Biplane rigs

Discussion in 'Multihulls' started by cutawaycafe, May 15, 2013.

  1. groper
    Joined: Jun 2011
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    groper Senior Member

    I think what it says is apparent wind angle 67degrees @ 11kts. Boat speed 8.31kts at 186degree heading? If so thats a true wind of 10.9kts @ 111deg off the bow. So the boat speed = 76% of the true wind speed on a broad reach.

    Back to michaels figures of 5.2kts in 6 knots true wind 119deg off the bow = 86% of the wind speed also on a broad reach, but much lighter air...

    Nothing here smells funny at all... so again whats the problem?
     
  2. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    The water is 18.6m deep

    Richard Woods
     
  3. Barra
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    Barra Junior Member

    With all the alterations going on at the builders expense I can,t help but feel sorry for the guy, is it only me that thinks this looks like designer R&d at owners expense.

    Yes standard sail area 95 m2. Michael stated his original bi rig had 90m2 plus wings.Somewhere I read booms 6 meters reduced to 5.5 to stop them striking lee mast,so hacking off 4 meters of mast is. Substantial. Contrary to what you may think you can't cut it off the top of the sail, ie the little pointy bit ,it's going to be a chunk approx 4m x 5.5 m per sail. I hope I'm wrong cause that leaves only 50 m 2 of cloth, total.

    Hope it all turns out well for the guy.
     
  4. groper
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    groper Senior Member

    In a word.... Yes!

    Mike and the other 2 guys, all building the same boats (schionning 12m with biplane rigs) designed the rig themselves as a collective effort with the help of carbon mast building and engineering professionals. I guess they went a little large at first as they knew they could cut it down later - you cant go the other way however if the rig was too short to begin with.

    Heres an idea, you could go and build your own boat, complete with rig, and come back here and tell us how it went for you...naturally, we will expect you get everything perfect first try... and if it does go well for you, we will call BS and tell you its just not possible...
     
  5. rob denney
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    rob denney Senior Member

    Where is this, please?
    The only complexity with a gybe is the need for the windward boom to gybe before the lee one so they don't clash. Sheet the ww on a little first and this is accomplished. No traveller, poles or headsail sheets to worry about and no broaching moment or the mainsail crashing into the shrouds when it is windy. In really strong winds and big waves, you can ease the sails round in front of the masts for a completely stress free gybe.
    Hoisting two small mains may be more work than hoisting one big one and unfurling a genoa as long as the boat is pointing near head to wind. Try it running square and the unstayed rig will be far easier.

    And yet "The boat goes like a rocket so I can't complain about performance". I have neither seen nor sailed the boat, but maybe low drag (no shrouds, diamonds, spreaders or striker), efficient leading edge shape, smooth transition from mast to sail and easily controlled draft on a rig that does not need constant tweeking is simply more efficient than a conventional rig? This makes much more sense to me than questioning the instruments. I expect we will get more feedback as Mike does more miles. Afaik, he is not a racing sailor, and apart from the rig, the boat is certainly not optimised for performance so there is probably more to come.

    Actually, what they show is the unreliability of a single wind strength reading in light air. In less than 6 knots of breeze, wind sheer has a huge effect on wind strength and direction with height. See Frank Bethwaite's book High Performance Sailing for examples and differences. I posted the readings to support "The boat goes like a rocket so I can't complain about performance", not to suggest it should be in the next America's Cup.

    You could try not putting the mast in the bows, removing the keel and using two hulls to run an anchor bridle. This seems to work pretty well on Mike's boat.
    As far as I know, none of the unstayed cats have the masts further forward than 5% of their length compared to the stayed rigs. Some have not moved them at all. As Mike has found, on a biplane rig, turning them slightly towards each other overcomes any tendency to drive the boat at anchor. The single wing masted cats have a choice of several methods, all of which work.

    rob
     
  6. Barra
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    Barra Junior Member

    Rob, you are the expert at forum circle work, so I'll try and keep this brief.

    You posted on SA quote" the boat sailed around at anchor,dragged a mooring buoy across the bay and was generally difficult to handle" unquote.

    You can't have it both ways.

    I've been around long enough to know that wing masts on cruisers are a pain, but somehow they keep popping up. Two wings mounted forward in a catamaran has got to take the cake though.
     
  7. rob denney
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    rob denney Senior Member

    Richard,
    Not putting words in your mouth, nor was I referring to your selective quotes from Lat 38 about the Freedom which was hit by lightning, yet was sailed down the coast of central America for repairs, indicating the mast damage was only minor, despite it being a major strike.

    I was referring to your claim "I know at least one carbon mast that shattered when hit by lightning, apparently shards of carbon mast pierced the deck". I asked for photos, boat name, details, etc, you did not reply.

    rob
     
  8. groper
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    groper Senior Member

    This one has been around for a while, 2005 IIRC... probably the first cruising cat to use the twin unstayed carbon wingmasts - bloody big ones too;

    [​IMG]

    Hasnt been capsized, pitchpoled or washed up on the rocks thus far... and its used in charter operation...

    Shows the toed in position of the wingmasts so the drive from each cancels the other out...

    [​IMG]
     

    Attached Files:

  9. Barra
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    Barra Junior Member

    Nice picture Groper, Sorry, what's your point? Take that up north and anchor in a wind against tide situation, with typical trades and the occasional thunder squall and let us know if it remains where you left it.

    I suppose you could go up 4 or 5 sizes in the ground tackle department but doesn't that defeat the purpose of a light weight performance orientated yacht.
     
  10. gypsy28
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    gypsy28 Senior Member

    Owner builder Mike seems entirely happy with his rigs. May I suggest that if you don't like them Barra, don't buy or build a cat with them....then everything will be ok in the world :p
     
  11. rob denney
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    rob denney Senior Member

    Brief is good, but you could be even briefer if you read what was written and assumed that I was trying to be constructive, not "forum circling" (whatever that is).

    Correct. Then he reduced the mast size and learnt how to trim them to prevent the problem.

    I'm not. The rig was too big and the masts were not trimmed correctly so it sailed all over the place. They were cut down and trimmed correctly. It didn't.

    Excellent. Could you tell us about your experience with unstayed wing masts on cruising catamarans (and monos if it is relevant), please.

    Maybe, but Mike seems to have solved the problems he had, is happy with the boat and rig, which "goes like a rocket so I can't complain about performance" and does not sail around on it's mooring. The other 2 (looks like there may be a third) are happy enough with Mike's results to proceed with theirs.

    Groper, Gypsy,
    Thanks, saved me some typing. Cool Change is awesome. 36,000 miles is impressive. Apparently Derek has 3 more similar rigs under construction.

    rob
     
  12. groper
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    groper Senior Member

    Rob,

    This may be in my future, so I couldnt resist :D :D :D

    [​IMG]
     
  13. Jim Caldwell
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    Jim Caldwell Senior Member

    Add two trunks and your all set and think of the gas you would save!
     
  14. he b gb
    Joined: Feb 2014
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    he b gb Junior Member

    hi groper, looks like you're seriously considering converting your boat to a biplane sailing rig, go for it! In one of your earlier posts you say you would consider round tube masts, I think this is probably a good way to go as it would take a fair bit of complexity (and expense) out of building them and sailing with them. I built my masts for approx 7 grand (for both) and about 8 months work. Unlike you I built them before the boat as I knew I would not have the patience to do it after the main build and I was extremely keen to go down the biplane path. I have now been sailing her for over 2 years and am extremely happy for going that way. My masts are not stub mounted but go through a conduit with bearings at deck and floor, offset at 200mm inboard of c/line. looking at your computer rendering of your rigs I would think maybe downsizing and moving aft might be a good idea to avoid going down the path of the Schionnings as the rendering looks to me to be as powerful as michealo's was before the cutdown (I realize this is your first rendering!) my masts are 40' 3" above deck and look almost embarrassingly small (on a 45'+28' platform) but it still powers up just fine even in light airs, especially on a close reach (apparent wind) which I think goes some way to explaining michaelo's fantastic numbers shown on another post. Might have something to do with 80' of luff? I hope you continue with your plans.
     

  15. groper
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    groper Senior Member

    Gday he b gb :) i like your boat, looks like it goes well in the video... i was hoping you could show us some more videos or in some way tell us a bit more about it. Do you know what it weighs? Looks like you have 2 of Rob Denny`s ballestron rigs on it? - although the booms are a tad different. Same size rigs by the sounds of it tho... How did you go about making the masts, vac bagging? 7 grand aint bad for 2 carbon masts...

    Yeah im considering the idea very carefully... the plan is reinforce the deck and sole areas to take the mast and bearings- same way are you did. But ill launch the boat as a powercat initially, then i can take my time building the rig, boards, cases and rudders. Once im ready, i can slip the boat, cut a few holes and drop in the masts and centerboard cases. After that id perform a transom extension to install the rudders and move the outboards onto pods in the inner chamfer panels.

    Normally people think of motor sailers as poor sailors and poor powerboats as it generally does neither very well -well ive always felt this way anyway... But i think this configuration might just be the ticket for the best of both cruising worlds and allow good performance either way using 60hp outboards @ 120kg ea - 3x the power, but less weight than saildrives. As far as i can tell, noones done this entire configuration before?
     
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