Seasickness on dive boats

What causes seasickness

DAN describes motion sickness as the result of a mismatch between the sensory input from the eyes and the inner ears. The NHS explains it the same way: the inner ear sends the brain signals that differ from what the eyes are seeing.^1,2

The NHS lists symptoms that can include dizziness, nausea, vomiting, headache, feeling cold and going pale, and sweating. DAN says a physician should evaluate persistent or unusually severe nausea, especially if other symptoms are present.^1,2

Why it matters for diving

DAN points out that seasick divers who rush into the water may take less care setting up their equipment or attending to their buddy. It also notes that vomiting underwater can be a real problem if a diver fouls the regulator's second stage or inhales water.¹

Measures without medication

Where you stand on the boat makes a difference. DAN suggests staying in the centre of the boat and avoiding upper or lower decks, where the motion is more pronounced, and choosing a well-ventilated spot; the NHS likewise suggests the middle of a boat and fresh air.^2,3

Both DAN and the NHS suggest looking at a fixed point in the distance, such as the horizon. DAN also notes that closing your eyes, or sitting where the rocking of the boat is not visible, can help, and advises staying away from strong fumes, particularly fuel.^1,2,3

• DAN advises avoiding alcohol and heavy meals the night before diving; the NHS advises against heavy meals, spicy food and alcohol shortly before or during travel.^2,3
• DAN says hydration is key and suggests drinking plenty of water.³
• The NHS advises not reading, watching films or using electronic devices while travelling.²
• DAN and the NHS both mention ginger, which some people find soothing.^2,3
• If you start to feel ill, DAN suggests asking to be one of the first to enter the water.³

Medication and diving

DAN notes that drowsiness is a side effect of many motion-sickness medications, and that most oral ones cause mild drowsiness. Its page on over-the-counter medicines adds that nitrogen may enhance a drug's sedative effect and that such effects may increase the chance of nitrogen narcosis.^1,3,4

DAN suggests trying a medication once on a day when you do not need your wits about you, or starting it at least one or two days before diving, to see how it affects you, and it says not to dive under the influence of any medication you are using for the first time.^3,4

DAN's travel medical guide describes the scopolamine patch as the preferred treatment for divers, noting that the U.S. Navy found minimal adverse effects in divers, and recommends wearing one for at least 24 hours to test its effects before it is needed. DAN lists dry mouth and blurred vision as the most common side effects, says that removing a patch worn for more than three days can cause withdrawal symptoms that overlap with those of decompression sickness, and says patch wearers who develop dizziness, nausea or vomiting within 24 hours of a dive should contact a physician.^1,3

DAN also notes that guidelines for motion-sickness medicines regularly say to consult a physician before use. For your own situation, speak to a dive physician or contact DAN.⁴

When not to dive

DAN advises that divers who are seriously affected by motion sickness should not start a dive until their symptoms improve. It also says to exercise caution with severe nausea and that it may be best to cancel the dive.¹

DAN's pages differ in emphasis: its seasickness article suggests that a diver who starts to feel ill ask to be one of the first to enter the water, while its travel medical guide says divers seriously affected by motion sickness should not start a dive until symptoms improve, and that with severe nausea it may be best to cancel the dive.^1,3

Before you go

• DAN suggests trying a motion-sickness medication on a day when you do not need to be alert, before relying on it for diving.^3,4
• DAN recommends wearing a scopolamine patch for at least 24 hours to test its effects before it is needed.¹
• DAN advises avoiding alcohol and heavy meals the night before, and drinking plenty of water.³
• DAN suggests standing in the centre of the boat, in a well-ventilated area, and looking at the horizon.³
• DAN notes that seasick divers who rush into the water may take less care with their equipment and their buddy.¹
• Ask a dive physician or DAN about medication for your own case.⁴