Since towing requires extra equipment you should know how to use the pieces that are connected to you, the pilot, and be aware of the type of tow system that is being used.
Bridles
Tow bridles are rope or webbing that connect your two main carabiners to the tow-line and allow you to disconnect when necessary. There are many different types of bridles used to tow paragliders aloft, but the two most common are 1-piece and 2-piece. 1-piece bridles are attached together at the release mechanism end and when released from the line, do not fall to each side of your harness. This reduces the risk of tangling with your reserve handle and requires no extra action after releasing from the tow-line. However, they do make it more difficult to get into and out of your harness so they are not recommended for flying over water. 2-piece bridles fall apart at the release mechanism end after releasing from the tow- line. After releasing you will need to place the two pieces in your lap to avoid interference with your reserve handle.
Both bridle types, when connected to the line, form a “V” between the tow line, and your two carabiners. The release mechanism is located at the farthest end from you, and the release handle should be easily within reach. The other ends should always be connected to the top of your carabiners with webbing loops. NEVER attach the bridles in such a way that it applies force to the stitching of your harness or in which they could cross-load the carabiners during flight. There shouldn’t be any hard or heavy parts on the bridles. In the event of a weak link break or line failure, the bridles could snap back into the pilot and heavy objects could lead to injury. The weak link, which sits between the line and the bridles, should be reachable with a hook knife.
Some bridles have “tow-assists” or “speed-assists” which connect to your speed system and speed the glider up during the launch and tow. They help to mediate the increased angle of attack during a tow and in all but a very few cases are considered much safer than towing without a speed assist. If the glider being towed has any tendency to hang back while ground handling, is old, or is lightly loaded, a speed assist system may be required for a safe tow. Heavily loaded gliders, or fast, performance gliders may not need a tow-assist. Contacting the wings manufacturer for a recommendation may be in order.
The release mechanism, which will release the tow line from your bridles, should be simple, reliable, and work properly with no tow force, and extremely high tow forces. The most common mechanism is a rope 3-ring-circus which has been adapted from skydiving releases. They are light, reliable, and distribute the load throughout the release allowing it to work under very high forces. It is extremely important that you are familiar with the type of release on your bridles, and what mistakes you can make when connecting it. In the case of a rope 3-ring-circus the longest loop should ALWAYS be the one passed through the weak link. The release trigger or handle should be reachable by either hand when the tow-line is pulled to 60o either side of straight- ahead ahead, 90o down and 180o down and back.
The release handle should be on the opposite side of your harness from your reserve handle for consistency. You will have to fly one handed (both brakes in one hand) during the release and you should be in the habit of using the same hand to release, and get into the harness if it is not fitted with a stirrup.
Weak Links
Weak Links or safety links are required on every tow and should be rated to a strength of no more than 150% of the total pilot weight. They are usually connected between the tow line and the bridles and stay connected to the pilots bridle when the pilot releases. By keeping the weak link on the bridles each pilot keeps the weak link that is properly sized for them, and it prevents abrasion wear on the tow bridles. When the force on the pilot is too great the weak link is designed to break, preventing excessive forces on the canopy. They are NOT designed to prevent lockout! Weak links that are too weak may break while the pilot is still close to the ground leading to a surge where the pilot swings forward or backward into the ground. Weak links should be changed regularly to ensure that they are still rated for the proper strength and don’t break prematurely.
Hook Knife & Extra Reserve
If something goes wrong with the tow, a hook knife can potentially save your life. All pilots on tow MUST have a hook knife. It should be sharp and unused, but one that is made of steel and hasn't been used much or is in very good condition will do the trick. If the tow line fails to release from the bridles for any reason, a hook knife may help you free yourself. Be sure to attach the knife to your harness in such a way that you can easily release it from its case with one hand. Many people make the mistake of attaching it without this thought and find themselves unable to get the knife with one hand. The tow-tech operating the winch will also have at least one hook knife (most good tech operators will have 2 0r 3) within easy reach in case an emergency situation presents itself.
In addition to having a good hook knife, many SIV instructors are making a second reserve part of their mandatory gear for anyone on tow. As per USHPA regulations, every pilot must fly with a reserve, but having a second reserve in a belly mount container can add an additional measure of safety especially if the pilot is training in advanced maneuvers. There are a few videos that show how an situation where the main glider and reserve become entangled and the second reserve saved the pilot’s life.
Tow Lines
Various types of line or rope can be used for towing. The most popular types are Nylon and SpectraTM because of their durability and strength. Nylon line has a much greater stretch than SpectraTM and can dampen oscillations during a tow. Generally it results in a smoother tow but is not as strong. Spectra lines have less drag and will result in higher tows but is more expensive and not as forgiving.
Tow Systems
There are 3 different types of tow systems commonly in use for paragliders. The static line, stationary winch, and pay-out winch. All of them must be able to limit or reduce the tow force, zero the force (hook knife), and be able to gradually increase and decrease the tow force. Under no circumstances should the line be tied to the spool in such a way that if the line were pulled to the end, it wouldn’t automatically separate from the spool. A reversing pulley may be used in some circumstances and should be able to swivel without binding the tow line between the wheel and block. Typically the tow-lines are Spectra/Dyneema which is light and does not stretch. However, for a smoother tow other lines may be used which, while heavier, will stretch and provide a cushion against bumps in the air or tow surface.
Static line systems use a fixed length of line attached to a moving vehicle and requires an extremely skilled Tow-Op. The Tow-Op monitors the tension with a pressure gauge and adjusts the vehicle speed accordingly. It requires a smooth road or body of water. Static line towing is NOT recommended for paragliders.
Stationary winches (Pay-in or Scooter tow) remain at one end of the field or road and spool the line onto a drum to generate tension. The Tow-Op is able to adjust the tension with a hydraulic pump or with the engine throttle during the tow and can pay-out line if necessary. This is a popular method for rough fields and when using pulleys. The altitude attainable is less than a pay-out winch on a moving vehicle but requires less operating distance.
Pay-out winches are mounted on moving vehicles and release line from the drum as the tow progresses. The pressure is moderated by the speed of the vehicle and the hydraulics of the winch itself. It’s the most popular method for maneuvers courses where the winch is mounted on a boat that can travel in large circles around the lake, towing the pilot to altitudes sufficient for maneuvers. Payout winches typically have a “rewind” system for reeling the line back in after a tow.