Squeezing the Air
Wind acts like water flowing through a hose. If you put your thumb over the end, the water sprays faster. The same volume of water must pass through a smaller opening, so it accelerates.
The same physics applies to wind flowing through geographic restrictions.
Bernoulli's Principle
When airflow is constricted, velocity increases and pressure decreases. The air must accelerate to maintain the same mass flow rate through a narrower passage.
This is the Venturi effect—named after Italian physicist Giovanni Venturi
Geographic Acceleration
This happens naturally when wind encounters terrain features:
- Gaps between islands: Wind funnels through the strait
- Narrow valleys: Mountains on both sides squeeze airflow
- Headlands: Wind accelerates around the point
- River mouths: Narrowing channel speeds up wind
- Harbor entrances: Breakwalls create artificial funnels
The air accelerates to push through the restriction, often gaining 30-50% more speed.
The Acceleration Multiplier
Wind speed increase depends on how much the channel narrows:
Channel Width vs Speed Increase
Wide funnel (50% narrowing)
Gentle acceleration
+20-30%
Moderate funnel (60-70% narrowing)
Noticeable boost
+30-50%
Tight funnel (80%+ narrowing)
Dramatic acceleration
+50-100%
Example: 12 knots becomes 18 knots in a tight gap (+50%)
Using It to Your Advantage
You can use the Venturi effect to save a light wind session:
- Forecast 10 knots: A funnel spot might deliver 15 knots—suddenly rideable
- Direction matters: Wind must flow perpendicular to the gap for maximum effect
- Position strategically: Launch directly in the accelerated zone
- Beware turbulence edges: Wind can be gusty at the funnel exit
The Funnel Lifecycle
Before the Gap
Wide area, normal wind speed, laminar flow
In the Gap
Narrow channel, accelerated wind (+3-7 knots), smooth but strong
After the Gap
Wind fans out, speed drops, turbulence forms as flow expands
How to Find Venturi Spots
Study maps and satellite imagery to identify:
Venturi Spot Checklist
Look for straits: Channels between islands or landmasses
Check harbor entrances: Breakwall gaps create reliable funnels
Find river mouths: Especially those that narrow significantly
Align with wind: Funnel must face the wind direction (±30°)
Measure narrowing: Use map scale to estimate acceleration
Examples in the Wild
Classic Venturi locations wingfoilers use:
- Strait between two islands (e.g., Golden Gate, SF)
- Gap in a harbor breakwall
- River mouth narrowing into ocean
- Canyon or valley aligned with prevailing wind
- Under bridges with narrow passages
- Between headlands on a coastline
Summary
Study the map. If the wind flows through a narrow channel, add 30-50% to the forecast speed. The Venturi effect can transform marginal wind into epic sessions—but only if the geography and wind direction align perfectly.