SMBs (Surface Marker Buoys):
What You Need to Know

Introduction

A Surface Marker Buoy (SMB) is an essential piece of safety equipment for divers. Whether you're diving in open water, near boat traffic, or doing decompression stops, an SMB helps you signal your location, assist with safe ascents, and improve visibility to surface support.

Note: This guide specifically covers dSMBs (delayed Surface Marker Buoys)—the kind you deploy underwater before ascending, not the kind towed on the surface during a dive.

SMB vs. dSMB: What’s the Difference?

Although often used interchangeably, there's a technical difference between an SMB and a dSMB:

This guide is all about dSMBs—inflatable buoys designed to be deployed from underwater, typically at the end of a dive. They help boats or surface support locate you before you surface, and provide a visual reference during ascent.

1. What Is an dSMB and Why Do You Need One?

A dSMB is a brightly colored inflatable tube that divers deploy to signal their position. It serves two main functions:

1. Surface Signaling – In areas with boat traffic, an dSMB makes you highly visible, reducing the risk of accidents.
2. Controlled Ascents – An dSMB deployed from depth acts as a visual reference, helping divers ascend at a safe rate and complete safety stops.

Many dive training agencies—including GUE, SDI, and SSI—recommend carrying an dSMB on every dive, especially for drift diving, deep dives, or dives with strong currents.

Personal Note: I carry an dSMB on every dive in my left pocket. This is my personal preference—but it’s also standard practice among GUE divers.

2. Should Your dSMB Be Pre-Attached to a Spool?

One common question divers face is whether to pre-attach their dSMB to a spool or keep them separate.

Pre-Attached dSMB & Spool (Preferred)

• Faster and more efficient to deploy
• Less risk of fumbling or losing gear
• No delay during emergency use

I personally prefer my dSMB to be pre-attached by threading it through a pre-tied loop in the spool line. This creates a secure knot and removes the need for clipping or rigging mid-dive.

Separate dSMB & Spool

• Modular—you can change out lines or dSMBs easily
• Slower to set up
• Higher chance of entanglement or dropping gear

For most divers, pre-attaching the dSMB is the best option.

3. Inflation Methods: Oral, LP Hose, and CO2 Cartridges

Oral Inflation (Preferred)

• Precise and reliable
• No gear dependency
• Works in any environment

Most dSMBs use a push-in oral valve, which requires pressing it with your lips or teeth to inflate. I strongly prefer dSMBs like Halcyon’s, which use a one-way valve—you simply exhale into it without holding the valve open.

LP Hose Inflation

• Quick if your inflator hose is available
• Adds bulk and handling complexity
• Risk of overfilling

CO2 Cartridge Inflation

• Inflates instantly
• Can fail, leak, or run out
• Not travel-friendly (airline restrictions)

Bottom line: Oral inflation—especially with a one-way valve—is the most reliable and versatile method.

4. How to Deploy an dSMB (Without Tangling or Losing It)

Step-by-Step Deployment from Depth

1. Look Up First – While in trim, look over both shoulders to check for boats, divers, or other hazards above.
2. Prepare Your Gear – If not already attached, thread the dSMB through the pre-tied loop in your spool line to form a secure knot.
3. Inflate the dSMB – Use oral inflation (preferred), LP hose, or a regulator purge (for open-ended dSMBs).
4. Release and Control – Let the dSMB rise slowly. Do not let go of the spool. Keep a gentle grip as the line unspools.
5. Monitor Buoyancy & Position – Keep the spool clear of your body. Ensure no gear or hoses catch the line.
6. Ascend Safely – Use the dSMB line as your visual ascent reference. Maintain ~10 ft/min ascent rate.

Common Mistakes

• Overfilling – Can cause rupture or loss of control
• Not looking up first – May hit a diver or boat
• Releasing the spool – You lose the dSMB
• Poor line management – Leads to entanglement
• Deploying too late – No time for surface to spot you

5. Deploying in Strong Currents

• Always deploy from depth before surfacing so the boat can track you.
• Use a larger dSMB (5–7 ft) for visibility.
• Keep light tension on the line to keep the dSMB upright in current.
• Practice ahead of time—current + stress = higher chance of mistakes.

6. Emergency Use: dSMB as a Distress Tool

• If you surface alone or lose your buddy, deploy your dSMB before surfacing.
• Yellow or Pink dSMBs are sometimes used to signal emergency or need for assistance.
• Some dSMBs include slates or note sleeves to write surface messages (e.g., “low on gas”).

7. Maintaining Your dSMB and Spool

• Check for leaks periodically—inflate it on land to confirm it holds air.
• Inspect your spool for tangles, frays, and salt buildup.
• Store it correctly—rolled neatly, stored in your left pocket or pouch for consistency.

8. Choosing the Right dSMB for Your Diving Needs

Final Thoughts

An dSMB is one of the most important pieces of safety gear a diver can carry. It improves visibility, facilitates safe ascents, and can even save your life in an emergency.

• Choose a closed-end dSMB with a one-way oral valve
• Pre-attach it to your spool for immediate use
• Practice deploying it before your next dive

Got questions or want to share your own dSMB setup? Reach out to Dive Otter!