Foiling

Discussion in 'Sunfish Talk' started by Blue Heron, Aug 30, 2013.

  1. Blue Heron

    Blue Heron Member

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    On an earlier thread, there was some discussion about building a foiling Sunfish that would be similar to a Moth. I thing it's a great idea, but I have a question: How big a foil would be required to lift a Sunfish (130lbs) and it's occupant (figure 200lbs... so 330lbs total) at speeds that a Sunfish could normally reach (maybe 8 knots?) ? Once on foil you'd go faster, but wouldn't you have to first GET up onto the foils? I'm just asking.....
     
  2. sailcraftri

    sailcraftri Well-Known Member

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    You would be surprised how little foil area is required. Just look at the size of the foils for the 72 ft Americas Cup catamarans. Sure they are big, but not compared to what they are lifting. Airplane wings are bigger due to the medium they work in, air. Boat foils work in the water which is denser than air. It also depends on which airfoil shape you use.
     
  3. minifish2

    minifish2 Active Member

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    Check out this video on YouTube. This is what gave me the idea for that earlier thread. This Laser and sailor are atleast as has heavy as a Sunfish.



    On other videos by these folks we saw that the blade wings extended almost the width of the boat, but that also seems to have aided stability. The board is inserted in the trunk from below while tipping the boat on its side in shallow water, and extended down as the boat is sailed out to appropriate depth.

    http://www.sailmix.com/wp-content/uploads/2013/08/1097815_10151826975919636_1443782359_o.jpg

    From the waves (and absence of white caps) as well as the other sailboats (no reefing, and notice that 29er type boat), we can see that this isn't crazy conditions. In this video, also note that they are sometimes using a smaller area Radial sail than the fill rig Laser.

    One of my follow-up thoughts on this is, if we want to start off simpler, use a 75 lb Minifish hull for a prototype, and experiment with sail sizes (minifish 2, full Sunfish, windsurf etc), whatever works. Better yet, go with a 'proven' high performance Minifish rig like the one discussed on this board a couple of times in the past:

    http://earwigoagin.blogspot.com/2010/10/another-classic-moth-frankenboat-fish.html

    As we can see, this minifish with enhanced rig was being raced as a non-foiling moth.

    Once we get the blades figured out - which with the collective brainpower and do-it-yourself expertise on this board seems at least possible - we can maybe all start converting and foiling at home.

    This could add some excitement to Sunfish ownership. Look at it this way - if we could develop cheap accessible foils, your not-waterlogged Sunfish might get a little bump in respect (and maybe resale) in the sailing world.
     
  4. Blue Heron

    Blue Heron Member

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    That's an intersting video. thanks for posting it. do you have a guestimate of how fast he's going?

    Yes I agree that the conditions aren't extreme, maybe 8-10 knt winds or so. I noticed in the vid that the boat has a moth-style trim control arm next to the daggerboard. Do you have (or know of) a picture of the linkage? Does it control the pitch of the main foil, or the rudder trim tab? In my mind, building it is not the problem. The trick is to design it and figure out how to control the pitch fore and aft...... once that's done, building it would be quite straightforward.

    You can learn a lot from the underside pic. I notice that the rudder trim-tab is ~10-15% of the main foil's area... maybe a little less, which is in keeping with aircraft design. I'd guess that this would vary depending on where the CG is located relative to the main foil. I also noticed that the foil is straight with no dihedral, which would make it easier to construct.

    I like where you are going here. I've pondered the idea of a moth'd -out Sunfish before..... maybe it's time to actually build one.
     
  5. minifish2

    minifish2 Active Member

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    There are a few possibilities - and probbly ome combinations of these - for adjusting pitch. On a moth and presumably minifish or sunfish, this also can even include seating position - sit way aft to angle up, way forward to level. Maybe and/or a mechanical wand-controlled arrangement like that Laser version. Plus perhaps some other approaches.

    Given that the Sunfish trunk width is uniform vs the Laser, for example, we can get it even simpler, with a narrow verticle foil section that pivots fore and aft within a fixed trunk sleeve, with the control arm end of the strut sticking straight out of the top of the trunk. As we could see from the Laser foil pictures, that wouldn't work in a Laser's tapered trunk, but maybe something simple like that could make thismuch more 'do it yourself' for sunfish.

    Sailing groups in general seem disproportionately blessed with engineering talent, and Sunfish fleets often have the added advantage of also attracting resourceful, frugal folks, so maybe we can collectively figure this out.
     
  6. danpal

    danpal Active Member

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    Maybe we could get NH1-PAD involved since he was successful in his Sunfishamaran development...
     
  7. Blue Heron

    Blue Heron Member

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    OK... I spent some time reading the technical papers about foiling Moths that are published on the Internet. If you Google "International Moth Foil Design", several come up.

    The technology is not very complicated, and should be rather easy to duplicate for our Sunfish. The difficult design work has already been done, and is published. Most of the theoretical studies use an all-up weight of 240 lbs.... while ours would be approx 310 lbs. That's about a 30% difference, which means to be effective we'd have to scale our foil surface areas up by 30%. That gives you a main foil of approx 40"x 6" to duplicate the lifting capability of the first generation (straight wing ) boats. It's not rocket surgery.

    The control mechanism is not overly complicated, either. Anyone who has ever built a radio controlled airplane should be able to grasp the mechanics of it. While the materials / structural requirements are much greater due to the much heavier loads, the concepts are very similar. The main control element is just a flap on the primary foil, controlled by a wand via a mechanical linkage.

    now... I'm not an AutoCAD user, so all of my work is done via pencil and paper. Over the next few days I'll work out the basic scale- up and post some prelim designs. The more I study this, the more do-able it seems.

    Dave
     
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  8. meech

    meech Member

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  9. minifish2

    minifish2 Active Member

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    That's the same Laser that is filmed in that youtube video link above, so we know those particular foils work. So that's something.

    As I understand it, that Laser supposedly uses stock Laser rudder brackets, which suggests that the foiling ridder does not have to bear a heavy load. As with the Laser, we could substitute the longer foiled blade for the angled stock Sunfish blade, use stronger non-pop-up cheeks, etc.
     
  10. Blue Heron

    Blue Heron Member

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    Hello fellow foilers. I wanted to let everyone know that I haven't forgotten about this project. My short absence is due to the weather having turned beautiful here: I've been out sailing! BUT....I've also been working on the foiling idea.

    Minifish's comment about the rudder bracket is a valid one. Pondering the loading, I guestimated that the bracket will have to hold about 1/3rd of the weight of the entire vessel and occupant. This means it needs to be able to withstand a static load of ~120lbs or so, PLUS any dynamic loads / safety factor. At the moment, I don't know what is. With a 2:1 safety factor, that would be 240lbs..... with a 1.5 factor (like an aircraft would use) it would be 180 lbs. Since I don't have an old Sunfish to do a possibly destructive test on, I haven't loaded a bracket to see if it would take the load. My guess is that it will.... but it needs to be tested.

    The other load is at the DB Trunk. The load there with a 1.5 safety factor is ~360lbs. I serious doubt if the trunk itself will take the load...... BUT a distributed load around the rolled lip of a later boat will easily handle it. I'm thinking a semi-rigid X running across the deck, centered over the modified DB and clamped to the gunwale lip.

    Between the X brace and the rudder bracket lies the cockpit, which should be able to handle the full load.

    On the foil: what to make it out of? IF this is a prototype, then I'd vote for laminated Rock Maple. Yes... wood.... for two reasons: It's easy to work for folks without the skills / tools required for carbon fiber.... AND it has a proven track record in making aircraft / airboat propellers which are much more heavily loaded than our foil will be.

    I'll post more in a few days.

    Dave
     
  11. Light and Variable Winds

    Light and Variable Winds Well-Known Member

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    This looks like a lot of fun—geesh—and I was going to start a new thread on engineering two canted daggerboard trunks! :cool:
     
  12. Blue Heron

    Blue Heron Member

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    Ok..... I've finished my calcs for a foiling Sunfish based on a direct scale up from a moth. the numbers are below. Sorry about the format. It's an import from excel, and it looks kind of funky. For each dimension there are two numbers. The first one is the orignal Moth dimension, the second number is what the scaled up version would require for similar performance. The one dimension that stands out is the amount of mainsail required..... BUT since we aren't trying to replicate the actual moth performance, we should be able to get by with our smaller mainsail.

    Mothcalcs Moth Sunfish
    boat mass W helm 264 lbs 310.00 lbs
    1.174242 factor
    DB length 39 in 45.80- not a critical dimension
    DB chord 4.68 in 5.50
    DB thickness 0.312 in 0.37
    Rudder length 35.1 in 41.22- not a critical dimension
    rudder chord 4.68 in 5.50
    rudder thickness 0.312 in 0.37
    DB Foil length 0.39 in 0.46
    DB Foil root chord 4.68 in 5.50
    DB foil tip chord 2.73 in 3.21
    DB foil thickness 0.312 in 0.37
    Set 2 degrees 2.00 degrees
    Rudder Foil length 31.2 in 36.64
    RF root chord 4.68 in 5.50
    RF tip chord 2.73 in 3.21
    RF foil thickness 0.312 in 0.37
    Sail Area 84.5 squ ft 99.22 squ ft
    (required for equal performqnce)

    So this is what I'll be drawing up...... more to follow

    by the way: canting keels can be VERY fast. they would be worth investigating. It looks to me like there is a growing amount of support for development class Sunfish. Maybe one day we'll hold an Unlimited class regatta!
     
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  13. Modul8

    Modul8 New Member

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    I'm interested in this project, and I'd like to try my hand at 3D modelling the foiling system for the sunfish. I don't own one (yet) but I'm interested in making sailing more fun for the masses, and thereby making sailing more popular and accessible . If you want your napkin sketches turned into 2d or 3d, PM me.
     
  14. Modul8

    Modul8 New Member

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    sunfish rudder foil- naca0008.JPG
    rudder foil per above specs. 2 deg lift NACA 0008 foil for high speed, 5.5 chord continuous for vertical, same foil for horizontal, 3.21 chord at tip. 2 pounds of maple (assumed solid) perhaps a little heavier if reinforced at the root of the horizontal (recommended) Now for the daggerboard. :) o
     
    Last edited: Nov 27, 2013
  15. Modul8

    Modul8 New Member

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    sunfish and foils
     

    Attached Files:

  16. Wavedancer

    Wavedancer Upside down? Staff Member

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    Looking forward to seeing the fish fly!
     
  17. Modul8

    Modul8 New Member

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    I'm trying to figure out some sort of tiller-based controls for the pitch of the rudder, so the sailor can change the angle of attack plus or minus from the standard 2 degrees specified. Not sure how this would affect stability or ride height but it should help to trim the attitude of the boat while in flight. or not. I'm no marine engineer. I don't even own a sunfish. I'm just a CAD monkey.
     
  18. california_dude

    california_dude New Member

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    Well, are you guys going to build it or not? If you wait long enough I will beat you to it and post photos of one I will make out of aluminum or titanium. It will be definitely not made of wood.
     
  19. Blue Heron II

    Blue Heron II New Member

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    Hello California Dude, Modul8 and others..... after spending a considerable amount of time on this one, my conclusion about a foiling Sunfish is this: while theoretically possible, it's not worth the effort. The real problem lies not with the hull form, but rather with the low aspect lateen sail .... which does not appear to generate sufficient forward thrust in relation to its heeling forces. To counter this heeling moment, you would have to add hiking gear or wings.... and even then, the power may not be sufficient. So... to cut to the chase, I've dropped that line of experimentation in favor of other pursuits.
     
    Last edited by a moderator: Aug 5, 2014
  20. beldar boathead

    beldar boathead Well-Known Member

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    I am not surprised that you came to this conclusion. One question - how likely do you think it would be you could get a Sunfish up on the foils on a beam reach? On a windy day there is a lot of power on a reach, without any more heeling moment than a Laser, and certainly less than a laser going upwind in a breeze.
     

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