How do we integrate sea ice into weather routing? To simulate routes ahead of the circumnavigation, this seemed essential to us. Together with Meltemus, we created a specific module for qtVlm routing software!
Preparing an Arctic circumnavigation under pure sail, without motor assistance, demands a unique requirement: being able to navigate through areas subject to the presence, sometimes massive, of sea ice, without taking unnecessary risks. However, dynamically integrating sea ice density into routing calculations performed by software like Adrena or qtVlm was previously impossible.
The Challenge: An Unusable "Ice" Constraint
I personally use qtVlm, a free navigation software developed by Meltemus (Philippe Lelong), enabling weather routing, polar management, GRIB files, routes, and various sensor integrations. While preparing routing simulations for the Arctic circumnavigation, I noticed that although qtVlm displayed sea ice density data from GRIB files (such as AMSR2 or NOAA publications), it was impossible to integrate them directly as a routing constraint. Two insufficient alternatives were available:
- Creating fixed barrier shapefiles that ignore ice evolution over time;
- Or ignoring ice altogether in routing calculations, which was out of the question.
Proposed Solution: Speed Dependent on Ice Density
I proposed a simple and practical solution to Philippe Lelong, lead developer of qtVlm: introducing a speed reduction formula based on sea ice density, with a maximum density threshold beyond which speed drops to zero.
Proposed Formula:
- Vb: effective speed in sea ice
- Vm: speed in open water (from boat polars)
- Dg: ice density at time T
- Dgmax: user-defined maximum passable ice density
This formula offers two major advantages:
- Implementation Simplicity: only one user parameter to define.
- Algorithmic Elegance: the routing engine naturally "avoids" zones where speed falls to zero, without artificial constraints.
Implementation: Fast and Efficient Response
Philippe responded positively. In less than a week, a beta version of qtVlm incorporating this new logic was released. Key additions include:
- New "Ice Density" field visible in route tables and route histograms.
- Speed reduction coefficient visible on STW hover.
- Progressive speed reduction based on ice concentration.
The system works seamlessly: during testing, generated routes naturally bypass heavy ice concentration areas without manual intervention.