Don’t go down without it

Among the essential equipment every diver should own and use is an item that, surprisingly, many divers either do not own or do not bring with them on every dive. That item is a Surface Marker Buoy or SMB.

What is an SMB?

To answer this question, you need not look any further than the top of the page. You most likely recognized this as soon as you saw it.

An SMB is a bright-colored, inflatable tube designed to alert boaters and other divers to the presence of divers below. Unlike a dive flag and float, an SMB is not something you have to tow with you for the entire dive. Instead, you can wait to deploy it until just before you ascend.

Why you need one

In South Florida, boaters pose a substantial risk to divers. Even in good conditions, a diver’s head sticking up above the water can be surprisingly hard to see. And, if that diver is just below the surface, they are effectively invisible. Thus, an SMB can serve as a more visible warning to boaters to stay clear. But this is not the only function SMBs serve.

If diving from shore, your group leader should be towing a dive flag and float. But what happens if you become separated from the rest of your team, including the person with the flag and float? In this instance, an SMB can warn boaters that there is someone just below the surface. And, if your buddies surface just before you do, it will alert them to where you are.

SMBs are an integral part of South Florida drift diving. If you deploy an SMB prior to ascending, by the time you complete your safety stop, there is a good possibility your dive boat captain will have seen it and be ready to pick you up.

Let’s say you are diving from a boat that is either anchored or tied up to a wreck. If you become separated from the wreck or otherwise get caught down current, your deployed SMB will alert the captain to what has happened. It will allow him to keep an eye on you until he is able to come pick you up.

Essential features

When shopping for an SMB, here are the things you should look for:

Color: You won’t have a lot of options here. Most SMBs are bright orange; a few are bright yellow. If you have a choice, the determining factor would be: What stands out best in your local environment?

Size: Where lift bag size if denoted by their lifting capacity in pounds, there is no comparable rating system for SMBs. Most SMBs are around four to fine inches in diameter and at least four feet high. There are also large-capacity models that are at least twice the diameter and a minimum of six feet high. These are popular among tech divers.

Inflation options: You will need at least two means of inflating your SMB. Every SMB should have an oral inflator; this is something you use chiefly at the surface. You also need a means of inflating the SMB underwater using your regulator. This leads to the next questions, which are…

Open-ended…? Most SMBs are open at the bottom. This allows you to inflate them underwater using air from your regulator. The downside here is that, should your SMB pop out of the water when it surfaces, it will deflate and collapse. If it does, you will not be able to re-inflate it until you surface. Some SMBs will have a baffle at the bottom that makes it easy for air to enter but hard to escape.

…or sealed? Some higher-end SMBs are totally sealed at the bottom. Once inflated, air will not come out until you let it out. This eliminates the possibility of the SMB deflating and collapsing at the surface. This type of SMB will have a special inlet valve that allows you to inflate the SMB using air from a low-pressure inflation hose. Of course, this means you will need to equip your regulator with an additional LP inflator hose. This is the fastest and easiest way to inflate an SMB underwater. It further eliminates any risk of getting a regulator second stage entangled in the SMB.

O/P valve: If your SMB is sealed or has a baffle at the bottom, it will need to be equipped with an overpressure-relief or O/P valve. This will prevent air in the SMB from over-expanding and bursting the SMB on the way to the surface. You will also need it to be able to deflate and stow the SMB when done.

Reflective tape: Your SMB should have a piece of reflective tape on both sides near the top. This is so it can be seen at night…assuming someone knows to shine a light in your general direction. This why, if diving at night, it is a good idea to also attach a chemical light to the top of your SMB.

Attachment ring: You will need some sort of a D-ring at the bottom of the SMB to which you can attach the line from a reel or spool. We will discuss why shortly.

Stowage and carrying options: Your SMB will have some sort of strap that allows you to stow it in a rolled-up position. This is something that should be easy to use but not come easily undone. Most divers will clip their SMB to a D-ring on their BC harness. This D-ring should be far enough back so that the SMB does not dangle below you (SMBs can be a serious entanglement hazard). Alternately, you can stow a small SMB in a special sleeve or thigh pocket to further reduce the entanglement hazard.

Deployability is the thing

Among the scariest stories we’ve heard was from a dive boat captain in Boca Raton. While cruising at a leisurely pace, he looked down to see that he’d just missed a diver from another boat by mere inches. That diver was feverishly trying to get his SMB inflated. While he did, his head would disappear in the trough between waves, making him unseen and unseeable.

This underscores why it’s essential you not wait until surfacing to deploy your SMB. You need to do it at depth so that it is waiting for you when you arrive at the top..

Remember this: It will take you at least two to three minutes to ascend from depth plus another three minutes for a safety stop. If you deploy your SMB before ascending, that’s five or more minutes your SMB will be at the surface marking your spot. This will alert the captain to your location and increase the likelihood of him being able to pick you up shortly after surfacing.

SMBs are often referred to as DSMBs, with the D standing for Deployed or Deployable. This underscores why deployability is essential to effective SMB use. It leads to the other item you will need to use your (D)SMB effectively.

Reel or spool?

Your SMB is designed to be used in conjunction with a reel or spool. What is the difference between the two?

A reel is something you typically see cave and wreck-penetration divers use. It will have a frame, a handle, a spool with line and a winding knob with which to turn the spool. The upside of reels is that they can provide the easiest way to retrieve line; you just turn the crank. The downside is that they are expensive, bulky and easily jam. A jam is not something you want to happen while trying to ascend.

A spool is what you have if you remove everything from a reel except the drum holding the guideline. Spools are inexpensive, compact and almost impossible to jam. They are a little more of a pain to wind up; however, we are only talking about a hundred feet or less here. It’s not like you are going thousands of feet back in a cave.

For most divers, a spool is the better choice. Your spool will come with a double-ended stainless snap. You use this to both lock down the spool and attach it to a D-ring on your harness.

Using your SMB

It’s important to understand that learning to deploy an SMB is not a do-it-yourself proposition. You are going to want to work with an experienced instructor.

Fortunately, it is not as though you need to take an SMB Deployment Specialty Diver course. Learning to use an SMB is something that can easily be worked into most advanced or specialty diver courses — or even just a guided dive.

What we are going to do now is give you an overview of some of the steps involved in SMB deployment. This will give you an idea of what you will practice under instructor supervision. For simplicity, we will assume you are using a spool, although the same steps apply to reels.

It takes teamwork

Deploying an SMB takes more than two hands. You need two hands to inflate the SMB and another two to handle the reel or spool.

Unfortunately, unless you grew up next to a nuclear power plant, you only have two hands. What you do have, however, is a buddy. This allows you to have one buddy who will inflate the SMB at depth while the other manages the spool and guideline.

Of course, if you have become separated from your teammates, you won’t have that extra set of hands. Ask your instructor how he would handle this situation given the equipment you own.

Getting ready

Before sending your SMB on its way, there are several things you need to do to get ready. These include:

You will need to unclip your SMB from your harness (or take it out of its sleeve or pocket) and unroll it completely. This will allow it to fill easily.

You will need to make sure the guideline is firmly attached to the D-ring at the bottom of the SMB.

You will also need to ensure your spool is not locked down. As soon as you start putting air in it, your SMB will want to take off for the surface. If the spool is locked down, the SMB may try to take you with it.

Both you and your buddy will want to be slightly negative at this point.

If you are the one inflating the SMB, slight negative buoyancy will help you hold it down while you inflate it.

The buddy managing the spool will want slight negative buoyancy so that he can maintain tension on the line during the SMB’s ascent.

How much air?

Keep in mind the fact you do not need to fully inflate the SMB at depth. In fact, the SMB would likely get away from you long before you could. The amount of air needed for the SMB to arrive at the surface fully inflated depends on depth. For example:

At a depth of 33, the SMB will only need to be half full.
At 66 feet, just one-third full.
At 99 feet, just one-quarter full.

Inflating the SMB

Inflating the SMB will depend on the type of SMB you have.

If it is the type you can inflate from a low-pressure inflator hose, you need only press the end of the hose against the special inflation valve. When you get sufficient air inside the SMB, just let go.

If you must inflate the SMB using air from a regulator, things get a bit trickier.

One method is to place your alternate-air-source second stage under the SMB’s bottom opening, mouthpiece up, and then depress the purge button. The only problem here is that, if your second stage becomes entangled in the SMB, you are both going up together.

The other popular method is to cock your head sideways so that one side of your regulator’s exhaust tee is pointing straight up. Now hold the open end of the SMB over this and your exhaust bubbles will inflate it. This poses less risk of entanglement.

Time to let go

If you have made yourself slightly negative, you should be able to hold the SMB down long enough to get it adequately inflated before letting go. Just be prepared in case the SMB decides to take off on its own. You don’t want to be dragged up with it.

Once the SMB is on its way, the buddy with the spool becomes responsible for controlling it. It’s important to maintain tension on the line so that the SMB doesn’t pop out of the water and deflate. The buddy with the spool will also need to maintain this downward tension with the SMB breaks the surface so that it points straight up and can be seen.

Time to wind things up

With the SMB deployed, it’s time to begin your ascent. Winding a spool takes time and, thus, helps ensure a nice, slow ascent.

The buddy with the spool will need to maintain slight negative buoyancy throughout the ascent and safety stop. When you reach safety stop depth, the buddy can simply lock down the spool and clip it to a shoulder D-ring. This will leave him suspended a constant distance from the surface.

When the safety stop is complete, unlock the spool and ascend the final 15-20 feet to the surface. You will want to cover this distance very slowly.

When you reach the surface, lock down the spool and leave it attached to the SMB. You can continue to hold down on the bottom of the SMB with your hand so that it remains upright.

When the boat comes to pick you up, hand the SMB and spool up to the crew as a single unit. Your work here is now done — except, of course, for getting out of the water.

You got questions? We have answers.

If you have questions about SMB use, you’ll find us more than happy to answer them. We can also help you pick out the best SMB for you. Just ask.