Terms of use

Last updated 10 November 2026

Who we are

ProSail is run by MuMu Media Ltd. These terms cover this website, the ProSail race briefings and reviews, and the ProSail planning software during its free test. We will publish separate terms for paid plans before we take any payment. By using ProSail you agree to these terms.

ProSail is a planning aid, not a navigation system

ProSail helps you think through a passage or race before you sail. It does not replace official forecasts, nautical charts, tidal data, notices to mariners, a proper passage plan or the judgement of the skipper. Do not use it to navigate.

• Forecasts are uncertain. Fifty forecasts show more of that uncertainty than one, but all fifty can still be wrong, and the weather you meet can sit outside every one of them.
• Routes, departure times, arrival windows and courses to steer are estimates from a computer model of your boat. Your boat, sails, crew and sea state will differ.
• The charts and map data come from open sources that can be incomplete, out of date or wrong. The routing engine does not know about every hazard, restricted area, traffic separation scheme rule or shallow patch.
• A route exported to your plotter must be checked against an official chart before you follow it.

The skipper is always responsible for the safety of the boat and everyone on board, for deciding whether and when to sail, and for meeting the rules that apply, including the collision regulations and the duty to plan a passage under SOLAS chapter V.

Race briefings and reviews

Briefings and reviews are our own analysis, published for interest. They are not instructions for any boat, and a review of a past race is written with hindsight that nobody on the water had.

The free test

The planning software is in an early test. It may change, have errors or be unavailable, and we may end the test or remove plans at any time. Please tell us when something looks wrong.

Using the site fairly

Please only sign up with your own email address, and do not try to break, overload or copy the service.

Data and credits

Forecasts come from ECMWF, ocean and tidal data from the Copernicus Marine Service, and map data from OpenStreetMap contributors and Open Waters Seamap. These sources supply their data as is, and so do we.

Our responsibility to you

We provide ProSail as is. As far as the law allows, we are not liable for any loss or damage that comes from using it, or from relying on a forecast, route, briefing or review. Nothing in these terms limits our liability for death or personal injury caused by our negligence, for fraud, or for anything else the law does not let us limit.

Changes and law

We may update these terms, and the date at the top will show when. These terms are governed by the law of England and Wales. Questions to support@mumumedia.co.uk.