Final answer:
The primary responsibility of the observer on a boat used for water skiing is to ensure the safety of the skier by watching them at all times and communicating with the boat driver. The observer also needs to maintain a lookout for other hazards in the water.
Step-by-step explanation:
The primary responsibility of the observer on a boat used for water skiing is to ensure the safety of the skier. The observer's main role is to watch the skier at all times and communicate with the boat driver to give directions and signals. They are responsible for alerting the driver if the skier falls or if any other hazards are present.
Additionally, the observer should maintain a constant lookout for other boats, swimmers, or obstacles in the water to ensure a safe environment for the skier. They should also be familiar with hand signals and proper communication protocols to relay messages effectively between the driver and the skier.