A flotation agent including an oxidized paraffinic product which may be a Fischer-Tropach reaction product obtained by way of the Fischer-Tropsch reaction from carbon monoxide and hydrogen feed. The power supply board 20 includes a connecting portion 20c connected with the connector 21 so as to be electrically connected to the light source 18 via the connector 21. A first global positioning system generates a first position signal corresponding to a position of the first vehicle.