1.Density of the material building the raft must be lower than the water. <span>2. Material must not react with water. </span> <span>3.Material must have high strength. </span> <span>4.Raft must be wide in-order to avoid drawing in the river.</span>
No light does not need medium to travel.Its an electromagnetic(EM) wave.All EM waves travel independent of medium. In contrast mechanical waves need a medium,sound waves,shock waves are mechanical and they need medium to transfer energy or travel.