How To Prevent Sea Sickness When Scuba Diving: Your Complete Guide

Sea sickness is one of the most common worries among new and experienced divers alike, and for good reason. Whether you are crossing from Koh Samui on a speedboat, taking the Lomprayah catamaran to Koh Tao for the first time, or bobbing at anchor above a dive site in the Gulf of Thailand, the motion of the sea can catch even seasoned travellers off guard.

The bright side is that sea sickness is always preventable, or at the very least manageable, with the right preparation. This guide covers everything you need to know to prevent sea sickness before you even leave the shore, and how to recover quickly so that nothing gets between you and the underwater world you came to explore.

What Causes Sea Sickness?

Before you can prevent sea sickness, it is important to understand why it happens. Sea sickness, technically a form of motion sickness, occurs when your brain receives conflicting signals from your sensory systems.

Your inner ears (the vestibular system) detect the rolling and pitching of the boat. Your muscles and joints register the shifting of your weight. But if you are sitting inside a cabin or looking down at your dive gear, your eyes are telling your brain that your surroundings are perfectly still. This sensory mismatch confuses the brain, triggering a cascade of symptoms that can range from mild queasiness to full vomiting.

Common symptoms of sea sickness include:

• Nausea and an unsettled stomach
• Dizziness or a spinning sensation
• Pale, clammy skin
• Excessive saliva or a dry mouth
• Headache or a feeling of pressure behind the eyes
• Fatigue and a general sense of feeling unwell
• Vomiting in more severe cases

The important thing to remember is that sea sickness is a physiological response, not a sign of weakness. Studies suggest that some people vary in their susceptibility, but given a sufficient stimulus, almost all people with functional vestibular systems can develop motion sickness.

How To Prevent Sea Sickness: Before You Leave The Shore

The steps you take in the 24 hours before your boat journey can make an enormous difference to how you feel on the water:

The Night Before

Your choices the evening before a dive day have a direct bearing on how your body handles the motion of a boat. 

Follow these guidelines the night before:

• Avoid alcohol entirely: According to Divers Alert Network (DAN), a hangover dramatically worsens seasickness. The dehydration and inner ear disruption caused by alcohol amplify every symptom. 

• Eat a light, balanced evening meal: Avoid very spicy, rich, or fatty food. A heavy stomach heading into a rocking boat is a recipe for trouble.

• Get a full night of sleep: Fatigue lowers your body’s tolerance for sensory conflict. A well-rested body adapts to the motion of a boat far more readily.

• Stay well hydrated: Drink plenty of water throughout the day before your trip. Dehydration is both a cause and an accelerant of seasickness symptoms.

• Consider starting medication: If you know you are susceptible, some divers find that taking an antiemetic such as Bonine (meclizine) the evening before a dive day, not just the morning of, produces better results. See the medication section below.

The Morning of Your Dive

On the morning of your trip, small decisions matter significantly:

• Eat a light breakfast: An empty stomach is no protection against seasickness and is often more sensitive to irritation than a settled one. Opt for plain, bland food such as toast, crackers, a banana, or plain rice. Avoid dairy, eggs, very strong coffee, or anything greasy.

• Take oral medication at the right time: Most antihistamine-based seasickness tablets need to be taken 1–2 hours before boarding, not once you are already feeling unwell. Timing is everything.

• Apply a scopolamine patch if using one: These must be applied at least 8 hours before exposure. If you are taking a morning ferry, apply the patch the night before. Check with a pharmacist or doctor in advance regarding suitability for diving. For a full list of health and safety essentials to bring on your trip, see our Koh Tao packing guide.

• Avoid excessive caffeine: A strong coffee can increase anxiety and gastric activity, neither of which helps on a moving vessel.

• Dress comfortably: Tight waistbands or wetsuits donned too early can add pressure to your abdomen and worsen nausea.

Seasickness Medication: What Works for Divers

The choice of medication matters greatly for divers because many standard options carry side effects, particularly drowsiness, that are incompatible with safe scuba diving. 

The table below summarises the main options, their timing, and their compatibility with diving:

What Are The Natural Remedies Worth Trying

Not everyone wants to rely on medication, and for milder cases of seasickness, several natural approaches have genuine merit:

• Ginger is the most evidence-supported natural remedy. Fresh ginger, ginger chews, ginger capsules, or ginger tea can all help reduce nausea. There are no significant side effects, making it a sensible first choice for divers worried about drowsiness.

• Peppermint has a calming effect on the stomach and is available in tea form or as peppermint oil to inhale. The scent alone can reduce the feeling of nausea for some people.

• Acupressure (P6 point) involves applying firm pressure to a specific point on the inner wrist, approximately three finger-widths below the wrist crease. Sea-Band wristbands apply constant pressure to this point. Evidence is mixed, but many divers swear by them, and there is no downside to wearing them alongside other prevention methods.

• Fresh air and the horizon, staying on deck and fixing your gaze on the horizon, is one of the most effective behavioural strategies available. More on this in the next section.

What To Do On The Boat For Seasickness

Once you are aboard the dive boat, where you sit and how you behave has a significant impact on whether sea sickness takes hold.

Choose Your Position Wisely

Behaviours That Prevent Seasickness On The Boat

Can You Still Dive If You Were Seasick?

It depends, as many divers find their symptoms vanish the moment they descend. Once submerged, the rocking stops and the sensory conflict resolves. The descent itself is often an instant cure.

That said, if your seasickness was severe, weigh these before entering the water:

• Dehydration — Vomiting causes fluid and electrolyte loss. Rehydrate properly before deciding whether to dive; dehydration increases your risk of decompression sickness.

• Medication drowsiness — If you have taken a sedating antihistamine, do not dive. Drowsiness impairs judgement, reaction time, and your ability to equalise safely.

• Residual dizziness — If you still feel dizzy at the surface, skip the dive. Dizziness underwater can be dangerous and may be mistaken for inner ear barotrauma.

• Fatigue — If the crossing has left you exhausted, rest and consider sitting out the first dive.

   

Always speak to your instructor or divemaster before entering the water. At Buceo en La Bombona, we will always prioritise your safety over a rushed dive schedule. If seasickness has left you feeling anxious about getting in the water, our guide on overcoming scuba diving fear may help.

Electrolyte Replacement After Seasickness

Rehydration after vomiting is not optional; it is a diving safety requirement. Vomiting depletes fluids and key electrolytes (sodium, potassium, magnesium, chloride), all of which your body needs to safely off-gas nitrogen after a dive.

If you have been repeatedly sick and feel weak or confused, do not dive that day. Rest, rehydrate, and consult a pharmacist or doctor if symptoms continue.

Seasickness on the Koh Tao Ferry: What to Expect

For many divers, their first encounter with seasickness comes before they even reach the dive site, during the ferry or speedboat journey to Koh Tao itself.

The main ferry routes and their typical conditions are summarised below:

Tips specific to the Koh Tao ferry:

• Book morning departures when seas are typically calmer, particularly if you are susceptible to motion sickness

• On the Lomprayah catamaran, choose outdoor deck seating at the rear of the upper level for the best combination of horizon view and stable position

• Take your medication at the right time for the ferry duration (check timing against the table in the medication section above)

• Have your ginger or Sea-Bands ready before boarding rather than scrambling for them mid-crossing
  
  

Final Thought

Sea sickness should never be a reason not to dive. At La Bombona Diving, we have worked with hundreds of divers who were convinced that their tendency to feel seasick would rule out a Koh Tao diving experience, and almost all of them went on to enjoy incredible dives. The key is preparation, not willpower.

Pack your ginger, take your medication at the right time, eat sensibly, get a good night’s sleep, and tell us if you are feeling off on the way out. We have experienced instructors, small-group sizes, and we will always prioritise your comfort and safety over a rushed dive schedule. The ocean will still be there; we just want to make sure you can enjoy it fully when you get there.

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