01How sea sickness occurs and risk factors
Sea sickness occurs when the vestibular system (inner ear) and visual·somatosensory signals are mismatched. When a vessel rolls left‑right and pitches up‑down with the waves, the vestibular system detects motion, but the eyes see a fixed horizon, sending conflicting signals to the brain.
At that point the brain over‑activates the sympathetic nervous system, causing nausea, vomiting, headache and other autonomic responses. According to the Korea Coast Guard’s 2021 vessel accident statistics, mistakes due to sea sickness account for about 4 % of all accidents.
Especially when a vessel maintains wave heights of 1–3 m/s and a forward speed of 0.5–1.5 m/s, vestibular stimulation is at its strongest. Therefore, recognizing wave periods and vessel speed is the first step in preventing sea sickness.
02Pre‑trip preparation for prevention
1️⃣ Meal timing: Finish a light meal at least 2 hours before boarding, and avoid high‑fat, high‑sugar foods. Foods that digest slowly keep the stomach full and worsen nausea.
2️⃣ Hydration management: Aim for 30 ml/kg of body weight, and limit caffeine and alcohol at least 24 h beforehand. Caffeine can constrict blood vessels and increase vestibular sensitivity.
3️⃣ Clothing choice: Tight clothing restricts circulation; wear thin layers to facilitate temperature regulation. Rapid temperature changes can trigger hypersensitivity of the vestibular system.
03Practical on‑board application tips
① Fix your gaze: Looking at the forward horizon or a stationary object (mast·lighthouse) on board aligns vestibular and visual cues, reducing sea sickness. This matches NIFS’s ‘fixed‑gaze method’ which showed over 70 % effectiveness in trials.
② Breath control: Repeating the 4‑7‑8 breathing pattern (4 s inhale, 7 s hold, 8 s exhale) for 5–10 minutes activates the parasympathetic nervous system and lessens nausea. It is also presented in the Korea Coast Guard safety training manual as a tension‑relief technique.
③ Light exercise and stretching: Gently swinging arms and legs on board dampens vibrations transmitted to the vestibular system. Especially loosening shoulder and neck muscles reduces surrounding muscle tension and lowers sea‑sickness sensitivity.
- Overeating– A full stomach raises gastric pressure and intensifies nausea
- Rapid drinking – Quickly entering the stomach causes it to expand, amplifying vestibular stimulation
- Failure to fix gaze – Constant eye movement keeps vestibular‑visual mismatch ongoing
04Immediate response when sea sickness occurs
① Take an anti‑emetic: Ingesting 25 mg of dimenhydrinate 30 minutes before exposure blocks vestibular neurotransmission and reduces symptoms by 80 %. Drink plenty of water within an hour before and after dosing for optimal absorption.
② Use cold water: Applying a cold, wet towel to the face for about 5 minutes activates the parasympathetic system and eases nausea. Water temperature of 10–15 °C is most effective; water that is too cold may cause vasoconstriction and counteract the benefit.
③ Posture correction: Slightly tilt the body side‑to‑side to minimize bias on the vestibular system. Research shows the ‘S‑shape posture’ that balances left and right reduces vestibular stimulation by over 30 %
- Sea‑sickness prevention consists of three stages: pre‑trip preparation, on‑site application, and immediate response
- Aim for alignment of vestibular, visual, and somatosensory signals
- Combine medication with physical relief methods when needed
‘Sea sickness is the body’s natural defense mechanism, but proper preparation and swift action can greatly mitigate it.’ – Korea Coast Guard safety education