Cruising Cat Hull Styles

Discussion in 'Multihulls' started by sirrahfishing, Oct 11, 2010.

  1. sirrahfishing
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    sirrahfishing Junior Member

    Reply to Richard Woods

    Richard,

    I now realize was an amatuer start in this forum by me and deserved the feedback I got. Thanks for your input.

    Glenn
     
  2. sirrahfishing
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    sirrahfishing Junior Member

    Reply to Ray

    Thanks Ray. Amatuer start by me.
     
  3. sirrahfishing
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    sirrahfishing Junior Member

    Reply to Phil

    Thanks for taking the time Phil. I have not been out hunting for info during the planning stage so as not to influence the process with constant left field queries. I trust the result I have and the people that got me there. Second guessing the people in the know all the way would have derailed the process (I wouldn't like it if the shoe was on the other foot). That is why I didn't do this to now. First big $ cheque about to go out so first big reality check underway. Looks like you were it. Glad you weighed in but I must admit you scared the bejesus out of me with your reply and this influenced my second post. Nothing more sobering than blowing a heap of cash on a possible mistake.

    Sincerely,

    Glenn
     
  4. waikikin
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    waikikin Senior Member

    Glenn, does the draght figure include stern gear/rudders or just the hull?
     
  5. catsketcher
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    catsketcher Senior Member

    it is left field

    Sirrah,

    The design is out of the ordinary and seems as though the material is seriously driving the design. A couple of things I can see from the pics.

    The forefoot is very deep. It is rare (I have never seen) a forefoot that is the deepest part of the boat. This will resist tacking and may exacerbate rounding up in waves. In fact I am concerned that this design is pushing the flat aluminum and then rounded section further than it should. With such a heavy cat I really so no reason why the designer would not use similar techniques to other flat panel designers such as Oram and Schionning. Flat bottoms are fine if they rarely come out of the water.

    As I see it the hull "looks" as though the CB is too far aft. It is so important to get the CB (centre of bouyancy) in a good spot in a cat hull. A hull like this will tend to go bow down as it is depressed. This will happen to the lee hull and is exactly what you don't want. But you may have lots of heavy things down back so this may be fine - I would need to do a weight audit of the deck and interior to see.

    I am not happy to see the kick in the rounded section about 60% aft where it meets the flat side panel. This seems like a basic drawing mistake. If I was lofting this I would fair out this bump. As stated before water doesn't like corners.

    Overall I am guessing that the builder has had a big input into the design. I would caution worrying too much about building the hulls quickly. A bloke in the next suburb is building a Fusion 40. All fully moulded and the bare shell can be put together in weeks. He is probably a year away after 3 and a half years. Richard Woods spent more time installing his depth sounder than laying up one hull of his 30 something footer. So be very very careful about compromising hull design to get the hulls built quicker. This boat will still be e big build. If you really want to be scared a friend built the hulls of his 38 footer when I did - in 1996. My boat has had a refit and he is still building.

    I would look over some of Lock Crowther's cats - Tafua was good alloy cat built by a single bloke - John Nicholls. Lock also did a few other big alloy cats. Kerr cats in QLD also do nice boats.

    Think resale. You are going to want to sell this thing one day. If you go with a no name designer that is very different from normal the resale price will be probably 20-30% less (maybe 50%) than the same type of boat from Crowther or Kerr, Snell or Waller. (Ply designs are a good base for alloy plate) I have seen people try to tag their boats to a "proper" designer when they can't sell them. There have been more than a few mongrel Crowthers, Snells and Pivers out there that the designers wouldn't recognise.

    Before you part with any hard earned get on a bus and find a few alloy cats to crawl through. You never know, you may find one secondhand for cheaper than you can build. You will get a better appreciation for what can and should be done with the material. If you think the money spent for a few drawings is a lot I am guessing $20 000 just for winches and blocks on deck. The rig could go to $50 000 and much more. Get the design absolutely right before you commit big bucks to the thing. A little spent looking and getting a different viewpoint is well spent.

    Talk to Kerr and Incat Crowther. Talk Talk and get questions asked before you are comitted emotionally and financially.

    cheers

    Phil
     
  6. yipster
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    yipster designer

    thats wise advice as these basic hull sketch-up's stay unreadable to me [​IMG]
    and i'm not talking if cabinets be build in square or follow cad hull contour drawings
     
  7. eastcape
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    eastcape Senior Member

    Hi Glenn,

    After reading this forum, I am just a little surprised that your designer is pushing you toward using this hull shape. A 60' project is a little too big to be experimental with in my opinion. If it is a failure, then the designers reputation as a "boat designer" will be in tatters. It is important that before you commence in building this size vessel that the overall design will meet all of your expectations. It appears to me, that at this stage everyone is concerned with the plate development to create the hull shape, rather than looking at the performance and the overall balance of the design.

    The most important part of designing or building a 60' boat is research. I think it is a good thing that you have asked the questions on this forum when you did, and now you are getting some sound advice from other members. A great designer once told me" If it looks right, then it probably is" In this case, something doesn't look quite right to me. I hope you find a solution and succeed with your project.

    All the best,
    Noah
     
    1 person likes this.
  8. catsketcher
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    catsketcher Senior Member

    Not Incat Crowther - Stuart Bloomfield now sells the Crowther alloy designs and has a few of his own.
     
  9. catsketcher
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    catsketcher Senior Member

    Another look at the drawings

    It looks to me as if the builder wants a nice easy job. I have spent many hours dreaming of easier to build techniques but I never thought of this. I always wanted the hulls to look normalish still.

    Underwater up front the rounded hull is a projection of a cone. As cones have straight sides the keel line is straight. This is where the lack of rocker and deep forefoot are mandated.

    The hull sides are flat plate with no compound. I would think that a slight compound would be a good idea to reduce stiffener requirements.

    The aft end underwater is where the conic projection meets a compound curve section - no attempt at fairing or blending. It has a stuck on cone part with a compound curve bum - hence the distortion and concavity nearer the waterline.

    But wait on - if this boat was designed by someone who knew something then the bottom curve of the transom would be near the waterline. Look at the last station on the stern view. I am guessing the transom bottom is only 200mm above the deepest part of the hull so someone has definitely stuffed up. The transom will be immersed (guessing here) by about 400-500mm. Real drag. There is no way the transom will be where it should be unless the boat is built out of carbon and then why is the hull so wide? Good hulls have the bottom of the transom pretty where the designer wants the maximum waterline beam. It designing 101.

    Some real basics of hull design have been violated here. My concerned and heartfelt advice Glenn is run. Hold your chequebook very tightly and get away from these blokes you should not trust. They are innovating with crazy ideas with YOUR money.

    I have seen two cases of designers experimenting with other peoples money and it wasn't pretty. Get on the bus, the plane or the car but don't hand over any more cash till you have talked to other designers.

    sincerely

    Phil
     
  10. oldsailor7
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    oldsailor7 Senior Member

    I agree with Phil.
    I built a 52' cruising Cat and it was a successful boat,
    But then I only Built it, I didn't design it. It was designed by a well known designer of successful boats.

    Stu Bloomfield was Lock Crowthers top draughtsman/designer in his own right. I can only reccommend that you talk to him. I was recently aboard a 50' design of his ---and it was superb.
     
  11. cavalier mk2
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    cavalier mk2 Senior Member

    Choy Design has done some aluminum cats, as well as at least one for production.
     
  12. Petros
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    Petros Senior Member

    All good comments above. It has been my experience with smaller cats, and observation on larger ones, that those fine sexy sharp bows have a tendency to bury when driven hard. They slice through waves nicely with less pounding, but once submerged they provide little additional bouncy, and very quickly bury themselves. This almost always results in a pitch pole. We got lucky in a race when we almost pitch poled when this happened, I ended up in the water ahead of the boat still tethered to the trapeze line. The boat fell back on its hulls when I released the jib sheet, I was quickly dragged until I could stop my windmilling on the surface of the water and grab the rudder and climb back aboard.

    I have no experience with cruising cats, but it seems to me based on this experience (and seeing it happen to many other racing cats) that you want as much bouncy in the bows as practical in a cruising cat to prevent this from happening. When driven hard, or in large waves, the narrow bows can bury themselves without any effort. Consider also that in cursing configuration you will have a lot more mass driving the boat forward into the waves. Buoyant bows will tend to pound more in rough water, but I think that is the price for more bouncy up front. The extra volume will have the added benefit of giving you more internal hull space as well.

    With these issues perhaps you should consider a proven design.

    Good luck. Few are lucky enough to have the resources to put such a project together. You are doing the right thing, asking question before you get too far committed. Also you should go read the recent threads about failed builds, and all the cost and heart ache that goes with it.

    Also, on many forums you have to have a pretty thick skin, there are always a few members who shoot the newbie before they ask any questions.
     
  13. sirrahfishing
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    sirrahfishing Junior Member

    Reply to waikikin

    Only the hull as drawn and only approxiamate. Original plan inc gear is approx 1.5mt fully loaded.
     
  14. sirrahfishing
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    sirrahfishing Junior Member

    Thankyou to all, esp Phil. I won't take up any more of you time. Very appreciated. I am off to do some more research.
     

  15. catsketcher
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    catsketcher Senior Member

    Cheers Glenn and let us know if we can assist later on. Good luck with the build. Mine was a defining part of my life.
     
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