Deep Vee Hull Design

Discussion in 'Boat Design' started by an2reir, Mar 10, 2021.

  1. an2reir
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    an2reir fifty boat designs

    Bonjour from the south of France I wish you all a very good spring ! I am working on the design of a deep vee hull boat with jet propulsion system ; I did design my hull geometry with a stern deadrise angle of 20 degrees and I am doing speed planing predictions in Rhino Marine wich is the predecessor of Orca
    1.I wonder does anybody have experience with Rhino Marine or Orca speed prediction software? The software says only the planing surfaces up to the chine should be included in the model and only half of the planning boat bottom. I am not sure if up to the chine is to include the surface of the hull topsides upper than chines that is immersed or not as a boat is immersed typically a little lower than the chine surface.
    2. I see many jet boats hull geometry shows a cut of the at stern I wonder why is that ? By shortening the waterline there should be a lowering of the weight but as well a diminishing of speed and yet for example Wally 110 hull shows such a cutout at rear where the jets are fitted on the transom ?
     

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    Last edited: Mar 10, 2021
  2. Alexander Peter Bromley
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    Alexander Peter Bromley Junior Member

    1. As far as I know for Orca3D you will only include the surfaces the hull will be planning off Ie just the hull bottom and chines.
    2. I'm no expert as to why Wally uses the undercut but to me it makes sense because jets protrude quite far from the transom which can create a collision danger for docking and/or provides a swim platform beyond the jets when boarding back on the boat won't be amongst the jets.
     
  3. an2reir
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    an2reir fifty boat designs

    Hi Alex

    thanks for your feedback

    1.Yes indeed I did read the Crca instructions on youtube it is half hull up to chines surface included only and without stern ( attached image)
    2. I see large jet propulsion deep vee boats like this one I here attach - and I wonder could that overhang be there only to protect the jets? As the lenght of the waterline got smaller hence a potential lowering of the speed and they could have protected the jets with a platform mounted on the transom?
     

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  4. DogCavalry
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    DogCavalry I aim to misbehave.

    There is no lowering of speed with reduced waterline, on a planing boat. It does however move the center of dynamic lift forward, toward the CofG,which may be very desirable, from a stability point of view.
     
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  5. BlueBell
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    BlueBell "Whatever..."

    Good point DogC. In fact, the speed increases, due to less wetted area.
    This could be hugely beneficial as you say.

    This is going to catch Baeckmo's eye.
     
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  6. Mr Efficiency
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    Mr Efficiency Senior Member

    This deep vee 24' boat is regarded as one of the softest rides around, I wonder how much the unusual strake treatment has to do with that. Look carefully and you will notice what I am talking about.
    BASS.jpg
     
  7. an2reir
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    an2reir fifty boat designs

    Thank you for your feedback. Here is another exaple of a 3x Jet propulsion deep vee 80 ft watercraft wich has the overhang at the stern and is seem here in all itys splendor. The deadrise is 20 degrees at stern. Interesting the vessel does not show much planning in the video I was thinking the reason may be the with the adjusting of the center weight with distributing weight at the rear of the jets but the video on Youtube seems to indicate there may as well be other functional reasons visby.jpg
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    I don't think that overhang has any hydrodynamic significance, it acts to hide the ironmongery protruding from the boat, which might spoil the appearance.
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    In a word - aesthetics.

    We do this too on our designs.
    There is nothing hydrodynamic about it - by definition it can't be as it is above the waterline anyway.

    It helps to smooth out a blunt vertical transom, when the deck and superstructure/deckhouse is often with a degree of styling..thus it is a simple means to not 'upset' this style that has been created.
    It can also form a nice platform - as it is then easier for maintenance of the jets later too.
     
  10. an2reir
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    an2reir fifty boat designs

    Thanks for the feedback here is another example, I would think the engineers would do everything to balance the centers of weight and lift...... RMK_Marine_IDEF_2015_FACM_TTHB-1_FMC_69_1.jpg
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    It isn't in the water, forget about it.
     
  12. an2reir
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    an2reir fifty boat designs

    Now after I did three speed predictions with different values of the height of center of weight on my deep vee hull design I think my concept looks quite good. Nonetheless the speed power curve I get from my software the Orca depends of some variables like an input of Overall Propulsive Coefficient that I did write as 60 % . And Percent Design Margin ? I think however the Overall propulsive coefficient may be higher in jet propulsion ? Here I marked a very rough guess estimation of a possible location of the center of weight on the wally 110 having in mind where the fuel and water tanks probably are and the weight of 3 diesels ; wally5a.jpg I wonder may the center of weight be about 2 meters above waterline?
     
  13. an2reir
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    an2reir fifty boat designs

    In regards the overhang at the stern I think the justifications are functional as a large power craft needs to be mooring with stern and the jeets need to stay well clear from the piers or shore sometimes needs to tow other craft or the deck to be accessed from the stern, therefore it seems to make sense an overhang above the jets would provide a platform to do that and to protect as well the jets the engineers from Damen Screen-Shot-2013-10-31-at-9.07.18-AM.png Holland found this solution where they choose to have the overhang acting as part of the immersed hull as well
     
  14. an2reir
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    an2reir fifty boat designs

    thank you all for your feedback I did succeed to clarify why the overhang is there and as well I suceeded a series og good speed predictions with the Orca planing by the Savitsky software . input  Artemis  speed prediction.jpg [/ATTACH] input  Artemis  speed prediction  2.jpg
     

  15. baeckmo
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    baeckmo Hydrodynamics

    That solution may cause trouble for the jet manoeuvering. When rotating "on the spot", the outflow from the reverse bucket will interfere with the inside of the hull extension and reduce steering force.
     
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