DIY Simple Catamaran Sailboat Design

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

  1. scotdomergue
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    scotdomergue Scot

    The picture looks OK to me. You can stitch it together once the top panels are ready, then place the bulkheads and see how it looks again. My impression is that it makes sense to go ahead . . . check everything each step of the way, you can run a line from bow to stern and that may help see how alignment is doing. With the Marsh Duck I drilled a hole in the one bulkhead that stuck up, hole at the height of the bow/stern and centered, and that helped with checking alignment; I put a mark at center of the top of the other bulkhead that was at the height of bow/stern. You have some adjustability as you stitch it together, start with it a little loose and tighten as you get it aligned. If there are some small gaps in the joints you can fill with thickened epoxy. Perfection is seldom possible and not needed. Good luck! Scot
     
  2. WilliamPrince
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    WilliamPrince Junior Member

    Oh god I just drilled about 50 holes, wondering why my brand new drill and drillbit weren't working very well, and making a lot of smoke, then realized my drill was set to turn the wrong way.

    Im learning.
     
  3. scotdomergue
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    scotdomergue Scot

    nothing quite like a little experience! }:cool:
     
  4. upchurchmr
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    upchurchmr Senior Member

    You don't have to tell us EVERYTHING.
    Most of us hide some of the worst mistakes.
     
  5. WilliamPrince
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    WilliamPrince Junior Member

    Okay, I have stitched up the bottom panels, and it honestly went together pretty nicely. I do have a few concerns with the alignment - the consequences, I think, of my mistake with the alignment of the mid panels - but in general it came together quite well. Details of the work can be seen here: http://youtu.be/xfGkARTL2sc

    I am now however at somewhat of a standstill. To sew on the top panels, I need the frames in, and I still havent cut any shapes into the larger, inner bulkheads, as I need to. To know where to cut, I need to decide how I am going to arrange the inside, with sleeping, storage, all that jazz. Basically, I need to design the boat. To get a better idea of what I will be storing where, I will go ahead and buy most of my supplies for the trip, as well as bring my belongings to the hostel so I can arrange them as they will be in the boat. I guess I will also be able to store stuff in my ama to some degree... But that will come at the end I think.

    I will draw something up tomorrow, when I have the food, water, and gear, so that I can run a layout by you guys to see what you think.

    What should I generally be going for in terms of my weight distribution? I know I need the heaviest things along the keel, and to make it as symmetrical as possible, but other than that I am not sure. I am thinking I will carry 14 gallons of water along the keel in the middle of the boat, which will span directly under my main platform for sleeping/living.

    I have seen some people mention foam, or airtight compartments in the ends... Well, all thoughts and input appreciated. Will have a more accurate estimation of everything tomorrow. Thanks, as always!
     
  6. scotdomergue
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    scotdomergue Scot

    You seem to be on the right track. How is it going now?

    I'd try to keep your main platform pretty low so that you'll be more stable when you're asleep and in general . . .
     
  7. WilliamPrince
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    WilliamPrince Junior Member

    Its going well, just got the top panel in and I am sewing it in now.

    A quick question... How important are spacers? They are a real pain in the *** to put in, and I would much prefer to do it without. Is this acceptable? Or would that weaken the whole thing significantly?
     

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  8. scotdomergue
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    scotdomergue Scot

    Looking good!

    Spacers? What spacers are you talking about? Stitch & Glue on the Marsh Duck didn't involve anything I'd call spacers . . .

    There does need to be a little room to get epoxy into the joints. On the Marsh Duck, the different angles of the panels meant that there was a V shaped space (tight wood to wood on the inside, a bit apart on the outside. That was enough. On the bulkhead to hull panel joints I Left the stitches a little loose until I pushed some epoxy into the joints and then tightened. I then coved the joints which provides more strength.

    I noticed in your pictures that the bottom seemed to overlap the sides in some places and the sides overlapped the bottom in others, that the two appeared to come together without much of a V to the joint, and that you have thin pieces of wood (tongue depressors?) in the joints. Are those the spacers?

    As long as there's room for you to get epoxy into the joints, and you're going to fiberglass completely over the joints, I'm not sure there's a need for spacers . . .

    And I'm not sure that I fully understand . . .

    Very cool to see your boat coming together!
     
  9. WilliamPrince
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    WilliamPrince Junior Member

    Okay, basically you just said what I wanted to hear, so I am glad! There is ample space for epoxy in my joints, but I had been instructed by a few guides to put the spacers (tongue depressors) in with my stitches. But it is a huge pain in the ***, and doesn't even make much difference.

    Anyways, I have another small problem which I want to ask about before I glue anything. My hull is a tiny bit off center (about 1.5 cm at the most) meaning, the hull extends more to the left side of the centerline than the right side by that much, near the inside bulkheads. Is this a serious problem? I don't see much way to fix it... Advice appreciated.

    As for everything else, well it is pretty much square and correct! I can hardly believe it but the measuring tape does not lie. Well, when I figure out this, I will epoxy the insides of the joints, and, if I have enough fiberglass, the outsides as well. If I don't have enough for the outside, I will go ahead and buy the large fiberglass tape, and just do that. I will do the large fiberglassing regardless of whether or not I have enough of the 6inch roll.

    What do you think I should do to the inside? Should I put fiberglass sheeting all over the inside, like I will the outside? Well, my other option is just to coat everythig with epoxy... What do you guys think?
     

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  10. upchurchmr
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    upchurchmr Senior Member

    Epoxy without glass does not have much strength, easy to scratch, scrape off.

    Fix your off center before you epoxy the joints. Do whatever you have to. Take it apart, set up a centerline on the bottom panel, and measure from the center to the edges and make them the same. Put the left side on top of the right and make them both the same. Cut the edges as required, then use a batten (maybe 3/4 x 3/4) to make the curve fair on both, then check again.

    You will hate the boat not going straight when another 2 hours of work would have made it right.
     
  11. Petros
    Joined: Oct 2007
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    Petros Senior Member

    there are actually very few hulls that are perfectly symmetrical. the problem on a small light boat that you row or paddle, you will have to correct for it not tracking perfectly. If it is off by a lot, this can be very annoying and tiring. when under sail the hull is seldom symmetrical in the water anyway, and it is trimmed out with the rudder.

    If you have convinced yourself it is not worth fixing you can always reduced the effect of any asymmetry by putting on a small skag and than putting a trim tab on it. this will increased the drag ever so slightly, but the skag might make it paddle more in a straight line anyway (flat bottom boats tend to swing to the left and right with each successive stroke on each side of the boat, the skag greatly reduce this tendency). the skag can also help you keep it in a straight line when paddling in a cross wind (of course you might want to have the sail up in those conditions anyway, presuming the sail is functional).

    on a sailboat symmetry is over rated, on a canoe or kayak, it is pretty important. even so, I have paddled a number of skin 0n frame kayaks were were clearly not symmetrical yet they paddled fine with no noticeable tendency to pull one way or the other. But I have also paddled a skin on frame kayak about ten miles across a lake and back in a cross wind that kept wanting to turn down wind, it was a real PIA. the unsymmetrical part of the hull it turns out was in the stern, I ripped the skin off and corrected the frame, after reskining it the problem was solved.

    I would say if the asymmetry was in the bow and not too much (1-2 percent or less perhaps?), it will not likely affect you much, if it is in the stern, best fix it unless you expect to be using the rudder under sail most of the time.

    It would be safest to eliminated it as much as possible, you can also layer up some foam or light wood where it is unsymmetrical to balance it out (what the water sees is all that matters, not the how the hull is made). As long as it does not add too much weigh to of course.

    You will have to decide, the boat will float and likely sail without issue even if not symmetrical. Any problems with asymmetry would occur when you are paddling it, and it may or may not be large enough to worry about, if noticeable you can usually correct it with a small skag in the back with a trim tab.

    Nice looking hull btw, keep at it.
     
  12. scotdomergue
    Joined: Jan 2009
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    scotdomergue Scot

    Not much to add . . . Is the asymmetry only or mainly at the top (rail/gunnel)? Mainly down around the chines? If it's fairly symmetrical below waterline it won't have much impact paddling. As mentioned by others, symmetry isn't so important for sailing.

    In the picture, the side panel on the right looks slightly behind the one on the left. Evening that up could help correct symmetry (or might be a result of correcting in other ways) . You may be able to add a little something between bulkhead(s) and panel(s) (small pieces of wood shaped to create correct alignment and eventually epoxied into place) and/or loosen/tighten ties to help straighten things . . .

    Good luck with it!
     
  13. WilliamPrince
    Joined: Oct 2013
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    WilliamPrince Junior Member

    Okay, after agonizing over it for a while, taking the frames out and trying to adjust it, I still came out with about a half inch difference... Well I am just going to leave it. I am going to start filleting the seams now, between the stitches.

    Petros, could you explain something a little more about that skeg idea? Well, I won't know if I need it until I take it for a ride, but it is good to know I have other choices out there.
     
  14. Petros
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    Petros Senior Member

    all a skag (or skeg) is, is a fin in the water on the aft part of the hull, they can also be retractable but that complicates it a lot. A trim tab on it could be a little square of aluminum glued near the trailing edge that you bend (like a fixed mini rudder) until it trims out any attendance for the hull to turn to one side or the other when gliding along in calm water, no wind and balanced on an even keel.

    this is a simple fixed skag, much larger than you would need:

    [​IMG]

    this is one for a kayak sized hull that would be suitable for your boat:

    [​IMG]
     

  15. WilliamPrince
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    WilliamPrince Junior Member

    Will my rudder act as a skeg? Or, could I design it in such a way that it acts as one?

    Okay, I am currently epoxying 6oz cloth on the chines, almost done with the outside. For myself, as well as opening it up for any comments, I will make a list of the things I must do in the future.

    1. Do the inside chines with cloth, epoxy
    2. Install frames
    3. Epoxy inside of boat
    3. Inner compartments/access
    4. Get a mast
    5. Mast attachment
    6. Gunnels
    6. Epoxy end pours
    7. Cover center of boat (bed)
    8. Rudder and housing/skeg
    9. Anchor and housing (need help with this!)
    10. Finish ama
    11. Connection with ama
    12. Adjustable seat (need to be high enough to paddle, but not too high)
    13. Bottom reinforcement
    14. Cover fore and aft compartments/access
    15. Sand and fair
    16. Paint

    **** I have a lot to do. Gotta get to work.
     
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