two trailer sailers to make a cat

Discussion in 'Multihulls' started by markcampbell, Apr 17, 2006.

  1. markcampbell
    Joined: Apr 2006
    Posts: 8
    Likes: 0, Points: 0, Legacy Rep: 9
    Location: new zealand

    markcampbell markc

    I have the opportunity of purchasing two 26 ft noeleda trailer sailors and am thinking of converting these hulls to a single catamaran - Im thinking of positioning the pontoons exterior at 65-70% the length of the hulls
    IE 20 ft width

    the pontoon beam waterline width is 5 foot 6 inches leaving a waterline width between pontoons of 9 feet

    Has anyone tried this
    Does anyone know of anyone who has tried this
    Any ideas would be a great help

    How does the width of the pontoons affect steering capabilities and

    What is the wave disturbance between pontoons called IE the radiating bow wave leaving the bow and meeting the other bow wave called and where can we research this and what are the formulas

    what are the formulas for bow wave disturbance other other hull ie port pontoon bow wave on inside of starboard rear pontoon

    we are thinking of attaching the hulls with aluminum 75ml * 75ml box section in 3 places any comments


    we are thinking of leaving the mast and boom in place and have two masts and booms any comments we know annie hill recently built a junk rigged cat
    with masts on each pontoon




    thanks
     
  2. frosh
    Joined: Jan 2005
    Posts: 621
    Likes: 14, Points: 0, Legacy Rep: 44
    Location: AUSTRALIA

    frosh Senior Member

    Frankenstein's catamaran

    Hi Mark, I have only one bit of advice DON'T DO IT. It could be the biggest mistake of your life. The fact that no yacht designer has ever configured a catamaran with hulls of this length/beam ratio should send an ominous message. Also your overall weight will be ridiculously high! This is only for starters. Best to stick to conventional ideas unless you are willing to create a disaster that will eventually have to be thrown away! :(
     
  3. Figgy
    Joined: Feb 2006
    Posts: 315
    Likes: 12, Points: 0, Legacy Rep: 88
    Location: Boot Key

    Figgy Senior Member

    "Frankenstein's Catamaran"!?! HAHA! Seriously tho', Frosh is right. Really wouldnt be a good move unless you have WAY too much money. Try to something else with the hulls.
     
  4. SeaSpark
    Joined: Mar 2006
    Posts: 593
    Likes: 17, Points: 0, Legacy Rep: 96
    Location: Holland

    SeaSpark -

  5. markcampbell
    Joined: Apr 2006
    Posts: 8
    Likes: 0, Points: 0, Legacy Rep: 9
    Location: new zealand

    markcampbell markc

    1 opinions are cheap
    2 we need formulas
    3 what is the width to length ratio and why
    4 where can we research this
    5 Rounded and wider pontoons should make the turning arcs easier
    6 the distance between the two internal hulls and possible drag from bow waves is the hydro dynamic question that we are asking
     
  6. Figgy
    Joined: Feb 2006
    Posts: 315
    Likes: 12, Points: 0, Legacy Rep: 88
    Location: Boot Key

    Figgy Senior Member

    1. So are ideas
    2. Be more specific. Formulas for what?
    3. Usually the beam is half of the l.o.a. You can make it as wide as you want though. If your going to break the mold, shatter it!
    4. There is a couple of programs. Search this thread. http://boatdesign.net/forums/forumdisplay.php?f=4
    5. Aero-hydrodynamics of sailing by C.A.Marchaj. Part 1 chapter G
    6. See #4
     
  7. frosh
    Joined: Jan 2005
    Posts: 621
    Likes: 14, Points: 0, Legacy Rep: 44
    Location: AUSTRALIA

    frosh Senior Member

    You have got to be joking, yes, unfortunately no!

    Mark, To say to people more experienced than you, and in all seriousness that their opinion is cheap is a bloody insult. Why bother asking for advice if you already know all the answers. If that is your attitude then state what you intend to do, and also state that you dont want any responses to your posting!:mad:
     
  8. CT 249
    Joined: Dec 2004
    Posts: 1,701
    Likes: 78, Points: 48, Legacy Rep: 467
    Location: Sydney Australia

    CT 249 Senior Member

    Probably not a good idea to post "Any ideas would be a great help" and then say you don't want opinions.

    I have sailed two small cats with wide-beam hulls. Both were very slow and handled poorly.

    Because of the popularity of catamaran ferries, I think there have been many studies on wave interaction. I've never really looked at them (it's not my interest) but I seem to recall that there is still no universal method for calculation. I may be wrong, but a trip to the library of any university with a NA course should tell you.



    Has anyone tried this
    Does anyone know of anyone who has tried this
     
  9. marshmat
    Joined: Apr 2005
    Posts: 4,127
    Likes: 146, Points: 0, Legacy Rep: 2043
    Location: Ontario

    marshmat Senior Member

    I agree with frosh and figgy. These hulls (length/beam 4.7) are too stubby and fat for a catamaran. Cats generally don't work with length/beam under about 8; 10-14 is not uncommon.
    Three 75mm square aluminum tubes cannot possibly hold up to the loads this thing would be under while out in waves. Cats of this size and weight generally have an elaborate 3-dimensional truss-like structure in the centre to take these loads.
    I would strongly suggest you keep these monohulls as monohulls. Joining them into a cat would give you an overweight, tricky to handle boat that would have a hard time staying intact in any sort of seas.
    There has been a great deal of work done on wave interaction within the hulls of a cat. Mostly it involves a lot of tank testing as well as CFD and the results are unique to a particular hull family.
     
  10. markcampbell
    Joined: Apr 2006
    Posts: 8
    Likes: 0, Points: 0, Legacy Rep: 9
    Location: new zealand

    markcampbell markc

    1 the tendency for cruising cat hulls is going wider to accommodate double beds lower in the pontoons.
    2 we anticipate this cat with a bridge deck and fiberglass bracing as a small coastal cruising cat. Thanks for the information about the alloy beams not being strong enough of course they wont be.
    3 the pontoons with a wider and shallower hulls will have a shallower draft, compared with an exact same weighted vessel.
    4 speed is not critical and a loss of speed around 20% on a similar weighted cat would be acceptable
     
  11. hansp77
    Joined: Mar 2006
    Posts: 690
    Likes: 34, Points: 0, Legacy Rep: 200
    Location: Melbourne Australia

    hansp77

    mark man,
    what do you want to hear?
    do you want to hear that it's a great idea?

    Well, to someone like me, who really doesn't know jack about catamarans, about wave interaction within the hulls, about stress loading, or about boat design in general, let me tell you this-

    mark, that's a great idea!
    well maybe not great, nor actually original, but sort of interesting at least,

    that is of course, untill I hear from those that actually do know about catamarans and advanced boat design, telling you that this is actually A VERY BAD IDEA.

    Now of course every one is free to do whatever they want, including suicide, and or wanton destruction of two perfectly good sailing boats.

    If you have actually read through the link that SeaSpark provided
    http://www.boatdesign.net/forums/sho...ight=J24 Hobie
    then you will have witnessed another individual (Delane) who is stubbornly set upon following through with one of these plans, against all the provided expert advice. Now who knows, improvisation and going against the flow is not fundamentally an incorrect practice, and actually lies at the base of some of humanities most revolutionary breakthroughs. As apposed to you however, Delane has managed (its not too hard) to humblely acknowledge, if not accept, the effort, advice and dissuasions that the experts have offered him (considering he and you have asked for such). He has managed to not directly offend or insult anyone. This is something that if you plan to continue battling out this idea of yours upon this forum, you might want to take notice of.

    p.s. Cocky point form replies, and stating that "of course" the alloy beams that you had asked for advice upon won't be strong enough, don't exactly warm ones opinion of you.

    p.s.s. In my short time on this forum (be that only slightly longer than you), I have found that the people who offer me advice upon my novice questions and queeries generally know what the hell they are talking about, and do so in a polite and generous manner. If you do choose to contradict or criticise as "cheap" their opinions, then you had better know what the hell you are talking about.

    Good luck with your two boats,
    and better luck if they ever do turn into one.
    You may just need it.
     
    1 person likes this.
  12. Figgy
    Joined: Feb 2006
    Posts: 315
    Likes: 12, Points: 0, Legacy Rep: 88
    Location: Boot Key

    Figgy Senior Member

    Man, this guy has a stiff one for a cat!
    Well said Hansp77, but I'm giong to humor him.
    A shallower draft than what? It might sit higher on the water lines, but thats it. And after you make your bridge deck, with a HUGE rig to push her through the water, I'm not so sure. Have you found out how much the hull displaces?

    Now I havent crunched numbers, nor am I about to for this project, but thats a good start. Atleast you won't be shocked on your first outing.
    Check it out Mark, you're going to sink a huge amount of cash into something like this. To retro-fit two hulls like this is going to take some engineering. You can't just slap on a few cross beams, fiberglass them up and go.
    Just buy a new cat, don't do this.
     
  13. marshmat
    Joined: Apr 2005
    Posts: 4,127
    Likes: 146, Points: 0, Legacy Rep: 2043
    Location: Ontario

    marshmat Senior Member

    I second that.
     
  14. frosh
    Joined: Jan 2005
    Posts: 621
    Likes: 14, Points: 0, Legacy Rep: 44
    Location: AUSTRALIA

    frosh Senior Member

    Mark, ask yourself honestly, why do want to create a cat in the unusual way that you proposed at the beginning.
    These are some of the possibilities, trying to get inside your head (figuratively speaking only)
    (1) You see it as cheaper option than buying a good condition existing cat.
    (2) You want to try something out that will be uniquely yours and will work pretty well.
    (3) You want to be some sort of design pioneer establishing a new design trend, and you will get the kudos for the brilliant idea.
    (4) You see it as way to get a reasonable performing cat with heaps more living space than any existing cat of the same overall length.
    (5) I can't imagine any other reason you might have!

    MY ANSWERS
    (1) Maybe if you are getting the trailer sailers almost for free.
    (2) It will be uniquely yours, but almost positively will not work well.
    (3) Wishfull thinking! More likely embarrasment!
    (4) It will give you heaps more living space at the dock, I wouldnt want to take it anywhere.
    (5) The idea of posting on this forum is to get feedback and learn from it, even so called experts who have designed boats all their life are still learning and occasionally make mistakes. Mistakes are OK per se, but really dumb when you have been well warned in advance.

    I agree with the others, if you want a cat, buy one, there are a huge number on the market for heaps less money than replacement cost.
     

  15. markcampbell
    Joined: Apr 2006
    Posts: 8
    Likes: 0, Points: 0, Legacy Rep: 9
    Location: new zealand

    markcampbell markc

    1 New purchase price for cat at 26ft @ $200 000
    2 2 glass hulls only 10% wider on water line with all partitioning, keels, steering, rigging, etc all to within 10% average fit out of new cats means a saving of hundreds of hours skilled labour and materials
    3 retrofit is limited to opening cutting open both insides of pontoons @ 500ml above waterline, using the internal fibreglass cut outs and windows as external forms for marrying up the bridgedeck sides and glassing up a bridge deck
    4 extra weight of bridge deck say 500kgs will provide adequate areas for diagonal bracing
    5 the wider pontoons will handle the extra weight better than any other arrangment
    6 26ft is our porposed length price is very important
    7 we know you guys already think this will frankeinstien but we are not asking about your opinion of appearances merely the forward speed and hoe it will be affected and why
    8 the other main question is manuoverability and turning
    9 we look forward to exact replies and to those who have given them so far thankyou
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.