also reduced the width of the boats in the early 1970s. The gates were hung about 10 cm above the water. When racers began making lower-volume boats, the gates were raised in response to fears that new boats would be of such low volume as to create a hazard to the paddler. Their low-volume sterns allow the boat to slice through the water in a quick turn, or "pivot". Typically, new racing boats cost between $1,200 and $2,500 (or $850 onwards for the cheapest constructions in fiberglass). Usually boats are made with carbon fiber, Kevlar and fiberglass cloth, using epoxy or polyester resin to hold the layers together. Foam sandwich construction in between layers of carbon, Kevlar, or Aramid is another technique in use to increase the stiffness of slalom boats. In 2005 the minimum length of these boats was reduced from 4 meters down to 3.5 meters, causing a flurry of new, faster boat designs which are able to navigate courses with more speed and precision. The shorter length also allows for easier navigation and less boat damage in the smaller manmade river beds that are prevalent in current elite competitions. Boat design progression is rather limited year to year. Directly from the 2017 ICF Canoe Slalom Rules: 7.1.1 Measurements All types of K1 Minimum length 3.50 m minimum width 0.60 m All types of C1 Minimum length 3.50 m minimum width 0.60 m All types of C2 Minimum length 4.10 m minimum width 0.75 m 7.1.2 Minimum Weight of Boats (The minimum weight of the boat is determined when the boat is dry. The weight minimums were raised for 2017.) All types of K1 . (Previously 8 kg). All types of C1 . (Previously 8 kg). All types of C2 . 7.1.3 All boats must have a minimum radius at each end of horizontally and vertically. 7.1.4 Rudders are prohibited on all boats 7.1.5 Boats must be designed to, and remain within, the required dimensions. 7.1.6 Kayaks are decked boats, which must be propelled by double-bladed paddles and inside which the competitors sit. Canoes are decked boats that must be propelled by single-bladed paddles and inside which the competitors kneel. There are rules governing almost every aspect of slalom equipment used in major competition, including sponsor advertisement. Some of these rules vary from country to country; each national canoe and kayak governing body publishes its own variation of