Which sail rig for my Cat?

Discussion in 'Boat Design' started by groper, Jul 26, 2013.

  1. groper
    Joined: Jun 2011
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    groper Senior Member

    As some of you already know, im building a 35ft catamaran in foam/glass. It was originally going to be just a powercat, and it will still be launched as a powercat, and used like this for quite some time.

    However, i know myself quite well and me being me, no doubt ill want a sail rig on it at some point in the future - most likely when i have the time to venture further away from home on longer voyages.

    So i thought it would be prudent, to at least allow for a sail rig in the structural construction, whilst its still in construction, and thus avoid major changes at a later date. I want to be able to drop the rig on and go sailing, when the time arises.

    Therefore, i need to figure out what type and size of rig ill use, so i can make the structural allowances for it before i get to painting and fitout etc.

    The rig that seems most appropriate to me right now, is a moderate size rotating wingmast, and a large genoa - no mainsail. The rotating mast is simply to reduce drag. Im also considering a short footed mainsail, but id like to avoid that if i can get enough power without one. Id like to avoid another sheet, winches, halyard etc etc... Chris WSihtes mastfoil concept is appealing, but getting the whole mechanism working and sorting out the bugs with stability and everything else seems like too much hard work, but i like the idea.

    I also like the idea of the Mast aft concept, but making changes to the original design to accommodate it is prohibitive - i dont want back stays anywhere near the aft of the boat, and building a compression beam back there is much more effort than stepping the mast on the foreward beam bulkheads - which already has reinforcing in it to take mast compression load.

    So i have a 10.6m LWL, the Jib tack to mast step is 4m, and id like to keep the rear chainplates no further aft than 3m behind the mast step.

    Ive also considered a freestanding carbon wingmast - and have viewed plans to build one. Might be another possibility, although the cost is a bit more and it doesnt really make sense if its going to be a mainless rig.

    Any thoughts?
     
  2. groper
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    groper Senior Member

    Oh, i forgot to mention, the daggerboard and rudder issue...

    The plan was to make rudder cassettes, and just remove the rudder blade and stow them when used as a powercat.

    The daggerboards are giving me the most headaches. I dont really like them at all, and would rather not have them. But the sail plan of a headsail only means are very forward CE. This means ill have a very lee helm boat if i cant do something about it. Are there any solutions for daggerboards that dont involve a sliding board through a case in the hull?
     
  3. El_Guero

    El_Guero Previous Member

    Try a bi-plane rig. Bi-plane rigging (two masts) gives you two smaller main sails with about the same forward drive, but with smaller sails and masts, there is usually a lower cost. And if cost is not a big driver, you can go with wings, over traditional sails.

    The bi-plane rig itself lowers the stresses on the boat, and the costs - usually, not always.

    If you can get a decent wing set up, she will fly - almost literally.

    But, you would be very un-orthodox.

    :D
     
  4. groper
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    groper Senior Member

    I did consider the biplane setup, using 2 unstayed carbon masts, but the bury inside the hulls completely destroyed the interior arrangement, it doesn't work for me. Twin stayed masts I haven't considerd yet, seems messy with wires going everywhere... 2 masts, 2 booms seems like more windage etc I still want to keep the boat looking clean...
     
  5. El_Guero

    El_Guero Previous Member

    Why not put them at the inside edges of the the hulls? You have to have a cross member there anyway.

    I am not an NA, but my gasp of engineering is pretty decent. Not placing the single mast in between the hulls greatly reduces the actual forces the cross members have to compensate for - the reason some people prefer a mono-hull over a cat for sailing. But, if you build the cross member to handle a single mast, handling two smaller masts should be fairly straight forward.
     
  6. messabout
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    messabout Senior Member

    A power cat and a sailing cat are two different breeds of cat. There are serious design differences. Yes you could sail a power cat, if you must, but then it is likely to become a dog.

    Actually you can sail a power cat but it would be slower, less weatherly and not very pleasing. You can sail a washtub but not with great pleasure of efficiency.

    Now I will await the inevitable rebuttals from those who know more cats than I do.
     
  7. upchurchmr
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    upchurchmr Senior Member

    Messabout

    If you wanted a rebuttal - sorry - I agree with you.

    Groper,

    You could always go for leeboards Personally I consider them hideous but people have made them work.
    I suggest you go for a completely conventional sloop rig. You are going to have enough problems using a power cat hull and trying to get it to sail well. Don't ruin the sailpower portion also by trying something unconventional.

    Looking forward to the plan. How about pictures of drawings of the cat you are making?
     
  8. groper
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    groper Senior Member

    Yes im aware that the powercat hull will never be ideal for a sailboat. But never the less, i do have contingencies for that if i really wanted it to sail well - extend the transoms with a shallow run aft, which will not only increase the length, but move the center of buoyancy forward. This would only happen if i made the decision to convert it into a full blown sailing cat, which would also mean reducing the engine sizes and a few other things etc. I think perhaps as i grow older my desires will fall more into line with just stooging around sailing, seeing the world type of thing. You never know...?

    For now tho, im thinking more along the lines of a motor sailer... The only reason im considering the sail rig, is to save huge fuel bills and for peace and quiet - basically just for long distance voyages when the winds are favorable.

    The original design was very similar to a sailing cat, dimensionally and structurally that is. Just the hull bouyancy distribution was very aft for reduced trim under engine power.

    I drew this up to illustrate a standard bermudan rig on the original design. Considering a small boom of 2.5m length whereby i can put a mainsail sheet track directly above the aft cabin bulkhead, simple to reinforce this for it at this time. Again, i dont want the sailtrack or any other clutter on the backdeck ie on the rear beam where most sailing cats put them. Also i will make the mast stiff enough to not need spreaders, just a good clean rotating wingmast. The idea is to keep the sail plan small in area, but high efficiency to keep the weights and loads reasonable.

    The boat will weigh approx 1.6tonnes empty shell. A bit over 2 tonnes with fitout.
    Max displacement is 4 tonnes.
    LWL is 10.6m.
    Mast height = 10.6m.
    Genoa Area as illustrated = 30m2.
    Mainsail area as illustrated = 20m2
    Limiting Righting moment = 50kN.m

    [​IMG]

    [​IMG]

    [​IMG]
     
  9. michael pierzga
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    michael pierzga Senior Member

    A mast affects close in maneuverability , causes your boat to tack around at anchor, adds windage and reduces fuell effeciency when motoring upwind , disrupts the deck ergonomics and is eye watering expensive.

    Since this is a future wish, Id wait until systems like skysail are proven. http://www.renderboys.nl/images/renderboys_kitetender01.jpg

    Perhaps communicating with http://www.kitetender.nl/ will give you ideas about what is possible for your powercat.
     
  10. groper
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    groper Senior Member

    Yep, i would love to get a kite system working and do away with a mast entirely, not to mention all the clutter that goes with it, but i just dont think its reliable enough at this point - i have many years kitesurfing experience so i understand the problems with it, mainly to do with long distance cruising, and there are many... a simple day toy would be no problem to implement, as many kite boats have demonstrated.
     
  11. waikikin
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    waikikin Senior Member

    Maybe an A frame/sheerlegs style rig, stable & self erecting so easy to drop on/off with twin headstays(kinda like the old hitchhikers) & shrouds. What your building is like a "test bed" vessel, forget the daggers until you decide you decide need them..... then just glue & tab the cases in..... rudders.... fit the tubes or pintles to transoms & remove or add as wanted! As nted there would be compromses as a sailing vessel but I reckon you'd get along at a fair crack off the wind.
    Jeff.
     
  12. groper
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    groper Senior Member

    Looking at the CE vs CLR, ill definately need some form of daggerboard to prevent a severe lee helm balance. This is a result of the aft buoyancy distribution and relatively forward placed rig... i dont think i have much choice unless i only ever want to run downwind... Such a limitation makes the whole idea not worth doing i reckon...

    Sounds a bit ridiculous, but i thought of inward canting daggerfoils which would double as hydrofoils when under power and to compensate for the low buoyancy bows under sail... again, it just seems a little too fraught with problems and complications...
     
  13. rwatson
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    rwatson Senior Member

    Its so obvious - you need a Flettner Rotor :p

    Not only will you have a unique boat, but most importantly, create a new thread that will provide years of entertaining argument and lost tempers.

    Go on - you know you want to :D
     
  14. waikikin
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    waikikin Senior Member

    So long as he glues it on.................:p:D

    But seriously, the daggers would improve low speed handling under power also, more predictable with some extra lateral resistance & less likely for the bows to "pay off" in a cross breeze even with the twin engines.
    Jeff.
     

  15. waikikin
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    waikikin Senior Member

    You could fit them to a rotating barrel.......... like a steerable canard & adjust attack angles etc..... to vary the lift & leeway........ let us know how it goes;):cool:
    Jeff.
     
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