International Moth Design

Discussion in 'Boat Design' started by BigYeet, Feb 20, 2020.

  1. BigYeet
    Joined: Feb 2020
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    BigYeet Big yeet

    BUTTERFLY pic 3.jpg BUTTERFLY picture.jpg BUTTERFLY pic 2.jpg Hey everyone! I'm designing a moth that I am planning to make. I just want everyones thoughts about the boat.
    Cheers
     
  2. wet feet
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    wet feet Senior Member

    I wish you well with the endeavour.What the original post doesn't say is whether you have spent any time sailing a Moth.If not,I suggest you get hold of one as soon as possible and get a couple of hundred hours of experience to build on.The rendering looks capably done but most of the Moths I have seen in the last few years had wings that were integrated with the rig and your appear to be a bit far aft to make much of a difference in this respect.The amount of wing that can be used to move weight around and adjust the balance of the boat looks rather minimal but you may have the technique to overcome this apparent short distance.More detail design appears to be needed in respect of the rudder gantry before building.
     
  3. BigYeet
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    BigYeet Big yeet

    Thanks for you post, I haven't spent any time in a moth but I only just started high school and I will not be able to get a moth but I might be able to sail a freinds wazp.As for you suggestions for the wings, I will be attatching supports for the mast to the wing. Some wing bars are much smaller than mine and I think it is a good size.
     
  4. Richard Woods
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    Richard Woods Woods Designs

    I have a friend who was your age a couple of years ago and he did something similar. Plywood shell carbon over. I helped him do sea trials with the foils before he fitted the rig. Very impressive to see it lift out at about 6 knots. Unfortunately he didn't get the wing/rig framing right and it broke when he dry tested the rig. So he never sailed it.

    I assume you are on the FB Moth groups. They are very active

    Yes try a Wazp, easier than a Moth. What do you normally sail?

    RW
     
  5. BigYeet
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    BigYeet Big yeet

    It is very impresive for the boat to fly in 6 knots, its a shame about the frame breaking though. I have been looking at some of the different moth FB groups and I normaly sail a Starling (nz one man boat)
     
  6. wet feet
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    wet feet Senior Member

    A bit of time in a Wazsp will be a solid foundation for learning about sailing a foiler.Anything learned can be worked into the evolutions of the design,and there will be several.I'm sure Richard will confirm that the first version is rarely exactly the same as the version that actually gets built.
     
  7. Richard Woods
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    Richard Woods Woods Designs

    Thats a really nice boat. I didn't see any sailing, just in the Auckland museum and club dinghy parks. Pity there are none in the UK. We have the Streaker etc instead. I used to race a low rider Moth. Now have a RS Aero, only a few in NZ at present

    RW
     
  8. BlueBell
    Joined: May 2017
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    BlueBell "Whatever..."

    Looks great.
    Lets see some more detail though.
     
  9. BigYeet
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    BigYeet Big yeet

    Thank for the suggestions so far, I will definetly be adding some more detail. If anyone knows anything about wand setup/ mechanism and rudder angle changing system etc, please tell me.
    Thanks
     
  10. wet feet
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    wet feet Senior Member

    I have a few photos from previous London dinghy shows that may show a little of the general ways of going about creating the systems.In fact next weekend sees this year's dinghy show and I will be there with a camera.Sadly the number of interesting boats is declining and most of the space is occupied by the bigger manufacturers.I also have a feeling this year might be the last reasonably well attended dinghy show as before next year there will be a financial penalty for anybody driving anything other than an ultra low emission car within the North circular road.The same concern has been expressed by the model engineering fraternity who hold their annual show in the same place.

    This was from 2010 as far as I remember.You will be able to see the way in which the wings are integrated with the shrouds and how some of the rudder gantries are pivoted.I don't think the wand system is particularly clear but you may find enough information from other sources to fill in the gaps.
     

    Attached Files:

  11. Doug Halsey
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    Doug Halsey Senior Member

    I think you could learn a lot just by looking at the photos of all the bits & pieces in the Mach2 webshop (& similar sites for the other types of Moths)
    Mach2 Shop https://www.kasail.com/mach2/product
     
  12. ziper1221
    Joined: May 2018
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    Location: florida

    ziper1221 Junior Member

    The wingbar angle looks a bit low. When heeled to windward, the higher the wingbar is the more righting moment you will have, at the cost of more difficult boat handling. In addition to the shroud concerns raised by other posters, you will want to get your weight a little further forward, especially when sailing upwind. The gantry is adjustable for rudder aoa, but that is just to get in the right range. All the sailing adjustment happens in the tiller. There is a worm gear that pushes the whole rudder and tiller against the pin, fore and aft.
     
  13. BigYeet
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    BigYeet Big yeet

    Thanks for your posts so far guys I will definitely be taking these into account. If anybody knows about good shapes for the foil struts and foils please tell me
    Thanks again!
     
  14. ziper1221
    Joined: May 2018
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    Location: florida

    ziper1221 Junior Member

    NACA 63-412 is the old standard, but I'm sure it's well out of date by now. I don't know what sections Mach 2 or Maguire uses. I've been meaning to try out different sections with xfoil but I haven't gotten around to it yet
     

  15. James Tomlinson
    Joined: Jul 2020
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    Location: UK

    James Tomlinson New Member

    Hello

    Interesting design, good to see home build interest.
    The design looks good.
    Like a lennon thinnair maybe.
    Cant tell if a chime or just the DWL.
    Straight into it, lots of comments on your design.

    First off, your wings. The rise in the wings is very low. We are seeing wings rise very high now as there are gains to be made for righting moment (RM); max beam is defined transversely, wings going higher up to the max beam, when sailing and heeling to windward the windward wing will reach a wider beam. Increasing RM etc.

    Secondly your wings look slightly far back. The human CoG should be behind the daggerboard, but it looks as though your leading wing might want to go slightly further forward.
    There also looks to be no wingbar supports. Maybe you can work a way to do so, great! But might be needed.
    And are you thinking solid wings, or tubes with the tramps around?
    The wing shape could also slope down more towards the transom to reduce drag when the leeward wing is canted up.

    Mast stump is kinda minimum 260mm long generally speaking.
    On mach2, mast stump is about 900mm from the bow.
    The mainfoil at 1600mm from the bow.
    The freeboard of the hull 300mm, but changes to 540mm where the foredeck is.
    Beam is 300mm widest.
    From the mast stump, 90 degree out the shroud is 680mm transversely out, and then 310mm aft (hard to explain in text).
    On other boats, CWP 0.75

    To my eye, the freeboard looks low. The volume in the hull as a result looks low. You need to displace the human effectively. There is float is the wing bladder + the hull volume.
    Your DWL is not important.

    On the drawing is it a chime line or DWL we are seeing?
    What is the beam?
    Why have you added a foredeck? It is so minimal, the amount of work needed might not be worth it. Trend is moving away from foredecks now.

    You seem to have a narrow angle of entry at the bow, and a wide flat stern. Kinda contrasting.
    The sides of the moth still slab sided, adding aero drag. It’s a balance to achieve a low wetted surface area and low aero drag.
    My preference is more volume in bow and stern. But in the bow, creating a shape that is not slab sided.

    You can develop a wooden mould, female or male actually. Transverse frames with longitudinal battens or something.
    Hull construction isn’t too ridiculously complex, and a wet layup is ok too.
    A good layup could be;
    1 layer 200gsm Uni Weave
    5mm Core foam
    2 layer 200gsm Biax Weave

    If you search through the forums, and facebook groups. You will find reference points, dimensions etc.

    Overall id say biggest thing to improve on is the wing rise.
    Would be good to see more details really. How wings attach, bulkheads, bowsprit entry etc.
    Could add a lot more, but feel that my help for now.
    Designing the moth is about designing for every eventuality, so that later in production you don’t have to deal with a problem as an after thought. Rather a thought through solution from the start.
     
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