Bi-Plane rig on a 20m cat

Discussion in 'Multihulls' started by Becaris, Jun 28, 2010.

  1. Becaris
    Joined: Aug 2008
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    Becaris Junior Member

    Thanks for the information, Gary. I agree completely that each rig has it's compromises. I'm just trying to get a feel for the good and bad with this rig and then see if it fits my needs.
     
  2. Bruce Woods
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    Bruce Woods Senior Member

    Gary, You seem to be confused and are having difficulty comprehending the various posts. I suggest you reread what has actually been written.

    At the end of the day its each to their own. I do however have mixed feelings for those who are jumping on the Bi-Rig catamaran bandwagon and building boats, as most seem to have very little sailing experience. Try reading some of the many bi rig cat blogs that are springing up on the net.

    We went through a period a while back where some builders were talking buyers into composite rotating wing masts for their cruisers, and we all know how that ended up. Lets hope the "Bi Rig cat fad" turns out well for those involved.
     
  3. Alex.A
    Joined: Feb 2010
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    Alex.A Senior Member

    Out Ther Hings Need Testing And Shown Results -if It Works And Is Shown As Such.......
     
  4. catsketcher
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    catsketcher Senior Member

    And no I haven't sailed one

    I have already made my declaration but the idea of goosewinging offshore would need to be well proven for me. On any deep run I use a preventer on my main to avoid gybing. This would be harder on the bi plane rig. As such you could get hit in the head by two sails rather than one - too far down and the leeward main can flip over and too far up and the windward one bites.

    It may be possible to rig preventers forward but I would like to see this technique proven in waves under autopilot. I am sure I could do it for a while at the tiller but a cruising rig needs to be self tending. Like Bruce says a main aint that good for square running.

    In Australia we tend to have racing rigs devolved for the cruiser. Interestingly some very experienced designers -Snell, Hitch have developed rigs with large genoas (or no mains) to cater for the long trips downwind here. For me I think the best compromise is a 7/8 wishbone rig with a large reacher. Get the CE up front for downwind.

    One of the best ways to use other people's experiences is to find the individual who best appears like you and uses their boat as you would. I seem to have most in common with Thomas Firth Jones rather than Schionning or Parlier. He found Dandy an interesting but unsuccessful experiment. Sadly with the large investment in the few biplane rigged cruisers made by their owners we are unlikely to get a reliable take on the concept until they have sold them and have the freedom to make their statements without dragging the price of their own boat down or up.

    cheers

    Phil
     
  5. Becaris
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    Becaris Junior Member

    I understand your concern, but let's look at how an unstayed biplane rig would be configured for going down wind.

    If you look at this mock-up you can see how the booms are forward of center line, and just how far the wind would have to come around, or how far the boat would have to twist to get the wind behind the sail. Not only that, but as I mentioned, as the boat twists, one of the two sails will come more directly into the wind, which will help to recenter the boat.

    I will be chartering such a bi-plane rigged yacht which has unstayed masts and seeing how it performs down wind for myself, but the theory seems sound enough as you can see from this attached mock-up.
     

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  6. Becaris
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    Becaris Junior Member

    And, as for putting up a lot of sail down wind, check out what you could put up in this configuration by hoisting a square spinnaker between those masts.
     

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  7. Gary Baigent
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    Gary Baigent Senior Member

    Hey, running flatoff is the slowest, the most plodding and also the most dangerous point of downwind sailing and where you are most likely to get caught in an unintentional gybe. Better performance, and safer, to head up a few degrees and get the rig breathing - and you will breath better too. Instead of complicated vangs, you need full, or half, wishbone booms on a bi-plane setup to keep the sails a decent shape - and if you gybe, they take all the sting out of the manoeuvre.
     
  8. Becaris
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    Becaris Junior Member

    I've sailed on the North Sea of Germany, and done some racing up there, so I'm well familiar with how to configure my sails. However, there are definitely lazy days, soft winds and smooth seas, with the wind behind us where we sailed goose winged. In those conditions this configuration of sail would work out nicely. Certainly, while we were in gale force winds with 40' swells we weren't running like this. ;)
     
  9. BigCat
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    BigCat Junior Member

  10. Becaris
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    Becaris Junior Member

    Yeah, I've been to your site before, just not something I'm interested in sailing, though I wish you well with it.
     
  11. truecougarblue
    Joined: Dec 2011
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    truecougarblue Junior Member

    Becaris, did you ever settle your design for back up propulsion? My nascent project parallels yours in many respects and I've been looking at using hydrogen fuel cells as my backup power.

    Any thoughts? I don't mean to threadjack but it just seems that a system that passively produces hydrogen from seawater using photovoltaics/wind whenever the battery packs are charged could score some high points for synergy as a system. A 20M cat probably has a decent volume below the water line for storage as well, at least I know mine will.

    Also, what HP requirement did you establish? I always remember hearing the rule of thumb of 5HP/ton for displacement yachts. Sometimes I wonder if maybe most builders start out with far too many horses in the first place because it just isn't sexy to say that your million dollar yacht has twin 20HP diesels. :)

    Thanks in advance for any reply, I'd love to see your project some day when you have time, looks like we are both in Lala land.
     
  12. Corley
    Joined: Oct 2009
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    Corley epoxy coated

    I have a friend who is building a 12m biplane schionning cat with freestanding carbon rotating rigs It's not my cup of tea but it will be interesting to see how it goes he should be launching in 2012.
     
  13. Becaris
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    Becaris Junior Member

    Actually, I only just started looking at fuel cells. I would be very interested in hearing what you have found, and what fuel cell units you are considering. Right now I am planning my back power to come from two 26 kwh diesel generators that will be coming out soon from Polar Power. They are very light weight units. Here is the link:
    http://www.polardcmarine.com/polarpower/applications/military/apu/

    For motors I'm going with 20 kwh motors, so with the twin generators I can power them continuously off diesel if needed. But I don't intend to do that much. I'll sail when I can, and I will have a 6 kwh solar array using the big Sunpower panels, and eight Corvus AT 6500 battery modules (six for the motors, two as house batteries) for enough power to easily push me at a decent speed for a good six hours (or more) before I need to use diesel.

    As for the 5 HP per ton, it's a little harder to figure since I am going electric, but my boat isn't too heavy for her size, dry weight about 22,000 lb. 20 kwh motors should push her fine. I even considered 10 kwh, but after getting some expert consultation, decided to go with the extra thrust for emergency situations. Once I found the 26 kwh generators at 140 kgs each, I was sold. I can push the motors at max if I need to, even after running out of battery power if I need to really move. Yet, the Corvus batteries will drive me most distances I want to travel on motors, without using diesel.

    I'm adding a couple wind generators as well, and using a diesel tender so that I only have to have diesel fuel on board, everything else will be electric (no propane, no gas). I'll post some pictures of my project as things get past the hull and bridge stage (where I am now).
     
  14. Becaris
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    Becaris Junior Member

    I will be interested in how that goes. I was convinced by discussions with Eric Sponberg (and others) that going with twin carbon fiber unstayed masts would be a bit expensive and put too much weight up high (due to the thickness necessary because of a the righting moment of a cat). Their arguments were pretty convincing, and so I've reverted to a more standard mast with rigging (sigh). But... I'm still interested, and I'm still considering the possibility of using stayed carbon fiber masts as a biplane rig. However, for now I'm back to a more standard single stick unless other things change my mind. I am interested in any cat that tries a biplane rig though, I'd like to see beyond theory how it works out (or doesn't).
     

  15. Corley
    Joined: Oct 2009
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    Location: Melbourne, Australia

    Corley epoxy coated

    Here are some shots of Mike's cat it will be good to see how the boat goes. He has fitted the mast stubs in preperation for the freestanding rotating rigs. He has also integrated a Chris White/Bob Oram style front cockpit in the boat should make a pleasant driving position when it's not too lumpy.

    Interestingly enough behind his boat in the pic's is Ian's self designed trailable pod cat it also has a freestanding rotating carbon rig just a single mast though. I'll have to see if I have some photo's of it. He has taken his time building and the standard of workmanship is really high. The boat is going to run an arrangement similar to an aerorig once again designed by Ian.
     

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