6.5 to 7.5 metre performance/cruise multihulls

Discussion in 'Multihulls' started by Gary Baigent, Feb 27, 2015.

  1. redreuben
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    redreuben redreuben

  2. Doug Lord
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    Doug Lord Flight Ready

    Welcome to the forum, Sparta!
     
  3. Gary Baigent
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    Gary Baigent Senior Member

    Changed main hull, looked too clumsy before, (in forced attempt to be average with interior), so lowered freeboard, (still adequate room belowdecks) for a small boat, that is, changed transom; you have to be able to easily climb aboard, imo, after swimming/cleaning. Otherwise concept remains the same.
    Hello Sparta, will look out for you since you sail in the same area as us.
     

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  4. Gary Baigent
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    Gary Baigent Senior Member

    patzefran

    Join Date: Feb 2011
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    Location: france
    Excellent program, Gary ! I wish I coulld built that light, but I can't achieve ! Wil you use stressed plywood again ? keep us informed of your building progress, I shall do for my Strike 20., Some photos of my last build :
    https://www.dropbox.com/sh/eyvyt831b...HiHDOcoDa?dl=0
    Too high weight for my taste, but very competitive compared to beach cats and much more geriatric to sail !
    As you can see from the rig I am also anactive A class cat sailor, unfortunately near retirement as I am getting close to 7 first digit ! full foiling without regulation is a younger matter !
    Cheers

    Patrick

    If you bend ply you can get away with murder - using a very narrow thickness gauge ... that is, if you coat it after tensioning with epoxy, glass and carbon.
    6mm strip planked cedar or paulownia is also excellent because once you fair it you're down to 4-4.5 mm, then epoxy. But bending thin ply is much faster in building time.
    I'm drawing up full size the double main hull ring frames at the moment.
    And also figuring out the main beam swivelling design and locking pins. The small cabin top will have to swing with it - and then there is the water sealing problems below it to design.
     
  5. Gary Baigent
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    Gary Baigent Senior Member

    Rough of the beam/cabin/cockpit setup, which will pivot fore and aft with the beam as one unit, sort of like a tank gun turrnet. When opened for sailing, the assemby will be locked with pins and bolts. To be able to do this the cockpit will have a flat floor (crew will sit on low seats either side).
    With beam fore and aft for trailering, a rain cover will be required over the opening into the hull.
    To get the platform ready to sail (not counting mast lifting) will only be a few minutes work.
    Will be way lighter (and way less complicated) than a Farrier setup. And a lot quicker than sliding beam designs and so on.
    Yes, the locking system will have to be carefully thought out - but I don't see any problems there.
    What say the experts?
     

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  6. oldsailor7
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    oldsailor7 Senior Member

    Gary, you mentioned the Holtom foiler there. Many moons ago he was working on a 50 ft version and was going to patent his idea.
    Did anything become of that?
     
  7. Gary Baigent
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    Gary Baigent Senior Member

    These 2 images from Malcolm McKintyre's Holtom Foiler patent. The boat was 52 feet length - but I've never heard of the craft being built. The third image is his original prototype sailing version of the proposed big boat.
     

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  8. patzefran
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    patzefran patzefran

    Hi Gary
    Your new mainhull looks nice ! Did you design for flying the mainhull ?
    It seems difficult to achieve this flared shape with stressed ply, even with 3 mm okoume.Will you build in 6 mm red cedar or polownia strip planking ?
    Your thick foils looks to have somewhat low aspect ratio. Why do you prefer this solution against a little outrigger + higher aspect ratio foil ?
    Have you a quick method to compute the developped pannels or do you use a mock up for stressed ply hulls (like Gougeons) ?
    Last question, have you any GPS velocity data for Syd performance, upwind and downwind ?
    Cheers

    Patrick

    PS. I sold my A class cat to day !
     
  9. Gary Baigent
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    Gary Baigent Senior Member

    Patrick, I'm in a bit of quandry with the 6.5.
    Initially I wanted a simple boat. That could be quickly demounted/mounted for transport - so the floats/foils could not be very long - so as to fit crosswise on trailer for road width legalities when the beam is swung 90 degrees. So a combination of float/foil was the solution, I thought. But that is not easy. If I go to 40-45 degree angled "floils" then yes, the aspect ratio is low and not the best for speed and efficiency - but it means less complication when the beam is swung. Alternatively I could go to say, 20 degree angled conventional looking short floats (similar to Sid's) and then have curved foils going through them. But that is getting complicated. So I need to find out how good are the semi-triangular "floils" in real life. I've sailed (long time ago) on Noel Fuller's little Sabrina with this floil setup - and the boat performed very well in high winds but its windward performance was weak. So I need to somehow design a decent semi-triangular floil that does a good lifting job - and then add a main hull daggerboard for windward sailing. The 6.5 will be mostly foil stabilized although I believe, in fresher winds, the main hull will be levered out. The rudder will be inverted T to allow level flying.
    You can get the convex and concave hull cross section shapes easily enough with thin ply - just need heavy props and weights pressuring the concave areas to the frames. But strip planked Paulownia would be less hassle, however a longer build time. Haven't decided yet what I'll use.
    The computer program is ... my trial and error in-skull history.
    I have GPS - but am always far too busy helming/sheeting to use it when sailing fast in Sid. All I can say is that it is very fast and points very high. Nothing so far I've sailed against has the slightest chance of competing. But then I've never lined up with the hot 32/33 AC foiling cats here on the Waitemata. My thoughts are that Sid would beat them in light weather, (Sid's Bruce Number is very high, around 2.6 with all sail) but probably lose out in a breeze. But then Sid cost 7 grand (without sails) and not a quarter plus million. Better make that half a million, anyone know?
    photograph: Noel Fuller's Sabrina
     

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  10. patzefran
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    patzefran patzefran

    Thanks for your reply, Gary. I understand your trade off about "floiils", congratulation for the new word !
    You confirm I need to be an artist to design stressed ply ! this is not the case.
    As I am a former racer, I always use GPS for training Solo. I use cheap Garmin Foretrex 301 braced on my boom (one each side) to check instant velocity an course. You can also just switch it and forget, then use your recorded data on your laptop with a free software such as gps action replay (gpsar) to check your performance. Upwind velocity of my classic A cat was up to 11.5 kt upwind and downwind near 19 kt with average velocities around 17. My Tremolino was 8/9 upwind and 16 maximum downwind with around 14 average (some people claim higher velocities as 20 + kt but I am very doubtful).
    With my little Strike 15, at this time (less than 10 records) it is 10.5 upwind and 13.5 downwind. From my experience (I owned a 32 ft racing tri and a Formula 40 catamaran) I think most people are claiming exagerated performance !
    Cheers
    Patrick
     
  11. Gary Baigent
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    Gary Baigent Senior Member

    No, no, never said you have to be an artist to bend ply. It's just the sort of way I approach it. Compared to boatbuilding experts, (I've spent time at Cookson Boats) I am a disgrace ... but that's the only way I can achieve a so-so result.
    Thanks for the GPS performance verifying suggestions; will do so.
    An interesting and true result occurred when I ran with no sail, just the wing mast on Supplejack (32 foot catamaran), averaged 17 knots for 25 minutes to reach shelter. Wind was very high and gusting.
     
  12. patzefran
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    patzefran patzefran

    Do you use female mold frames, like for strip planking, to control shape ?
    I achieved also very high speed (don't know which !) with my Twiggy Trimaran under bare poles in the eighties. It was a 70 kt thunderstorm, plenty of sunk monohulls and drowned people all around ! we just sailed near flat with the tri, same thing for a Formula 40 in the same place. Highest wind I endured afloat in my life (at least on a sailboat). I got plenty of wind (no waves) near cape horn, but on a big passenger cruising boat (250 m !) with 2 electrical motor pods and 2 airplane reactors / turbines to provide current.
     
  13. Gary Baigent
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    Gary Baigent Senior Member

    I strip planked with paulownia the 11.5 metre airfoil beam of Groucho and yes, did that in female frames.
    So, this is turning into tiger country sailing. In New Zealand we have the famous/infamous Cook Strait. That gets everyone going a bit too.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    Gary, the spray coming off the lee floil in your last picture is astounding. Reminds me of the spray off a standard kiteboard. Seems like huge drag?
     

  15. Gary Baigent
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    Gary Baigent Senior Member

    I'm wondering if it really is drag because that is spray being deflected upwards and outwards by the lee float/foil at 65-70 degree angle, (because of heeling) - and must be creating considerable lift.
    Would disturbed aerial spray really produce drag? A little, yes, but surely the lift produced would easily compensate.
    Here's another Sabrina shot with the doughty Fuller helming. The little boat was fast reaching but slid sideways beating. However, although there are huge clouds of spray, look at main hull wake; that boat is moving. Also I can see in this second Sabrina image, that Noel has increased the "floil" size; perhaps a third more volume of the foil in the first photograph.
    Last shot is of a couple of float/foils I built for a friend who has a sailing kayak trimaran type.
     

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