× Frequently Asked Question

Welcome to Great Lakes & Seaway Shipping Online's Vessel Passage Maps. These AIS-derived maps show current vessel locations throughout the Great Lakes. The following are frequently asked questions about the maps

On June 28, 2011 we went live with our new version of the map, this has been in development since 2008 and incorporates many new features that were requested. We are still making a few updates that should be complete in late July.

We are updating this documentation to reflect the changes, please check back for updates.

If you would like to use the old map please visit http://ais.boatnerd.com/v1

What is AIS? The Automatic Identification System (AIS) is a radio-based system used by ships and vessel traffic services to track the location of ships. Its primary purpose is collision avoidance. AIS uses digital radio signals transmitted over VHF maritime channels 87B (161.975 MHz) and 88B (162.025 MHz) to broadcast information about a ship including its name, position, speed, course, dimensions, destination, and status. The use of AIS is mandated for international ships over 300 gross tons under the International Convention for the Safety of Life at Sea (SOLAS). US and Canadian laws require its eventual use on the Great Lakes for ships over a certain tonnage. Some vessels, such as ferries operating on a constant route, are exempted.

How is AIS information obtained? Anyone with a marine radio that can monitor channels 87B or 88B can pick up AIS transmissions. However they are digital signals that must be decoded for a human to understand them. Inexpensive software packages are available to do this decoding, as well as more advanced navigation devices. While AIS can provide a simple text output, it is typically combined with some sort of electronic mapping or charting program. This page uses base maps provided by Google Maps with data pulled from a custom database.



As radio signals, AIS transmissions have a limited range. This site extends the coverage range by linking multiple radio receivers through the Internet and combining all received AIS information onto one map.

Is this information current? The data shown on these maps is a few minutes up to an hour old depending on the station and delay in updates. AIS requires speed, position and course information to be broadcast every 2 to 10 seconds while underway and every 3 minutes while docked. Other information, such as ship size and destination, is to be broadcast every 6 minutes. This site itself refreshes every 10 minutes, so information could be perhaps 15 minutes or older at times.

What do the ship icons show? Each ship is shown by an icon. The pointed end of the icon shows the rough direction of travel. There is a "tail" behind the ship showing its course over the past 10 minutes. The ships name is shown next to the icon.

How do I get more details? By double clicking on the icon (not on the name box), a supplementary box shows up listing the: ship name, MMSI, ship type, latitude and longitude, speed, course, heading dimensions and status. Note that all this information is supplied by the vessel or personnel on board. We cannot correct spelling errors or incorrect data coming from a ship's transmitter. MMSI is the ships Maritime Mobile Service Identity, a nine digit unique identifier.

Latitude and Longitude are shown in decimal degrees.

Speed is over ground speed in knots

Course is the actual direction being traveled at the last reporting time.

Heading is the intended direction of travel.

Can I have my area appear on the Maps? If you would like to host a receiver please e-mail, all that is needed is a location near the water with an always -on Internet connection (like cable or DSL) where we can place an antenna and small receiver box. There is no cost for the equipment that we will maintain, the box uses minimal bandwidth and does not open any security holes. If you are using an AIS plotting software you can upload directly to our database via TCP/IP or UDP/IP upload, please e-mail for instructions.

Do all vessels have a AIS transmitter? No. Vessels under a certain size do not have to have AIS transmitters. Not all ferries who travel a constant route, regardless of size carry a transmitter.

Why can't I find a particular vessel? Vessels that are laid up or are inactive do not always transmit an AIS signal. In addition, AIS transmissions, like all radio signals, have a variable range depending on transmission power and atmospheric condition. Finally, the current coverage is limited due to the current number of active receivers. Great Lakes & Seaway Shipping Online's volunteer staff is working diligently to provide the best coverage possible within the constraints of its limited non-profit budget.

Why are these called maps and not charts? The Map Tiles used as a base map for this page do not show water depths, aids to navigation, or any of the other features that set navigation charts apart from maps. While it should be obvious, it must be stated: Do not use these maps for navigation purposes. Not only are they not charts, they are not always completely up to date maps or images and will show land where there is actual a channel. For the most accurate view change the map type to satellite. We are working on a version that will display nautical charts.

Why are the ships on top of each other? When viewing the satellite or map view and a small scale (zoomed out), the icon or name label of one ship will often block the view of another icon or name label. Simply zoom in on that location using the zoom slider and position keys on the left side of the screen. At larger scales the labels won't overlap unless the ships are right next to each other. If that is the case, double click on the ship icons to get more detail, including the ships name.

Why are the vessel dimensions incorrect? Dimensions are entered by the vessel in meters, our system converts these to feet. If the dimensions were not entered correctly by the vessel it will not convert correctly.

Why are some vessels listed as an incorrect type? Vessel type (freighter, tug, passenger, etc.) are enter by the vessel when they configure the AIS system, if they entered the wrong information it will dispaly incorrectly. We are updating the system so we can manually define the type for better sorting.

Why is a vessel shown on land? When using either the satellite or map view at a large scale (zoomed in), the ship icon will appear to be on land. The maps, the satellite photos have a certain range or degree of accuracy. The accuracy of a graphical AIS display can only be as good as the combined accuracy of its mapping and equipment components. So docked ships sometimes appear to be on dry land next to the dock instead of in the water. If a ship shows up miles from the nearest lake, it is likely a problem with its AIS transmitter or the electronic navigation system it might be linked to.

Is that an actual photo of the ship? When using the satellite view, photos of actual ships appear in certain locations. These are ships that were there when the photo was taken, which may have been several years ago. Do not confuse these photographed ships with the AIS location icons.