open bridgedeck catamaran design

Discussion in 'Multihulls' started by BobH, Apr 17, 2015.

  1. brian eiland
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    brian eiland Senior Member

    I agree with your use of the wishbone boom and its taming of that sail, and the simplified rigging. ...one of the reasons I chose it for the mizzen sail on my aft-mast rig.

    But I do have a couple of questions about your posting.
    1) What does the speaderless rig have to do with the use of the staysail?
    2) Does your spreaderless rig really have about the same amount of wire as a double diamond rig?
     
  2. brian eiland
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    brian eiland Senior Member

    Have you got a link to that youtube video,...for those of use that are a bit challenged with some of this computer tech...:D
     
  3. BobH
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    BobH Junior Member

    The idea for this sail control originally was not so much to pull the top to windward. It was to be a substitute for having an expensive carbon free-standing mast of just the right stiffness that would bend and dump air in gusts. Getting the stiffness just right is a big problem in itself it seems, let alone the cost of a single carbon mast. I was thinking of how I could use a cheap aluminum extrusion (flagpole/light pole) of sufficient strength (it would be excessively stiff also), still get that action of dumping excessive wind, and have a system that could be tuned after installation.

    As you say..."a world of hurt."
     
  4. brian eiland
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    brian eiland Senior Member

    Just curious, why you might not consider bringing all of the shrouds (lowers and intermediates) to the same anchor point as the cap shrouds? (I assume the cap shrouds you are speaking of go to the masthead?)

    And I assume that the head of your mainsail in the first reefed position is very near the point of attachment of your intermediate shrouds?
     
    Last edited: May 1, 2015
  5. Boatguy30
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    Boatguy30 Senior Member

    I'd be interested to hear how the ketch rig works on this size cat. I am racing the Mug race on a friends 23' Precision since my 34' sloop rigged cat won't clear the 44' bridges. We took it out yesterday for a test sail and when hit by maybe a 12 knot puff; put the rail under and rounded up even after easing the main. Hard to imagine how people still consider those things suitable sailboats!
     
  6. catsketcher
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    catsketcher Senior Member

    Gday Brian and Bob

    I am not very proud of the Youtube vid - the boat got a refit and major repaint after the video but it does show the wishbone in use. I also do use a prodder now and never have the reacher on the bow like in the vid.

    https://www.youtube.com/watch?v=XEiIQn6Ikls

    As to the questions

    - staysail. The typical double diamond rig used on a boat this size has no inner forestay (leading to the intermediate hounds). This rig design needs an inner forestay to stop the mast inverting. The inner forestay leads about 50% of the distance from the mast to the forestay allowing the genoa to pass through pretty easily - much easier than a proper cutter like a Searunner when tacking. We don't use the rig like a cutter. When the wind blows up we furl the genoa and raise the staysail(storm jib). This brings the CE aft on the headsail which is exactly what you want when you reef the main and its CE comes forward. The boat stays balanced.
    - the designer - Robin Chamberlin - calculated the amount of wire as being the same. A double diamond rig will have 5 or 6 wires keeping the mast in column as well as the caps. We have 6 and two of these are very short - no spreaders too which may help.
    - Going to the main chainplates with intermediates and lowers - don't do it. I have been on cats with this and you get a faceful of wire every time you walk forward. It is really annoying and maybe dangerous on a dark night. The staying angle with the chainplates at the cabin side is still very wide.
    - Reefing - I have a reef that is about 1.2 metres which would bring the head to the hounds - but I never use it and go straight to the next one. Remember the inner forestay means the rig never even thinks about inverting - it is pretty bulletproof and gives great security. On my old Twiggy rig the mast would invert as soon as I reefed making the main very full which was not what I wanted. We fly the storm jib and trundle to windward as fast as we can handle - about 8 knots max in big winds, You don't want to go any faster on a 4000kg cruising boat or your crew will get off next stop and you may break expensive things.

    Bob - I don't get how staying the sail will help with the freestanding mast. I think any alloy tube that bent too much would come close to failure. Now if you just get those lines and put them onto the mast instead you may have something.

    cheers

    Phil
     
  7. brian eiland
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    brian eiland Senior Member

    Construction Methods

    Have you looked into other construction methods? The epoxy/cedar strip method is quite labor and time consuming as I understand it. Hear are a couple of alternatives you might have a look at:
    1) ....for instance like this Dudley Dix build
    Building the DH550 radius chine plywood catamaran

    2) or Derek Kelsall's KSS construction method,....stands for Kelsall Swiftsure Sandwich ,...as I suggested here for another project I was very interested in.
    http://www.trawlerforum.com/forums/showpost.php?p=175507&postcount=109

    http://www.trawlerforum.com/forums/showpost.php?p=270901&postcount=300

    Make a visit to his site for even more info.


    3) building a Schionng kit cat
    http://diy-yachts.com/forum/viewtopic.php?f=23&t=239
     
  8. BobH
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    BobH Junior Member

    cedar strip

    Brian,
    I like the freedom of form the strip method allows. Besides, there is no better smell in the workshop than fresh cut cedar;). I live in the PNW of the US so I have local access to really good quality material at a reasonable cost. The form of the bow is from that of an Adirondack Guide boat....they're built with strips on cut frames.

    I've kept the mizzen, but worked a wishbone onto the main. Like you said, if I have the one, why not both? As for the ketch form...remember the design brief is for a motorsailer...if I bought a boat right now, it would be a used Fisher 30 to refit...or maybe a Presto 30 for coastal sailing, but I want to have the virtues of a cat along with good motoring capability.
     

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    Last edited: May 16, 2015
  9. brian eiland
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    brian eiland Senior Member

  10. Gary Baigent
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    Gary Baigent Senior Member

    Good ideas aboard this cat but holy defecation, it is very ugly.
    There is a saying that beauty is what beauty does, or something, meaning ugliness doesn't matter as long as it is functional - but I disagree, aesthetics is very important and real art is the combination of the two.
     
  11. catsketcher
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    catsketcher Senior Member

    Gday Bob

    I have realistic ideas about whether a plan will come to fruition but I like to write anyway so here goes about bows.

    The reverse bow really gets me scatching my head when I see it on almost all cruising cats. Bow shape is not something you put onto a hull, it is dictated by hull flare. You can only couple your flared hull shape with a reverse bow by getting ugly with the shapes up front. There are a couple of modern cruising cats by very well known designers that have just squashed the bows around as though they softened the bow in a oven and ran the top under a truck. So I would say "Draw the hull and let the bow come along as they choose"

    That is why Gary's boats are true to me. He can't make the bows do what he wants as he uses ply and ply will not let you pull it around.

    I still don't get the mizzen thing. Even if you want to motorsail I can't see why you need to have a mizzen on a sub 45ft cat. I sail in up to 35 knots with the staysail and a reefed main. The ketch rig will be heavier, harder to handle and more expensive but if you like it, you can build it however you want.

    My prediction is - within 6 months of cruising that cockpit will be protected by a windscreen and dodger. I would design it in now as it it will be better to have it in the initial design.

    cheers

    Phil
     
  12. brian eiland
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    brian eiland Senior Member

    Rig again

    Sorry to be such a nuisance Bob, but a new posting about some catamaran molds for sale came to my attention
    http://www.boatdesign.net/forums/boat-molds/smg-50-catamaran-moulds-sale-53235.html#post736712

    The reason I mention it here is to have you take a look at the rig they utilized on this vessel,...very simple,...and apparently from many responders very efficient. They built 6 vessels, and from the sounds of it all owners were quite pleased with the performance. granted you may not be pleased with the 'modern look' of the vessel itself, but the use of a simple a-frame rig (with NO booms) might just have justification on your smaller vessel.

    There are a number of other discussions of A-frame, bi-pod mast rigs in this discussion thread I introduced some time ago:
    http://www.boatdesign.net/forums/boat-design/wishbone-sailing-rig-1999.html
    Have a look at one in particular called Catbird Suite
    http://www.boatdesign.net/forums/boat-design/wishbone-sailing-rig-1999-18.html#post630936
     
  13. BobH
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    BobH Junior Member

  14. waikikin
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    waikikin Senior Member

    Looks nice,

    Still a lot like camping & very exposed to elements, other 38' cats can be very comfy & get you out of wind & sun.
    Jeff.
     

  15. saltdragon
    Joined: Oct 2014
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    saltdragon Junior Member

    I like the rendering of the new deck house, now listen to the others and just get rid of the mizzen and you are almost there:) I sailed on a couple of ketches and yawls on short handed deliveries and found the mizzen a pain in the stern! They always needed attention just when you had enough to do, apart from cluttering up the place, and didn't add anything to the sailing. As Newick would say KISS.
    I'm also not sure about the reverse bow, I think I vaguely understand the theory, however the practically worries me. A walk around any marina will show lots of pulpits and bows with scratches and dings in them. Having the first part of the bow which is under water being the first part to touch another boat or harbour wall, cannot be anything other than trouble. Million pound multihulls and dinghies OK but motorsailing cruisers, why ask for trouble? Just the musings of an old fella:confused: It's your dream.
     
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