Modular Cruising Catamaran

Discussion in 'Multihulls' started by ImaginaryNumber, Jul 19, 2009.

  1. BigCat
    Joined: Jan 2008
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    Location: near Seattle

    BigCat Junior Member

    This thread is pretty much a description of BigCat

    A lot of the ideas being discussed in this thread are ideas that went into the BigCat design at - A boat to be built in pieces that are to be transported without any wide loads, an unstayed biplane rig with reefing and furling wingsails, etc.

    The calculations have all been done to the satisfaction of the USCG for a passenger boat capable of legally carrying 149 day passengers in US waters, plus crew. I sailed across the Pacific Ocean in a boat with unstayed masts, and would never go back if I could possibly help it.

    My mast design isn't the lightest available, but it is easy to build- two half masts made in a female mold with an overlap to be bonded together with commercially made epoxy putty. The vertical uni is carbon fiber, the +45-45 for torquing strains is e-glass, and the resin is vinylester.

    I have never seen anyone remark on this fact, but the biplane rig placement of the masts greatly increases the boat's stability by increasing its roll moment of inertia, per the findings after the Fastnet debacle. :eek:
  2. Wildside247
    Joined: May 2010
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    Location: South Australia

    Wildside247 New Member

    G'day all,

    Gee there is a lot of off-topic cra...I mean really valuable stuff on this thread!!! I read the first few pages and the last few, but then just jumped to the end. If you really want to find a portable pod cat go to
    and look for an old add for a boat called 'Kirra'

    If I had the money and other necessary resources I'd track one down and build it!!

    Good luck!

  3. Sundevil
    Joined: Jan 2012
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    Location: Ohio, USA

    Sundevil Junior Member

    So, has anyone made one of these modular cruising catamarans yet?

    I was going to make a new thread, but my question related to this topic.

    Take a look at this design:

    I would like the hulls to extend out 10 feet further in the front and have a net for relaxing and for stability, but that is about the only modification I would make. Well, besides making the top out of solar panels and transom steps down to the water...

    But, is there anything like the homemade kit ultralight airplane concept in the boat building world? Where you have a few steps to fully complete a hull, and then start over and complete the second hull, then build the deck, build the walls, build the roof, etc... all as separate pieces that come together?
  4. yellowcat
    Joined: Feb 2007
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    Location: canada

    yellowcat Junior Member

    Hi sundevil
    Look at the multihullblog from Kurt Hughes. Go to building technique, there is a video , funny but it shows part of the CM idea, read all of his blog, very informative and motivates . You can buy a dvd from Kurt. It is more detailed, i did but i scrached it now it stops half way grrrrr. This is a CM mold technique, you can go from there . It is a fast and sort of easy way to build stuff. Not only hulls or boats for that matter. You could build yourself an aerodynamic dome cabin for a lost atoll in the pacific .
    I looked at corecell and mix of carbon/fiberGlass for a total infusion cat. In a lost atoll, it will be hard to repair, so i will stick to marine ply and epoxy. Also, from comments we get from people using sophisticated composites systems, each of these designs are done for a specific use. I had to repair 3 of my boats with foam cores. If i recall one was with divinycell and i dont remember the other name. For example, all my kiteskis in foam cores are destroyed and i still use my wood cores (good qualities) skis. They seem to resist multiple flexes and banging. My friends wished they had kept their old wooden skis. The only thing that breaks down in all the skis is the plastic underskin that overheats (at 50 mph ) with ice friction.
    One thing i am looking at but not decided yet, it is a polycarbonate skin for the underwater components. Antifouling systems / epoxy / wood modulus of elasticity (PC moves) are in the balance, but shock resistance is interesting.
    There is a guy in Pompano Florida that builds transparent canoes, and i think small transparent sailboats. He was selling the Trifoiler from Hobiecat. If you want i can search it for you.
    There are boat kits on the market but start with KH's blog, you will get the idea.
    You are in Ohio , we are not close but not extremely far away. I am in Sherbrooke Qc . I dont know how many sheets of plywood you will need. How big a boat do you want ?
    A 20 'container from Asia holds about 2500 sheets (min. order) of 1/8"x4'x8' marine ply. Part about 1000 sheets for my boat, another part left over for my friend who uses marine ply for window framing. But the price is much lower . I am getting references for quality manufacturers in Asia, they are not all bad ... and i would give priority to a boat builder for left overs. Check the prices in your area. Noah's boat supply is pretty much our reference in our area, about half way .
    But if you need only a few sheets, you may want to buy them locally full okoume BS stamped is pretty much the standard now. Balsa (there is another one) is the core wood. NOT IN WATER .
  5. Sundevil
    Joined: Jan 2012
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    Location: Ohio, USA

    Sundevil Junior Member

    While those boats look very nice, I'm not really looking to build a typical boat. I don't have that many people to help, and let's just say buying an older boat that needs a little cosmetic repair would be much easier for me and more of my skill level.

    However, the older boats have some issues and aren't exactly setup the way I would like. My ideas might be a little crazy, but I would need to get a professional to look at them first.

    I read his blog, and he says this:
    I didn't know that. And in terms of build speed, I would think that building storage hulls and having all of the living space on the deck would be the way to go. Your hulls hold air pockets, tanks, batteries, supplies, and gear. And the hulls are bolted onto the deck once you are ready to put the boat together. Then you build the walls, roof, and finish off the interior. I would outsource the fabric work and seats. Basically, I would want to make this like a giant Lego project and have as many parts already made as possible. :D

    Now, making sure that this boat is seaworthy and can handle 8' waves and 50 knot winds is another question.

    I think my ideal boat would be 40-45', but the enclosed area would only be the essentials. And even then, it can be left open to allow wind to pass through.

    Something like this:
  6. yellowcat
    Joined: Feb 2007
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    Location: canada

    yellowcat Junior Member

    I see what you want to achieve. This is a great project. I have a 10ft x 40 ft x 8'2" h garage into which i would like to build my 60 ft cat. I will have double the surface by the time when materials arrive, plywood do require space. They are light at 8 pds a piece , and need to be scarfed , we are looking at a simple method to scarf them, i dont want to risk scarfing from China ... but alot of pieces could be precut before shipping.

    The way i want to do it is modular also. 12 pieces for the hulls, (2 more for the activity raft) , 10 pieces for the beams (2 more for the raft beams and assembly of the cat), 18 pieces for the roof superstructure holding the Lexan sheets arched for aerodynamics and ease to lift and lower the roof (still or cruise). Each piece can be simply transported on a trailer behind a pickup. (some even behind a car).

    I have to consider wheel chair access for my very good friend and for my wife's habbit to fall down the stairs ... We dont want to live (sleep) in a basement , we visited and cruised on all types of vessels, and these are the primary constraints.

    We love 8 ft ceilings most of the times, most of the times the cat will be at rest, but not us kiting and on Nacras.

    My belief is that the lightest boat is the better. Like i mentionned i dont think fancy composites are for my hulls. Maybe for the superstructure, but using light wood smartly, i think i can have an easy to repair and fairly light boat in ply epoxy. Cost also in the balance.

    For using close to 90% of the wood (we lose for the cuts and scarfs) , i intent to use stacked layers (cake beams) for the bulkheads and arches. I will be testing some shapes after our parking / sewage infrastucture in our condo project is done around midoctober. I have meranti available ply for testing and some okoume ply left over.
    The rudder okoume project repair came out pretty nice.

    I want to use light rigs , hence kites will be part of the fun cruising. I try to have many uses for the same thing onboard. Yes the nacra masts (twin) will play part of the propulsion in combo with the kites. The slenderness and hydrodynamics of the hulls (friction friction friction) is the key.

    If i may suggest, dont be too uptight about your living essentials onboard, we always end up carrying more than what we thought, often for safety and good conscience ...

    Solar PV panels are fun , but i will not yet use too much of those, something else is coming up. I await the commercialisation of the product before . They are building the shop. It should be a zero $ heat and ac house concept. We'll see, but i was so impressed at their lighting systems, they can lit a rink with fraction of the power needed.

    Hybrid is the way to go for now. Internal combustion engines are getting better and hydrogen will certainly play.

    Yep modular is the way to go.

  7. champ0815
    Joined: Apr 2008
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    Location: Munich, Germany

    champ0815 Senior Member

    May I ask for details?
  8. yellowcat
    Joined: Feb 2007
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    Location: canada

    yellowcat Junior Member

    I can ask them how far they are. Last time i went to the new shop, they were building a full scale house mock up. I dont know where they are on a NHL refit lighting project for a well knowned rink. I saw the lights , awsome ! Another plus is the reduction of the shadowing , crucial for tv.
    For their ac/heating systems, it is not new science, it is based on the Peltier system, when you reverse that system you get electricity. Check on wikipedia. But the performance of past systems such as my own cooler/heater was not very energy efficient. The efficiency came from other benefits like no freon , etc.

    PV solar panels can be boosted with parabolic mirrors, but you have to transfer the heat into water (for showers, etc) otherwise your cells will burn. Go with hybrid cells i dont know better ones yet.

    Don't forget you can make electricity pretty easily, not fuel ... "H" yes but watch out ... did we say that water is H2O ?

    One can produce alot of electricity if one needs alot of it, sometimes you can do without any electricity. For example, if you have water bags and your batteries sit on top, the weight of the batteries will generate a flow depending on the weight, that flow can circulate into a radiant heating system , showers, etc. No pump required, but you need to lift the batteries. Do you do your exercises each day anyway ? Of course you are an internal combustion engine and consume ... you produce also compost, compost can heat water.

    Wind turbines and hydro turbines will be a must , doesn't have to be noisy.

    These topics are seemingly out of context, but in a boat, everything is interconnected. Modular means you have to think connections, wifi, etc.

    For me the catamaran is the best compromise, i.e. ease to modular, and other things. I like the trimarans , they are faster ... we'll see ... and have many sailing advantages.

    I just checked, my friend and contact is on vacation untill labor day, he is also helping me with imports from China. Lets see if i can disturb him on vacation. We used to be hockey teammates ...

  9. El_Guero

    El_Guero Previous Member

    That is a thin skin.

    Do you have plans you are working from? Are you working with an NA?

    Usually, cruising Cats are faster than cruising tris. And more room.

    How will you connect the modular hulls to get to 60'?
  10. yellowcat
    Joined: Feb 2007
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    Location: canada

    yellowcat Junior Member

    Hi El Guero
    3/8" skin with biax FBG wetted on top of skin, and ,( this is what i am studying) a 1/8" or thinner polycarbonate skin epoxied to the FBG biax . I may not need much antifouling on the polycarbonate, i dont know yet i have to do some testing with dipped samples. With silicone it seems nothing holds on tigh to it, teflon has been working well but i am looking at the interlux antifouling for now and i am studying if it will destroy the Lexan .

    I did testing though on the flex of the Lexan and it is ok to follow the hull round shapes.

    I am refreshing my design with better technique (assembly at marinas, and construction), more versatile, but roughly the cat hull is made of 12 parts. 6 in water (up to 1 ft higher than the waterline), and 6 out of water
    modules for storage of toys and water/batteries/fuel/food/spare rigs, and more.
    For example, the central hulls are 32 ft long, the aft hulls are 14 ft long, and the bow hulls are 14 ft long (mostly a crash box ensemble of air bags between bulkheads) (that is growing to 16'-0" ft long for a very shap water entry) all total 60 -62.
    The in water part fits into a 32"x32" square, and the out of water fits into 32"x64".
    The central hull is also made of twin modules, for ease of replacing the inwater central module (the crucial module) in case of bottom repairs needed. This is why the Lexan.
    The play raft (not as thick skinned) is identical to the inwater central module, they can be easily switched. Awaiting the repair of the true module. Yes the raft is 32 ft long twin hulls, a cat raft.
    Front and aft modules can be unbolted to pivot inward (for docking) BOW and STERN and outward for access to toys and stuff sliding out. The best design so far is a reversed U pin hinge that can extend a little . The same pins are used for the dagger boards strengthening upon cruising.
    I have to run , my client has arrived.
    The pivoting only happens to get less marina or locks fees.
    I know it may sound complicated, but after making a scaled work model, my helpers now understand. My engineer too .
  11. El_Guero

    El_Guero Previous Member

    Would you post pictures of the model?
  12. yellowcat
    Joined: Feb 2007
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    Location: canada

    yellowcat Junior Member

    I guess i could, but how ? i will have to update it, we keep playing with it and we cut it out for detail explanations to my friends. Some parts cannot be snowned yet, i need to finalize my drawings for possible patents. The retractable beams settings are quite something, can go from 40 feet beam to 17 feet beam ... i guess i'll name them like marina beam, locks beam, fast cruise beam, slow cruise beam, balcony beam, beach beam and mooring beam. Any beam suggestions ? Preset the pin holes to those.
    It will not stop, a surprise job just came in , i have to measure a fire rebuild, people are living in hotels awaiting my work... can't they be more carefull !
    Got to run.
  13. Deering
    Joined: Feb 2005
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    Location: Juneau, Alaska

    Deering Senior Member

    Hello I.N.

    Not sure if you're still tracking here as I've not seen a post from you in awhile. Haven't logged onto the site in awhile so am catching up with the skirmishes.

    I live in Southeast Alaska and own a catamaran, though not one with a big useless stick poking up out of it (or two!). My first question: Do you have much experience cruising in these waters?

    Some comments on your requirements, and I'll leave the technical debates on hull sizes and mast types to others:

    1. Composting toilet? Huh? No one uses those on a boat around here. You have a big ocean with lots of flushing. Let nature do its thing. When you're dried out on a flat...use a bucket.

    2. For cruising this coastline, you need good motors, not sails. This isn't sailing country. Make sure you have adequate fuel tankage...then double it. Fuel docks are few and far between. 90% of your miles will be under power here.

    3. You won't do much cruising in the gets dark around here early and stays dark late. The weather is crap. The winds are fierce (with every shore a lee shore). Sailing off to Mexico or HI makes good sense - living aboard a boat in a SE Alaskan winter is no picnic.

    4. Heating the boat - it's actually not THAT cold around here - think Seattle ten degrees F colder. You'll likely never experience single digits F, and frequently be above freezing.

    5. Living in a hull makes more energy sense than in a box suspended in the air. The water will be above 40F while the air will be colder. If you're living in a cat, just hunker down in one heated hull for the winter. Make the hull out of foam/glass/epoxy and it'll have good R-value built in. You can build it much like plywood, but it's lighter (and more expensive). Heating a big box like you're describing will require a good bit of fuel. You might equip the boat with a small wood stove so you can harvest your own heating fuel in remote areas.

    6. For the winter, if you stay north, there are lots of little villages where you can park your boat in and connect to shore power and use harbor showers. Saves considerably on fuel costs and generator usage. In some towns you can get a gym membership - important to stay fit as you get older.

    7. Not all that many places you can dry out regularly. This is a steep coastline. Don't see any point in it, other than occasional hull maintenance. Lots of sharp rock around here - not many ply/epoxy hulls that can handle it unless you design in a substantial grounding shoe, maybe of aluminum. That will add weight. The flat areas are typically river deltas - depending on the season, drying out in those locations is an invitation to have a grizzly bear crawling around on your boat.

    8. Outboards are nice, but you'll be bucking lots of big current here. 9.9 hp is probably small. Look for something larger, probably 20 hp minimum.

    9. 200 ft of all-chain rode is overkill. And way heavy for a small cat. Go with 60 ft of chain and 350 ft of nylon. A Bruce anchor works well in these rocky waters.

    10 6 months of provisions seems like overkill here. Are you a felon on the run hiding from the FBI? There are plenty of small towns where you can reprovision and be on your way.

    And finally, why not go with a trimaran rather than a cat? It seems that might meet many of your transportability and liveaboard requirements.
  14. yellowcat
    Joined: Feb 2007
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    Location: canada

    yellowcat Junior Member

    Hi Deering
    Your comments are good. In Quebec, we have similarities in environmental issues, despite the very short winter days and very long summer days you have. We get some -30c so for living aboard, in winter, i would move to ... not on land ... bylaws ... Nova Scotia ... brrrrr !

    I am not totaly a snowbird enthusiast, we actually do more stuff in winter , ski, snow/ice kite, hockey, Xcountry, BUT does it ever feel good getting off the plane on the tarmack in some carib. islands ...

    My first design idea was for a trimaran . Offers many advantages on both side of the multis and monos fence. Full modularity is limited to small tri units. A bit like a Proa . But the Proa has good potential for kite sailors.
    The Proa could have done the job for wheelchair access too. Only on the upper level.

    The Cat seems to be the best compromise so far, but I have a softspot for twin tips (ProaCat?). Could be added on , and the daggerboards could do it both ways . Rigging needs more studies. Sort of like a windsurf rig keeping the tensions on one side. But need to design a retainer for windshifts.

  15. frenette
    Joined: May 2011
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    Location: Southern California

    frenette Junior Member

    I just came back from Alaska so your thoughts on what works there is very timely to me.

    On outboards I'm putting a cat together so I'm interested in how you arrived at 20hp. I must admit I didn't see much with anything below 100hp per outboard. I see the need to get h*** off the water from time to time up there. However the distance that can be traveled with a given amount of gas on smaller outboards does come into play.

    As far as winter goes I don't plan to be there much past hunting season if I stick around that long. They build some interesting green houses around the sail boats up there. Given the snow stories a cat with a wide bridge deck could be broken in half with the kind of snow falls in Valdez for example. Deck shovelers are a cottage industry and even they fail to keep up from time to time. Think what 36" of lake effect (read wet snow) can do to your boat in 1 night?

    On ground tackle it's been my experience that the chain shouldn't normally be much longer than about 1/2 the length of the boat. If you don't need a power winch to get the anchor up you loose the weight off the boat. And one less thing to fail.

    Growing up around bush pilots has made me a sailor at heart. Hours upon hours of listening to engines roar gives it's own addition to quiet. I think from the time I started driving, I didn't spend a week up there that I wasn't fixing an engine of one kind of another.

    On supplies you shouldn't need to plan for more than a week normally. Los Angeles to Hawaii is what about 2 weeks of food. You will likely find you need to gas up at least once a week if not more. I have talked commercial fisherman who planned to spend 12 days on there boats but this is more to really poor boat design (read solid glass boat build in the 60's not used as designed...)
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