Modular Cruising Catamaran

Discussion in 'Multihulls' started by ImaginaryNumber, Jul 19, 2009.

  1. Fanie
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    Fanie Fanie

    Hello ImaginaryNumber,

    I apologise if this was suggested in between all the bickering loke old wiemen earlier in this thread, I just couldn't read through it all.

    I have the same problem you have, getting the boat to water, although in my case it's much worse, I live 450km from the nearest coast :( and apart from that it is too darn expensive to leave a boat in a marina.

    I have decided to make my boat foldable, to some extent like cat2fold did.
    Since you want a full bridgedeck I am sure it can be placed once the hulls are on the water.

    The hulls can be trailed. If you want wider hulls the trafic guys could assist with a once off trip to the water, but it would still fit on a road.

    The cabin can be made to fit, taken off and again fitted back in it's place. The cabin can be transported also on a trailer on it's rear and sideways, It should fit on a flat bed.

    Since you are going to transport it only once, you could also use solid beams and not hinged ones. With a bit of carefull design when assembled the parts could fit together while supporting each other to maintain position, which would make final assembling / glassing possible even on the water.

    Nothing is impossible and yes, it is always more difficult than anticipated at first :D
     
  2. ThomD
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    ThomD Senior Member

    "In brief, after several years, he replaced the rig with a stayed rig. He found that he was unable to adequately control sail shape in heavy air."

    It isn't as though he replaced the rig with a nice simple pole and triangular sail like his freestanding rig, then declared victory because it was so much more controlable, he went to a pretty nearly opposite level of tech that was more comtrolable, and a lot of other things to boot. You have well related his remarlks, just some context for the heck of it.

    "Bear in mind that unstayed masts for a cat must have much heavier scantlings than the equivalent sized rig for a monohull, because of the enormous initial stability of the cat."

    Keeping also in mind that if it is split between two hulls that would reduce the requirements somewhat, if for two spars.
     
  3. rob denney
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    rob denney Senior Member

    G'day,

    Too much nonsense on this thread to read it all, so apologies if this has been said.

    The unstayed mast option for a cruising cat is by far the most sensible option. Cheaper, lighter overall and with a lower centre of gravity it is also much safer to sail and to operate. The scantlings are actually far lighter than for a stayed rig as they are more localised. They are also in directions (tension and compression) suitable for easy application rather than in inefficient bending.

    The 15m/50' boat in the video at http://www.youtube.com/watch?v=8chR6DAFjGA has an unstayed mast which weighs the same as the alloy mast and rigging of a cat with the same righting moment and sail area. The boat is also modular. The beams, hulls and bridgedeck all fit together without bolts or fastenings. Put the windward hull on it's side and it is 2.7m/9' high.

    regards,

    Rob
     
  4. masalai
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    masalai masalai

    ONLY for a proa...
     
  5. rob denney
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    rob denney Senior Member

    Why ONLY in a proa? Why won't it work in a cat, either in one hull (the easiest option) or in the middle where the conventional mast is located.

    rob.
     
  6. masalai
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    masalai masalai

    That debate has occurred on another thread and I am not qualified to further pursue the matter.... It was a consideration in research for my build...
     
  7. rob denney
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    rob denney Senior Member

    Could you tell us where this thread is, please, as I don't recall any threads where the suitability of an unstayed rig for a proa vs a cat was discussed. As there is no reason for them not to work on a cat as well as they do on a proa, I suspect it would be a very short thread.

    'Search' bought up a few threads about unstayed rigs, but apart from someone having trouble sailing backwards out of an anchorage without a jib, and some wild, unproven gossip about a carbon mast exploding in a shower of red hot razor sharps shards in a lightning strike, there don't seem to be any reasons why an unstayed rig would not suit a cruising cat.

    Again, this is not a surprise as there are no reasons which come close to outweighing the benefits.

    Perhaps you could also tell us why you decided against it, and whether "it" was an unstayed ballestron, biplane or una rig.

    Ta
     
  8. masalai
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    masalai masalai

    Somewhere? 'unstayed masts' were debated quite a while ago but I am not sure in the thread title... There was no serious debate, just a few posts in favour and against mainly experiential comment... which left me with the view that there would be no advantage in looking at unstayed, as too difficult to implement - I think it related to a wishbone type setup????
     
  9. rob denney
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    rob denney Senior Member

    I have no idea what it was related to as a wishbone works extremely well on the unstayed Wylie cat rigs. Bob Oram (your designer, I think?) is a big fan of unstayed rigs and there is far less work involved in designing and building a boat for an unstayed rig than for a stayed one. There is also far less ongoing work and cost as there is no maintenance and no need to inspect the rigging daily and replace it every few years. All of which are good reasons to use one, but pretty insignificant compared to the ease of use.

    I strongly recommend some "serious debate" and perhaps a revision of your view.

    I am now living on the Gold Coast. I believe you are in Brisbane? If so and you ever get down this way, drop in and take my 25' proa and it's unstayed rig for a sail. May give you an appreciation of what you are missing out on.

    regards,

    rob
     
  10. Fanie
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    Fanie Fanie

    I am in favour of unstayed masts as well. If I one day get there, my cat would have two unstayed masts if I still go sail boat by then. The stays clutter a boat consderably (imo) and will eliminate the clanking noise in the wind as well especially at anchor.

    The little experience I had with stand alone masts was good up to now, they just have to be made stiff. Yeah yeah I know what to add :D
     
  11. rayaldridge
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    rayaldridge Senior Member

    One issue is cost. For the smaller boats I'm interested in, a stayed mast can be built from timber fairly cheaply, and not everyone can afford a carbon spar. Another issue that concerned me when I was considering an unstayed mast for my little open bridgedeck cat was how to support it out on the beam. I considered struts, which worked well on the model. But eventually I concluded that in order to have a sufficiently strong timber spar, it would mean a lot more weight aloft than the stayed rig I finally decided on.
     
  12. rob denney
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    rob denney Senior Member

    G'day,

    How deep is your beam, and how long is your mast? We put an unstayed mast on a heavy 37' open bridgedeck cat. 13m mast had 750mm between the bearings. Works well. http://www.harryproa.com/MASTS/Taywun/Taywun.htm

    Do you have the costs for the wooden mast and all the gear (shrouds, turnbuckles, chainplates, additional beefing up, etc) required to hold it up? Be interesting to compare it to the cost of the unstayed carbon tube on my Elementarry or a similar boat. What is the righting moment, sail area and mast height for your boat?

    What weight did you get for the unstayed wooden mast? Was it hollow?

    regards,

    rob
     
  13. rayaldridge
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    rayaldridge Senior Member

    Rob, I fear we're working at completely different edges of the technical spectrum.

    [​IMG]


    This picture will probably tell you everything you need to know. Total cost was under $200 for the whole rig. The mast, for example, cost less than $15, as it was laminated from a couple of carefully-selected construction grade 2X4s.

    This design was an attempt to come up with a multihull version of the many small simple open monohull cruisers-- something that a relatively poor person could afford to build.-- a kind of entry-level catamaran for those who might like to experiment with the many virtues of multis. (Obviously, performance was not a priority.) There aren't any similar cats available, so far as I know, which was why I drew it instead of buying plans from a real designer.
     
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  14. rob denney
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    rob denney Senior Member

    G'day,

    Perhaps at different ends of the tech spec, but we are both trying to build boats as cheaply as possible. Yours to cruise/fish/have fun in, mine to go fast/be easy to sail.

    The set up you have would be hard to emulate in an unstayed rig, nearest would be a second hand laser/OK dinghy/Finn/windsurfer rig mounted in each hull.

    $200 is a cheap rig. Comparatively, the materials for the mast and boom on my Elementarry (lighter boat, similar sail area) cost $Aus600/$US480. A large percentage difference, but not so much more money to pay if you want all the advantages of an unstayed rig. Having said which, if I wanted a boat for me and my kid to fish, cruise, learn boats and mess about in, the Slider rig would be much more suitable than an unstayed rig.

    Look forward to seeing the next one in the series.

    regards,

    Rob
     

  15. rayaldridge
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    rayaldridge Senior Member

    Rob, I appreciate the kind words. As I'm sure you know, being a contrarian isn't always fun, but it has its rewards.

    The cartop cat I'm building now is going to be a lot cheaper than Slider was-- almost no hardware, except for blocks, rudder gudgeons and pintles, and a few cleats. Rig's another stayed sprit, held up by cheap Dyneema cord. It's aimed at the same functional niche as a PD racer, though it'll cost a bit more than that. You might say I'm devolving.

    But after that, I'd like to draw a fast trailerable cruising cat, just to avoid falling into a rut.
     
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