What just happened on the water near you?
Five Blasts reads the AIS signals ships broadcast and posts a short card when something happens on the water: a ship reports aground, an anchor starts to drag, two vessels pass too close.
- Five short blasts
- Under the Navigation Rules, five or more short blasts on the horn means danger, or that you can't tell what the other boat is doing. That's the name.
- From AIS, not radio
- Ships broadcast where they are, how fast they're going and what they're doing. Five Blasts watches that data and posts when a rule trips.
- One harbor at a time
- Each harbor is built from its own channels, anchorages and place names. The first is Charleston, South Carolina.
Built on vessel movement, not radio.
Every vessel with AIS reports where it is, how fast it's going, and what it's doing: under way, at anchor, aground. Five Blasts checks each report against a few fixed rules and posts only when one of them trips. That includes the things nobody calls in.
The ship's own AIS status says aground or not under command, on two reports in a row. One report can be a typo. An AIS distress beacon in the harbor counts too.
A ship at anchor ends up more than 100 m from where it set its anchor (big ships get one and a half lengths, since they swing wider), or keeps moving faster than 1 knot for three minutes.
A ship 50 m or longer sits under half a knot in the shipping channel for five minutes. Anchorages and turning basins don't count.
Two vessels on course to pass within a tenth of a nautical mile in the next ten minutes. A tug alongside its ship is docking, not a near miss.
Ships 50 m or longer, tugs, pilot boats and ferries coming in from sea or heading out. Pleasure boats are never posted.
If a ship trips two rules at once, say it stops in the channel and then reports aground, you get one card with both, not two. Only distress, anchor drags and blocked channels are meant to send a notification.
First harbor: Charleston.
All of Charleston Harbor from day one: the jetties and the entrance channel, the anchorages, Rebellion and Hog Island reaches, and up the Cooper and Wando rivers to the terminals.
Area
About 24 by 19 km, from the Morris Island Lighthouse to the Leatherman and Wando Welch terminals.
Not covered
- North Charleston Terminal. It's north of the area.
- Boats without AIS. Big commercial ships have to carry it. Plenty of small boats, most small sailboats included, don't, so they won't show up.
- Gaps in the public AIS feed. If a ship goes quiet, the card says so. It doesn't guess.
What it looks like
These are drawings of the app's screens with a sample event, not screenshots. Real screenshots go here when the app ships.
CHARLESTON
Cargo ship aground near Fort Sumter
SAMPLE VESSEL · cargo ship
SAMPLE TUG is dragging anchor in the Cooper River
Cargo ship aground near Fort Sumter
SAMPLE VESSEL · cargo ship
Speed
- 0.0 kn
Course
- 088°
Status
- Aground
How we detected it
14:01Ship's AIS status changed from underway to aground
14:03Confirmed on two reports in a row, so not a typo
LIVE MAP
SAMPLE VESSEL
Cargo ship · Fort Sumter
Speed
- 0.0 kn
Course
- 088°
Status
- Aground