Suggestion require for developing lines of a shallow draft oil tanker

Discussion in 'Boat Design' started by manon, Dec 12, 2012.

  1. manon
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    manon Junior Member

    Dear members,
    I am in the middle of designing a shallow draft oil tanker. The principle particulars are as following:
    LENGTH OVERALL 48.56 M
    LENGTH LWL 46.37 M
    LENGTH BP 46.80 M
    BREADTH MLD 10.00 M
    DEPTH MLD 2.60 M
    DRAFT LOADED 2.00 M

    Hydrostatic particulars, LCG, VCG, Light weight data is in the attached excel file and, the lines plan is uploaded in cad format. For better visualization, rhino model is also uploaded.

    Can anyone please check the lines plan and other particulars whether I am in right path or not?
     

    Attached Files:

  2. Ad Hoc
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    Ad Hoc Naval Architect

    If the lines satisfy the SOR...and the powering..that is all you need to do.
     
  3. manon
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    manon Junior Member

    Thanks for your quick response.

    I have checked the stability at different loading condition in hydromax. It satisfies. About powering, I will do it in Navcad.

    It would be better for me, if you please check the fore and aft end so that I can achieve a better flow characteristics and optimized lines.
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    That is dictated by the location of the engine and the prop diameter and its position relative to the hull. But wherever it is, you should aim for a min of 15% tip clearance...20% is better.
     
  5. manon
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    manon Junior Member

    Tip clearance is 20%. Prop dia is 1.3 m. But I am a bit concern about the aft end. In order to avoid wet transom, the rise of stern become around 15 degree. thus the size of transom become around 0.5m. Any suggestion about the rise of stern?
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Thus, what is the full load displacement, from the SOR...and then, with the lines drawn as they are, what is the powering/resistance? With the installed power, does she meet speed?...if so....there is little else to worry about...whether the transom is wet or not....does it matter if she meets speed?
     
  7. gonzo
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    gonzo Senior Member

    Looking at the draft and propeller diameter, it looks like the tips are quite close to the surface even at full load. Is it in a pocket or tunnel to prevent ventilation?
     
  8. manon
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    manon Junior Member

    Full load condition gives 2.058m draft aft. I have 20% tip clearance. Wont it be enough? Actually I have some design constraints, draft limitation and capacity requirement. Look at the principal particulars, B/T=5, not good. But I had to choose it because of the draft limitation and increased beam instead of length (since it will increase stability and reduce building cost by reducing light weight. Increase in resistance wont be too significant, I guess) to meet volume capacity of 630 m3.
     
  9. gonzo
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    gonzo Senior Member

    The propeller is usually higher than the keel for protection. If you have maybe .25m from the bottom, the tip will be at .5m from the surface. Have you considered if it will come out of the water when the ship pitches, and if so if it acceptable?
     
  10. manon
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    manon Junior Member

    Gonzo,
    Thank you for your valuable comments.
    'If you have maybe .25m from the bottom, the tip will be at .5m from the surface', you are right about this.

    Now, at this design stage, so far I understand, pitching wont be a problem in loaded condition, since it will only move through river and maximum wave height will be around 0.3-0.4 meter. Its small L/B ratio (L/B=4.6) will restrict pitching as well (please suggest me if I am wrong at this point). I there are other aspects about pitching which I have not considered yet, but at this point it looks like propeller wont come out at full load condition.

    I actually I am bit concern about the stern angle (rise of bottom at stern to transom), which is around 15 degree. This is high, but I had to allow it to accommodate the propeller and to have better engine room. Position of LCB is suitable place to provide favorable trim in light and loaded conditions.
     
  11. gonzo
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    gonzo Senior Member

    If the design is only for protected waters, pitching won't be a problem, agreed. However, ventilation is a problem when the tips are close to the surface. I think that tucking the propeller under the stern or making a partial tunnel may be a good thing.
     
  12. bajansailor
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    bajansailor Marine Surveyor

  13. JSL
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    JSL Senior Member

    A shallow hull. Check your bending moment vs the hull section modulus to make sure the hull won't snap in half. The river may be kind but haulout, running aground, etc. may not. Also check your pollution regs - can you use a single hull 'tanker'?
     
  14. Tackwise
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    Tackwise Member

    Fully loaded will be the least of your problems. Will it always be fully loaded, or will it sail partially loaded or even in ballast? Generally tankers do a lot of sailing time in ballast!

    What is the immersion of your ship in ballast? the propeller must function in ballast as well! Generally shallow water vessel's propellers and tunnels are designed with Ballast depth in mind. Although it is killing for your overall performance it generally necessary!

    Shallow water vessels are also generally outfitted with nozzles! Due to draft restrictions you need more thrust with a smaller diameter propeller, which makes the nozzle propeller a good choice.
    Nozzle propellers are also less prone to ventilation than open propellers!
    Also with nozzle propellers you are able to integrate the propeller within a tunnel which will decrease the ventilation problems further.

    The aft ship of a shallow water vessel will generally incorporate quite a huge portion of tunnel. See picture for some tunnels on shallow water barges! Those tunnels are generally designed to be immersed about 10-15 cm in ballast conditions. If you look at the nozzles (propeller not yet fitted), you can see they extend quite a bit above the lower edge of the tunnel! With those tunnels they have been able to increase the propellers diameter above water level!

    I am not a fan of these however depending on the operational profile of your tanker they may be required!

    [​IMG]
     

  15. Tackwise
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    Tackwise Member

    Also an additional note on power prediction,
    Your vessel is sailing in shallow water... Most Power prediction programs are not equipped for power predictions in shallow water!

    There is a natural speed limit on shallow water which is dictated by the depth! So no matter how big your vessel or how much power is installed at a certain depth all vessels will sail at the same speed! (with the exception of all exceptions!:p)
     
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