Hull shape design advice for 11.5m, 8kts, Fn=0.4

Discussion in 'Boat Design' started by ram68ocean, Jul 12, 2021.

  1. Alik
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    Alik Senior Member

    Hull shape is not the priority in small craft design. There is very common misconception that some 'big name' designers know the secrets of hull shaping, and the others do not.

    First, one needs to define parameters of the boat. There is no point to look at shape improvement if the boat is 2 tons overweight.
    Run parametric study of Your design first. Maybe after all, You will decide that the boat should be longer. Taking rather heavy weight but making it 17m instead of 11.5 will be a big improvement on hull efficiency.
    Again, not the shape, play with parameters of the hull first!
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    No detail was given about the duty of this thing, other than a "survey boat" whatever that means, I am tipping there would be a mutiny on board well before the 4000 NM was reached.
     
  3. ram68ocean
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    ram68ocean Junior Member

    Hello, the vessels carries a good number of sensors and transducers for sea bottom survey mainly. The transducers are sensitive to 10 degrees on the vertical line, meaning that reducing roll and pitch to under 10 deg. would be ideal. Transducers could potentially be carried in the bottom of sort of bulb keel (as in a sailing yacht).
    Thus the client is having in mind a wave-piercing hull to keep pitching low. I am assessing now if this is the most suitable bow shape, as in my mind wave-piercing is used for higher speeds 20+ knots, or Froude numbers above 0.85, but I could be wrong.
    upload_2021-7-14_0-16-11.png
    As you all well suggested, I want to focus first on internal spaces, weights, GA and then hull shape. Client is mainly focused initially on hull shape alternatives and keen on wave-piercing hull. I think is feasible but it might be 2-3 meters longer that way.
     
  4. ram68ocean
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    ram68ocean Junior Member

    Here's the basic GA I have so far:
    upload_2021-7-14_0-22-54.png
    It seems that the containerization won't be possible, it needs a wider beam for sure and also length especially for a more 'wave-piercing' bow, which I guess it could make it up to 3 meters longer.
    Forgot to mention that this is a vessel without crew as it is controlled remotely from the distance.
    Still on my to-do list: complete equipment list and weight estimate, power calculation, chose a set of generators, fuel consumption estimation, fuel tank sizing, etc.
    Then look closer to hull shapes.
    So far I have sketched the following:
    upload_2021-7-14_0-30-29.png

    upload_2021-7-14_0-30-49.png

    upload_2021-7-14_0-30-57.png
     
  5. ram68ocean
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    ram68ocean Junior Member

    I just posted initial GA. And realised that it wont fit inside the container. Will go with your suggestion of the flat-rack. Then beam and length are not limited any more.
     
  6. ram68ocean
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    ram68ocean Junior Member

    That boat looks great. I can't see any details of the underwater hull though. How does it behaves in open water (bigger waves)?
    What do you think of this hull type for this vessel?
    [​IMG]
    Any advice for the process on getting a first estimate for fuel consumption, sizing the fuel tanks when having 2x gensets and electric thrusters? Also, for power required, and selecting the electric thrusters and generators? Thank you.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    The client shouldn't be interested in anything other than a design that gets the job done to the specified requirements, which on the face of it (4000 nm) appears to be impossible in a small vessel at 8 knots. Presumably this is a manned vessel, with all the accommodation requirements that implies, for weeks at a time, with the likelihood it could become very uncomfortable in a small vessel, if forced to stay at sea. I get the feeling your boat is about 200 feet short of what a long range survey vessel might need to be.
     
    Last edited: Jul 13, 2021
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  8. bajansailor
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    bajansailor Marine Surveyor

    Ram has noted in post #19 above that this vessel will be unmanned, which makes a lot of sense. But his comment is rather hidden.

    Ram, re the top GA in post #19, the engines you have shown are enormous! Even if you have no crew or stores, you will fill up the boat with engines and fuel, and there won't be any space left for survey equipment.

    In view of how this will be an unmanned survey vessel, with an (almost impossibly) long range requirement, how about making it a catamaran instead?
    Have two small electric motors driving it, and the deck (or a canopy above the deck) covered with solar panels to provide a charge for the batteries.
    With no requirement for carrying stores for the crew, she could then potentially have a very long range, if she is self sufficient re power from the solar panels.
    And with a cat you need not worry too much about large heel angles due to rolling. Unless you encounter some nasty weather......

    You mention that it is 'controlled remotely from the distance' - how far away will the operator(s) be? Literally hundreds of miles, and the controls are via satellite communications?
     
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  9. Alik
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    Alik Senior Member

    I see a good use of Maxsurf hull library in the hull shapes... ;)
    If it is a real boat, hull shape should be designed by professional. No dummy stuff from Maxsurf...
     
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  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Unmanned, is that really allowable under maritime law ?
     
  11. Alik
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    Alik Senior Member

    Actually yes. There are IMO documents on unmanned craft already, see 'autonomous shipping'.
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    Surprised you do not know about THIS
     
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  13. Mr Efficiency
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    Mr Efficiency Senior Member

    How much would compliance cost ? I expect it would be pretty exacting
     
  14. ram68ocean
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    ram68ocean Junior Member

    Hello Mr. Efficiency: I totally agree with "The client shouldn't be interested in anything other than a design that gets the job done to the specified requirements,..." well said! I am trying to get the owner to understand this in a professional way.
    It is indeed an unmanned vessel. You can search for ASV or USV, there are already many vessels built like that either catamaran, trimarans or with a slender hull bow. Some cool examples here, here, here (images), Sea Hunter USV, here, etc.
    upload_2021-7-14_9-29-3.png upload_2021-7-14_9-34-36.png
    The purpose is to reduce fuel consumption, emissions, increase endurance, reduce risks.
    There's no galley, accommodation, heads. It's a new game.
     

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  15. ram68ocean
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    ram68ocean Junior Member

    - Yes it looks the generators are way too big, I started on the bigger end to be conservative. They should be of high rating (continous), commercial grade, and they are usually bigger than leisure rating. What do you normally do to chose proper gensets (not engines) for electric drives ?
    - I really do like making a catamaran or trimaran, or even a SWATH. I have proposed this to the client but in his view a wave-piercing monohull is a better option...
    I like this one as an example. Even thought of shock absorber hull to isolate the platform. It should be able to operate world wide, even at higher latitudes for long range so just solar panels I am afraid won't be enough(?). Thus the large fuel tanks requirements (5-8 m^3 ??).
    It will be exposed to open sea water and nasty weather, so a cat or tri becomes less attractive having to maintain roll and pitch angels to less than 10 deg ideally for most of the time.
     
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