Cruising Cat Hull Styles

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

  1. sirrahfishing
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    sirrahfishing Junior Member

    I am planning to build a 60 footer. Need to resolve a query. Any help would be apreciated. Which hull style would be best?
     

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  2. catsketcher
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    catsketcher Senior Member

    You're kidding

    You are going to build and design a 60 ft cat and you can't draw or design. Best advice you will get - get real and pay one of the good designers in your part of the world.

    Phil
     
  3. waikikin
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    waikikin Senior Member

    Hi Sirrahfishing, of the pics offerred the first would be the better one, the design of a 60' cat is quite an undertaking, let alone the building, get an estimate on design & construction costs from a Naval Arcitect or designer experienced in this style of boat. Sort out your preferences for material & intended use power/sail etc. All the best in your endeavours from Jeff.
     
  4. Becaris
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    Becaris Junior Member

    It's really too bad people don't read. The OP didn't say he was going to design a boat, he said he was going to build one. This can mean many things including having it built by professionals. He came to a boat design forum (the name of this forum for gods sake) and asked a simple question about what kind of hull style would be best for a 60' cat, what he didn't ask for was to be told he had to go somewhere else, or not design a boat or be told what he can't do.

    Having a little knowledge prior to going to seeking a designer or builder for your boat is a smart thing to do. So, why don't we quit telling him what he should do and start answering his question (assuming you know the answer). It's a valid question, though likely with several answers depending on his goal for the boat. I'd like to read the discussion of options IF it could stay on topic.
     
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  5. terhohalme
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    terhohalme BEng Boat Technology

    From these two I would go for the first. Really can't realize the underwater shape of the second hull. Have you got lines (body) drawing of your hulls?
     
  6. Pouakai
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    Pouakai Junior Member

    Is this a thing among Aussies? a NSW v. Queensland thing perhaps? Seems pretty harsh on the basis of one post. Then again Australia is a small place, so maybe you know each other already:D

    Some of the worlds best designers started out without formal training in 'drawing'. Bruce Farr didn't even draw his early boats, he just started building them and went from there. Some very big multi's have been built with minimal design, including the Polynesians who sailed all round the pacific on them, including documented return trips from NZ to the Cooks. I could never work out why the Polynesians always managed miss Australia though....

    Back to the question, first hull looks the better of the two, unless, the 2nd one is a radical axe bow that I can't make out due the perspective.

    http://www.boatdesign.net/forums/archive/t-15624.html
     
  7. catsketcher
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    catsketcher Senior Member

    Still you are kidding

    Have you guys built a big boat?

    Cmon - If you can't produce a lines plan so that others can see that you are choosing between then this is all a waste of time. Such a cat will take at least 10 000 hours to produce. To suggest that getting a few hours spent on producing drawings that show a proper hull shape is not time well spent is not helping.

    After building four boats I feel it is probably better to give a dose of reality first up. During every build there have been terrible times when I have been in the dumps because I made a mistake that sometimes took days of effort and lots of money to put right. I have seen guys in tears as they contemplate breaking up something they have spent years building after going down a badly designed road. So yes I may seem harsh but as I see it this build shows no chance if the standard of build is a bad as the standard of design. You don't always need yes men to help you build.

    Cheers

    Phil
     
  8. Pouakai
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    Pouakai Junior Member

    You are absolutely right of course, I was just suggesting a professional drawing shouldn't be a prerequisite for discussion.
     
  9. sirrahfishing
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    sirrahfishing Junior Member

    Bit more info from the thread originator

    Geez Phil you assume too much, should I have posted my resume first.

    My cheque book has already had the dose of reality from my engineer - don't need one from you.

    I sketched this up in Google Sketchup from the plan to get an international dose of reality - sorry I mean feedback. I am financed and just about to make the raw materials buy numero uno ($95K). Before I start I just had a question I wanted to ask someone who hasn’t got a conflict of interest.

    I came into this forum (first time I have ever joined a forum) because it looked like a genuine place to ask some dumb questions so I don't get half way through, spit the dummy and waste huge amounts of $ and time on mistakes that maybe someone else had made before. The only perfect set of plans is as built, not as drawn.

    The reason I ask is because the second picture provides a combination of increased stem (bow) buoyancy, wave slice and the keel is horizontal for nearly 2/3 of the hull from the bow. In doing so it looks like it adds a larger wetted area with a minimal amount of weight but increases the WL buoyancy 12.5% so the wetted area is theoretically reduced. Same hull finesse ratio and stability ratios. In fact if you cut the vessel at the WL the only diff is below the water. Also the idea of the wave slice and circular stern is apparently to reduce wave generation / interaction.

    It was offered to me as an option over the traditional ellipsoidal/circular hull after I had put together my intended inventory. To me the idea had some merit but I haven't seen anything else like it in the cruising catamaran fleet, hence I asked the question.

    Does anyone have some thoughts about the hull shape based on those factors? Google Sketchup files attached at zip.

    PS - Phil - I don’t even know you but reality I can deal with. Thanks to all others for their support. I don’t know you either but wish I did.

    PPS – I didn't read in the disclaimer on the forum signup that you aren't allowed to ask dumb questions. If it is there my apologies.
     

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  10. rayaldridge
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    rayaldridge Senior Member

    It's not so much that the question is dumb-- I've sure asked a lot of those. It's that I can't tell much from the drawings you provided. I'd need three views of the hulls to see what the shapes actually are.
     
  11. Richard Woods
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    Richard Woods Woods Designs

    I would read all Phil's comments with care. he knows more than most about multihulls.

    I agree with Ray. You should have given much more detail in your first post if you wanted useful comments.

    Like: Is it a 60ft powercat, sailing cat, race boat, day sailer, charter boat, liveaboard cruiser??

    They will all have different hull shapes, so the "best" one cannot be determined until we know what you want the boat to be used for

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  12. catsketcher
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    catsketcher Senior Member

    Excellent

    Gday Sirrah

    I am glad that you are serious but to really help I need to be able to view the hull better. I tried but I didn't get to see it in my version of Rhino.

    Then to be really helpful you need to get honest and frank.

    What are you going to build the boat from? What will you use it for? How many people does it need to carry? Does it need good weight carrying capacity? Power/sail/fast power/fuel economy important or not.

    The reason for the above is that if you are not absolutely honest the boat will suffer. Case in point - a bloke built a Chamberlin13.5m sailing cat. Two sisterships had already been built and crossed oceans. Third builder adds a heap of stuff - hot water tanks in the aft beam, crows nest up the mast, takes every tool he owns on board. Guess what - the boat doesn't sail like its sisterships. When I met him he was building extra hulls underneath the hulls to support the extra weight he installed. If only he had been honest with the designer he could have built the boat a bit bigger from the start.

    If you can try again with the Rhino files and then export the files as a Jpeg or Gif (Rhino lets you do that) or print it as PDF and we can see that.

    If you do that we can get cracking

    cheers

    Phil
     
  13. waikikin
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    waikikin Senior Member

    Hi Sirrahfishing,
    the second drawing is a fair way from what I'm used to seeing, it may well be the "new thing" & a roaring success - only testing can prove really.
    So far as I know in displacment hulls, "water don't like surprises" to quote I don't remember who, the deep bow might make some handling issues esp if its on a sailing boat & I remember some water taxis(power) that had a deep bow & some peculiarities from an opperators perspective. Theres been a power tri featured in posts to cruisers & sailors forum under the title beaus boat http://www.cruisersforum.com/forums/f48/beaus-boat-9093.html with "similar" features in alu, check it out if you havn't seen it. A 60' cat would be sweet machine to own, personaly I couldn't afford one & to a new style of design could be risky, of course your circumstances may be different. By the way, any relative of Bruce? Regards from Jeff.
     
  14. sirrahfishing
    Joined: Oct 2010
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    sirrahfishing Junior Member

    OK - now I am getting the jist of this

    First of all thanks for taking the time. I am all ears. At the moment I have the builder in one ear and the designer/engineer in the other. Have many years experience with them so have great trust in them.

    I am a ex-navy seaman officer / hydrographer. Worked the dream now want to live it. This will test you - Guiriger Reef - where is it?

    Anyway basic details are (if I miss any let me know):

    Type: sailing / cruising cat
    Length: 18mt
    Material: Aluminium
    Displacement: 21t approx (based on material weight ~ 15t + current inventory plan of 6t) expect max to be 24t
    Draught: ~0.8mt
    Mast Height: 73ft
    Rig: Fractional 7/8
    Mast: Aluminium
    Tender: Seadoo
    Berths: 2 x double
    Crew: 4

    Aspect diagrams of the hull in question are:
     

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  15. sirrahfishing
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    sirrahfishing Junior Member

    Reply to Jeff

    Jeff,

    Had a look at the link. Nice. Definitely facing the same geometrical contrainsts I am with plate aluminium. Sorry no relation. Had to sell my house to pay for this.

    Glenn
     
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