DIY Simple Catamaran Sailboat Design

Discussion in 'Boat Design' started by WilliamPrince, Oct 10, 2013.

  1. El_Guero

    El_Guero Previous Member

  2. Skyak
    Joined: Jul 2012
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    Skyak Senior Member


    Lets take the main hull decisions in steps. The first factor to consider is 'how do the accommodations work?' What I think you should do is spend a moment thinking about spending the night on the boat, on the beach or at anchor or sailing. What I would like to see you have is a comfortable place to sleep and sit in the boat covered, dry, protected from rain and wave splash. Preferably with room left to pop out quickly if say the anchor drags. What you can do is draw the outline of the boat on the ground and put your gear or packs representing your gear inside the hull to check how it fits. I am wondering how your bike fits in. It will take lots of space and you will want to pack it with things that you will not need to get at and cover it up in the front (might interfere with sail control) or the back of the boat. You would prefer to stow dense heavy things like cans and water low and toward the middle so I think you would consider a floor with storage below in the middle. When you have done this you will have your own strong opinion on how long and how wide you want the main hull to be.

    You mentioned a tent. I don't know if this tent is of any use on the boat or if you would prefer to make an enclosure integrated to the boat. If you go the skinny traditional outrigger design you could make a platform on it and set up your tent on top.

    About the hull design and board design -traditional outrigger canoes had pointy triangular bottoms and skinny hulls but did not have lee boards or dagger boards. The positive is it's one less part but it means that the main hull is useless without the outrigger. Modern multihulls have boards or keel. You can do a lee board on the side of the main between the hulls.

    When you know how long and wide you want the main hull to be we can decide the shape.
     
  3. WilliamPrince
    Joined: Oct 2013
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    WilliamPrince Junior Member

    Comfort is not much of an issue for me, as long as I have sleeping berth of at least 7'x2', preferably around 1.5 feet deep, if not deeper. I think the obvious place for this is the center of the hull, above a lower level of maybe 1 foot of storage for heavy things, like water and food. At each ends of the canoe could be ~4 feet of storage. Well honestly I don't need all of that for storage. Maybe I could have some airtight containers at the end to keep me relatively afloat in the event of a hull breach. This brings me to a 15 foot canoe which, although buildable, seems awfully small for the journey.

    I also need a seat from which I can sail the boat and row from. I dont want this to be too far above the water line, as it would make my rowing much harder, and I would be more protected the lower I was. I also need a place for the mast, and an attachment for the leeboard.

    I was locked out of my workshop all day today, but this has been fixed as I made a replacement key when I got it back. I will wake up early tomorrow and make up for it by finishing the ama, hopefully.

    2 construction related questions...

    1. What is the best way to cut triangular chines to fit the corners, all I have are 40mmx25mm rectangular chines. I have a saw and a manual planer, but no power tools.

    2. How will attach the 2 hulls? Or what kind of socket do I need to build into the ama to accept the attachment. Well I guess those questions go hand in hand...
     
  4. El_Guero

    El_Guero Previous Member

    Without power tools, would it hurt you to just use the chines as they are? It would save time, hand saw will cut it, but take longer.

    Attaching the hulls will be a preference.

    Some use rope and lash together, I think it is nylon. I always get nylon and ploy mixed up - one stretches real bad when wet, so satay away from the stretchy stuff.

    Some use epoxy, or glue and permanently fix together.

    15 foot seems a little short.

    Did you look at the canoes above? They use a wherry type hull, but give you a sleeping arrangement in the front of the hull - a small cubby.

    Don't get locked out - that is never fun.
     
  5. Petros
    Joined: Oct 2007
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    Petros Senior Member

    Do not use nylon where it gets wet, it will elongate and loosen up, knots will fall out, etc. Use polyester cord or line, about the same cost and strength by it is more stable and will not stretch as much.

    I would go about 18 ft length, it will give you more room and will make a noticeable difference in comfort and speed when in heavy chop, or at least 16 ft as a very minimum.

    This guy built a minimal boat for long distance sailing and rowing, with a sleeping compartment, called the Marsh Duck. I have met the designer and seen the boat (I had actually had long email discussions with him about it when he was designing it and offer a few ideas that he incorporated into the design). It has been used for several month long trips around the Pacific Northwest. It is 18 ft long with a 42" beam (not counting the "wings"). I would prefer it as a trimaran and perhaps a narrower hull, but this is all the space you need to get out of the weather and store enough supplies for multi-day traveling. you can find details about it over on the Duckworks boatbuilding site.

    [​IMG]
     
  6. Skyak
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    Skyak Senior Member

    Based on your description of needs I still favor the JEM canoe for the main. It sounds like the others recommend a similar size and the JEM is very efficient use of 3 sheets. The alternative is to make a rectangular flat bottom hull of your own 16 to 18 ft long. I don't think you need to raise the floor more than the height of a can. About rowing -there are highy developed dimensions for efficient rowing. I am not sure that you have room for oars because of the outrigger. outrigger canoes are generally paddled. Would you consider building the JEM main hull, loading it up and seeing how it sails and paddles before building the outrigger and ama?

    Sockets are one way to connect the ama. I am not a big fan because I see the socket being full of water all the time and the end grain of the aka sitting in it -not good. An alternative is to lash the two together. Lashing lacks the stiffness of a socket mount, but that also makes it tougher.

    About cutting chine logs, you are going to need a saw that can cut the shapes out of plywood, and you will also need a saw that can cut lumber lengthwise accurately. Most builders have at least a jig saw for the ply and a circular saw for the lumber. Hand tool fans use bow saws with a wide variety of blades for both of the purposes. If you can find the blades you can build a bow saw. I think a jig saw would be a good investment -they are cheap and you will cut more accurately. A jig saw is poorly suited to big rip cuts needed to make chine logs. It would be best to find someone with a table saw you can borrow (buy them a blade or two). The other thing I should mention is that stitch and glue construction does not need chine logs and you have plenty of epoxy. Cut the plywood with the jigsaw and save the fine sawdust. Plane the edges of the plywood so they will meet together at a large flat surface when stitched together in the hull shape. After you glue these flat edges together and pull the stitches you will make thickened epoxy with the wood four (sawdust) so it is like peanut butter and fill the inside of the joints so they have a one or two inch fillet. When this fillet is covered with fiberglass inside and out it will be stronger than if it was a glued chine log.

    Epoxy is wonderful stuff eh?
     
  7. Skyak
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    Skyak Senior Member

    Hi Petro,
    I am surprised by the mast height of this rowing canoe. Do you know much about the loading of this boat and how well it worked? I am wondering what sail the JEM canoe could carry with 200lbs of supplies solidly stowed in the bottom 4 inches of the hull.
     
  8. El_Guero

    El_Guero Previous Member

    Petros,

    I like that Marsh Duck! How would it be different from the ones I posted about earlier?

    And the Duckworks pages: http://www.duckworksmagazine.com/13/designs/marshduck/index.htm#.Umgk6RYeXzI / http://www.duckworksbbs.com/plans/domergue/marshduck/index.htm And his blog page: http://scotdomergueblog.wordpress.com .

    The difference in price plans is not a great range, CLC does offer the opportunity to purchase study plans .... I will do that soon.

    Wayne
     

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  9. El_Guero

    El_Guero Previous Member

    And I almost forgot the most important ingredient!

    You need bottles of Tabasco .... from the brothers who crossed the Atlantic in an outrigger canoe - http://www.duckworksmagazine.com/09/outings/french/index.htm .... They used 30 bottles, but I think you can get by with about 10 ... Don't you?

    wayne
     
  10. WilliamPrince
    Joined: Oct 2013
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    WilliamPrince Junior Member

    The duck boat seems great.. I will write a more detailed reply tonight, with pictures of my current building status, but I have just learned something that is worrying. My plywood, though advertised at 6mm in all respects, is actually 4mm. I have 3 sheets of this. Is this plywood unsafe to use on my hull? Can I return these sheets I wonder...

    As for the tabasco... I think if I only packed 30 bottles I might find myself out in the middle of the ocean, no land in sight, running seriously low on tabasco. Not sure if I could make it through a situation like that.
     
    Last edited: Oct 23, 2013
  11. El_Guero

    El_Guero Previous Member

  12. Petros
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    Petros Senior Member

    the carbon mast is from a sailboard (it was free from a friend-an older design that is obsolete for most performance sailboarders), the sail was off something else that he altered to fit. He has sailed it to Victoria from Bellingham, and than over to Port Townsed for the wooden boat festival in September. He was living on board it with his girlfriend, though it was designed for long distance solo travel. I did not get a chance to try it out, but he was very pleased with the results and is very enthusiastic about selling plans for it. I know he is likes rowing long distances and has much experience in rowing shells, when he was in the design phase I tried to convince him that using a kayak paddle would be simple and it too was suited to long distance paddling (which I have done), but he insisted that rowing was far more efficient and want it to be a row boat. I told him that for long distances I just as soon wait for favorable wind, and if it sailed well that would be the primary means that would drive it anyway. Rowing would just be a the axillary means of propulsion, and that a kayak paddle would be lighter and take up much less space when not in use, no oar locks or slinding seat, etc. But he went with a rowing shell design, and adapted it with a dagger board, rudder and sailing rig.

    Reading the description from the duckworks page would tell you as much as I know about its capacity and performance.
     
  13. El_Guero

    El_Guero Previous Member

    1/4" instead of 3/8's? I am not sure that would make a difference, the quality of the ply would be of greater concern to me. Are the surfaces free of defects? Do they look like one sheet of veneer?

    And are you wrapping this in fiberglass?
     
  14. WilliamPrince
    Joined: Oct 2013
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    WilliamPrince Junior Member

    To clear things up, I did not realize the distinction between rowing and paddling. Frankly, whichever form of propulsion will be more effective and easier to implement, I will be happy with that one. To me, that seems like paddling with a double ended kayak paddle, and that will be easy to find a good paddle as well.

    As for the hull design, I think the Jem looks to be a great craft for me in many regards. The ease of construction, minimal overhead in terms of cost of materials, the wide beam... I think it would be a great base for my boat. That being said, I also really like many of the features of the Marsh Duck, as well as some of the plans linked by El_Guero, like the raised and covered cubbies at the ends of the boat, for storage and even sleeping. Maybe it would be simple to incorporate those features into the Jem design, it is hard to tell for me.

    I am really not even opposed to a monohull design; if I take it out and it sails well and paddles well and handles generaly well in water, maybe I will just stick with it. I guess I wont have the same stability as with an outrigger but.. Well I'm only 19, stability is for old men.

    As for building the main hull first - I think that is a great idea. The ama I am building now will not neccesarily be the ama I use on my journey, although if it works out to be so, of course I am happy. The ama I am building is mainly for practice, to get familiar with the tools and processes I will need to build a seaworthy boat. I will be finished probably tomorrow, I am somewhat stuck on what to do with these chines... If I do them without planing them to shape, the entire shape of the ama will change, as there will be right angles at the corners. Anyways, I am attaching some pics so you can get the idea of how I am building. All critiques appreciated!

    Cannot figure out how to attach multiple pics.. And embedding them in my post fcks up all the formating. Geez.
     

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  15. El_Guero

    El_Guero Previous Member

    Stability is for sleeping ....

    :)
     
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