When taxiing with the engine idling or at a low RPM, the seaplane will remain in what is considered a displacement condition similar to being at rest on the water (Fig. 15-4). This is the "idling" position. The recommended taxi speed is usually below 6 or 7 knots so that the propeller will not pick up water spray which causes serious erosion of the propeller blades. In calm or light wind conditions, the elevator control should be held full back to raise the seaplane's nose and further reduce the possibility of water spray on the propeller, and to improve overall maneuverability of the seaplane. This is particularly true if it is equipped with water rudders because more rudder area is kept in the water. Since seaplanes have no brakes, it is especially important to taxi at this slow speed in congested or confined areas because inertia forces build up rapidly, making the seaplane vulnerable to serious damage even in minor collisions.