A fluid cooler, fluid cooler core and method of condensing gas is disclosed. The keyboard is of the type having keys and having a shell surrounding the keys. Each of the tubular fenders is independently extendable along a substantial portion of the length of the watercraft. Each of the non-tracking sensors is further arranged at a substantially equal first angular distance from its immediate non-tracking sensor neighbors, two endmost non-tracking sensors defining an angular gap. As the volume intake is determined by the clearance, the system is set by means of a pre-actuation to an initial condition before each actual measurement. The control signal is received as remote identifying information by the other digital communication devices within the communication range.