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Surface Marker Buoy (SMB) – Why Is It Important and What Do the Colors Mean?

A Surface Marker Buoy (SMB) is one of the most important safety devices for divers. It allows divers to be visible at the surface and signals boats that divers are ascending. Especially in popular dive areas like Koh Chang, where many boats operate, a highly visible SMB is essential.

1. What Is an SMB Used For?

An SMB serves various purposes:

Safe Ascent: Especially in areas with boat traffic, an SMB makes ascents much safer.
Marking Dive Sites: It signals to other boats that divers are underwater.
Emergency Communication: Certain SMB colors can indicate emergency situations.
Drift Dives: During current dives, an SMB helps make a diver’s position visible.

2. What Do the SMB Colors Mean?

SMBs come in different colors, each with a specific meaning:

Color	Meaning	Usage
Orange / Yellow	Attention	Recreational and technical diving: Standard SMB for marking a diver’s ascent.
Red or Orange	Attention	Technical diving: Used to signal a normal ascent as planned.
Yellow (solid color)	Emergency	Technical diving: Used to indicate an emergency underwater (e.g., gas supply issue, deco problem). Often accompanied by a note or spool.

3. Technical Diving and the Correct SMB Usage

A technical dive is any dive deeper than 40 meters or requiring planned decompression stops. In technical diving, proper SMB usage is critical:

Red or Orange SMB (Planned End of Dive): In technical diving, the red or orange SMB is deployed at the start of the ascent. This signals to the boat that everything is okay and the dive is ending as planned.
Yellow SMB (Emergency): If an emergency occurs, a yellow SMB is deployed on the same line. This signals the boat crew that assistance is required.
Instructions for the Crew: The yellow SMB is often sent up with a note or spool to inform the crew what is needed (e.g., additional gas, medical help, a standby diver).
Technical SMBs Have Higher Lift Capacity: SMBs for technical diving should have a minimum of 20 kg of lift. This allows them to serve as an emergency buoyancy device, for example, if a BCD fails.

4. When and How Should an SMB Be Used?

All divers should know how to properly deploy an SMB. Here are the key points:

Before Ascending: The SMB is typically deployed at a depth of 5–10 meters.
Using a Spool: In technical diving, a spool is commonly used to deploy an SMB without drifting to the surface.
Slow, Controlled Ascent: The ascent should be gradual to avoid decompression problems.
Open Water vs. Boat Proximity: SMBs are primarily used when ascending in open water. If divers are surfacing directly next to their dive boat, it is generally unnecessary to deploy an SMB.
One SMB Per Team or Group Is Enough: It is not required for each diver to deploy an SMB. Usually, one diver in a team or group deploys the SMB, allowing the boat to track the entire group’s ascent.

5. Why Is an SMB Essential on Koh Chang?

Koh Chang is a popular diving destination with high boat traffic. Deploying an SMB ensures divers are seen early. Especially at dive sites like the HTMS Chang wreck or in current-prone areas, SMBs are critical for safety.

Conclusion

An SMB is an essential safety device for all divers. Choosing the right color and using it correctly can make the difference between a safe and a risky dive. Whether you’re a recreational or technical diver, knowing how to use an SMB is a fundamental skill!

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