Small Diving Vessels: How to Identify Them and Navigate Safely

When operating a boat on inland waters, coastal areas, or the Great Lakes, recognizing special-purpose vessels is essential for safety. One of the most important vessels to identify correctly is a small diving vessel, as divers may be in the water nearby and vulnerable.

Day Shapes and Flags for Small Diving Vessels

A small diving vessel may display one of two internationally recognized signals during the day:

• International Code Flag “A” (Alpha)
  A blue-and-white swallow-tailed flag indicating that the vessel has a diver down and is restricted in its ability to maneuver. Other vessels must keep well clear and proceed at slow speed.
• Red-and-White Diver Down Flag
  A red flag with a white diagonal stripe, commonly used in inland and U.S. waters. This flag signals that divers are in the water and that extra caution is required.

Either flag warns nearby boaters to maintain a safe distance and be prepared to alter course.

Night and Restricted Visibility Signals

When visibility is reduced or at night, a small diving vessel displays three all-round lights in a vertical line:

• Red (top)
• White (middle)
• Red (bottom)

These lights make the vessel identifiable from all directions, whether you are approaching abeam, ahead, or astern, as illustrated in the image.

What Boaters Must Do

If you see a vessel displaying diving signals:

• Reduce speed immediately
• Keep well clear of the vessel and surrounding water
• Avoid creating wake
• Be alert for divers surfacing away from the boat

In many areas, including the Great Lakes, laws require vessels to stay a minimum distance away from dive flags and diving vessels.

Why This Matters

Divers often surface unexpectedly and may be far from their vessel. Understanding and respecting diving signals is critical to preventing serious injuries or fatalities. Safe boating begins with knowledge, awareness, and courtesy on the water.

Learn More About Navigation and Boating Safety

Understanding navigation rules, vessel signals, and safety practices is a core part of becoming a confident boater or sailor.

Lake St. Clair Sailing School offers hands-on instruction covering navigation rules, safety equipment, and real-world boating scenarios on Lake St. Clair.

📞 Call: (586) 770-2518
🌐 Visit: https://lakestclairsailingschool.com
⛵ Learn to Sail in Michigan with Confidence

Small diving vessel
or	Day signs
Abeam, port side	Ahead	As