TECHNICAL -
July 16, 2026
Speed polars: how is a catamaran's performance calculated?
How do you know if a catamaran is sailing at its optimal speed?
How do you choose the right angle to the wind to gain efficiency?
The answer lies in one key tool: the speed polar. A true reference in sailing, it lets you anticipate a boat's performance based on wind, angle, and sail configuration. But how is a polar designed? Is it theoretical, or based on real-world testing? And how do you use it in practice on board?
Let's break it down.
Speed polar: a simple, concrete definition
A speed polar is a graphical representation of a boat's theoretical performance.
It shows the boat's speed
• Based on wind strength
• Based on the angle to the wind
In other words, it answers an essential sailing question: How fast can I go in these conditions, and at what angle is my speed optimized?
The polar turns complex data into a simple, practical decision-making tool for sailing.
How are a catamaran's polars created?
Creating a polar can follow two main approaches:
1. The theoretical approach (calculation software)
Polars are generated using software specialized in naval architecture (Computational Fluid Dynamics: CFD). For the Excess 13, they were developed by the Marc Lombard Yacht Design firm.
This software takes into account:
• Hull resistance
• Appendages (keels, rudders)
• The sail plan
• Wind/hull interaction
⚠️ Important: Not all software uses the same parameters or algorithms. This means polars from different design firms cannot be compared directly.
At MLYD, the software used consists of industry-standard tools, configured and fine-tuned to match the boat's real-world behavior as closely as possible.
2. The empirical approach (real-world testing)
Theory alone isn't enough. For the Excess 13, the polars were tested at sea for six months.
Why? Because a theoretical polar assumes:
• Perfectly trimmed sails
• An optimized sail plan
• Ideal conditions
But the real sea is always more complex.
Real-world testing makes it possible to:
• Adjust the data
• Correct discrepancies
• Bring theory closer to reality
It's this dual approach (calculation + sea trials) that guarantees the reliability of the polars.
The limits of a speed polar
A polar remains a decision-support tool. It cannot:
• Precisely measure wave intensity
• Replace the skipper's experience
• Anticipate every weather variable
It models an optimal speed under given conditions, but it doesn't sail the boat for you. The quality of the software also affects how well it simulates sea state and its impact on overall performance.
How do you use a polar while sailing?
A high-performing catamaran doesn't just sail "on a heading." It sails at the right angle to the wind.
The polar lets you:
• Identify the optimal angle when sailing upwind
• Determine the best point of sail downwind
• Optimize your course
• Choose between speed and comfort
It becomes a true strategic tool for improving sailing efficiency.
A different polar depending on the boat's configuration
One essential point: every configuration affects performance. On the Excess 13, several parameters change the polars:
• 3 loading levels (light, intermediate, loaded)
• 2 rig types (Standard and Pulse Line)
That amounts to 6 different polars, tailored to the boat's actual configuration. The goal: the best possible balance between weight, rig, and performance.
Boat speed based on true wind speed (TWS) and angle (TWA)
Apparent wind speed (AWS) based on angle and true wind strength
Velocity Made Good (VMG): optimized speed upwind and downwind
In summary: what is a polar really for?
A speed polar lets you:
• Anticipate a catamaran's performance
• Optimize your angle to the wind
• Sail more efficiently
• Better understand how your boat behaves
Now polars hold no more secrets for you: they give you the benchmarks to optimize your sailing, but it's always your feel at the helm that will make the real difference!
