Heat Exhaustion and Heat Stroke on a Boat: Prevention, Warning Signs and What to Do

Use a bimini top, T-top canvas, umbrella or a rigged tarp. The CDC's advice for long hot days is to stay in the shade as much as possible and take breaks. Rotate people into the shade, especially kids and older guests. Our bimini guide covers repairs and replacement.

The CDC recommends carrying water and drinking throughout the day, and limiting drinks high in sugar, caffeine and alcohol. A simple check it suggests: light yellow or clear urine usually means you're drinking enough. Keep water in a cooler, within reach of every seat, and make drinking a routine at every stop.

Light-colored, loose, lightweight clothing, a wide-brim hat and sunglasses. The CDC gives the same advice for infants and children. Reapply sunscreen; sunburn makes it harder for the body to cool.

Fish or ski in the early morning or evening, the coolest parts of the day, as the CDC suggests. Take swim breaks with the engine off and everyone away from the exhaust. Don't let the operator skip water; a dizzy or confused skipper is a danger to everyone.

The National Weather Service lists painful muscle cramps and spasms, usually in the legs or belly, with heavy sweating. First aid it describes: firm pressure or gentle massage on the cramp and sips of water, unless the person feels nauseated. Get medical help if cramps last more than an hour. Treat cramps as a warning to get into the shade and cool off.

Signs the NWS lists: heavy sweating; weakness or tiredness; cool, pale, clammy skin; a fast, weak pulse; muscle cramps; dizziness, nausea or vomiting; headache; fainting. First aid, from the NWS and Mayo Clinic:

1. Move them into the shade and out of the sun.
2. Loosen or remove extra clothing.
3. Cool them with cool, wet cloths, a spray of water and fanning.
4. Offer sips of cool water or a sports drink if they're alert and not vomiting.
5. Get medical help right away if they vomit, get worse, or don't improve within an hour.

Mayo Clinic notes untreated heat exhaustion can lead to heat stroke, so head back to the dock rather than "riding it out."

Signs the NWS lists: throbbing headache; confusion; slurred speech; nausea; dizziness; body temperature above 103°F; hot, red, dry or damp skin; a rapid, strong pulse; fainting or unconsciousness. The key difference from heat exhaustion is a change in the brain: confusion, odd behavior, slurred speech or passing out.

• Call 911 or the Coast Guard on VHF 16 immediately. The NWS calls heat stroke a severe medical emergency where delay can be fatal. Give your position and ask where emergency services can meet you.
• Start cooling right away while you head in or wait.
• Don't give fluids to someone with heat stroke, per the NWS; they may not be able to swallow safely.
• Don't give fever medicine. MedlinePlus says not to give aspirin or acetaminophen for heat illness (they won't help and may harm), and not to give salt tablets or drinks with alcohol or caffeine.
• About the temperature: the NWS lists heat stroke at a body temperature above 103°F, MedlinePlus above 104°F. Don't wait for a thermometer; confusion or fainting in the heat is enough to call. MedlinePlus also notes sweating may stop as heat stroke sets in.

The Red Cross says to begin rapid cooling while waiting for emergency medical services. Its preferred method is cold-water immersion up to the neck; if that isn't possible, it lists ice packs, cooling towels, misting and fanning, or a combination. On a boat:

• Get them into shade, lying down, with clothing loosened.
• Soak towels in cooler ice water and cover as much of the body as you can, changing them often.
• Put ice or cold packs on the neck, armpits and groin.
• Spray or pour water and fan them.
• Don't put a confused or fainting person over the side to cool off; they can drown. Only use the water if they're held securely, wearing a life jacket, and you have the people to get them back aboard.

The NWS notes that a fan can make you hotter when the heat index is in the high 90s or above; wet skin plus moving air works better than a fan alone.

Headache, dizziness, nausea and weakness are also signs of CO poisoning. The Coast Guard says CO can make you sick in seconds and builds up near the stern, at idle and even after engines are off. If the person was near the transom, swim platform or in a cabin with an engine or generator running, move everyone to fresh air at the bow and treat it as possible CO; our CO guide covers alarms.

The CDC explains that infants and young children rely on others to keep them cool and hydrated. Keep them in the shade, in light clothing, drinking regularly, and avoid very cold or sugary drinks. The CDC warns that parked cars can heat up dangerously fast, even with a window open; a closed cabin or console on a boat sitting in the sun can do the same, so never leave a child (or pet) in one. A child who becomes unusually sleepy, cranky, flushed or stops sweating needs immediate cooling and medical help.

The American Kennel Club notes dogs cool themselves mainly by panting and through their paw pads, and that heatstroke can develop in minutes. Early signs include heavy panting, drooling and red gums; severe signs include collapse and shock. AKC's first aid:

• Get the dog into shade and moving air.
• Wet the dog with cool or tepid water, not ice-cold, especially on the belly.
• Offer room-temperature water if the dog is alert.
• See a veterinarian even if the dog seems to recover; heatstroke can cause hidden internal damage.

Hot decks can burn paws; put down a wet towel or mat. Our pets guide covers more.

Add heat to your pre-departure briefing: where the water and shade are, and "tell me if you feel dizzy, sick or crampy." People rarely notice their own confusion, so pair up and check on each other, especially anyone who's been fishing in the sun or drinking.