Salt Adds Buoyancy
Salt water is denser than fresh water. Dissolved salt adds mass to the liquid without adding volume. This density helps you in two ways: it makes your board float better, and it gives your foil more resistance to push against.
The difference is subtle but measurable. Ocean riders switching to lakes often struggle—and blame their technique. The real culprit is physics.
The Physics
Fresh water has a density of 1.00 g/cm³. Salt water (seawater at average salinity) has a density of 1.025 g/cm³. That's a 2.5% increase. This affects both buoyancy (Archimedes' Principle) and foil lift (which depends on fluid density).
Lift = ½ × density × velocity² × area × CL → 2.5% more density = 2.5% more lift
The Lake Deficit
Fresh water is "thin." When you wing foil on a lake, your board sinks lower in the water. It sticks to the surface more. You need more speed to break free and get up on foil.
Once you are flying, the foil generates slightly less lift due to lower water density. You might feel like you are riding a smaller front wing—because, effectively, you are. The wing's lift coefficient is the same, but the fluid density multiplier is lower.
The deficit compounds: harder to get up, harder to stay up. Marginal sessions in the ocean become impossible on the lake.
Density Impact on Performance
Salt Water (Ocean)
1.025 g/cm³
Board floats higher, foil generates 2.5% more lift
Fresh Water (Lake)
1.00 g/cm³
Board sinks lower, foil generates 2.5% less lift
Gear Adjustments
If you usually ride in the ocean and take a trip to a lake, you may need to size up. Use a board with 5 to 10 more liters of volume. This compensates for the reduced buoyancy, keeping you higher in the water during starts.
Use a slightly larger front foil—100-200 cm² more surface area—to compensate for the lack of density. This restores the lift you'd normally get from saltwater.
If you ride exclusively on lakes, you don't need to adjust anything—your quiver is already optimized. But if you're an ocean rider visiting a lake (or vice versa), expect the gear that works at home to feel "off."
The Compounding Effect
The density difference affects more than just raw lift. It also changes:
- Stall speed: You need slightly more speed to stay on foil in fresh water
- Pumping efficiency: Each pump stroke generates less lift, making it harder to recover from touchdowns
- Glide: Lower density means less momentum transfer from water to foil
- Board release: Fresh water creates more suction on the board surface during takeoff
Practical Tips
Ocean to lake: Add 5-10L board volume, increase foil size by 100-200 cm²
Lake to ocean: Size down—your usual gear will feel overpowered and floaty
Brackish water: Estuaries and river mouths have intermediate density—split the difference
Temperature matters too: Cold fresh water is denser than warm fresh water—winter lakes perform slightly better
Why Lakes Feel Sticky
Fresh water has higher surface tension than salt water. This creates more "suction" on your board as you try to break free. Combined with lower buoyancy, it explains why lake starts feel labored compared to ocean starts.
The solution: commit harder to your initial pump strokes. You need more speed to overcome the combined drag of surface tension and reduced lift.
The Mental Game
Many riders blame themselves when switching from ocean to lake. They assume they've gotten worse or lost fitness. In reality, the physics changed. Understanding this removes the frustration.
If you struggle on a lake with your ocean gear, it's not you—it's the water. Size up and enjoy the session.
Summary
Lake riding requires more power. If you struggle to get on foil in fresh water, do not blame your skills. Blame the lack of salt. Fresh water is 2.5% less dense than seawater, reducing both buoyancy and foil lift. Compensate by adding 5-10L of board volume and 100-200 cm² of foil area. Ocean riders switching to lakes need bigger gear. Lake riders switching to oceans should size down. The difference is small but significant—especially in marginal wind.