SMB's and DSMB's- What's the big difference?
For some it's all the same thing - a device that is used to signal your position on the surface.
Let's start at the basics first; an SMB is short for Surface Marker Buoy and a DSMB is short for Delayed Surface Marker Buoy. There is a big variety of SMB's and DSMB's available on the market today, which poses the Question: Which one is the best suited to my needs as a diver?
Let's look at the basic SMB.
A basic one can be a hard plastic buoy with a line connected to a reel which is then carried by the diver for the duration of the dive. For the traveling divers, an inflatable version of the buoy is available as well.
There is one more version of a SMB commonly referred to as a "Safety Sausage" (Tongue in cheek;P) which is a tube like object that can be inflated to mark your position. These SMB's are open at the bottom to allow for inflation using the second stage of a regulator. They don't seal at the bottom in anyway, which means the diver would have to keep it closed at the bottom.
A big mistake divers make is to "launch" these SMB's from depth (meaning any given depth underwater). Why is this a mistake?- Let's look at how DSMB's work!
Let's look at the DSMB's.
A basic DSMB is designed like the SMB but with an added difference, it has a over-pressurization valve (Dump valve), it is longer in length and is either sealed or able to automatically seal at the bottom. When "launching" a DSMB, you have it connected to a line and reel to keep it aligned with your current position.
So why would you need to use a DSMB rather than a basic SMB when you want to signal your position from depth? - If you "launch" a basic SMB from depth, the SMB moves around due to the resistance of the water which can cause the air inside the SMB to escape and you could end up with only a small portion of the SMB sticking out of the water. This makes it very difficult for boats to spot on the surface!
With a DSMB, you can inflate it as much as possible (usually until it starts to change your buoyancy) and then "launch" it. The DSMB will make it to the surface completely inflated and will stick out quite well, due to it's longer length, allowing boat traffic to easily that someone is in the water. The over-pressurization valve will automatically vent excess air out of the DSMB to keep it from rupturing.
We hope this helped!
Safe diving to you all!!