Is the Backstairs Passage rough? What to expect on the crossing
Sometimes, and more often in winter. The passage is about 14 km wide at its narrowest and is described as subject to strong currents, heavy tidal swells and steep breaking seas. The SeaLink crossing takes about 45 minutes, and services can be disrupted by weather.
Crossing the Backstairs Passage this week? Dizzout is drug-free sound therapy you can start in your seat on the crossing, with relief in about 90 seconds.Starts in your browser ยท works with any headphones
Stop seasickness. Get your personalized Dizzout plan. Paid subscription for full access.
On your phone? Scan to start there.
Passage ยท South Australia ยท Reputation among passengers: has a long-standing reputation for rough passages.
- Low
- Moderate
- High
- Very high
Roughness summarises typical reported conditions for this crossing, not a forecast for any given sailing.
Narrow tidal channel, Southern Ocean wind
In the Nausea Index table of the 121 sea crossings we cover, the Backstairs Passage is rated rough, one of 34 in that band, with 6 rated higher. Full table: the roughest sea crossings, ranked.
Key facts
- The Backstairs Passage is a passage, and passenger reports place it in the high roughness band.
- The mechanism behind that reputation: Narrow tidal channel, Southern Ocean wind.
- Conditions are reported roughest in June, July, August, September and October.
- The calmest months are usually March and April.
Why is the Backstairs Passage so rough?
Funnel and current. The relatively shallow Gulf St Vincent joins the Southern Ocean through the deeper Backstairs Passage, so this narrow channel is subject to strong currents, heavy tidal swells and steep breaking seas. At Cape Willoughby, on the passage, the mean 9am wind is 26.3 km/h over the year and reaches 29.1 km/h in August.
When is the Backstairs Passage roughest?
Wind is strongest in the cold months. At Cape Willoughby the mean wind is highest from June to October, with 9am means of 28.8 km/h in July and 29.1 km/h in August, and a 3pm mean of 29.8 km/h in July. It is lightest in March and April, when the 9am means are 24.1 and 24.5 km/h.
| Roughest water in Jan | Roughest water in Feb | Roughest water in Mar | Roughest water in Apr | Roughest water in May | Roughest water in Jun | Roughest water in Jul | Roughest water in Aug | Roughest water in Sep | Roughest water in Oct | Roughest water in Nov | Roughest water in Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Mixed | Mixed | Calm | Calm | Mixed | Rough | Rough | Rough | Rough | Rough | Mixed | Mixed |
Typical seasonal pattern, not a forecast. Any month can deliver a calm crossing or a bad one. Check the marine forecast for your sailing date. Select a month to see every sea and ferry crossing ranked for it.
Where to be on board
Front to back
- Bow (front)Avoid
- MidshipBest
- Stern (aft)OK
The crossing: About 45 minutes
Roughest stretch: The open passage between Cape Jervis and Penneshaw
Sit low and near the middle. On a 45-minute crossing the open part is most of the trip.
Get your read
A few quick questions about you, then your trip. Nothing is saved or sent.
Step 1: about you
How you usually react to travel is the single best signal. These come from the validated MSSQ.
Step 2: your trip
Pick the kind of trip you are planning.
Crossing the Backstairs Passage? Have Dizzout ready
Stop seasickness
Dizzout is drug-free sound therapy you can start in your seat on the crossing, with relief in about 90 seconds. It plays precisely calibrated audio through any headphones you already own, wired or Bluetooth. Free to download.
Get your personalized Dizzout plan. Paid subscription for full access.
30,000+ travelers in 30+ countries ยท How we count
On your phone? Scan to start there.
Comparing apps first? See how the motion sickness apps compare
Not travelling yet? Remind me the day before my trip
Know someone who gets motion sick?
Send them the app that helps stop it, drug-free, in about 90 seconds, works with any headphones. Free to download.
The crossings that cross it
| Route | Typical duration | What to know |
|---|---|---|
| Cape Jervis to Penneshaw (Kangaroo Island) | about 45 minutes | SeaLink. The ferry route is 16 km, and the passage is about 14 km wide at its narrowest. |
| Penneshaw to Cape Jervis | about 45 minutes | The same SeaLink service in the other direction. |
What helps on this crossing
- Book June to October with a flexible ticket. The mean wind at Cape Willoughby is highest then, and ferry services can occasionally be disrupted by weather.
- The crossing takes about 45 minutes, so the rough part is short. Keep your eyes on the horizon for the whole run and put your phone away.
- March and April have the lightest winds of the year. If your dates are flexible, they are the months to aim for.
For the full toolkit see the seasickness guide, or what to do once it has already started. For what the trials actually say about the oldest trick on that list, see the verdict on looking at the horizon. If the rocking follows you ashore afterwards, that is land sickness, which is normal, and it passes.
Frequently asked questions
Is the Backstairs Passage rough in July?
July is among the roughest months. At Cape Willoughby on the passage, the mean 9am wind is 28.8 km/h and the mean 3pm wind is 29.8 km/h, the highest 3pm figure of the year. The tourism association notes that ferry services can occasionally be disrupted by weather.
Is the Backstairs Passage rough in March?
March is one of the calmest months. The mean wind at Cape Willoughby is 24.1 km/h at 9am and 24.2 km/h at 3pm, and the 9am figure is the lowest of the year.
How long is the ferry to Kangaroo Island?
SeaLink says its Cape Jervis to Penneshaw ferry takes about 45 minutes. The Kangaroo Island tourism association gives the route as 16 km.
Why is the Backstairs Passage so rough?
The relatively shallow Gulf St Vincent joins the Southern Ocean through the deeper passage. That makes the narrow channel subject to strong currents, heavy tidal swells and steep breaking seas.
Other crossings
Sources & further reading
- https://en.wikipedia.org/wiki/Backstairs_Passage
- https://www.bom.gov.au/climate/averages/tables/cw_022803.shtml
- https://www.tourkangarooisland.com.au/kangaroo-island-sealink-ferry
- https://www.tourkangarooisland.com.au/visit/travel/getting-to-kangaroo-island
- https://www.sealink.com.au/kangaroo-island/sealink-kangaroo-island-ferry/
Sea conditions described here are typical patterns drawn from published marine and operator information as of July 2026, not a forecast: conditions on any given sailing depend on the weather that day, and any month can deliver a calm crossing or a bad one. Route and operator names are trademarks of their respective owners; Dizzout is not affiliated with or endorsed by them. Seasickness sensitivity varies from person to person; this page is informational and not medical advice.