Quick answer

Most boats need roughly 2 to 3 kgf of thrust per foot of length to hold the bow in a 15-knot crosswind: around 30–40 kgf for a 20-footer, 75–100 kgf for a 40-footer and 150+ kgf past 55 feet. Tall, light boats with lots of windage and sailboats need more.

How this calculator works

Thrusters fight the wind, so the estimate starts there. We work out your boat's side profile above the waterline from its length, type and windage, then calculate the wind force on that area at the speed you pick, using the standard drag formula (force grows with the square of wind speed, so going from 15 to 20 knots almost doubles it). We then adjust for hull type. Sailboats get a bump because their pivot point sits further forward, which shortens the thruster's lever arm.

What it does not know

Displacement, keel shape, exact superstructure, current and how fast you need the bow to swing all matter. Treat the number as a starting range, not a purchase order. Thruster makers publish their own charts; ours lines up with them for typical boats, and we confirm every size against the actual hull before quoting.

Picking a design wind

12–15 knots: protected marinas, fair-weather boating.
15–20 knots: most owners. Handles a breezy afternoon at the fuel dock.
20–25+ knots: exposed marinas, charter boats, short-handed cruising.

More on this in how to size a bow thruster.

Tunnel size
Voltage