Home grown Laser Hydrofoils

Discussion in 'Sailboats' started by Kevin Charles Rissell, Aug 1, 2019.

  1. Kevin Charles Rissell
    Joined: Aug 2019
    Posts: 21
    Likes: 7, Points: 3
    Location: Oakland, MD, USA

    Kevin Charles Rissell Junior Member

    It sails fine when not foiling, though not quite the same as a standard Laser. The foils having much less cord makes the sideslip more noticeable in low wind/low speed conditions noticeable.

    Tacking requires more ‘authority’. In other words you have to tack hard and quick to have enough momentum to avoid getting in irons at the end of the tack. It seems counter intuitive, but because of the increase in sideslip, a smooth arcing tack loses more momentum throughout the tack than shoving it over hard.

    For ver. 2.0 I intend to increase the cord of the rudder by 2 inches, and the cord of the daggerboard by 4 inches, roughly.

    Finally, there’s very little ‘underside anchor’ effect, and once you’re up to speed, most points of sail seem just as fast as a standard Laser. Sideslip affects the acceleration though, so getting up to speed takes longer, and beats and very close reaches are definitely a struggle to keep your speed up on. Definitely slower on those points of sail.

    Honestly, I was pleasantly surprised at the lack of ‘underside anchor’ effect. I really expected it to be a very large obstacle to successful foiling.
     
  2. J Smythe
    Joined: Jul 2019
    Posts: 20
    Likes: 3, Points: 3
    Location: USA

    J Smythe Junior Member

    That's great. Imagine taking that baby for a ride not knowing some madman had put foils on it, and the shock on your face when you start to "magically" float for some reason.....before eating it in the drink due to not realizing what was happening.
     
  3. Kevin Charles Rissell
    Joined: Aug 2019
    Posts: 21
    Likes: 7, Points: 3
    Location: Oakland, MD, USA

    Kevin Charles Rissell Junior Member

    I can imagine, and in fact have done almost exactly that.

    The first time it started to fly, I was frozen with surprise, excitement, and considerable anxiety about not knowing what exactly I should be doing, if anything, now that the foils were actually doing what they were made to do.

    Being frozen in place meant I didn’t shift my weight. Consequently, the increasing take-off angle of attack, due to the frozen, aft-weighting and completely overwhelmed designer, overcame any input from the wand to reduce lift, the main foil broke the surface of the water and immediately losing all lift resulting in the Laser landing back on the water hard and with a pronounced bow-down attitude.

    In other words, it porpoised badly and crashed down hard, taking about 3 inches of water over the deck....

    I was amazed that I wasn’t flung off, and how easy it was, under the right circumstances, to completely fill the foot-well in one swift motion....

    Still, you couldn’t have wiped the smile off my face with an angle grinder.
     
  4. J Smythe
    Joined: Jul 2019
    Posts: 20
    Likes: 3, Points: 3
    Location: USA

    J Smythe Junior Member

    You've got to figure out a way to be able to have it in the water for friends that don't know about it, and then take them for a ride and see what happens when you start flying.
     
  5. Kevin Charles Rissell
    Joined: Aug 2019
    Posts: 21
    Likes: 7, Points: 3
    Location: Oakland, MD, USA

    Kevin Charles Rissell Junior Member

    That would be interesting, though the white gap seals on the foils are kinda hard to hide even in murky lake water.
     
  6. Xtractif
    Joined: Oct 2019
    Posts: 10
    Likes: 0, Points: 1
    Location: Uk

    Xtractif Junior Member

    the Glide free rudder has a thumb screw at the top, do you need to change the rudder wing very much once the foils are trimmed, think the moth has twist grip adjustment but is it necessary on a laser?
     
  7. Kevin Charles Rissell
    Joined: Aug 2019
    Posts: 21
    Likes: 7, Points: 3
    Location: Oakland, MD, USA

    Kevin Charles Rissell Junior Member

    I found that once I got the adjustment right on the rudder that it was easier to shift my weight forward to control the ride.

    I also found that even small adjustments to the rudder made a big difference in take-off. Too much lift with the rudder kept the nose glued to the water.

    The new set I am making now for next summer is going to have a significant reduction in surface area for the rudder foil, and a slightly larger increase in area for the main foil, as well as a little more span. I’m also printing the plugs for the foils to enhance the quality of the molds I pull from them.
     
  8. Xtractif
    Joined: Oct 2019
    Posts: 10
    Likes: 0, Points: 1
    Location: Uk

    Xtractif Junior Member

    I don’t have any experience but have been looking at laser foil designs
    What cord sizes are you using?
    It seem that the board foils have developed better foils and if you are moulding foils you could improve the stability with diheadral or anheadral and sweeped back wings
    Have you seen the foilsz kit for laser?
    3D Renderings https://www.foilsz.com/index.php/foilsz/3d-renderings

    BR Foil Front Horizont https://www.kasail.com/bladerider/view/570

    M2 Rear Anhedral Foil - Medium https://www.kasail.com/bladerider/view/664
     
    Last edited: Oct 13, 2019
  9. Kevin Charles Rissell
    Joined: Aug 2019
    Posts: 21
    Likes: 7, Points: 3
    Location: Oakland, MD, USA

    Kevin Charles Rissell Junior Member

    I have in fact reviewed these foils, and as an amateur I doubt I can do better, though speaking as someone who’s funds are limited and as someone with a passion for building things on my own, I still prefer to make my own instead of buying someone else’s.

    Please take note that the kits, Foilsz and Glide Free, and the Waszp all appear to use the same foils.

    The balance with the flat horizontal foils wasn’t bad at all. After the first couple of days, I foiled the rest of the summer without rolling the boat over or getting thrown off.

    The foils I’m making over the winter have a slight curving anhedral with winglet-like curved up tip. The overall shape is a modified elliptical wing with a gradual sweep back.

    The foils in the pictures have a cord of about 6.5 inches sweeping back slightly to 5.5 inches at the tip. The verticals were 5 inches in cord. I plane on increasing the vertical foils to 8 inches. The side slip was very noticeable until the boat was up to speed and even then far more than with a standard Laser board.

    The rudder worked fine with the thinner cord, except when trying to turn the boat with little speed. I might keep the rudder vertical cord down to 6 inches to reduce wetted area.
     
  10. Xtractif
    Joined: Oct 2019
    Posts: 10
    Likes: 0, Points: 1
    Location: Uk

    Xtractif Junior Member

    I was looking at using wind knife masts 270mm extrusion
    www.windknife.com http://www.windknife.com/

    It seems you need about 3000 cm2 front foil, like the Mach 2 foil

    The gong foil xxl is 2500 cm2

    GONG FOIL ALLVATOR SURF/SUP FRONT WING XXL/100 CM - GONG Galaxy https://www.gong-galaxy.com/en/product/gong-foil-allvator-surf-sup-front-wing-xxl-100-cm-2/

    good to make your own foils but development takes time and money

    Can see the development coming together to to reduce cost dramatically

    good luck with your project and a great experience which looks real fun

    The Foiling Dinghy. Foiling for everyone. Learn more about hydrofoiling. http://foilingdinghy.com/

    mike
     
  11. Kevin Charles Rissell
    Joined: Aug 2019
    Posts: 21
    Likes: 7, Points: 3
    Location: Oakland, MD, USA

    Kevin Charles Rissell Junior Member


    Thanks. Good luck in your endeavors.

    The foiling dinghy looks interesting but complicated with the rocking foil configuration, especially since T-foil dinghy sailing is proven and well developed.

    Developing them for the Laser was partly due to a long time dream/goal to actually try to make hydrofoils for a Laser, and partly due to the cost of production kits. While Foilsz are supposed to be somewhere between 3000-4300 Australian, the Glide Free foils were 5800 Australian when they came out. I spent somewhere around 1500 US dollars to make mine out of Carbon Fiber, whereas theirs are Aluminum.

    My goal with my next set is to need only 9-10 knots to foil, and to be able to foil upwind.
     
  12. Xtractif
    Joined: Oct 2019
    Posts: 10
    Likes: 0, Points: 1
    Location: Uk

    Xtractif Junior Member

    Have you seen this study?
     

    Attached Files:

  13. Kevin Charles Rissell
    Joined: Aug 2019
    Posts: 21
    Likes: 7, Points: 3
    Location: Oakland, MD, USA

    Kevin Charles Rissell Junior Member

    Thank you. I had not read this study. Very interesting reading. A lot of my study mimics theirs, although I stopped short of the in depth mathematical analysis involved in this study. I'm correcting for my lack of in depth analysis for version 2.0 of my foils.

    Interestingly enough, they didn't explore the use of Sikaflex for the hinge, and they hinged the flap at the top of the flap, allowing for a turbulent flow to be created on the bottom of the airfoil surface.

    I fly gliders, and any turbulence created by airilon gaps is 'Bad'. Turbulence = drag. Top or bottom, drag is bad. Consequently, I created the hinge at the bottom of the foil out of Sikaflex (A caulking tube product that cures to produce a flexible rubber hinge. However, Sikaflex is hard enough that the width and depth of the hinge must be limited, so the hinge was approx 3mm thick and separated the flap from the foil by approx 5mm. This left a considerable gap at the top of the foil. Gap=Drag=Bad!

    So, I took a lesson from flying gliders: Gap Seals. Check them out on www.wingsandwheels.com. Thin strips of curved mylar that are adhered to the main foil section with the trailing edge of the mylar strip riding on the top of the flap, eliminating the majority, if not all of the gap between the foil and the flap. It seemed to work well, as the Laser foiled in less wind than I anticipated, there was no obvious 'fluttering' that would be felt if the gap seals weren't maintaining their connection to the flap. Of course, it's only anecdotal evidence, but....
     
    BlueBell likes this.
  14. OzFred
    Joined: Nov 2015
    Posts: 477
    Likes: 47, Points: 28, Legacy Rep: 16
    Location: Earth

    OzFred Senior Member

    Bladeriders (brand of Moth) used Sikaflex for the main foil hinge, it was OK but really only lasted about 12 months and took a fair bit of skill to get right. The gap between foil and flap was less than 3mm. After about 2010 all Moths moved to some other material for the hinge, with maybe a bit of Sika to fill the (very small) top gap if there was one.

    Moths have worked very hard to optimise the hinge and minimise the gap (I think most are 2mm or less). You should check out some current versions, they're works of art (and very expensive).

    A bottom hinge has been tried on a Moth based on the theory that it's better to have a smooth bottom surface (I believe John Ilet tried it around 2009 or 2010), but in practice it was way inferior to having the hinge on the top, at least for a hydrofoil.

    Foils are extremely sensitive to surface imperfections, they should be as fair as is humanly possible. A single piece of ribbon weed about 5 mm wide around the main foil will have a significant effect, two or three will prevent foiling. Weed on the vertical isn't as critical, but has an effect, particularly on the rudder.
     
    Doug Halsey likes this.

  15. Xtractif
    Joined: Oct 2019
    Posts: 10
    Likes: 0, Points: 1
    Location: Uk

    Xtractif Junior Member

    This may be a silly suggestion but wondered if you detach the flap and move it on a fuselage like the board foils as an elevator could it be smaller with more control and keep the main foil simple, it would be in turbulent flow but the board foils seem to work ok with a small stab foil although they do rely on body weigh to balance them
     
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.