Trimaran for R2AK & minimalist cruising

Discussion in 'Multihulls' started by scotdomergue, Nov 1, 2014.

  1. scotdomergue
    Joined: Jan 2009
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    Location: Twisp, WA USA

    scotdomergue Scot

    That Danny Greene design sounds interesting. I couldn't find it (tried Google on Danny Greene sailboat design and a couple of others, got lots on his book). If you happen to run across a link, I'd love to look at it.

    I've only tried on a drysuit once, so very limited experience. It was hard to get into it, and seemed very restrictive of movement and heavy, and yes, hot. I wasn't doing anything, and was out of it pretty quickly, but I can imagine sweating a lot in one! And even used they're $500 and up. The paddle pants and jacket were $100 each, new. On they feel pretty similar to any other outer layer. They have the same wrist neck and ankle closures as a dry suit. The pants waist has a big wide band that goes up pretty high and seals pretty well against whatever you have underneath. The top just has a drawstring, but it overlaps the pants by a foot or so. In my experience very little water gets in (at least within a few minutes, and what does get in warms up quickly as it does in a wetsuit. While totally waterproof, the materials is light weight, so one can wear a reasonable amount of clothing underneath to help with insulation and still not sweat like a pig. I've become a great fan.

    Current design has amas in the water 2 inches at rest (or one in perhaps 3" with the other out if one leans a little to one side. Displacement of the amas at rest is about half their weight, and wetted surface about 13 square feet between the two if balanced, a little less if leaning to one side, I think. It will be possible to change ama height fairly easily if I find I want them higher or lower.

    Somewhere I've picked up a 125% ama buoyancy figure for amas on cruising tris. I'm primarily interested in cruising, not racing - even if I'm entered in the R2AK. I have no intention of every getting the main hull airborne! I'll reef well before that happens. Many small home-built or kit tris seem to have very small amas, along with small sails (which makes sense with small amas). This makes them seem to me more canoes or kayaks with outriggers for stability rather than serious sailing tris.
     
  2. Corley
    Joined: Oct 2009
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    Location: Melbourne, Australia

    Corley epoxy coated

    The problem you are describing is pretty universal in small multihulls there is a fair bit of skin area in a performance trimaran which is why most kayak type trimarans have pretty small floats to try and keep the weight down. If you think about it you have to have sufficient displacement in the main hull and a certain number of appendages but you also want to maintain a high fineness ratio on the main hull for good performance.

    Have you seen the Sardine Run trimaran by Eric Henseval which is designed for raids? I know it's heavier than you proposed but I wouldn't be too obsessed with making the boat super lightweight if you can have some shelter and be comfortable that will improve your ability to perform well day after day. It also looks like a boat with good sailing performance.

    A stern sculling oar would probably be sufficient to propel the boat. Charles Meredith who competed in the Three Peaks Race with his 6 ton Chris White cat had a couple of human driven propellers on the sterns and they were able to propel the boat at about 1 knot or so when using them I think they were designed by Rick Willoughby who I think is or was a member of the forums here. I'd not leave building too late you need time to get to know your new boat and shake it down.
     
  3. scotdomergue
    Joined: Jan 2009
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    Location: Twisp, WA USA

    scotdomergue Scot

    I've looked at Sardine Run on the web a bit. Yes, it's heavier than what I intend.

    My boat will have fore and aft cabins, each a single berth as well as used for other things. I think she'll have as much comfort as Sardine Run.

    Light weight will make her easier to row and to paddle. It will also take less sail power to move her through the water at a given speed . . . not to mention dragging her up on a beach or transporting her.

    I rowed my Marsh Duck at about 4 knots and expect to be able to maintain 3 knots for extended periods in the new boat (sliding-seat rowing). The cockpit area will also be narrow enough (26" beam in this area) for good double-bladed kayak paddling when the amas are out for sailing - which I suspect will be faster than using a stern sculling oar.

    I plan to start building in early December and have her ready to do sea trials, modifications as needed, and then spend the month of May cruising on her and getting experience in the full variety of conditions before the R2AK in June.
     
  4. Petros
    Joined: Oct 2007
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    Location: Arlington, WA-USA

    Petros Senior Member

    Scot,

    No reason to hire a professional to design your tri, you know what you want, you have skills, and can learn what you lack. You likely can build the whole thing for far less than the design costs. Besides, most design professionals do not design such narrowly focused boats, you found yourself that there is really no design available like you need for this kind of sailing. Everyone has to start somewhere, and you actually have a head start over many amateur first time designers. Besides, developing the design is as satifyiing as building or actually sailing it, so no reason to for go that adventure in the name of expedience.

    A couple of things you might consider: try and rent, borrow or get out on as many small tris as you can before you finalize the design. It will give you some time in the type so you will have a better feel for how it all works together.

    I have a nice 16 ft plywood tri a friend of mine and I built for the Port Townsend Endensaw contest this last September, you are welcome to come use it anytime you are in the area and I am available. It was not my first tri, but it is the most complex one I built, the size and shape might be about what you are considering. It only cost about $250 in materials to build (no fiberglass or epoxy) and weights similar to what you are planning. I have incorporated a few improvements since the contest weekend and have been looking for a reason to go out on the water with again anyway, even this time of year.

    It is difficult to see your plans in your attachment since they will not open, but you might consider, so save weight and keep it simple, to do away with the dagger boards and make the ama with a sharp keel like to act like a keel, similar to the way the Hobie 14 and 16 work. We did that in the Edansaw contest boat and it worked well. It did not point as well as a nice high aspect dagger board would, but it was lighter, simpler to build (stronger hulls), and I think had much less drag, so it made up for the slight loss in pointing ability. If upwind performance it important in this race, this may not be such a good idea, but we were able to take our about all over puget sound without issues by carefully planning our tacks and route. all the way in and out of the harbor, and up on the beach and back. the photo below was by Richard Woods btw.
     

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  5. scotdomergue
    Joined: Jan 2009
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    Location: Twisp, WA USA

    scotdomergue Scot

    Petros,

    That's a nice looking little tri. I'd love to get out on her with you. I'll be in Seattle for Thanksgiving with family and I might be able to get myself to someplace it would make sense to meet, perhaps earlier in the week. Let me know what might work for you.

    I expect that upwind sailing will be a large part of the R2AK, so expect to keep the dagger board. It really doesn't need to weigh that much.
     
  6. redreuben
    Joined: Jan 2009
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    Location: South Lake Western Australia

    redreuben redreuben

    If you actually want a tilt at winning the thing why not look at a Proa ?
    Simpler build and cheaper and lighter.
    Rob Denny's Elementary with the camper float would be perfect.
     

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  7. haribo
    Joined: Oct 2012
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    Location: berlin

    haribo Junior Member

    designwind? % row % sail ?

    did you remember your treat from 2010?

    with the link to the row trimaran hallin:
    http://www.boatdesign.net/forums/sa...-powered-ocean-racing-36035-2.html#post441638

    or this trimaran row design:
    http://antrimdesign.com/30-trimaran-ocean-rowboat-orca.html

    both did not use dangerous moving systems for amas, you realy don´t need this problems in this size... not for transport not for beaching not for nothing

    so why not start with your Marsh Duck, adding wide beams and very smal amas, rowing inside the ama´s like both other trimaran rowingboats, and ask the following questions:

    - how much sail area will bring this boat at wind xy (designwindspeed) to the same speed as you can row it? and what is the price (the wight of daggerboard, rudder, mast, bigger beams, amas)

    - and what volume and form and position of the amas is necessary to sail it at this speed?

    I promis you the answer will never be "250 squerfeet sail area" or "125 % amavolume" for normal windspeed,

    - and the third question: how much faster can you row or sail this trimaran if the main hull is in his underwater volume l/b and prismatic coeffizient etc optimised, and what sail area and ama volume fits for that new speed (the smaler aka is faster but there will be no space to sleep into the hull....as in marsh, the cabin must lay higher....more wind drag is the price)

    IMO it make no sence to downgrade a sailing trimaran just for rowing, start with the best rowboat, and the trimaran-row boats are faster than the monos, and try to ad just so less sail that you can stop rowing 50% of the time (ergo 70% of the way...)


    designwindspeed and %row vers %sail, this are two missing key´s in your plan,
     
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