Boat Polars

Understand how boat performance is modeled in FairWinds using polar diagrams.

What Are Polars?

A polar diagram is a graph that shows a boat's speed at different wind speeds and angles. It's the fundamental data that determines how fast your boat will sail in any given conditions.

Key Components

• Wind Speed: True wind speed (horizontal axis or concentric circles)
• Wind Angle: Angle between boat heading and true wind (radial axis)
• Boat Speed: Predicted speed through water (values or contour lines)

Reading Polar Diagrams

Polar Plot Format

In a typical polar diagram:

• Center: The boat's position
• Radial Lines: Wind angles (0° = upwind, 180° = downwind)
• Concentric Circles: Boat speed in knots
• Curves: Each curve represents a different true wind speed

Example: IMOCA 60

At 12 knots of wind:

Boat Classes

FairWinds includes accurate polars for multiple boat classes:

IMOCA 60

• Type: Open 60-foot offshore racer
• Characteristics: Fast, foiling capable
• Best Conditions: Strong winds, open ocean
• Top Speed: 30+ knots

TP52

• Type: High-performance grand prix racer
• Characteristics: Excellent upwind, crew-intensive
• Best Conditions: Coastal racing, varied conditions
• Top Speed: 20+ knots

Class40

• Type: 40-foot offshore racer
• Characteristics: Versatile, good all-around performance
• Best Conditions: Medium-distance races
• Top Speed: 25+ knots

Figaro Beneteau 3

• Type: One-design offshore racer
• Characteristics: Equal performance, skill-based
• Best Conditions: Fair competition
• Top Speed: 18+ knots

Performance Factors

Velocity Made Good (VMG)

VMG is the component of boat speed in the direction of your target:

VMG = Boat Speed × cos(angle to target)

Key Concept: The fastest point of sail isn't always the fastest route to your destination.

Optimal Angles

For each wind speed, there are optimal angles for:

• Upwind VMG: Best angle when sailing toward the wind (typically 40-50°)
• Downwind VMG: Best angle when sailing away from the wind (typically 140-150°)

Factors Affecting Performance

Sea State

Wave conditions impact boat speed:

• Flat Water: Polars are most accurate
• Moderate Seas: 5-10% speed reduction
• Heavy Seas: 10-20% speed reduction

FairWinds adjusts performance based on wave forecasts.

Current

Ocean currents add or subtract from boat speed:

• Favorable Current: Increases speed over ground
• Adverse Current: Decreases speed over ground
• Routing Impact: Can change optimal route significantly

Using Polars for Strategy

Tacking Upwind

When sailing upwind:

1. Find optimal upwind VMG angle (e.g., 45°)
2. Tack when wind shifts or to avoid obstacles
3. Minimize time spent tacking (speed loss)

Jibing Downwind

When sailing downwind:

1. Find optimal downwind VMG angle (e.g., 145°)
2. Jibe to maintain optimal angle
3. Consider current when choosing which jibe

Reaching

On a reach (wind from the side):

• Often the fastest point of sail
• Minimal course changes needed
• Maximize time at these angles

Custom Polars

For advanced users and developers:

Polar File Format

Polars are stored in CSV format:

TWA,TWS_6,TWS_8,TWS_10,TWS_12,TWS_14
0,0,0,0,0,0
45,6.2,7.8,9.1,9.5,9.8
52,6.8,8.5,10.2,11.1,11.8
60,7.5,9.4,11.5,13.2,14.5
...

• TWA: True Wind Angle
• TWS_X: True Wind Speed at X knots
• Values: Boat speed in knots

Next Steps

• Learn about routing strategies
• Understand weather data
• Explore race formats