My fir foray into boat design...

Discussion in 'Sailboats' started by science abuse, Nov 23, 2009.

  1. science abuse
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    science abuse Junior Member

    ...and I'm still cheating a bit; I'm starting with some one elses hull.

    What I have is a coleman "scanoe". A 16ft long, 43" wide "canoe" with a flat transom. This thing blurs the line between canoe and johnboat.

    I fitted it with locks and 9ft oars 2 years ago, and I've put many miles on her in this configuration. I'm not done rowing, but I'm also not done tinkering.

    Recently, I've gotten ahold of a sail from an Escape Rumba.
    The design is still in develipment, but this is the rough assembly:

    Theorized rigging would be similar to that of the Zuma I grew up with, because it's familiar.

    Stability would be provided by the pair of outriggers spaced at 6ft from keel. Outriggers would be constructed of Owens Cornings finest pink foam, with a wrapping of fiberglass cloth and West Systems epoxy.

    The mast will be two-peice with 12" of male-female inteface; 6061-T6 aluminum cold-drawn tubing, .125 wall thickness, 2.0" OD and 2.25" OD respectively.

    The mast step will basically be a block. Constructed of a multilayer sandwich of foam and fiberglass 16" thick and 18" wide, it will fill the section of boat in witch it sits, and fastend to the gunwales with no fewer than 3 through-bolts per side. Current plans are to have the mast stayed, though it may prove strong enough to stand free. The forward outrigger poles with also mount to this peice, whilst the aft will be secured to the gunwalles by angle-stock.

    Yet to be solved: Mounting points on the foam bits. I'm thinking of setting wood in as "hard points" prior to fiberglassing. Are there better alternatives?

    Theories and experimentation:
    If able to rely on the outriggers for stability, i'd like to set up a "cockpit" at the aft of the boat, consisting of a comfy seat set low to the water, with pedal controls for the rudder.

    If needed to help tacking, the flat inside edge of the outriggers may each be fitted with 12"x 24" swing-keels, held by extension springs similar to the rudders on many beaching boats. This should allow safe beaching without having to pull them up manually.

    This is all on the drawing board at the moment, and I am very new to this. I guess I'm looking for ideas and critisism to help me refine the design before I start buying materials.
    Many thanks for reading!
  2. bistros

    bistros Previous Member

    I don't see any reference to a daggerboard above- going upwind will be dicey without one. The foam you are spec'ing is nice, but you can get white styro cheaper, and if you are glassing the outside, you may be spending more than necessary.

    Fixed position cockpit seating is a nice idea, but I'd consider adding trampoline material between the outriggers and sitting there instead. Improved righting moment, more space, more comfortable and almost no added weight. In addition you get to adjust fore-aft trim when needed. The foot pedals can go in my mind as well. Complicated and heavy compared to a tiller and carbon cross country ski pole extension.

    The crossmembers are critical and keeping them strong and aligned is a challenge. Most of the multi-hull folks spend a serious amount of time on that part of the design. I'm sure they'll chime in as I don't know a thing in this area.

    I think having two crossmembers up front may be one too many from a weight standpoint.

    Steve Clark proposed such a "frankenboat" conversion using a standard canoe a while ago - since you've got the outriggers, your performance would be a lot better using an old canoe for your Aka in the middle instead of your already functional scanoe. Here are the related threads in order:

    NOTE: skip to the middle thread if you are interested in staying directly on topic without the history and development for the conversation


    Steve is probably North America's most successful small boat builder from a volume standpoint, and he's a sailing canoe enthusiast of epic capability. (Oh yeah and a World Champion sailor)

  3. science abuse
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    science abuse Junior Member

    I picked that particular foam because I'd worked with it before, and I know the epoxy wont melt it. ;) If the polyeth' foam will do the job, I may well go with that. Adressing the daggerboard, I didn't want to compramise the hull below the water line. In point of fact, I'd really like to be able to strip it back down to a rower on occasion (hoping to row across Saginaw Bay this summer). The solution I'd come up with was the swinging keels on the outriggers:
    Not pictured: Any mounting or reinforcement what so ever. I'm aware that I'll need to make these strong against side loads. Option 2 would be to enlarge them and bring them in next to the hull as leeboards.

    The flat inside surface is also meant to make alignment easier. A laser pointer, some masking tape, a tape measure, and a flat perpendicular wall should get things right.

    The double-front crossmembers may indeed be overkill, I'm just trying to make doubly sure the thing doesn't fold up on me. ;) I have every intention of putting this in some rougher conditions: Runing before waves is addictive. The catch with that is, this won't bail itself. I have tonneau covers to manage spray for the rowing rig (I row the waves also), but it won't keep all of the water out.

    Maybe I'll just have to force myself to take it easy until I have time to build a dedicated hull, maybe next winter. Tramps are always "on the drawing board" but I'm not budgeted for them yet; I'd just like focus on getting this thing wet and blowing by April.

    Many thanks for the links, I'll have to spend my lunch break reading through them all. I may even sign up over there and resurect the thread.
  4. ancient kayaker
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    ancient kayaker aka Terry Haines

    I have also done that with a 14 ft canoe, but only one ama. I built the ama using plywood which made for very easy, light and quick construction and yielded a fair hull without much effort.

    Not sure why you would want to row a canoe instead of paddling and seeing where you are heading but that’s your choice. I just wanted to sail the canoe.

    It looks like you have around 80 sq ft of sail area, typical of canoe sailing. You are proposing an adequate mast for such a sail area and I would not expect you would need any standing rigging provided you can make the step strong enough. I am not familiar with the Zuma but you will need a mainsheet and a vang, that’s about it. It’s not rocket science.

    The outriggers (amas) look kind of large. Mine was 7 ft long and roughly 8" square midships and created a lot of drag. The boat only sailed well when the ama was out of the water. If you want some performance I would suggest smaller amas shaped like a mini-hydroplane with at most enough buoyancy to hold your weight standing on the gunnel, and mount them high. If you do have a cockpit ensure you can move easily to balance the boat with the small amas, which are only there to let you move around freely and give you time to react to a sudden squall. If on the other hand you are aiming at an instant trimaran then ignore these comments.

    A double cross-member is less efficient use of material than one large one. Stiffness is the most important thing rather than strength which is easy to achieve in a boat of this size, however with smaller amas that are kept out of the water it is sufficient merely to ensure it can hold your weight as far off-center as you plan to go.

    As you obviously are aware pedal controls for the rudder will lock you into one position. It is performance vs comfort, as always. I controlled my rudder using a lne that ran all around the gunnel through eyelets so I could reach it from anywhere in the boat.

    I don’t see why swing keels on each of the amas is any better than one on the main hull where you can get at it more easily. If performance is the goal a long narrow board will be better than a short wide one.

    Good luck and have fun!
  5. science abuse
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    science abuse Junior Member

    Your point about the forward cross members is MUCH appreciated. I'd kind of gotten mentally stuck with the most available diameter tubing I could find. For perhaps less money, I could open up the diameter and increase the stiffness and lessen the weight. Win Win Win. My supplier limits cold-drawn T6 tubing to 12ft, which is exactly what I need.

    This is actually my second attempt at outriggers. My las set was designed to keep the boat stable on open-water rows, island hopping, and free-diving. They also served as outboard riggers for the oars. I found the boat to be stable enough without them.

    They were 8ft long with a sharp V to the hull cross section. They were very low drag, but proved to be unnecessary weight. I still have them, and have considered doing "something" with them... anybody want them? lol

    Those taught me that I didn't need wood as an integral part of the structure, the foam and fiberglass was plenty stiff.

    The idea of making them longer (12ft) is to lower drag (Bernoulli), while increasing the planing surface area and buoyancy for the sail to push against. I never want to have let out sail because the wind is too strong, I just want to go faster. ;) I'm aware that they probably have enough buoyancy to make them a dodgy catamaran unto themselves.

    The rudder isn't pictured because it's still very much in the air. I've also theorized a pair that mount to the tail of the outriggers. This makes the assembly more modular, independent of the hull, less drilling.

    Regarding the keel, I don't want to go cutting into the hull. I'd like the boat to "wear many hats", and I'm also leery of getting a seal with the UHMW hull because I know first-hand how much it can expand and contract with temperature. Also; who knows, if I can make this thing 100% "piggyback", it may be marketable. :p

    It's something you must try. ;) It's a much more efficient use of your muscles than paddling, and gives you much better power and speed. Your action against the water is spread out over more muscles, so at an easy pace you use less energy. My longest open water trip thus far was 12mi, started at dawn and finished at lunch. The next proposed trip will be 20mi/day.
    But don't take my word for it, I stole the idea. :) Sculling shells are very quick, and numerous folk have crossed the great oceans in rowboats.
    This is the only video of my rig in action, pushing against some freshwater chop and broaching on the wave I tried to ride. Still, I could not have paddled the 100lb+, 43" wide canoe against those waves.
  6. ancient kayaker
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    ancient kayaker aka Terry Haines

    Those amas look very like the one I made. If they are much shorter than the canoe hull they will increase drag no matter how narrow they are due to skin friction. Mine was too large to keep it out of the water safely and too small to convert to a catamaran so it was sacrificed to a "scientific" experiment which was in itself very informative.

    Definitely don't cut into the hull to mount a keel, it isn't necessary. Just mount it on a pivot on one side of the main hull: technically it's called a leeboard and it will work just as well as a centerboard because the hull is not able to heel significantly. It can be cantilevered from the mast step. The off-center position is not important; boat designers do that a lot with daggerrboards that retract upwards into a trunk to preserve cabin space; symmetry is over-rated.

    My latest boat can be rowed: I admit I was surprised at how easy it was, but as my non-de-plume suggests I generally use a double bladed paddle which requires less skill and effort than a canoe paddle. My old canoe perished in a fire and my current canoes are, like my kayaks, meant for double-balded paddling. Rowing is fine when you have plenty of water but becomes more difficult when you have to squeeze along narrow streams and under bridges as I have to. Two of the bridges are so small it is easiest to use one oar against the overhead structure and pole the boat through; not enough width to row.
  7. science abuse
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    science abuse Junior Member

    I'd actually suggested this a few posts up. ;)

    Though using just one large one is something I'd not considered, favoring symmetry. As my nom de plume suggests, everything is an experiment, and trying it both ways should be fairly easy.

    I do always have a paddle, double or single, onboard for emergencies. Getting around the inland lakes here occasionally requires passing through a culvert or two.

    I remember now what led me to double front crossmembers: Mast stability. I didn't want to rely soley on the mounting points in the hull, the pair will take any fore-aft movement of the mast/step and spread the load out over the whole of the vessel.
  8. ancient kayaker
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    ancient kayaker aka Terry Haines

    If you have 2 leeboards deployed one at a time to the leeside the board can be arranged so the water pressure forces it against the side of the hull. However you will have to change it at each tack, form the cockpit if you have one. With one board the pivot must handle force from either side so it should be stronger -swings and roundabouts.

    The mast forces on the crossmembers will be primarily torsion; provided you can anchor it adequately to the gunnel a single larger diameter tube will be stiffer (and likely cheaper) than two smaller ones of the same total weight. However, that may be moot since the mast step will be stiffer than crossmembers provided it is a good fit inside the hull, even without a bottom through bolt. That is the way I did mine, the crossmember held it down against the bottom; however it had standing rigging.
  9. science abuse
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    science abuse Junior Member

    I've decided it would be a good idea to do a scale model before I start buildiong, basing the scale on balsa material thicknesses. It should help me sort out my forming and construction process.
  10. messabout
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    messabout Senior Member

    I will stick my paddle/oar/sail in here and claim that a 43" boat does not need outriggers. The presumed extra stability of the amas will not make the boat go faster even with too much sail. More than likely it will be slower, gusts be damned. Just use a smaller sail and forget all that messy tubing and other doo- dads. The speed of the boat is predominately determined by its' waterline length and less by the excess power you my want to stack onto it. Build a box like platform that will clamp to the sheer of the boat. That is your mast step and another clamp on to hold the lee boards. Now you can remove the sailing stuff and revert easily to power or row or even (perish the thought) paddle mode. Best of all you can rig for sailing in 3 or 4 minutes instead of having to spend no telling how long to bolt all those outrigger parts together at the launching site.
  11. BobBill
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    BobBill Senior Member

    Lee Boards

    Excellent point(s) by messabout. Maybe single ama, but with tramps, more crap can be sported about when necessary.

    I believe, if you search a bit, you just might find a lee board rig already made for canoes that will work just fine. Should not be hard to make, with notched anchors beams to fit rails, etc...thread going on lee boards also. Simple affairs along messabout's lines, they were popular when I was young.

    They were also tricky when under sail - my first capsize. Capitan Bob the sailor man dumped himself and soon to be wife in deep black swamp muck on lake near Waupaca, WI; she still brings it up on occasion.

    Incidentally, love your project. Please keep us too.


  12. Doug Lord
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    Doug Lord Flight Ready

    I've noticed that on the full size amas and particularly on the model you have placed the curved side of an asymetrical hull to the outside of the boat. To the extent such a hull develops lift(to windward) it would do better with the outside being flat. Take a look at a Hobie hull.
    Good Luck and have fun!
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