Instrument for marking a regatta course in a body of water and measuring environmental parameters, said instrument adapted to float at the surface of the body of water and comprising a collapsible mast comprising a plurality of hollow modules operable between a collapsed condition and a deployed condition, said mast, when deployed adapted to be disposed perpendicular to the surface, said instrument modules mounting a communications device with a transmitter of signals, a parameter-measuring device, and an inflatable and deflatable pneumatic-plastic float, said float, when deflated, being both collapsible to smaller dimensions, and transportable in compact carrier of reduced size,
- characterized in that when said mast is deployed perpendicular to the surface, said mast has the same thickness over all the deployed length thereof, and
- said pneumatic float is rigidly attached to the mast approximately in the center of the length thereof.