In order to safely perform a tow launch you should understand some risks, and basic forces that will be exerted on you during the tow. The tow system is designed to apply a relatively narrow pressure range to the glider. Too little pressure and the glider descends. Too much and over-tow or lockout can occur. When the system is working properly the tow operator is able to adjust the tow forces such that the glider gains altitude, without over-towing. Typical pressure for a pilot new to towing is 60-75% of their flying weight. However, there are some situations, depending on the type of tow system used, that can change the tow forces unexpectedly. Talking with the tow operator about your preferences before performing a towed launch can help avoid misunderstandings about tow pressure.
Line dig is the most common and occurs when the line on a pay-out winch has become stuck either between other lines or on part of the tow rig and suddenly stops paying out. The tow system instantly becomes a static tow and tow forces can escalate quickly depending on the speed of the tow vehicle. Use of a properly sized weak link will prevent anything more dangerous than a weak link break from occurring.
As line is spooled onto the drum during a pay-in tow the spool diameter increases and, at a constant RPM, the tow force exerted on the glider will decrease. During a pay-out tow, where the spool diameter decreases, the line force will increase. The tow operator should be aware of the trend and can adjust for either scenario.
When towing in a cross wind without the tow rig properly aligned with the wind the forces exerted on a glider can be higher than if towing directly into the wind. This is because the towing force is directed across the axle rather than at 90o. Part of the resistance from the glider is now fighting against the sideways pull of the tow line. Using a fairlead at the tow rig will allow the line to be presented at a 90o angle to the axle/spool at all times.
During any tow the force exerted by the tow line will pull the pilot ahead of the glider. This results in an increased angle of attack, and an increased wing loading especially at higher line angles. Most paragliders do not turn well at high angles of attack which may prompt the pilot to use more brake input to perform a turn. Because the glider is already at a high angle of attack, more brake may stall the glider. The increased wing loading has also increased your stall speed. Increased stall speed + increased angle of attack + brake is a dangerous combination. For this reason speed assists and light brake inputs are encouraged.