give you an idea of the rig types.
     

    Attached Files:

    Last edited: Jun 25, 2020
  13. Baronvonrort
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    Baronvonrort Junior Member

    We had a lot of water absorption in the Nomex core with 18ft skiffs built from Carbon Nomex. The boats would start out very light then get much heavier over time as the cells in the Nomex became waterlogged.
    Nothing worse than grinding out a crack and having water drip out.

    No idea how water gets in I suspect since they're laid up under vacuum you get a partial vacuum in the Nomex cells which helps to suck in the water.

    It wasn't really a problem on decks or high on topsides yet anything below waterline did end up waterlogged despite boats only being in the water for 3-4 hours a week at the most for saturday and sunday races.

    I would take the initial weight penalty of foam below waterline compared to Nomex it will probably end up lighter a few years down the track when the Nomex starts getting waterlogged.

    Foam core boats are easier to repair which is another thing to consider for cruising boats.
     
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  14. Xpert
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    Xpert Junior Member

    Hi Phil, could be similar to NIDAPLAST, but the core i'm using is called THERMHEX
     

  15. Xpert
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    Xpert Junior Member

    Great Answer !!!

    Well so far for the honeycomb hull structure i narrowed down to two options
    1. (Total 15mm) 3 layers Carbon Fiber 650gsm + 6mm honeycomb core + 2 layers Carbon Fiber 650gsm + 6mm honeycomb core + 2 layers Carbon Fiber 650gsm (Asymmetrical lay)
    2. (Total 15mm) 4 layers Carbon Fiber 650gsm + 12mm honeycomb core + 2 layers Carbon Fiber 650gsm (Asymmetrical lay)

    Yes, in the area of high impact or where extra resistance required will add more carbon/aramit or combination of it

    I suspect that moisture in the honeycomb (which is a big issue, can say huge) could be because of two reasons only:
    1. Water penetrate via outer or inner skin
    2. Condense due to thermal bridge

    Yes, foam is a great material but the issue which i sea in long run is delamination due to carbon vs foam expansion factor,
    but will have to check/study, may be there are some modern foam with similar expansion properties as carbon

    I've tested with (same thicknesses) samples and Fiber Glass + Foam is on average 30~35% heavier than Carbon Fiber + Honeycomb. (strength wise not ye tested)

    Yes, definitely i'm working in the direction of dagger board, hull shape, rigging all to be as efficient as possible.
     
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