Help! An evaluation of a small boat hydrostatics?

Discussion in 'Boat Design' started by kavos, Nov 21, 2014.

  1. TANSL
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    TANSL Senior Member

    I do not speak of a relationship, length / beam, you have to maintain. I'm talking about all relationships between the various dimensions.
    Each one manages hes fear as he wants. All the best.
     
  2. kavos
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    kavos carpenter, shipwright

    Yes, TANSL, I agree with you
     
  3. PAR
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    PAR Yacht Designer/Builder

    This isn't about creativity, but understanding. The boats you've posted are all tubs, every one and though someone might have built them in the distant past, it doesn't mean they where good at anything.

    You simply don't have the engineering and hydrodynamic skills yet, so being creative with shapes that will perform poorly, seems a foolish, if not costly way to learn.

    Be creative with the boat's styling and accoutrements and use a set of established plans, so at the very least it float right side up on launch day.
     
  4. kavos
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    kavos carpenter, shipwright

    Well, initially, asked for help wanted an opinion from people who might know ofabout how to improve some attributes that boat as displacement or what about the floor rise. I didn't ask for people who think they "deliver" lessons.
    The thread it isn't titled: :small boats are tubs or not?"
    I assume that all those people who spent time and ingenuity are only ignorant fools who know nothing of mechanics and only you can see that just made awkward tubs. I Inform you that thousands of people around the world use their designs boats as a yacht tender. But I do not know yet how many use yours ...
    Oh come on PAR, for God shake, you are just only a negative man.
    You do not even know what kind of skills I do have.
    By saying all those boats are all tubs, good for nothing seems a foolish, if not a cheap way to critisize.
    Anyway thank you for your time!
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    Most bath-tubs are not much shorter !
     
  6. FMS
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    FMS Senior Member

    Your first post stated "Last summer I counted the lines of a beautiful traditional small boat in the bay of Sithonia Halkidiki Greece. Then I modified these lines ... " You asked for an evaluation of "stability and performance" without specifying how you intended to use the boat or what you required from it. To improve some attributes it has to be known first what goals you are aiming for. Do you want a boat that is more pleasing to your eye which is apparently how you started, or a boat that performs a specific task or tasks better? Such a small boat will be a compromise that prioritizes the attributes which are most important to you.
     
  7. rwatson
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    rwatson Senior Member

    ... yeah, and the term "HELP!" in you post .... do you really want help or just some condescending tut-tutting ?

    You get expert, professional help for free and take it as an insult. Amazing :rolleyes:
     
  8. kavos
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    kavos carpenter, shipwright

    You've right FMS I wasn't so specific about how I intend to use the boat. So I repeat: I intend to use that boat in protected waters, to design a boat that it rows easily, propels nicely with a small outboard motor and will safely seat two persons. So tell me if you think that the specific boat can do that and -if not- explain the reasons and tell me what must to do.
    But let me ask you, without wishing to be rude, if it is a professional help just naming the small boats tubs
    I dont know what else to say...
    thanks
     
  9. TANSL
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    TANSL Senior Member

    A float for two people, unseaworthy motor or sailing, and that can only support a seated persons, is not a boat, is a bathtub. Why?, because it is very likely that passengers end up in the water. I do not know if this is a professional help but know it is the opinion of a professional. To be clear I'm not talking about your boat.
    My advice, if I may, in relation to your boat : work out a SOR (now you know what that means) and find the boat that best suits it. Do not do the reverse.
    And let me a thought, not very deep : some things are very nice but, although they float, they are not boats. Its functionality is similar to that of a vase: an ornament.
     
  10. PAR
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    PAR Yacht Designer/Builder

    Kavos, this isn't the best format to learn what you need to learn, though is a great place to ask specific questions or bounce around ideas. So the idea of getting the reasons and rational behind the flaws or short comings of the "tubs" I've less than diplomatically suggested, would simply be a dissertation of the things you need to learn. I've been a bit short about them, but actually, considering the things I see, quite nice about it, if a bit blunt. You can take the sugar coated version or the straight up version, which would you prefer.

    As previously mentioned, you need to establish what the goals for this little puppy are. This way you know what to shoot for with the design parameters. Guessing doesn't work well, though on a small boat like this, not a terribly expensive way to learn. Of course this is a slower way to learn, but it's effective, depending on how observant you might be.

    You've listed a few requirements, such as easy to row and maybe outboard powered too, with a crew of two. That's great, now what else? Will it be car topped, is there a target weight, building method perfused, can you accept the powering compromises, given the efficient rowing requirement, how about a sail, etc., etc., etc. The design process is about addressing the needs of the client (you I presume), so think of everything you'd like this boat to do, prioritize the list and start working through it for the inevitable conflicts. Putting bandages on the bleeding conflicts, is what yacht designers do. Yeah, it kind of sucks, but every so often you'll get a chance to do something cool and it makes all the hair pulling worth it.

    A simple, fairly efficient rowing tender. It'll suck (there I go again) with a outboard, but if the skipper keeps the throttle down, it'll behave. Plans are free (> http://www.duckworksmagazine.com/00/DM2000/columns/slogging/ApplePie/ApplePie2.pdf <) and if desired, the sides could be lapped with little trouble.

    [​IMG]
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    The little boats won't be upset by being called tubs, though I have seen people miffed by their boat being referred to as a "sub" !
     
  12. kavos
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    kavos carpenter, shipwright

    Thank you all a lot. I appreciate your tips
     
  13. NoEyeDeer
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    NoEyeDeer Senior Member

    Any of these tiny tubs, of around 2.2 metres or so, will not row easily with two people aboard. Yes, you can row them, but they'll row like a brick, and will basically stop dead between each stroke. Add any wind or tide on the nose and it will make them close to useless.

    If you go for a longer boat you will get much easier rowing with equal or better stability. So, unless there is some important reason why you have to make the thing so short, I would consider something significantly longer. Something around 3.6 metres would be a lot more useful, IMO.
     
  14. gonzo
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    gonzo Senior Member

    A tub is English slang for a very wide boat. It is not an insult to you, but a usual term for a boat that will not perform well in the areas of speed or power efficiency. On the other hand, it indicates a boat that will carry a lot of weight for its length. Dinghies are usually tubby because of length restrictions. If you want a boat that rows easily, short dinghies are not the answer.
     

  15. daiquiri
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    daiquiri Engineering and Design

    This is true, and can be confirmed by anyone who has tried to row a small sailboat dinghy.
     
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