Spray rails and chine strips on planing hull?

Discussion in 'Boat Design' started by John Slattery, Nov 12, 2023.

  1. John Slattery
    Joined: Feb 2023
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    Location: Jupiter, FL

    John Slattery Junior Member

    I am working on a design for a 28 ft v bottom (top speed of 50 kts cruise speed 30 kts) for which I am searching for ways to control spray to keep the passengers dry, without increasing vertical acceleration (G forces) when pounding through waves.

    I have read a few research papers on the effects of spray rails and chine strips across different sizes, shapes on configurations. But, the articles concentrate on separating the spray forward of the waterline away from the hull only for the purpose of reducing drag on the hull. I am more interested in the comfort of the passengers by keeping spray out of the cockpit and g forces down.

    Has anyone seen any research on spray rails and chine strips that focuses more on passenger comfort than efficiency? I will gladly give up a little efficiency for passenger comfort.

    Can anyone offer some ideas, particularly on shape and size of chines and strips to accomplish this?



    Thank you!!!!
     
    Last edited: Nov 12, 2023
  2. messabout
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    messabout Senior Member

    What is spray forward of the waterline? I presume that you mean the forward part of the hull, not the waterline.

    I suspect that spray rails contribute only marginally to reduce drag for a deep vee hull. They would help to avoid having solid water climb the sides of the boat. The supposed purpose is to deflect vertically moving water away from the hull .

    If the boat is slamming then there will be some spray. You an reduce the slamming force, and spray generation, by going slower. All the forces involved are subject to the laws of physics. Force is a function of velocity squared, both vertically and horizontally. Go slower and save the fillings in the teeth of the guests. A 28 footer at 30 to 50 knots will need a generous lot of power. Fuel consumption will be significant. Fuel weight is an important part of the design detail.
     
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  3. wet feet
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    wet feet Senior Member

    What worked on your most similar design?That would be the obvious starting point.I would be guessing that a 3 inch chine flat would be more effective than spray rails.
     
  4. kapnD
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    kapnD Senior Member

    Your goals are counter intuitive, comfort and speed of a 28’ boat at 50 knots or even at 30 cruise is not going to be kind to the passengers when it’s in rough seas.
    Spray rails may separate the flow of water up the side of the hull, but said spray is then airborne, and can still blow back over the boat, depending on wind and sea conditions.
    Chine flats should be designed for optimal planing assistance, spray abatement is not their job.
    You have provided precious little information here, do you have drawings or photos you’d share?
     
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  5. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    From limited experience on that size of boat, I don't think that either spray rails and/or chine strips is going to bother maximum speed to any real degree.
    kaqpnD got it right about the severe lack of comfort at those speeds, at any kind of sea.

    So, ignore performance issues, and concentrate on spray control.
    You have not bothered to provide any hull design, so you are going to have to do the work yourself.
    Have you flared the bow area ?
    Have you built a model, and tested it for spray patterns ?
    Its going to vary a lot on your shape. Chine runners seem to be the obvious first step, to cut the flung spray from the sharp bow edge.
     
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  6. DogCavalry
    Joined: Sep 2019
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    DogCavalry Senior Member

    Note how I didn't mention sea sleds? I'm feeling virtuous.
     
  7. DogCavalry
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    DogCavalry Senior Member

    I will add that whisker spray drag can be as much as 15% of hull/water drag, so spray rails make a meaningful contribution to hydrodynamic efficiency. But they do indeed turn that water into showers.
     
  8. BlueBell
    Joined: May 2017
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    BlueBell . . . _ _ _ . . . _ _ _

    I think covering your passengers may be the most effective method of keeping them dry at any speed in any weather.
     
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  9. DogCavalry
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    DogCavalry Senior Member

    Air conditioning in hot weather, heat in cold. And manage spinal compression injury with appropriate hull form.
     
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  10. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    I am just wondering if a catamaran hull form might be more suitable for the usage described, rather than a monohull?

    Or even a Hickman sea sled type of hull form?
    I have mentioned it for you :)

    Although a top speed requirement of 50 knots is still awfully fast - and even 30 knots on a 28' boat will probably still have the 'passengers' (is this a commercial boat design?) hanging on for dear life in anything more than a flat calm sea.
     
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  11. BlueBell
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    BlueBell . . . _ _ _ . . . _ _ _

    Ya, not a lot of information given by the OP...
    We have no idea about anything except top speed, cruise speed, and that there are passengers...

    EDIT: Oh, and 28' LOA
     
    Last edited: Nov 19, 2023
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  12. kapnD
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    kapnD Senior Member

    John?
     
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  13. BlueBell
    Joined: May 2017
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    BlueBell . . . _ _ _ . . . _ _ _

    Another abandoned thread it appears.
     
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