To determine if your dog is getting too hot or overexerted on the boat, watch for signs of distress such as excessive panting, drooling, lethargy, or a rapid heartbeat. Other indicators include a bright red tongue or gums, vomiting, or uncoordinated movement, which could signify heatstroke. If your dog seeks shade, seems restless, or refuses to play, these may also be signs they're overheating. Ensure they have access to fresh water and a shaded area at all times, and never hesitate to cool them down with water if they show these symptoms.