Hydrofoils for action sports generally consist of a front wing, rear wing, fuselage, mast, and board connection. The front wing, board connection, fuselage, and mast get a lot of attention as ways to change the accessibility or performance of the foil. Most often the rear wing is viewed as a package deal with the front wing. While the standard rear wing does most often suit the front wing, changing the rear wing can also have some beneficial effects on your experience. In this blog we will examine some beneficial effects a different rear wing can have and discuss some specific examples where we have found success in doing so.
Stability / maneuverability
One common reason to change a rear wing is to either gain stability or enhance the maneuverability of the foil. Generally speaking, the larger the rear wing wingspan, the more roll stability you will gain. The longer the chord dimension (leading edge to trailing edge), the more pitch stability you will gain. Conversely, smaller wingspans and narrower chords will make for a faster reaction in their roll and pitch directions.
For example, the Liquid Force Happy foil requires a bit more speed to gain stability than I typically like, especially in the pitch direction. This is largely due to its anemic rear wing that forces a heavy back foot until top speeds are reached. Rather than wear out your back foot or riding faster than is always necessary, adding a Liquid Force Rocket rear wing with double the chord length balances out the foil and makes it tons of fun at moderate speeds. The Rocket is slightly wider in its wingspan so it does gain a little extra roll stability, but since you can ride more comfortably at lower speeds with a balanced stance, the foil feels more free and playful.
A rear wing with anhedral (downward) or dihedral (upward) curve can also have a similar result. Anhedral curved rear wings will add roll stability. Too much anhedral curve, especially when paired with an anhedral front wing, can lead to decreased yaw: a "tracky" feeling or stiff-turning foil at higher speeds, similar to a quad fin setup on a surfboard. Anhedral rear wings are also beneficial in directing water flow during pumping, making them common in surf and SUP applications where low speed performance is prized.
GoFoil Kai and Iwa hydrofoil rear wings
The most dominant examples and long-standing anhedral surf wings have to be Gofoil surf foils. Their Kai and Iwa rear wings have a long history of surf stability and pump performance, largely due to their anhedral curve which is suited perfectly for their front wing design. Although the Iwa rear wing bears the same name as the Iwa front wing, it is most commonly used as the rear wing for the Maliko series wings for maximum lift and low speed stability. The smaller Kai rear wing is most commonly paired with the Nalu, Kai, and Iwa front wings for surf since it provides a more neutral stance as well as added pitch and roll response.
Dihedral rear wings are less common since they can feel tippy due to their reduced roll stability and because they decrease the effective lift without adding additional top speed. It is more common to see dihedral curves used in conjunction with an anhedral curve. By placing the anhedral curve in the middle and the dihedral curve on the outside, designers can harmonize the effects of each design. This hybrid design can be found in the most popular rear wing design in foiling thus far, the Slingshot 42.
Slingshot 42cm rear wing
You'll find this versatile wing featured in the Slingshot Hover Glide, Fkite, Fwake, Fsurf, and Fwind. The 42 offers something a little more spicy than a totally flat wing with just enough hybrid curve to add some yaw stability to their flatter wings and keep those wingtips bent away from the seafloor.
Winglets on a rear wing can also play a large part in the rider's foil experience. The addition of a rear wing with more winglet surface will increase yaw (twist) stability without effect on its pitch or roll. This can be good for having a "locked in" feeling at higher speeds or in powerful turns but may seem too "tracky" for loose riding styles. You will find these most commonly in beginner/intermediate kite foils where moderate speed rider confidence is the chief concern. The most exaggerated example of this can be found on the Duotone Speedster.
Duotone Speedster and GT hydrofoil wingsets
The Speedster features large winglets on both of its wings, which act like quad fins on a surfboard. At moderate speeds it gives a locked-in, confident feeling that beginners will appreciate. However, as speeds progress it gets to be a little tracky for my taste. To remedy that, I enjoy pairing it with Duotone's GT rear wing. The GT rear wing is just a touch smaller, sleeker and lacks the winglets. With the front wing already having large winglets, the GT rear will "break its chains" so to speak, allowing for squiggly lines and more control at high speeds.
Lift and stance balance
Every hydrofoil fanatic is familiar with the sensation of lift that comes from your foil. Most have experienced both extremes of too much or too little lift. These extremes are a reality, but sometimes the same sensation is simply due to poor equipment setup. For instance, if you have your foil set too far forward in relation to your foot stance, even riding at a slow speed can feel like too much lift due to the amount of weight required on your front foot to balance the foil. Similarly, putting your foil too far tailward can give the sensation that you do not have enough lift to ride because of the amount of back foot pressure needed.
Some boards are limited in this adjustment or may be set up for a certain type of foil and may require equipment change to adapt to every condition. If you are truly overwinged on a foil, it will become difficult to control the acceleration and heavy front foot pressure and become very tracky. If you are truly underwinged, you will have to pump to stay aloft and heavy rear foot pressure will not allow a glide, but rather, slow you down.
If you find that your board and foil setup are not underwinged but you still feel uncomfortable with your stance balance, you can consider using a different rear wing to help. Most commonly this is applied to wings that feel too "lifty", meaning you need to apply a lot of front foot pressure to balance it. This is a common issue for riders of the increasingly popular Moses Onda 91 with 633/483 wingset.
Moses 483, 330, 325mm rear wings
This foil's balance is quite a bit forward when compared to other foils. Since it has such a vast speed range, it is increasingly problematic when it accelerates well beyond comparable foils, producing additional lift. Even at 200 lbs, I find my back foot as much as 10" in front of the mast when riding near the top of its range. If you can mount it near the tail, you will probably be quite happy as long as you are free to move your feet about the board. If your board does not allow that, or you lock your feet down with straps, you may consider a smaller Moses 330 or 325 rear wing. Either will help tame that "lifty" feeling and balance your stance in speedier circumstances so you can take full advantage of its incredible range.
Minor effects - speed and lift
In addition to the more major benefits are some ancillary effects, mainly in the form of small changes in speed and lift. Larger rear wings will provide some additional lift, or at least the feeling of some extra lift depending on the model. However, the larger the rear wing, the more drag it will introduce and reduce the top end speed of the hydrofoil. On the other side, a smaller rear wing will reduce the lift and increase the top end speed slightly by reducing the drag it has. Don't expect a major speed range shift like you might find by changing the front wing by 30%. Rear wing change effects will be slight as the front wing does most of the heavy lifting in terms of drag and lift. The rear wing simply tweaks the maneuverability and center of balance.
Rear wing angle
The angle of attack the rear wing is set at has a massive effect on its performance. For most foils, the manufacturer has already figured that out for you. However, in some instances, shimming the rear wing can have some benefits if done correctly. If you want a little less "lifty" feeling foil, try to flatten the angle of attack. If you want a touch more "lifty" feeling, add more angle. You will want to do this bit by bit while you are at the beach to find the ideal setup. Most rear wings are set at 1.5-3 deg angles, so any change of a half degree is a lot.
Naish adjustable rear wing pitch
Some foils offer an adjustable rear wing (Naish) or come with washers for that purpose (Neil Pryde). If yours does not, thin washers or gaskets work best, but not all systems allow for it. Remember to use a washer or shim that supports the wing or you could end up with a squirrelly rear wing that feels out of control.
New gear is seeming to reveal itself daily. We do our best to ride and find solutions for any issues they present. Help us out... If you have found some success with frankensteining wing combinations, we'd love to hear about it. Having issues with a certain foil's performance? Give us a call or email; we may have a solution to help out.
Written and produced by Tucker Vantol, Ryan (Rygo) Goloversic
Mackite's resident surf and "Hydrofoil junkie." You can either catch him on the phones or on the water at dawn testing new gear. He is proficient at myriad sports, a shaper, and passionate about getting his water time. When he discovered kiteboarding it took over as his predominate sport. The same could be said about hydrofoiling.