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SailNavSim


What is this?

SailNavSim is a virtual sailing navigation simulator where you can sail and race with your friends and others online. You can participate in anything from a quick race across a small lake or harbour, or sail away on a month-long ocean passage to another continent or to your favourite remote island. The simulation runs in real time, so sailing over various distances will take as much time as you might expect in the real world. Anyone can sail, and no account creation or personal information is required!


How to participate

In order to sail, you must either create a new race or join an existing race before it has started. Everyone joining a race begins at the same starting position and is subject to the same weather conditions at this geographic position when the race begins.

Quick Start

A "quick start" mode is made available at the top of the main start page, where only your name (or alias) is needed as input. This will allow you to immediately start a single-player instance with some randomly chosen race parameters. To create a custom race, see below...

Creating a race

To create a race, fill out the form on the starting page with the following details:

Joining a race

To join a race, enter your name (or alias) and the race ID. The creator of the race (or another participant in the race) must provide you with this race ID, which is available to them once they have created or joined the race. Participants may join a race at any time up until the start time of the race, as specified by the creator.

You can also join any race advertised on the upcoming public races page. The race ID is shown there for each public race that has not yet started and is accepting new joiners.

Controlling your boat

Controlling your boat requires no specific knowledge of how to rig a boat or put up sails; all you really need is a basic understanding about the directions in which you can sail relative to the wind. There are three controls to your boat:

Wind response

Those who have sailed before, whether in the real or online world, may have come across a polar plot showing wind response curves for a particular boat at different wind speeds. Currently, only a single type of boat is modeled in SailNavSim, and every participant gets an instance of this same boat with this same wind response, as shown in the plot and table below for various wind speeds.

Polar plot showing boat speed over water (in knots) for various true wind speeds and angles from true wind direction
Boat wind response polar plot
Table of values for boat speed over water (in knots, to two decimal places) for various true wind speeds and angles from true wind direction
5 kt 10 kt 15 kt 20 kt 25 kt 30 kt 35 kt
30° 0.00 0.00 0.00 0.00 0.00 0.00 0.00
40° 2.86 4.96 5.60 5.94 5.82 5.44 5.34
50° 3.15 5.70 6.52 7.03 7.02 6.68 6.56
60° 3.40 6.14 6.99 7.51 7.46 7.02 6.91
70° 3.66 6.24 7.14 7.71 7.66 7.07 7.00
80° 3.79 6.34 7.29 7.91 7.91 7.37 7.26
90° 3.73 6.44 7.44 8.00 7.91 7.37 7.26
100° 3.67 6.51 7.45 8.11 8.10 7.41 7.26
110° 3.56 6.54 7.59 8.20 8.10 7.41 7.35
120° 3.43 6.40 7.57 8.20 8.16 7.67 7.61
130° 3.29 6.23 7.41 8.11 8.16 7.67 7.61
140° 3.01 5.70 7.20 8.03 8.21 7.92 7.87
150° 2.86 5.43 6.89 7.74 8.02 7.88 7.96
160° 2.70 5.06 6.43 7.37 7.77 7.58 7.70
170° 2.60 4.86 6.13 7.08 7.52 7.28 7.35
180° 2.50 4.63 5.69 6.60 6.96 6.42 6.39


As is evident from this data, the fastest point of sail relative to the true wind direction (visualize the wind on the plot as coming from the zero degree point, top to bottom) depends on the wind speed. Integrating this knowledge with the otherwise most direct geographical course to the finish location is a large part of what makes navigating in a sailing race -- particularly over vast distances with changing weather conditions along the way -- an interesting activity. With this boat, when steering within 30 degrees of directly into the wind, your sails will be ineffective in moving your boat along your chosen course. In this case, the force of the wind will begin to push your boat backwards, where you will see a negative speed over water for your set course. Steering directly into the wind has the same effect as taking your sails down, where your boat will be pushed "backwards" at 1/10th the wind speed.

Sea ice

One more variable that has an impact on your boat speed over water is sea ice. This value is calculated from sea surface temperature and water salinity, whenever these values are available. Although most of the ocean surface around the globe has no sea ice, in areas where it is present your boat will be slowed down in proportion to the amount of sea ice in that location, coming to a complete stop "over water" upon reaching 100% sea ice concentration. A global map showing the sea ice concentration, as modeled by the simulation, is one of the maps which can be found on the weather/ocean maps page.

Viewing your progress

Your boat progress and details are updated once per minute, and a few details (including position, speed over ground and true wind) are also shared with other participants in the race at a regular interval, which may be greater than one minute depending on how this was configured when the race was created. All boat status, geographical and weather information is provided on one page, with additional links to a maps page also provided. On the maps page, the weather map (from Windy.com) shows your boat position and approximate weather conditions at the present time. The race map (with OpenStreetMap tiles) shows the positions and recent tracks of all race participants as of the last shared reporting time, as well as the geographical bounding box for finishing the race. On this map, the race participant positions are displayed as boat icons, colour coded as follows:

Not Finished Finished Race
Your Boat Yellow boat Dark green boat
Others White boat Light green boat

Finishing a race

Each individual sailor may or may not finish the race, depending on whether they satisfy the race finish rules as specified when the race was created. Regardless of the outcome, all participants may continue to sail as long as they wish, subject to boat expiry rules.


Further details

The above information is certainly enough to get started in a race, but there's more you may still want to know, so feel free to continue below...

Your boat "key"

Since there is no requirement to create an account and no username or login required, your boat is set up with a unique key when you create or join a race. In a sense, this "key" takes the place of a username/password combination and should be treated as such. Just as sharing a race ID with anyone allows them to join that race, sharing your boat key with anyone will give them the ability to fully control your boat in the race. So it's up to you to keep it secret, or share it for the desired effect if you wish.

Date and time

All dates and times are currently presented in Coordinated Universal Time (UTC) or "Zulu" time (hence the "Z" suffix). For convenience, in many cases, the relative time (as of the page being loaded) is also shown alongside.

Boat expiry

Boats expire after 14 days of inactivity (that is, without any course change or start/stop commands) and are also removed from their race at that time.

Boat history

Hourly boat logs, which include the boat positions at the top of each hour, are kept for 30 days. Extended boat logs, which contain the boat positions at noon and midnight UTC (1200Z and 0000Z) for each day, are further retained for 365 days. This data is used to draw the historical boat tracks on the race map, and may also be used in the support of additional features in the future.

Weather and Ocean data

The weather and ocean data used here are sourced from the NOAA GFS (Global Forecast System) weather model forecasts and from the HYCOM ocean model. Data are chosen to approximate the weather and ocean conditions at any point on the globe at the current time. Although a number of different weather variables are displayed, only the following data currently have any effect on boats: wind direction and speed, ocean current direction and speed (where available), and sea ice concentration (calculated from sea surface temperature and water salinity, where available). Many of these variables can be found visualized on the weather/ocean maps page. The raw data from which these maps are generated is the same as the data used by the simulation.
But I see that the weather data shown to me doesn't agree with what's on the Windy.com map!
The weather information shown here may disagree with what you see on the weather map from Windy.com due to a combination of two main reasons:
  1. Windy.com uses the ECMWF weather model by default, which although should be very similar overall for relatively near-term forecast data within 6-9 hours (which SailNavSim uses), it can still differ from the data derived from the GFS model used here.
  2. SailNavSim "blends" data from two adjacent GFS forecast periods on an almost continuous basis. This means you won't get sudden sharp weather fronts taking over your boat at any time, but you will also experience more gradual changes in weather rather than sudden discontinuities every few hours when the latest weather model data is loaded.

Geography

As already mentioned, your boat will sail freely (subject to the weather, of course) while on water, but it will come to a stop upon reaching land and will need to be steered back towards water and "started" again. The geographical land/water data used is available for the entire globe to an accuracy of about 30 metres, so for the most part any land you see on an online map should be found just as well in the simulation at the same coordinates. SailNavSim also makes an attempt to ensure all geographical calculations take into account the realities of the Earth's shape, as one of the main goals is to model the real world as accurately as possible from a navigational standpoint, so all geographical calculations and information displayed to users ought to be reasonably accurate in these aspects.


I have a bug report, feature request, question or suggestion!

Great! I look forward to hearing from you, so please head on over to the Contact page and leave me a note.