Dan-O's first boat build. Small 8' Solar/Electric Cat!

Discussion in 'Boat Design' started by ElectroDanO, Sep 13, 2019.

  1. fallguy
    Joined: Dec 2016
    Posts: 3,488
    Likes: 474, Points: 93, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Why would you double end?
    The only way to not run a square transom for trolling motors is to bow mount, but you can't do that on double enders.

    so I am confused
     
  2. BlueBell
    Joined: May 2017
    Posts: 1,314
    Likes: 261, Points: 83
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    EDO,
    You know what's funny about that video.
    The boat would have less drag running backwards!
    A stabilized monohull would be of lower resistance.
     
  3. W9GFO
    Joined: Dec 2014
    Posts: 209
    Likes: 16, Points: 18, Legacy Rep: 39
    Location: Olalla, WA

    W9GFO Senior Member

    He has an incomplete understanding of hydrodynamics, specifically how a hull behaves at the interface of two fluids of vastly different densities. His reasoning is "reasonable" with regards to an object that does not operate near this interface (submerged/ does not make waves). It is not a "great design", that is why it is not mainstream. He is simply wrong.

    However, it won't really matter. The small performance loss due to the wrong hull shape will not be important. The motors they use will have plenty of power, the intend to fly it on foils.
     
  4. W9GFO
    Joined: Dec 2014
    Posts: 209
    Likes: 16, Points: 18, Legacy Rep: 39
    Location: Olalla, WA

    W9GFO Senior Member

    If you chop off the pointy part of the bow that is above the waterline, you will have a square transom in front. You could do the same to the stern of a double ender.
     
    fallguy likes this.
  5. fallguy
    Joined: Dec 2016
    Posts: 3,488
    Likes: 474, Points: 93, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    it will be funny looking for sure, but can work; have not seen it
     
  6. messabout
    Joined: Jan 2006
    Posts: 3,086
    Likes: 256, Points: 83, Legacy Rep: 1279
    Location: Lakeland Fl USA

    messabout Senior Member

    The builder is a craftsman with some technical misconceptions. W9GFO is correct in the the builder has gotten it wrong. The NASA sections are designed to create lift at some angle of incidence or other. Not what we need for a power boat.

    A good and well executed experiment none the less.
     
  7. clmanges
    Joined: Jul 2008
    Posts: 376
    Likes: 41, Points: 28, Legacy Rep: 32
    Location: Ohio

    clmanges Senior Member

    ElectroDanO, if you ever consider driving this with more than a trolling motor, you might want to consider asymmetric hulls. I just got done reading the whole 45 pages of the TEOTWAWKI thread, and the builder ran into a problem with the bow waves from the two hulls piling up between them and causing a problem.

    Not that I think these are great--I don't--but they've solved that problem:

    Wavewalk® Stable Fishing Kayaks, Portable Boats and Micro Skiffs – Wavewalk stable fishing kayaks, portable boats and skiffs http://wavewalk.com/blog/

    Just something to think about.
     
  8. ElectroDanO
    Joined: Jul 2019
    Posts: 12
    Likes: 0, Points: 1
    Location: Smyrna TN

    ElectroDanO Junior Member

    Thanks guys. Wave interference is something I'm a bit concerned about with this design. The hulls would be pretty wide and close together. That might be a deal breaker if that's going to kill speed badly. I guess I can look into asymmetrical hulls if that's a better design for this project. Hmmm. Well, here's some pictures of the not yet finished 12'x5'(1/10th scale) model of what I have in mind so far. Let me know if I'm on the right track or if this is a total disaster!o_O

    Edit: Wanted to add, to start with, the trolling motor would be clamped on to the rear bulkhead.

    [​IMG]
    [​IMG]
     
  9. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,031
    Likes: 626, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    The hulls don't need to be that wide, or the whole thing so narrow, do they ?
     
  10. fallguy
    Joined: Dec 2016
    Posts: 3,488
    Likes: 474, Points: 93, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    The design reminds me of a canoe I own that is less than a joy to paddle, bit does not tip easily. It has tons of displacement; too much.

    However, someone will have to explain the purpose here of narrow sterns. I see none. The narrow sterns offer little reduction in wsa and dramatically increase weight sensitivity and the hulls will need to be wider for the same weight sensitivity, but I have other concerns as well.

    Also, you have no flare to the hulls whatsoever. A flare to the hulls offers a number of advantages in the basic physics of boats. First, the hulls become only as wide as needed. This increases the critical length to beam ratio. For a 12 foot craft; if you can achieve 8:1 or better, why not. In your model, the hulls look about 2 feet wide all the time which gives you a ratio of 6. This is speed limiting in a cat.

    The prismatic coefficient I think of these hulls is not good; both the narrow sterns and the lack of any rocker rob you of that some.

    finally, not to beat up on you; the hulls are nearly touching each other and this will add even more troubles to this design as it will certainly cause interference drag.

    I am not a boat designer, but I don't think you want this design based on my limited understanding of cats and canoes.
     
  11. ElectroDanO
    Joined: Jul 2019
    Posts: 12
    Likes: 0, Points: 1
    Location: Smyrna TN

    ElectroDanO Junior Member

    Thanks for the replies! Again, sorry, this model is not done at all yet. The hulls will be narrower(12" max on the bottom) and it will have flare(16" at the top) and a little rocker. Still, this is close to what I have in mind and yes, the hulls will be close together. Please don't worry about "beating me up". I'd much rather scrap this $2 piece of cardboard that an 12' boat! Maybe I should look more into that Keyhaven mono design, but I still think a small double ender cat would be so cool!
     
  12. fallguy
    Joined: Dec 2016
    Posts: 3,488
    Likes: 474, Points: 93, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Do you understand the elemental basics of hull speeds in caramarans and how the length to beam ratios drive/limit the hull's capabilities?


    The numbers you cite are better than the appearance of the model... ?
     
  13. ElectroDanO
    Joined: Jul 2019
    Posts: 12
    Likes: 0, Points: 1
    Location: Smyrna TN

    ElectroDanO Junior Member

    I understand hull speed and length to beam ratio but when you throw in catamaran hull spacing, the math gets way over my head. I'm assuming that with the hulls this close together, wave interference is going to be an issue. How bad is that going to hurt speed?

    Again, this model is not done. I made the bulkheads a little big so I could play with spacing and width. I guess I shouldn't have posted pictures yet, but I wanted to give you guys a basic idea of my thoughts.
     
  14. fallguy
    Joined: Dec 2016
    Posts: 3,488
    Likes: 474, Points: 93, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    I think you have bigger problems with weight distribution with the double enders. Your ppi is going to be horrible with your recent statement of 12" waterline beam has me recalling this guy that built foam cat hulls and hated them. I'll try to find the thread. Before you build anything, you will want to do the hydrostatics.
     

  15. fallguy
    Joined: Dec 2016
    Posts: 3,488
    Likes: 474, Points: 93, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.