Long skinny boats

Discussion in 'Boat Design' started by TinyMan, Aug 26, 2005.

  1. TinyMan
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    TinyMan New Member

    Hello everyone, first time poster here. I have been reading these forums for a while and wanted to see what everyone thought about my personal crazy idea.

    Would it be possible to build in steel a very long and skinny boat. I am thinking something like 82" long yet only 10-12" wide. I am fascinated by the high efficiency of displacement speed boats, and want to push the limits a bit.

    I'm hoping that with a long waterline and very lean shape, it will be possible to push the boat to 1.5+ X displacement speed with very little power (200hp?)

    So, what is wrong with my plan, and why don't I ever see boats designed like this. Stability was a concern of mine, but with 6' of draft and a very heavy keel/ballast, I would think that this shape has immense reserve stability. The rounded bottom might make for more overall roll, but it should be controlled. or will it?

    My dream is to design a boat that can be cheaply constructed that will allow me to circle the globe, all while achieving good economy all around.

    I've attached an image which highlights a design that I am considering.
     

    Attached Files:

  2. water addict
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    water addict Naval Architect

    Your ideas aren't out of the ballpark, but your speed/power will likely not make it. Some naval combatants have geometries typical of what you are talking about. You can look on the federation of american scientists web site http://www.fas.org/man/dod-101/sys/ship/ where they have concise lists of navy ship dimensions. You can scale the ratios of L-B-T and displacement as well as speed and power to see what your design might be able to acheive.

    For geometrically similar hull forms, L-B-T all scale as the ratio of Lm/Lp.
    Power scales as (Lm/Lp)^(3.5). Speed scales as (Lm/Lp)^(0.5). This will not be exact, but will get you close.
     
  3. Bergalia
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    Bergalia Senior Member

    I think the first question is, TinyMan - why a long skinny boat ?
    For well over 3,000 years we've been taking to sea in short fat boats...Why are you trying to 'buck the tide' ?
    I also assume that you mean a boat 82 FEET long - not 82"(inches) by ten to twelve FEET wide and not 10-12" (inches wide).
    And while Water Addict's note on naval ship displacements may be valid for the US navy (a young service with much learn) the Royal Navy is seriously searching the efficiency virtues of shorter fatter vessels. :D
     
  4. marshmat
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    marshmat Senior Member

    I personally agree with the long skinny boat idea. I do think that attempting to push the hull beyond its natural hull speed will not work too well; speed/length ratio of 1.34 would be its natural preference but to get over 1.5 would require disgustingly huge motors.
    TinyMan- It's an interesting direction you're taking there; I would go for more rounded sections and fewer sharp corners below waterline. I like to think of such a hull as a series of foil sections revolved around the boat's longitudinal axis; this might be an interesting way to visualize your hull. I honestly don't see a huge advantage to short and fat except for marina fees (I'd sooner have 80'x12' than 60'x16' for the same deck area).
     
  5. FAST FRED
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    FAST FRED Senior Member

    "I do think that attempting to push the hull beyond its natural hull speed will not work too well; speed/length ratio of 1.34 would be its natural preference but to get over 1.5 would require disgustingly huge motors."

    That 1.34 is for fat piggy boats that are 3 or 4 times as long as they are wide.

    Once the L/B ratio gets to 8-1 (or better) "Hull Speed" is probably closer to 1.8 times the LWL ,
    so easy fast cruising , with out hundreds of HP are feasable.

    There was another Long Skinney Boats thread about a year ago that has some fine ideas and concepts.

    The real question is stability , should it be done with depth and a keel , or with small Ammas (trimiran floats).

    My opinion is the Tri would be better as their far easier in rolly harbor conditions , and the vessel could be lighter with no weighted keel.

    Some stability for sails is needed as their far easier to use as a "get Home" than spare engines , gensets with hyd shaft coupling or the other systems.

    While its not a cruising requirement, the TOP speed of a LSB would be higher if the hull was as light as can be.

    Not EZ to do when 2000 to 4000 G of fuel needs a home , but still a thought.


    With shallow draft the Bottom of the boat would be better if heavy enough to stand repeated groundings, there is seldom space for 65 to 85 ft boats in many harbors , but if you only draw 3 ft and can take the ground , there would be little competition for your mooring area.

    FAST FRED
     
  6. fcfc
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    fcfc Senior Member

  7. Leo Lazauskas
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    Leo Lazauskas Senior Member

    There are many designs for vessels with large L/B. The proceedings of the "FAST" series of conferences are a very good start if you want to see comparisons with multihulls and other types of high-speed vessels.

    Stability is, as you mention, a concern. Nigel Gee (and others) have proposed a high-speed pentamaran, which is a large central hull with four small amas. (The amas are not immersed when the vessel is travelling in calm water.)

    Regards,
    Leo.
     
  8. FAST FRED
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    FAST FRED Senior Member

    Leo,

    My "dream boat" would be 65 LOA and 8 BWL with an overall beam of just under 12ft to allow surface transportation.
    An old Commuter in style/profile but with offshore scantlings and range.

    Cost is ofcourse a problem , but NOT if weight can be carried.

    Very light construction costs loads more than just using 3/8 aluminum plate for the borrom that may see the ground and 1/4 for the hull & deck.

    To cruise at 12 to 14K what would be the power requirements to shove a 20,000lb boat comparted to a far less costly to construct 30,000 lb boat?

    I'm dreaming of a design that can get 5nm per gallon at cruise speed.

    Thanks,

    FAST FRED
     
  9. water addict
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    water addict Naval Architect

    Give us an example of the Royal Navy's search regarding short/fat vessels. I would be interested to hear. Of course I take issue with respect to your comment on the US navy, especially versus the Royal Navy, which is laughable by comparison (you asked for it).
     
  10. lewisboats
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    lewisboats Obsessed Member

    "I think the first question is, TinyMan - why a long skinny boat ?
    For well over 3,000 years we've been taking to sea in short fat boats...Why are you trying to 'buck the tide' ?
    I also assume that you mean a boat 82 FEET long - not 82"(inches) by ten to twelve FEET wide and not 10-12" (inches wide).
    And while Water Addict's note on naval ship displacements may be valid for the US navy (a young service with much learn) the Royal Navy is seriously searching the efficiency virtues of shorter fatter vessels. "


    "Give us an example of the Royal Navy's search regarding short/fat vessels. I would be interested to hear. Of course I take issue with respect to your comment on the US navy, especially versus the Royal Navy, which is laughable by comparison (you asked for it)."




    Oooooo...This otta be good!
    Aaaaannndd In this corner....wearing red, white and blue trunks... we have the brawny youngster packing 4 carrier groups (Nuke SuperCarrier, Guided missle cruiser, 2 guided missle destroyers, attack sub, and supply ship) and many smaller surface craft.
    In the other corner, also wearing red, white and blue trunks is the Past Master with upteen centuries of experience... although having lost a little mass recently, with only 3 smaller carriers, 14 frigates and 8 destroyers along with misc smaller surface craft.

    Gentlemen...shake hands, go to your corners and at the sound of the bell, come out swinging... :D

    All in fun now

    Steve
     
  11. Leo Lazauskas
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    Leo Lazauskas Senior Member

    It's not too difficult to calculate the drag and power requirements for vessels with your desired dimensions using a program like my "Michlet".

    If you are serious about researching the topic have a look at the High-Speed Sealift workshop proceedings at:

    http://www.ccdott.org/content/CS_fr.html

    Good luck,
    Leo.
     
  12. Bergalia
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    Bergalia Senior Member


    Their Lords - the Admiralty (RN) have been debating the virtues of short fat/long thins - since the mid-1980's - but due to frequent deaths among the assembly have so far failed to reach a final decision - though lower deck 'scuttlebutt' has it that any new ships ordred will be of the short fat variety. Alas, however, under the Mad Cow Thatcher most RN ships were decommissioned - and under the Phoney Blair no new ships have been ordered. So for the time being my argument must remain on hold. :(
    As for my tilt at the shortcomings of the US Navy... come on... can't you see when someone is pulling your leg.
    Trust me, I've been drunk enough in the company of US swabs, in more disgusting establishments, on more continents, than my old mum could wave a stick at. ;) But you still don't know how to play darts... :D
     
  13. Packeteer
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    Packeteer Junior Member

  14. fcfc
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    fcfc Senior Member


  15. blared
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    blared ALFA

    The thing with the skinny boats is that they shake too much. If its a ship no problem but if its a small boat I prefer the wide ones, more confy and less shaky.
     
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