16' Semi displacement electric cat

Discussion in 'Boat Design' started by Brentmctigue, Jun 21, 2020.

  1. fallguy
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    fallguy Senior Member

    I keep looking at your project and thinking you need a fresh start.

    The trouble you are having is trying to square peg the proverbial round hole with your 2.5m limitation and length limit. A won't fold or assemble 2.5m trimaran seems just silly to me. Am I wrong? Someone tell me.

    How about starting from scratch with the SOR and asking people jere for recommendations? You know you are probably headed to a monohull, but at least give it a try.
     
  2. Dejay
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    Dejay Senior Newbie

    Just by looks the amas seem to be a bit too small to provide enough stability, but that is absolutely uneducated guess.

    Here are a few papers I've found on trimaran wave interference (I have yet to properly read and comprehend them)

    https://sci-hub.tw/downloads-ii/2020-02-16/90/10.1016@j.oceaneng.2020.106938.pdf#view=FitH

    https://apps.dtic.mil/dtic/tr/fulltext/u2/a558354.pdf

    https://www.boatdesign.net/attachme...ship_-_fast_09_-_misine_et_al-_1_-pdf.100985/

    http://www.homepages.ed.ac.uk/shs/Climatechange/Flettner ship/task 2.40_9a.pdf
     
  3. Brentmctigue
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    Brentmctigue Junior Member

    I don’t think you're wrong. I think your being rather kind. It’s a bloody monster.
    Deejay thanks for the links.

    I’m open to suggestions.
    Main criteria; trailerable. Electric preferably. 4 people on board. Day boat runaround that can double for fishing with the grandkids. Displacement or not doesn’t matter as long as it can carry batteries for powering 8 hours on the water. Say 3 hours motoring.
     
  4. fallguy
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    fallguy Senior Member

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  5. Brentmctigue
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    Brentmctigue Junior Member

    AdHoc loves a “discussion” doesn’t he. Surprised that hull shape doesn’t contribute significantly to resistance.
     
  6. Brentmctigue
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    Brentmctigue Junior Member

    If I were to investigate a planing hull. Asymmetric catamaran hull form, where is a resource for hull lines.
     
  7. fallguy
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    fallguy Senior Member

    I don't think it wise to go to planing if you want electric. I would pay Richard Wood's for his Skoota 20 lines and adapt them to 2.5m wide if you can get electric into them. Fast build. Great boat. See the you tubes. You can probably beat the hull weight down with foam and pickup some loading. Skip the cabin, too, for a few pounds. Forget the folding part. See what he says. It might work really well.
     
  8. rxcomposite
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    rxcomposite Senior Member

    Trimaran are in between design between a mono and a cat in terms of stability. The outer hull starts at 2.5% of the total displacement and is located almost amidship for low froude number and located aft for high froude numbers. At 2.5% volume, it might not provide enough stability for a small boat. Increasing it to infinity would make its behavior like a cat with a penalty of such a large surface area.

    In short, Tris are for large boat to be practical (ie, moving about the deck) and are designed to be fast with the outerhull located aft.

    For a small tri, there is no room to move around in the center hull, omly on the deck. Stability becomes a problem.

    You like fast boat but you always design the hull with a rocker. You have the midship section correct but not the profile. It should have a partially immersed transom so it won't squat, Forward area should be parralel to waterline or even going deeper. Thats an NPN hull form.
     
  9. Brentmctigue
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    Brentmctigue Junior Member

    Thanks Fallguy, Ive emailed Richard and am awaiting his response.
     
  10. Brentmctigue
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    Brentmctigue Junior Member

    The large rocker is purely for displacement mode. Ive had a go at an asymmetric planing hull just to see what it looks like. Let me know what you think.
     

    Attached Files:

  11. Ad Hoc
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    Ad Hoc Naval Architect

    Sorry to say - it's terrible.
    You're focusing on the wrong issues...just because you have a software programme that can do Lines.. doesn't make the Lines any more or less suitable!
    You need to understand what hull shapes are for ...
     
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  12. Dejay
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    Dejay Senior Newbie

    I think the point is that rocker is for making the boat more easy to turn which is needed for a sailboat, not so much for a motor boat.
     
  13. Brentmctigue
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    Brentmctigue Junior Member

    Thanks Ad Hoc I thought it might be.
    I was at least comfortable (ignorantly) with a displacement hull. A planing hull I know is beyond even my general understanding and I don't intend to try and design one. I modeled it just to see if it would meet my aesthetic.
    NA's talk about the design spiral. Ive just been running in circles, though my time hasn't been wasted. Ive learned a great deal. As a design professional I don't mind paying for design, and I think its time to do just that.
    Cheers and thanks to everyone who contributed.
    b
     
  14. rxcomposite
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    rxcomposite Senior Member

    You are not even into design spiral yet. You have to design a suitable hull for the Fn you have chosen.
     

  15. Rurudyne
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    Rurudyne Senior Member

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