Getting All Mothy Up In Here

What in the world is that. Is that a boat? Is that a flying dirigible? Nay! It’s a moth! A moth is a kind of small, FAST, single-handed sailboat made for racing. Originated some time in the early 1900’s in North Carolina, the classic Moth can be any number of things: skiff, pram, scow, dinghy, basically anything within the restrictions of 75lbs, 72 Sw Fr sail area, and a maximum beam of 60 inches. What David Valham has done here is to make a Moth into a superior flying machine that’s riding on the edge of boatness, appearing to nearly take off!

Now, modern Moth boats look very similar to this Valham design, with the exception of a few factors: while the usual Moth has a couple of “wings” for the pilot to sit on, the Valham design turns these into actual wings, adding to the balance of the boat, adding to the speed. Furthermore, there’s a bunch of littler additions that make this lovely boat a Moth to behold:

Flexible Wing Mast

Lighter Beem Shape

Ergonomic Sitting Area (this is the wings)

Angle of Attack Indicator (rudder)

Rigged Handles for Easier Transport

Dihedral Angle on the Front

Higher Lifting Point

Double Wands on the Front

Now take a look at this bad boy, and tell me if you’d dare drive it. Part of the fun of this sport is the skill involved in keeping the boat upright. Learning how to run one of these splendid looking insects involves a lot of crashing and swimming. But! Once you’re up, you’re OFF!

Designer: David Valham

New Moth by David Valham








  • mif991 says:

    I don’t know a thing about sailing but it looks like you did your homework and it looks sweet, swift and sleek. Your model does justice to your beautiful sketchwork. Congrats. I hope you do well with it.

  • Confucius says:

    Nice work, good to see on here.

  • khidr_313 says:

    Very sweet! 3D printed! awesome! Very nicely executed!

  • kay warner says:

    Dude, how does a vertical sail give you vertical lift???! Are you sure that wing will generate lift???! Google ‘wing-in-ground effect’ genius.

    • david valham says:

      dude… the sail is not vertical (as you can se in the pic.), it leans to the windward side approximately 10 deg… have you tried to look how a windsurfer manages hi sail? and yes i know what ground effect is… you do obviously not. I don´t google for info, I read books (Understanding Flight)… google-genius.

      • kaywarner says:

        Look champion, 3rd Picture down, explanation of “Forces”, you have the x axis as “Sail Side Force” (which is fine) but you have a positive y labled as “Sail Lift”??! Do me a favor – find out how much lift you will get from the hydrofoil, then calculate how much lift you will get from the “wings”(!). Tell me how much they are contributing as a percent of total lift. Stick to drawing pictures.

        • david valham says:

          I´m getting a little tired of you questioning my research. But if you must know I got the info from I paper written by:

          Bill Beaver, U.S. Naval Academy Hydromechanics Lab, Annapolis, MD
          John Zseleczky, U.S. Naval Academy Hydromechanics Lab, Annapolis, MD

          I suggest you read it.

          I´m open for critic but I feel your tone is rude and that is why my last reply also had that tone.

      • ZM says:

        I am pretty sure the advantage of heel angle is not to get lift, but to acheive greater lateral resistance from the Foil….to go upwind better with so little of the daggerboard in the water the boat tends to point higher with the foil contributing to lateral resistance. Just a comment but the boat looks great!

  • Ed says:

    Why not build one?

    • david valham says:

      It would be cool to build one but I´m only a designer and do not have the skill or the time to.

      • Ian K Elliott says:

        Two mates in South Africa are making one.
        Greg Woolley (surfboard shaper whose using polystyrene successfully).
        Their problem is they launch thru some wild surf so the foils will be retractable.
        Oh and its a paddleski with outrigger and a crabclaw sail plan.
        They wanna troll offshore for big fish.
        Regards Ian

  • Jeff says:

    Hi David
    I like what you have done with the design. Looks stronger and more solid as well as cooler looking.

    Have you thought about giving the keel foil the ability to cant? This might allow upright flight and more efficent sailing versus leanign to windward.

    • david valham says:

      Tanks, I´m glad you like it.
      I have not thought about that, but it sounds like an interesting idea.

  • This is an interesting design. It certainly looks like a Moth (the insect kind!).

    One small point – with the wings canted downwards to the back at any speed would the helm not slide off the back?

    I am no expert, but when I sail my Moth, letting the sail out releases downward pressure on the bow and encourages the boat to foil. Or that’s what it certainly feels like.

    • david valham says:

      It sounds like you know what you talking about if you sail one.

      And you are right, I got a lot of inspiration from the insect. You have a point about sliding of to but hey… it´s only a concept and i´m glad that it makes people have toughs about it.

  • Love it!

    So, plans for sale (sail 😉 )?
    would love to build one, searching for a winter project 😛

    • david valham says:

      I´m glad you like it.

      Everything is available for the right price…he he…

      If you are serious about building it, let me know, I´m sure we can work something out.

  • Malcolm says:

    Hey Chris

    That looks like a fun moth any ideas on making plans available ?

  • JG says:


    Beautiful work, lovely renderings, great model, nice concept. Well done.

    One of the greatest speed limiting factors with current moth designs is their aerodynamic drag. I would imagine that your “lifting” wings would have more induced drag than non lifting wings as well as substantially greater form drag. At most speeds a moth operates at more than enough lift is created from the hydrofoil. The only time that you might want more lift would be below 8kts, and I imagine your wings would be making a negligible contribution to lift at those speeds. The other issue I see with those wings is that, unlike the hydrofoil, your wings are unable to “dump” lift (and drag) when required at high speed.

    Again, I love your work, very polished design.


    • david valham says:

      Tanks for the nice words JG.

      I think the points you have make sense. It will be calculation of pros an cons considering things as drag, groundeffect, roll-stability, dihedral angle (greater balance) and so on. The lift from the wings might allow the foils to be smaller and reduce friction in the water on one hand, but on the other hand increase the aerodynamic drag. During my brief research I discovered a lot of other benefits with the wings as better balance in the boat, and a force that might help the pilot in acting as a counterweight for the sail.

      About your last thought of dumping lift…You are absolutely right, but… would it not be cool if you could jump and fly a bit like a kitesurfer/windsurfer with the boat… I´d love that…


  • observer says:

    wing shape with lift would probably violate class sail area rules.

    • david valham says:

      Hmmm, maybe your right, but it´s worth a try don´t you think?

  • Doug Lord says:

    Outstanding design, David! If you get a chance check out “Moth on Foils” the most widely read Moth thread anywhere and check out the comments on your design.

    Very impressive, Doug Lord

    • david valham says:

      Tank´s Doug.

      Interesting reading the comments on my design. I love that you took my side in one of the comments, cheers!

      I find all the points they are making true and very real but in between the lines I read that they think that I haven’t thought about them in my work…

      That might be one of the big differences between designers and engineers, the later need to learn how to dream more. How to let a vision take form is not about all the limitations and don´ts, on the contrary, you need to embrace all the ideas and let them flourish. Not that I need to tell you that, but maybe some of the guys in the thread need to be reminded…

      And by the way, turtleneck no, expensive glasses OH YES… BLACK ONES.

      Have a good one Doug.


  • Malcolm says:


    I got it all wrong getting so excited about the beast. Any chance you can email me ?

  • Aloha David-san, “Very-Good” indeed Postively Go-Forward: Imua Ka Kou/ Ganbare Nei. Continue-On with your On-Fire Dreams and “given” Visions. You Da Man! Please try “talk-story with Bora Gulari , He Da Man to be your Test-Pilot-OK. GOD-Speed. Your’s for Joyfull Sailing/Foiling Expeiences. mahalo -n- aloha iruka-san.

  • mad sailor says:

    Really gorgeous job, I’m using it on my 3d design class as an example of great professional work, including innovative concepts, a lot of research and a perfect design process, from sketches to 3d printed model.
    As a sail-boat addict and a windsurfer without any tecnical knowledge, I think your horizontal wings will generate a lot of drag, so it will need much more power to work than a conventional moth. May be using larger an thinner wings, with a little lift-angle, like a glider or a bird fying close to water, I don’t know…

    • David Valham says:

      Thanks for all the inspiriting words. Interesting thoughts about how to reduce drag.

      It makes me glad that you feel that my work is good enough to use as an example in school.


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