Hull shape: what’s the consensus on extreme piercing/displacement/planing combo hulls for sailboats?

Discussion in 'Boat Design' started by Kingston, Sep 13, 2018.

  1. Kingston
    Joined: Sep 2018
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    Kingston Junior Member

    Hello,

    I’m interested in sailing and have been wondering about hull shapes for sailboats. I’ve found information about the type of hull I’ve been thinking about, examples are the Schulz Reverse Deadrise (SRD) and the Ulstein X-Bow, which both have displacement and planing characteristices.

    My general concept for the shape is an extremely thin and tall bow that slices waves, with a rounded midsection for displacement stability/comfort, then the stern half rising up into a waterline very flat planing surface. I’m imagining a standard keel and rudder.

    Does this exist for sailboats? Is it a terrible idea? Your thoughts are greatly appreciated.

    Thank you!
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Welcome to the forum Kingston.

    The problem with your question is that you are taking one aspect of the design, isolating it, and then trying to get the best out of it. Sounds nice, but design doesn't work that way.
    Since the design of a boat is greater than the sum of its individual parts.

    Thus, if your sole objective is as you state above (hull shapes), you then need to design you vessel. By that I mean you add cabins, setas, galley, engines, sails, anchors, showers etc etc..whatever is required to make your 'design' what it is you want. Each item has a footprint in terms of space, 3 dimensionally and weight. Once you have arranged all this and added up your total weight, you will find that your hull "choice" is rather limited in how it may be arranged. Nowt wrong with that, but you will then find all your "optimisation" exercises you wish to perform renders "The Design" unachievable.

    For example, the "best" hull you end up selecting using your parameters above yields a hull width of say 1.00m.
    Well, a berth is 7-800mm wide, which means you wont be able to get out of bed. You'll have step down onto it and not much else.
    Or
    The engine you choose is wider and taller than the hull shape so it wont fit in etc etc.

    Thus your first priority is to Design the boat. Then look at hull shapes etc etc.
     
  3. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    In short and with less paraphernalia, the first thing you should do is a SOR (Statement of Requirements) of your boat and a very preliminary General Arrangement drawing. Then generate some shapes, also very provisional, inspired by some previous design, and modify them little by little until achieving maximum fulfillment with the SOR.
    Good luck with your project and, if you need real practical help with it, do not hesitate to ask your question. Maybe the pm would be the most discreet way to communicate.
     
  4. Kingston
    Joined: Sep 2018
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    Kingston Junior Member

    Thank you for your reply. I was thinking mainly about a recreational day sailer/sailing dinghy under 20 feet, so livability is not a large concern for me (no galley, showers, etc.) In general, I was seeking initial guidance with this idea in terms of "yes, that shape would probably float, but it looks like when it's heeled over it won't be this or that."

    Thank you again and please let me know if you need me to be more specific. I've attached some very basic models.

    bdesign1.PNG bdesign2.PNG
     
  5. Kingston
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    Kingston Junior Member

    Thank you for your reply. I'm unfamiliar with SOR's, but I can say that to start I would be considering a vessel for recreational day sailing, not for living, eating, etc. so my design is primarily about performance, as I'm interested in what can be done to incorporate the initial stability of planing hulls and the overall stability of displacement hulls (are these the proper terms?).

    Thank you again and please let me know if I need to be more specific about my idea. I'll attach the photos I put in my other reply.

    bdesign1.PNG bdesign2.PNG
     
  6. JamesG123
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    JamesG123 Senior Member

    In preamble to what others have said about design, I understand that you have no sailing experience at this point? So you are kind of asking what kind of high performance sport car I should buy/design before you even know how to drive a car.

    Most sailors never max out the performance of even the most humble of hulls and sail plans, and most people can't give you an accurate description of a hull's sailing properties and character.

    I would say just go out and find an inexpensive sound and stable sailboat with which to "get your feet wet" (you will probably do more than that). And then you have a better understanding of the questions you should be asking and what works and what won't. Books (and the Intenet) only go so far.
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    The example i gave was merely indicative of the process. So you comments about:

    Suggests that the task ahead of you, is way beyond your knowledge. Since one liners that you seek will be filled with further Q&As which answers that will still elude you.

    They are indeed extremely basic not even "boat shaped". Thus you face a very long road ahead, or, just buy an off the shelf design.

    Very succinctly summarized by JG

     
  8. Kingston
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    Kingston Junior Member

    Oh I’m sorry I didn’t give enough information. I have some moderate sailing experience on a 16 ft day sailer and a small 8ft dinghy. I’ve also been on 25 and 35 ft boats, but haven’t sailed them myself. I’ve experienced planing and displacement sailboats and was wondering about boats with both concepts combined.
     
  9. Kingston
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    Kingston Junior Member

    I think I explained my idea poorly. At most I’m considering making a plywood <10 ft dinghy to play with the concept, nothing with large investments of money or time.
     
  10. JamesG123
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    JamesG123 Senior Member

    Yes, and your drawings are less than helpful. The description you gave in your first post sounded to me like pretty much the contemporary "performance cruiser" hull form.
    [​IMG]
     
  11. Kingston
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    Kingston Junior Member

    I’m sorry they’re so bad, but I have no formal training. I came here to learn and get advice, but it just seems like I’m being torn down for not knowing enough.
     
  12. JamesG123
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    JamesG123 Senior Member

    You're getting advice! Just not the kind you wanted. ;)
     
  13. Will Fraser
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    Will Fraser Senior Member

    It seems Schulz also designed and patented a keelboat hull in 2000: US6325009B1 - Sailboat for sailing in shallow water - Google Patents https://patents.google.com/patent/US6325009B1/en?inventor=Walter+A.+Schulz

    If you look at the hull sections and imagine the waterline in a heeled state, you can picture the concave submersed sections. There is however no deep-V section forward of and in line with the concave run aft.
    The main focus of the patent is shallow water sailing, but I would not be surprised if there is a link between his sailing hull design and his subsequent reverse deadrise patents for power boats.
    Sailboat that Sails in 3' of Water http://www.shannonyachts.com/sail351.html
     
  14. Kingston
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    Kingston Junior Member

    Yes, I can see that too. How could I move forward to learn more about how this certain hull (or any) would perform? Is there software that can render flows on a basic model? Or do I need to make a small physical model or test to see how it performs? Being as I’m just one person, how can I trial and error with this kind of thing? There’s a ton of reading out there, but I haven’t any idea where to start.

    Thank you!
     

  15. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    Hull design can get ridiculously complicated, fast.
    And sometimes it's completely counterintuitive!
    Unless you are willing to put in a lot of time and money
    in experimenting, trialing, modifying, rebuilding, changing, analysing,
    pulling your hair out, losing sleep, regretting, giving-up, spending more money,
    starting over, etc, etc, etc then look at hulls already made, tested and proven.
    Hulls with thousands and thousands of hours in all kinds of conditions by all kinds of skippers.

    From these you can see what meets your SOR and how.
    Perhaps a mix of hull designs, meaning a prototype needs to be made and sea-trialed.

    In the end you may look back and say, "Why didn't I just buy a production hull that best suited my needs?"
    Often it's because you didn't know any better and had an agenda...

    Carry on.
     
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