Minimize the effect on ship in shallow water

Discussion in 'Boat Design' started by manon, Nov 16, 2010.

  1. manon
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    manon Junior Member

    We all know about the effects of shallow water or shallow draft on the performance with respect to deep water. Well, for the vessels, that moves in the inland water ways, often have to move through the shallow water.

    Can anyone suggest, how should be the design of a vessel in order to minimize the effect of shallow water on the ship performance? Help me with some possible methods, calculations or tradition or anything else.

    Thanks in advance
     
  2. Leo Lazauskas
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    Leo Lazauskas Senior Member

    "Performance" is a very broad topic.

    My (free) program Michlet can calculate the total resistance of thin ships in finite depth. The optimisation module "Godzilla" can also search for ships with minimum total resistance given a set of constraints on the hull geometry. Of course, resistance is just one aspect of performance.

    Good luck!
    Leo.
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    Exactly!

    Also, what type of boats, slow, fast, etc etc...
     
  4. manon
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    manon Junior Member

    Thank you Leo Lazauskas and Ad Hoc, for your response. I am apologize for not being so exact.
    Well, the type of vessels are general cargo vessel Lbp up to 70m, beam 10-15m, draft max 4m.
    Also, passenger vessels of maximum permissible 70m.
    Also, feeder vessel.
    Actually, I just need some suggestion from experienced Naval Architects and hull form designer, in order to improve the performance of inland vessels of our country, as the type,dimension and speed described above. Here, performance can be figured out, in the point of view of improvement in the power requirement/fuel consumption/speed.

    Best Regards
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    Good training of the crew, proper and regular maintenance of the vessel, using up to date charts and competent experienced Captains, coupled with proper navigation aids in the waterways and emergency services on the routes planned.

    If you don’t address these, no matter how well designed the boat is you’ll continue to have accidents/problems.
     
  6. MikeJohns
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    MikeJohns Senior Member

    I'm not sure if this is what you are after, bit it might help, is this a student exercise?

    There have been some good papers on reducing squat. For an overview of what parameters you can change and their relationship have a look here:

    http://www.ship-squat.com/How_do_I_predict_Ship_Squat.htm
     

    Attached Files:

  7. Leo Lazauskas
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    Leo Lazauskas Senior Member

  8. Tackwise
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    Tackwise Member

    Development Centre for Ship Technology (DST) in Duisburg Germany is one of the few institutes with a lot of experience in shallow water effects on inland waterway vessels. Their site has some interesting articles which gives you some idea of the factors involved (for specifics you will need to contact them directly)
    http://www.dst-org.de/intro_e.htm

    Some relevant papers:
    http://www.iwwwfb.org/Abstracts/iwwwfb08/iwwwfb08_06.pdf
    http://cmst.curtin.edu.au/local/docs/pubs/gourlay-2007-flow_beneath_a_ship_at_small_underkeel_clearance.pdf

    What is the average waterdepth you will be designing for?

    Tackwise
     
  9. daiquiri
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    daiquiri Engineering and Design

  10. manon
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    manon Junior Member

    Many many thanks to all of you, the links provided will certainly help me a lot.

    Mike Johns: Yes sir, this is a student exercise, but actually I am interested to go as deep as possible regarding this problem for my better understanding.

    Tackwise: Average water depth 4,5 meter (in dry season)
     
  11. Tackwise
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    Tackwise Member

    Manon,

    Take into consideration that at an average waterdepth of 4,5m, your ship will most likely not be able to navigate at its maximum draught (4m)! (Depending speed and ship, squat can be as much as 0,5m) Your payload will therefore be considerably less during the dry seasons.

    My advise on design:
    Focus a good deal of your design effort on the aft ship. Take into consideration that the required inward flow of water to fill up the 'void' in the aft ship, needs to come from the sides of the vessel. You can generally assume that no flow will originate from under the vessel.

    Tackwise
     
  12. manon
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    manon Junior Member

    Tackwise,
    What should be the minimum depth under the keel to the river bed for which there will be no squat. I cant remember where I have found, but I have read somewhere that the minimum depth under the keel or ship bottom to the river bed should be greater than the half of the ship draft in order to have no effect of squat on that ship.......Is this assumption correct?

    Manon
     

  13. Tackwise
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    Tackwise Member

    Manon,

    There is a guideline that when the ration H/T drops below 1,5 the effects of squat becomes measurable. However beware of using such guidelines, as there are to many variables dictating the squat phenomena, such as the speed, shape of the ship, blockage effects, bottom characteristics (sand/mud), etc.

    I have looked into several squat calculations, and found the results to be scattered. Most calculations have been written for sea vessels entering shallow water. All of the effects encountered by an IWV navigating rivers and canals will therefore not have been taken into consideration!

    As so often seems to be the case in boat building: The infinite variables of real life are hard to summarize in an accurate but short calculation!!

    Tackwise
     
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