Mustard Dave
Contributor
It depends on the circumstances where and when I deploy it. If it is a fairly shallow wreck dive, I'd bag off at the shallowest part of the wreck, so I don't have as much line to reel in but have a visual reference of my depth to make buoyancy control easier. I still usually try to return to the shot rather than use a DSMB though.
When I first started using a DSMB, I had a self sealing type, so you open the bottom and squirt air in. I was taught a number of methods:
- Hold the bottom open and press the purge button on the octopus. This method is not always ideal as most my diving is in cold water. Pressing the purge button increases the chance of a freeflow.
- Hold the BCD inflater into the bottom and press both buttons simultaneously. This results in a stream of bubbles, but you have to watch your buoyancy. It may also be difficult to see the DSMB and you can increase the risk of it snagging and pulling you up.
- Turn your head to the left so the exhaust port of your second stage is pointing up, and exhale into the DSMB. I used to use this method. It was quite effective but you have to watch the line doesn't snag.
- Crack bottle. I've never tried one, but many swear by them. One type used a disposable CO2 bottle like you have in some air pistols and others have a small cylinder you charge using a decanting whip from your main cylinder before diving. With the latter type, you must close them before releasing. If you don't, you run the risk of water getting in and corroding the cylinder. As you can fill them yourself, many neglect to get them tested, and they are particularly prone to failure due to the possibility of water getting in. There are many accounts of crack bottles going 'bang'. The other issue is they are difficult to travel with as airlines don't often allow pressurised cylinders, even empty ones.
- My favourite type has a nipple that fits the quick connect on your BCD/suit inflate, but doesn't lock. I started using this type when I began using a CCR, as I cannot use option 3 any more. If I am diving open circuit, I disconnect the suit inflate and use that. If I am in a wetsuit, I leave my suit inflate connected, run it along the harness and tuck it behind a D-ring so I can find it when I need it, but it doesn't flap about. On CCR, I carry a side mounted ali-80 as a bailout. I have an inflater hose tucked in the hose tidy - this can be used to plumb the bailout into the rebreather of I have a problem with the on-board diluent, but mostly it will be used to inflate my blob.
One of our instructors at our club teaches students to kneel on the bottom and deploy as a buddy pair (one holds the reel and one inflates the blob). Whilst this is an easy way to do it, you have to bear in mind you don't always have a bottom to kneel on, and you may not always have a buddy! My preferred drill on buddy separation is to launch a DSMB, as it lets the first diver on the surface know where their buddy is and that they're okay. It is also a good idea to have your name in big letters on your blob so you can be identified.
I would always advise launching a blob any opportunity you get, as it keeps your skills sharp for when you really need to use them. At our local quarry, there is a plane near the entry point in about 14 metres. I like to use the wing-tip as a point to practice mid-water deployment.
There was an incident in the UK recently, where two divers were taken out to sea and had to be rescued. The skipper boat that collected them said the white of the tank helped spot them. Neither diver had a DSMB though, which would have made it much easier to spot them. It turned out they were from a university BSAC club and one was the Diving Officer!
