Paddlers' Dictionary
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Undercut Over time, rivers can erode out the bases of rocks that are in the path of the main current, forming undercut rocks. Undercuts represent an extreme hazard to boaters, since rescue is nearly impossible once someone becomes trapped under such a rock by the force of the current. Some, but NOT all, undercut rocks are characterized by the absence of a pillow on their up current face: the current goes under the rock rather than bouncing off. Some, but NOT all, undercut rocks may also be recognized by the presence of a current coming out from the under the rock on the down current side. Avoid undercuts, period.

Vacuum Bagging A fabrication technique where the fabric and resin layup, still in the mold, are bagged in plastic and a vacuum applied to flatten the materials and squeeze out excess resin. Produces strong, light boats with less effort than squeegeeing by hand.

Wet Exit Going into the water directly from your boat. It is imperative that both decked and open boaters be able to wet exit their boats quickly, smoothly and without tangling in gear, especially when in disoriented and violent whitewater (the usual conditions that mandate a wet exit.)

Whitewater Refers to the white foaming water produced when a river drips abruptly. It can range from a slight riffle to a major waterfall. Whitewater is produced in rivers and streams with adequate gradient and flow rate. Both are necessary. For example, most streams with an overall gradient of 20 feet per mile will produce whitewater. There must, of course, be sufficient flow to float your boat. High volume rivers often produce large rapids even though they have a slighter gradient. The Colorado River through the Grand Canyon has a gradient of nine feet per mile. Gradients above 50 feet per mile usually produce demanding whitewater. One hundred feet per mile is a severe gradient, although small creeks with gradients in excess of 200 feet per mile are regularly run by top paddlers. Conversely, large volumes of water moving down low gradient rivers will not produce whitewater.

Wildwater Racing Races are held on a section of whitewater river several miles long. The paddler selects the best route to run the course in the fastest time.