Dory in aluminium

Discussion in 'Boat Design' started by pafurijaz, Mar 14, 2018.

  1. pafurijaz
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    pafurijaz Junior Member

    Hi, I'm planning a boat on request, a small challenge, but I would like to avoid trivial mistakes, but I'm not expert at all.

    Below are the preliminary plans of the hull, from my point of view it seems to be fine, but I repeat I have no experience, as you can see the bottom is slightly curved and the boat will have a mounted an outboard engine.

    Any advice on both the general forms and the construction of reinforcements would be very welcome.
    Dory_Skiff_005.png
    Dory_Skiff_Barge_study_plan.png
    Dory_Skiff_Barge_study_plan_p.png

    Thanks. :)
     
  2. TANSL
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    TANSL Senior Member

    The cross sections in the bow area have a "V" shape but they are not straight lines but have a little concavity. This should be corrected. Maybe you need to improve the "fairing".
     
  3. messabout
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    messabout Senior Member

    The transom rake to accommodate an outboard motor is typically 14 to 15 degrees, not 12. Best consult the manufacturer of the proposed outboard for their best recommendation.

    This is to be a displacement hull presume. The fore and aft rocker will pretty much prevent the boat from planing.
     
  4. gonzo
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    gonzo Senior Member

    That would be great with a small outboard 4HP or less.
     
  5. pafurijaz
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    pafurijaz Junior Member

    I noticed that curve now, thank you, But the guy has changed his mind after I sent him the preliminary drawings.
    I try to ask with the guy, it is he who told me that inclination, thank you now I will tell you to check ..

    This is a very useful advice for me, now the guy has chanded idea but I finish anyway the prilimanary study.

    Thanks to everyone for the time this is the new boat, this is done again with the measures required by the guy. The model is very similar to those made by Glen-L, but this changes in size.

    Dory_Skiff_new.png
    Dory_Skiff_new1.png
    Dory_Skiff_GL_study_plan.png
    Dory_Skiff_GL_study_plan_p.png
    I hope this is the final shape.
     
  6. pafurijaz
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    pafurijaz Junior Member

    You're absolutely right, the fact is that it seems to me correctly done, and I have no experience, and any kind of advice are welcome, from size to the way of designing and building, everything I do is done with passion but with little knowledge in the nautical field.
     
  7. gonzo
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    gonzo Senior Member

    That new version will take more power and plane.
     
  8. TANSL
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    TANSL Senior Member

    The new version is much better, it is more elaborate, than the previous one. Congratulations, you are improving. But this version, or any other, by itself will not plan. It will only plan if it is endowed with the necessary power.I doubt very much that the OP wants to design a planing hull. What is likely is that it will raise the bow a lot, even if it does not reach the planing regimen.
     
  9. DCockey
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    DCockey Senior Member

    Agree, though with the flat bottom in anyone other than flat water it will slap or pound when planing. Would a shallow skeg or similar be advisable for directional stability?
    When a comment is made that a boat will plane it means that the shape is such that it will plane with sufficient power. Not all hull shapes will plane but the second design above will. The comments that "It will only plan if it is endowed with the necessary power" is unnecessary for anyone interested in power boats.

    The longitudinal trim of a boat when planing depends on the the trim of outboard and the location of the weight within the boat. If the boat has a single occupant sitting in the stern the boat is likely to plane with the bow high in the air. Move or add weight forward, and/or trim the engine down and the bow will come down.

    A similar shape power dories planing before landing on the beach:

     
  10. TANSL
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    TANSL Senior Member

    Actually no comment is necessary. Each one says what he thinks or comments what others say and that's it.
    I suppose a boat, even if it has no outboard engine, can also plan.
    The videos are very refreshing but I would not say that any of those boats reaches the planing regime. Or did you want to show me something else?
    And one more thing that intrigues me, why have you decided that the first model could not plan ?.
    Thanks for your always technical explanations. Since I do not expect them, I will not engage with you in a conversation with little basis. I, of course, have no way of knowing if the OP wants to plan or not, or with what power he wants to do. I think he was asking about other things.
     
  11. DCockey
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    DCockey Senior Member

    Obviously.
    In my opinion the boats are certainly planing, particularly before they get close to the beach. But perhaps you have different definition of planing.

    Where did I say the first design could not plane? I did not say anything about the first design.
     
  12. TANSL
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    TANSL Senior Member

    Let an expert say what things are like (post #207 in Froude and planing https://www.boatdesign.net/threads/froude-and-planing.57340/page-14#post-826033)
    You are right, you did not say it but it seemed to me, that was my mistake, that you were defending the position that now, with that new design, the dory could plan. Excuse me for my mistake.
     
  13. Ad Hoc
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    Ad Hoc Naval Architect

    Possibly. But an outboard with a small skeg may be sufficient.
    Adding a skeg of sorts to a hull form like this can sometimes be detrimental; makes it worse!
     
  14. pafurijaz
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    pafurijaz Junior Member

    Thanks for the advice that I will keep for me for other boats development that I will do in the future, here is a lot to learn from you, the guy did not give me much information, only the size and type of boat he wanted, he also told me that must have a specific angle of 12 degrees the stern, this time I add the model for Freeship and one for Rhino, the original was done in Blender. All the shape Is on a request, and he pointed me to an particular and specif boat the , to make, but in the first message, he asked me to do an other model the Happy Clam that I made for fun, but changed is mind immediately, and here we are.
    In this weekend I add some aluminum channel on floor and other detailing.
     

    Attached Files:


  15. pafurijaz
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    pafurijaz Junior Member

    I received some information on the outboard engine, he has a 25HP Suzuki, with 22” vertical from inside of mounting bracket to the anti-cavitation plate.
    And below the position of a generic motor on my design, is a generic because I can't find the dimension, and the brochure of the model give me a different spec, what is the right height of the transom for this engine?
    Suzuki 25hp brochure
    Dory_Skiff_new4.jpg

    And another thing, in the bow would be appropriate to do with a central plate or is sufficient the weld between only the side parts?
    The boat side are in aluminim 5mm.
    Dory 3d SketchFab
     
    Last edited: Mar 18, 2018
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