The SMB shown above was found lying on the stairs leading to the deck. It looked brand-new and may never have been in the water.
As we examined it, we realized this is not the type of SMB you should own. There are several problems with it that you should be aware of so that you do not invest in the wrong SMB.
A vital piece of gear
Ironically, like gloves and snorkels, Surface Marker Buoys or SMBs are one piece of equipment you do not need when diving Blue Grotto. However, when diving from a boat or anywhere there is boat traffic, having an SMB is vital. It lets your dive boat captain and other boats know where you are before you even surface.
A dive float and flag will accomplish the same thing in shallow water. However, in deeper water, towing a float and flag is impractical. Also, if you become separated from the person towing the flag, you must be able to deploy your own SMB.
It must be deployable
A friend who drives dive boats for a living told us about an incident that occurred when he was operating in seas that were higher than a diver’s head sticking out of the water. While cruising at 18 knots, he looked down to see that he’d passed within inches of a diver struggling to inflate his SMB at the surface.
This underscores the fact you can’t wait until surfacing to inflate your SMB. You must deploy it before surfacing. Among other things, this alerts your captain where you and your buddies will surface.
Increasingly, we see SMBs referred to as DSMBs, with the D standing for Deployed or Deployable. An SMB that can’t be deployed at depth isn’t worth having.
To deploy an SMB, you will need a reel or spool with enough line to reach the surface. Having just enough line to reach the surface is not enough. Due to differences in current speed between the surface and at depth, your line may go up at an angle. You need enough line to allow for this.
Unless you are a cave or wreck-penetration diver familiar with reels, you are likely better off sticking with a spool. Spools can’t jam the way reels can.
A variety of features
An SMB can have any number of features. Some are essential. Others are frivolous, like those SMBs topped with fish or other animals.
SMBs will often have words such as Diver Below printed on them. Some will have reflective panels, making them easier to see at night. There are even ones with transparent sleeves into which you can insert a chemical light stick.
Among the most significant differences between various SMBs are whether they are open-ended or non-open-ended. Each has its plusses and minuses.
Open-ended SMBs
As the name implies, open-ended SMBs are open at the bottom. This allows air to flow freely in and out, although some open-ended SMBs have baffles that reduce the rate at which air can exit.
The chief benefit of open-ended SMBs is that they give you more options for inflation underwater. We will cover those in a bit.
The chief drawback of this type of SMB is that unless you maintain constant, downward pressure on the line during and after ascent, the SMB can fall over and collapse. Ensuring the open end of the SMB is always underwater will prevent this.
Non-open-ended SMBs
This type of SMB is sealed at the top and bottom. Any air you add to it can’t escape unless you let it out manually or its overpressure relief valve activates.
When deploying an SMB at depth, you must remember Boyle’s Law. Filling an SMB one-third of the way at 20 m/66 ft means it will arrive at the surface full. If you add more air than this, it will overinflate on the way up. This is why having an overpressure relief valve on this type of SMB is critical.
The chief drawback of n on-open-ended SMBs is their limited inflation options. We will discuss these next.
Inflation options
There are several ways to inflate an SMB underwater. Some are better than others.
- Virtually every SMB will come with some sort of rudimentary oral inflator. These can be difficult to use and require repeatedly removing, replacing and clearing your regulator in the process. This is why they are the least desirable way to inflate an SMB.
- You can inflate an open-ended SMB by holding a second stage under the open end and pushing the purge button. However, this presents the risk of getting your second stage entangled in the SMB’s straps.
- A better way to inflate an open-ended SMB is to tilt your head and hold the open end of the SMB over the side of the exhaust tee from which the air is escaping. This presents less risk of entanglement.
Arguably, the best way to inflate an SMB underwater is to use air directly from your tank. Doing so will require that you equip your regulator first stage with an additional low-pressure inflator hose.
- You can get nozzles that will plug into the end of your extra low-pressure inflator hose. These will allow you to squirt air directly into the bottom of your open-ended SMB and present almost no risk of entanglement. They are also handy when inflating lift bags.
- Better quality SMBs will have a special oral inflator that fits the end of your extra low-pressure inflator hose. Pushing it in will automatically shoot air into the SMB. These can work with both open-ended and non-open-ended SMBs.
- Amazon even sells an aftermarket oral inflator you can retrofit to your SMB, adding the option to inflate the SMB using air directly from your tank.
Why it fails
The lost SMB we showed you at the beginning of this article has two serious flaws.
- To start, it can only be inflated orally. This is inconvenient and may even be dangerous.
- Second, it has no overpressure-relief valve. Thus, putting too much air in it at depth could cause it to burst like a balloon on the way up.
What this means is that this sort of SMB can only be inflated at the surface. And we’ve already explained why that is a bad idea.
You generally will not see this type of SMB for sale at professional dive centers. However, you will see them for sale online. This is most likely how the owner of the lost SMB came by theirs.
Two lessons here:
- Don’t purchase any dive gear made by people who don’t dive. They inevitably are copying equipment they don’t understand and are cutting corners when doing so.
- Items purchased at your local professional dive center may cost slightly more, but you will save in the long run because you will get equipment that better meets your needs.
Practice is essential
Many of the divers we see on dive boats are carrying SMBs they have never actually used. That’s unfortunate because deploying an SMB at depth requires practice. And what is one of the best places you can get that practice?
You guessed it: Blue Grotto.