4 Meter mono foiler project

Discussion in 'Sailboats' started by wind_apparent, Apr 27, 2008.

  1. wind_apparent
    Joined: Apr 2008
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    Location: boulder colorado

    wind_apparent wind driven speed addict

    so, I've been working on a 4 meter monofoiler formula for Lazy Americans like myself who would love to buy into the Moth foiler hype:p but don't want to hike anymore (trapeze), might be to heavy to competitively sail a boat that has 8sm of sail, but still want to go fast and fly above the water, (and who want a formula with a minimum weight so that things don't get to stupid, always fixing stuff, and blowing out, so homebuilders who cant deal with prepreg and an autocalv can still get going). I'm not a foil maniac, I just love the idea, there has been a lot of talk at my local pond about such a concept, (we all would build moths if it wasn't "so" little, and if we'd hiked on any boat since lasers in high school) its not "the peoples foiler" because your still going to have to work hard to sail it and stay out of the drink, and its going to be made out of carbon fiber, so it won't be cheap, but it will make foiling more accessible to normal sized people, not "average Joe" but average sized. Anyway, I've had a couple of threads about the rig for this warlock, but that question is now moot....anyway heres the formula as it stands so far, still working on the rig, so if anyone has any input about that or anything else, fire away. (please don't hijack this thread, if you don't like foilers, or doug lord (because you know he's going to bring it), just don't say anything,) please......

    SR-71 4meter Foiler Formula

    Single handed
    LOA: 4meter (+65cm gantry) (+ telescoping bow sprit if applicable)
    BAW: 38cm min (Beam at waterline)
    BAG: 75cm min (Beam At gunnel)
    BAR: 2.4m max (Beam at rack)
    SA: 10.75sm main (one sail only, plus a reaching spin if it proved to be worth it)
    Max Mast Length::?: 7m (looks like I'm going to try a Swift solo mast (6.935m) w/ a 2.7m boom)
    Trapeze: Yes
    *no multihull or windsurfers*
    *no kites*
    *Open Foil Plan* (must be centerline mounted)
    Min Weight: :?: (have to see what the proto comes in at and go from there)

    well there it is, have ater...........

    (this formula will change over time as the ideas get thrown around)
    Last edited: May 1, 2008
    1 person likes this.
  2. bistros

    bistros Previous Member

    Sounds interesting. Interesting that someone from Colorado is spec'ing metric!

    As far as mast length goes, to maintain the possibility of foiling gybes and tacks from a trap, you are going to have to maintain a seriously open route from one side to the other - probably running across like a skiff, so keeping enough room under the boom is critical. There isn't time for Contender/Finn-like dives under a low boom. This will help define the mast length.

    Are you considering a main+jib or a cat rigged main only? A jib wil help provide better initial rig balance, and get sail area lower with end plate effect. A self tacking jib that uses a SwiftSolo-like single sheeting system may be in order. I'd take a hard look at the SwiftSolo rig plan and the rigging developed over the past five years - it's now well refined and tested. Bill Hansen's sail developments which incorporate a lot of high speed windsurfer technology now applied to dinghies is worth a look as well.

    I'm having Ethan Bixby of North make a sail for a high performance single handed skiff I've been working on - similar overall dimensions, but not intended for foiling - more of an I-14 for one. I'm using a Proctor D tube cut down slightly, and a carbon boom on a loose footed full batten chop top main. I chose the Proctor D for low cost, and the wealth of knowledge tuning sails for that tube. Big asymmetrical spinnaker - sail plan somewhat like a Musto Performance Skiff, but much lighter overall - the completed hull weighed 75 pounds before paint. Constructed from cedar strips and okume plywood in a stringer and frame design.

    I live in a low wind venue, and we just don't get enough wind on a regular basis to build a boat around foiling.

    Keep us posted.
  3. Doug Lord

    Doug Lord Guest


    Build an RS600FF with a 10/1 L/B ratio (or skinnier) hull. Consider buoyancy pods even if they are removable after you get used to it. Even the Bladerider
    has buoyancy bags under the wings. Tis a great thing you're doing-I wish you the best!

    -Consider removable foil tips for light/heavy air
    -definitely go with retractable foils(like the RS foiler).
    - be sure to set up your main foil so that the angle of incidence can be varied on the water(like John Iletts "F Box").
    -You MIGHT even consider getting a used RS and sail it for a while -then build the new one.

    Attached Files:

  4. joz
    Joined: Jul 2002
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    Location: Melbourne, Australia

    joz Senior Member


    why don't you use the Int 3 metre Tri or even the 5 metre version to which would be more suitable for your needs.
  5. wind_apparent
    Joined: Apr 2008
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    Location: boulder colorado

    wind_apparent wind driven speed addict

    Funny, I've spent the last couple of days researching the "swift" mast and boom, I figure if I used them I could just put the boom lower on the mast in a musto type fashion, thereby gaining the extra .53sm I need to fit my fourmula, since the bend and spreaders and trap are already worked out it would be easy to get the sail made and the whole thing up and running without much tooling cost and R&d time, could even get together with the swift guys for higher bulk discounts if this formula was to catch on.

    thanks for the response, "like minds think thier great" I mean "great minds think alike":p
  6. wind_apparent
    Joined: Apr 2008
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    Location: boulder colorado

    wind_apparent wind driven speed addict

    I have already designed "wing end training wheels" so I can have a trimaran to train on at first. they will just Ubolt to the rack and come off just as easy.they are like little surf boards. I have also designed regular foils so that I can get used to the boat before I put foils on it (not fast ones, just so the boat will sail).....Retractable hydros are in the works, (beach foiler).

    as far as the RS600ff, not a fan of that boat , but that is where this idea originated, I wouldn't want to buy one, and where would the fun be in that ?
    half the fun is building and designing, I want to do something no one has done. I know you can understand that

    I don't know about the f-box, where do i go for info?

    thanks doug.
  7. wind_apparent
    Joined: Apr 2008
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    Location: boulder colorado

    wind_apparent wind driven speed addict

    tri's are an old idea, and to stable, i want to do something crazy;) mono foilers are what I'm into.........there are plenty of boats that are for everyone, the world dosen't need another laser clone. skiffs, fast cats, monofoilers, formula windsurfers, thats where its at for me.
  8. Doug Lord

    Doug Lord Guest

    WA, there is mention of the F box in an article on The Daily Sail* about Simon Paynes new Fastacraft Prowler "Zero". Go to "foilers" on that site.....The idea is to be able to change angle of incidence of the main foil by angling the vertical fin forwards or backwards-and to do it while out on the water. The advantage is to keep the foil operating at its lowest drag: Higher angle of incidence=bottom of vertical fin forward=light air, Lower angle of incidence=bottom of vertical fin aft=stronger wind.
    *I may have posted a link to it in an earlier post in this thread.
  9. wind_apparent
    Joined: Apr 2008
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    Location: boulder colorado

    wind_apparent wind driven speed addict

    so I've decided that my mast step location is going to be at 125cm back from the bow.....still working out the foil trunk location, I was thinking about 191cm back from the bow, but now I'm thinking about farther forward for stability after seeing the new foiling 18 skiff....er....a..... i mean 18foot oil rig....I've got to figure it out soon because its almost time to start putting my mold frame together.....
  10. wind_apparent
    Joined: Apr 2008
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    Location: boulder colorado

    wind_apparent wind driven speed addict

    its a great idea, but I don't think I'm going to mess with it on this first proto type, got enough stuff to figure out and mess with......maybe on the next one....
  11. Doug Lord

    Doug Lord Guest

    I don't blame you for not wanting to mess with it but consider making a "trunk within a trunk" for your main foil. That way you can add this facility later.
    I'm not sure I posted the M4 for you yet or my aeroSKIFF(I'm building an almost identical but larger version now) so here goes. Note the "buoyancy pods:

    Attached Files:

  12. Doug Lord

    Doug Lord Guest


    I posted this on your Multihulls thread but thought it would be relevant(for reference) in this thread:
    Some info that might help-the W/SA ratio for the Monnard design is under Peoples Foiler II. You'll notice it is in exactly the same ballpark as are these boats:
    New18 info and M4 added

    SA: 88.8sq.ft
    Sailing Weight(includes crew): 220lb.
    main foil area: 1.19 sq. ft.
    Foil Loading(Lbs per sq. ft. at 80% max boat weight with crew):147.89
    **W/SA: 2.47lb. per sq.ft.(sail loading)
    ***SA per sq.ft. of main foil area(a SA/ws ratio shortened to cover planform area of main foil only): 74.62
    For ease of comparison foil areas for the next two boats were arrived at by using the same FOIL LOADING as a Moth.
    Only upwind SA is considered. Moth crew=154lb.RS crew=160lb.; 18 crew =3X160lb.
    SA: 131 sq. ft.
    Sailing Weight(includes crew): 327lb.
    Main foil area: 1.76 sq.ft.
    Foil Loading: 147.89 lb. per sq.ft.
    **W/SA: 2.49 lb. per sq.ft.
    ***SA per sq. ft. main foil area: 74.43
    SA: 107 sq.ft.
    Sailing Weight(includes crew): 259
    Mainfoil area: 1.4 sq.ft.
    Foil Loading: 147.89 lb.
    W/SA: 2.42 lb. per sq.ft.
    ***SA per sq.ft.main foil area: 76.42
    New Foiling 18
    SA: 354 sq.ft.
    Sailing Weight(includes crew): 858lb
    Mainfoil area: 4.64 sq.ft.
    Foil Loading: 147.89lb. per sq. ft.
    **W/SA: 2.41 lb. per sq.ft.
    ***SA per sq.ft. main foil area: 75.86
    *SCP/Total Weight(Bethwaite ratio)
    New boat=39%
    Old boat= 33%
    Note the different weights of the boats . Then note the Sa/per sq.ft. main foil area-this is a comparison of Sail area to wetted surface when the boat is flying using just the planform area of the main foil for comparison-THEY ARE NEARLY THE SAME FOR ALL THREE BOATS. Note the W/SA is almost identical for all three boats. This means that all three boats will foil at about the same time adjusted for differences in rig efficiency(Moth probably the best) and for hull L/B ratio as a measure of early takeoff potential(Moth by far the best). As I just said there are other factors and details that will marginally affect performance but this clearly shows how close all three boats are in their ability to fly despite the fact that the RS is 2.5 times heavier than a Moth and the 18 is 5.6 times as heavy as a Moth.
    What counts is power to weight ratio as a first look. A more detailed look showing a comparison of SA/ws ratios for all three boats reinforces the accuracy of the power to weight ratio.
    * For those that don't know Bethwaites ratio SCP/TOTAL WEIGHT is calculated as follows:
    1) SCP= Righting Moment divided by the distance between the CE and the CLR
    2) SCP is then divided by TOTAL WEIGHT(boat plus crew)
    3) originally designed to see if a skiff had the power to plane upwind which,according to Bethwaite, it would do with an answer(in %) over 30.
    4) Since the Moth is the baseline for all foiler comparisons comparing the Moth ratio with any other foiler is instructive.
    5) One of the beauties of SCP/TOTAL WEIGHT is that it comes up with the SAME NUMBER whether calculated in English or Metric units.
    ** W/SA= TOTAL WEIGHT(boat+crew)in pounds divided by SA in sq.ft. This is a comparison that is very relevant AS A FIRST LOOK at two different foilers. It has the drawback that it ASSUMES that the two boats have the RM to carry the sail they have. It basically describes the weight per sq.ft. of SA which is the sail loading(similar to wing loading). Compare to the Moth ratio.
    *** SA per sq.ft. of mainfoil area=The SA divided by the area of of one side of the mainfoil. It is a shortform of a SAIL AREA/WETTED SURFACE ratio which is most applicable to "airplane" foil configurations with the mainfoil carrying 80% of the load. Moth is the baseline.
  13. wind_apparent
    Joined: Apr 2008
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    Location: boulder colorado

    wind_apparent wind driven speed addict

    nice work doug......

    I even printed it off the other thread so that I could look at it while I was drawing, comes in handy.....how much sail area does the M4 have? what did you do to support the mast step? (not shrouds, structuraly)
  14. Doug Lord

    Doug Lord Guest

    Bi-Foiler World

    M4 SA is in the data above. Keep in mind that the foil area is an estimate based on giving these other boats the same FOIL LOADING as an early Moth.
    Still very interesting how close they all are.... The M4 has been inactive for a year or so. Last time I contacted him the designer, Simon Maguire said he was leaving on a round the world trip. His boat is particularly interesting because,as a singlehander ,it comes in between a Moth and an RS600FF.Here is the (neglected) M4 website:
    The JM 4.6 specs(Monnard):
    The RF600FF site:
    These boats are all exciting dvelopments in this incredible revolution and have inspired me and,I'm sure,many others! Hope this helps-these are hard sites to find......

    Attached Files:

  15. Doug Lord

    Doug Lord Guest


    Its not that hard to rig up. On my first boat I designed a worm drive arrangement where you turned a knob to angle the board-I didn't use it because I got in too much of a hurry. I NEEDED IT! Without it it is a real ***** to change the angle of incidence of the foil.Whether you make it so that it can be adjusted on the water or not it is CRITICAL that you have the ability to change the angle of incidence of the main foil! And preferably the rudder foil as well. The more(and easier) adjustments you have the easier it will be to set the boat up initially. The inside of the daggerboard case was bigger (f&A) than the board at the top of the trunk. Its easy to make a fixed system that you have to come into the beach to adjust OR you can take the extra time in building to make it adjustable on the water. On my new boat it will be adjustable on the water-too much hassle the other way-at least for initial set up. Keep in mind that approximately 80% of the all up sailing weight of the boat including crew will be on the pin or other means you use to vertically restrain the board.

    Attached Files:

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