Best free-standing rig for small, light race-cruise tri?

Discussion in 'Boat Design' started by scotdomergue, Nov 6, 2014.

  1. Nick_Sinev
    Joined: Aug 2014
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    Nick_Sinev Junior Member

    CT249, thanks for really interesting and comprehensive reply!
    "Wingmill" looks really unusual, I'll try to find more info about this vessel.
     
  2. Skyak
    Joined: Jul 2012
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    Location: United States

    Skyak Senior Member

    Scott,
    glad to see you back. Quite a challenge you have ahead with R2A -that's some serious sheite. I feel the need to talk a bit about the givens you have already listed. I could be wrong, but this is what R2A looks like to me.
    -cold water, like 'dead in an hour' cold, and you could be more than an hour away from rescue.
    -inside passage will be strong tidal currents with lighter winds on the nose or from behind, with the occasional blast of wind falling from the mountains.
    -outside the winds will be better sailing and you won't have adverse currents half the time, but the new killer is waves. I would guess there is a better than 50% of encountering waves bigger than your boat.

    19X14 Trimaran -this implies a fast light boat that is still very small relative to natural phenomenon in your path. It kind of implies you are in it to win but you will be beaten by a bigger sailboat that takes a direct outside route. The first question in my mind is how do you handle a capsize? Your 250sf of sail comment implies that you plan a typical fast tri with ama flotation much greater than full displacement. But that is too big for the crew to right. It also implies very high rig forces.

    Designing a rig for a sailboat, the strength required is set by the righting moment of the hull. Mutihull rigs need to be much stronger than monohull rigs for this reason. Just to get in the ballpark, your tri has at least 7000ft lbs of righting. Wind surf masts are more than an order of magnitude too small. It would solve the righting question, but you you would need to bring a dozen because they would snap like twigs. Dingy masts like the Finn would be better but still one tenth of what you need. I wonder if the whole idea of the unstayed mast was based on the false hope you could easily put it up and down? An unstayed mast for a half ton tri capable of 250sf sail will not be easy up and down without serious rigging. Then there are structural issues -an unstayed mast will need to be in line with the forward aka (moving it will torque the boat) and an unstayed mast does not have enough forestay tension for a good upwind jib. With all these limitations, it is not easy to design such a rig in the size you are looking for.

    For reference check out the f-22:

    http://www.f-boat.com/pages/trimarans/F-22.html

    Closer to the size and materials you intend see the scarab 18:

    http://www.teamscarab.com.au/scarab18/design.html

    The F-22 is what you need and could win. The scarab is about the size you plan and in ply. Study plans would be a good deal for $15 if only for the scantlings.

    To better guide you, can you tell us what route do you plan? Are you trying to win or just stay alive in a nice boat with future value? There really aren't any rules that I can see. What's to stop Bob Perry's Sliver design from sailing up for the prize? "Honey, I'm taking the boat up to Alaska to pick up $10,000. See you in a few days!"
     
  3. messabout
    Joined: Jan 2006
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    messabout Senior Member

    I am a fan of unstayed rigs, but only for small rigs 10 square meters or less. Sure it can be done with larger sail plan forms but there are penalties for doing so. The structural implications among them. Free standing rigs with rotating mast, can weather vane which is occasionally an advantage. A small saving in drag from the wire is also worth consideration.

    In the final analysis a rig with wire is still the most practical. So what if you have to connect three, probably four terminals when rigging up or down. Ninety seconds maybe. a supported rig will give you some control of the jib stay. Can't do that with a free standing mast.

    Gonzo has made a salient observation. A Hobie 18 rig would fit your tri and provide a gracious plenty of drive. You can find those on the used market for a modest price and you already know that it can drive a multi at impressive velocities. Why re-invent the wheel. The Hobie, Tornado, and other rigs are proven in spades.
     
  4. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    Remember there are two waypoints in the race. Seymour Narrows, which forces everyone to go "inside" and then up Johnston Strait. And Bella Bella (presumably Shearwater marina), which encourages people to carry on inside.

    However if there is a good S wind then it will probably be faster to go outside round the island and back south to Bella Bella. That will be an interesting tactical decision. North of Bella Bella it will be outside all the way for the fastest sailing

    The problem with small boats like the F22 (or even a beach cat) is that you'll probably be forced to go with two crew, for weight reduction and lack of space, whereas I think three would be better

    Oh, and the structures lecturer on my yacht design course always said "if in doubt add a wire"

    Richard Woods
     

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

    scotdomergue Scot

    Yes, a small, light tri. I've been thinking for over a year that my next boat would be a small, light, cruising tri with amas that can be brought in for sliding seat rowing. The R2AK has accelerated the process and influenced design a little, though not much.

    I DON'T expect to win the R2AK. I hope my boat will be fast for what she is but I also expect that there will be some very fast larger multi-hulls entered and that one of those will win.

    It will be a very interesting race. The rules will keep it inside Vancouver Island up to Queen Charlotte Sound, and also require going via Bella Bella. Depending on conditions we probably will go up Hecate Strait rather than the narrow Inside Passage channels, though only if it appears safe given conditions at the time and weather forecasts.

    For me, small is beautiful and light even better. Minimalist cruising is more important than racing or ultimate speed. But speed is fun and has other advantages as well.

    I spent 3 months cruising the southern half of the R2AK race area on my Marsh Duck in 2013, so I'm familiar with the area and it's challenges. I'm doing a lot of studying of the northern half of the area and recognize that it may well offer even greater challenges. We'll be prepared (as best one can be on a very small boat).

    The 250 square feet is for light wind performance, we'll reef as winds increase. The cat-ketch rig splits and lowers things. No jib. The windsurfer masts will be reinforced (essentially doubled in the lower, higher stress area). I'm pretty certain I'll go ahead as currently planned. It's an experimental boat and rig, but I think it will work fairly well. We'll see.

    Thanks for all your thoughts!
    Scot

     
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