Expedition 13 Mail Buoy: December 14

The propellers are made of carbon fiber and are very strong, so it would probably do more damage to the shark than sentry. A broken or lost propeller is no problem because Sentry is programmed to adjust its thrust if that happens, as well. If an animal bumped into the vehicle body, Sentry would just recover and resume its course. In fact, currents knock it around all the time.