SMB inflation issues

[HenrikBP]

Very cool and useful factual information Akimbo. Thank you. Looking forward to the radar test report.

Henrik

 

[sotgecho]

Of course, the other downside of a 6'+ bag is figuring out how to carry the beast due to the significantly larger size.

I used this method with the exact same SMB and it works really well. Just make sure to carefully fold and deflate the smb by removing the opv first; fold and then replace it prior to putting in the storage pack. I clip my reel to my butt d-ring for storage.

Halcyon smb modification - shorter webbing? - Page 2 - DIR Explorers

 

[Splitlip]

A little more clarification is needed here. There are three types of SMBs:

1. Open circuit. The SMB is completely open on the bottom - pretty much an inverted sock that can be filled by bubbling air in the bottom by mouth or with a second stage. But it ca dump the gas if tension on the line is not maintained, allowing it to lay flat on the surface.

2. Semi- closed circuit. The SMB is open on the bottom but uses a cone shaped valve that allows air to be bubbled into the bottom by mouth or with a second stage, but helps retain the gas if the bag is laying flat on the surface. They do however require an OPV to prevent rupture due to gas expansion as they rise to the surface.

3. Closed circuit. The SMB is a closed system filled through an inflator stem. Thee bags will require an OPM to prevent the bag from potentially bursting on the way to the surface. But they will stay inflated indefinitely even if laying flat on the surface.

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Size matters.

I see technical divers in training using a small, skinny, 3-4 ft tall SMB to make it easier to fully inflate the SMB in training, usually launched from shallow depths, in order to meet a course standard. I don't think that transfers well to the real world where a skinny 3-4' tall bag is very hard to see at any distance in 3-4' waves.
Personally, I'd rather have a half inflated 6 or 7 ft SMB than a fully inflated 3 or 4 ft SMB as the larger SMB will be much wider and easier to see. And when launched from depth coming off a wreck, a 6 or 7 ft SMB does not take that much gas to fill when you're launching it from 150-200' ft.

On the other hand, it takes a degree of negative buoyancy to get an SMB to stand up. That is only a pound or so with a 3-4' SMB, but is more like 5-6 pounds for a 6-7' SMB. Consequently a tall bag is difficult to use in a recreational situation where a diver is near neutral at their safety stop with no gas in the wing or BC.

Thank you DA. I have said it all before, but somehow never get my points across as well as you seem to have done. LOL. (emphisis added )

 

[Splitlip]

I carry my big closed circuit Halcyon between my back an plate in the Halcyon MC storage pack. I inflate it with an LP hose.

Here's a tip for open and semi closed circuit DSMB's. When I used them, the first thing I did to get them to stand up was to dump air from my BC into the bag. (I am always a little negative to make the tube stay upright at the surface) In any event, I'd move gas from my BC to the marker and it would stand up while I sorted things out. Doing it this way, my buoyancy remained constant.

Just to put bag size versus inflation in perspective, most manufacturers of SMBs (semi-closed circuit models with an over-pressure valve and oral and/or one-way bottom fill) indicate buoyancy when full. That can be converted to air volume. I measured my full-to-deflated lung capacity by repeatedly blowing air into a graduated 2½ Liter plastic bottle using a short hose and a deep sink. One Liter of air equals 2.2 Lbs (2.264 Lbs in sea water) of displacement.

I came up with a little over 4 Liters. So for me, that is about 18 Lbs displacement with one lung-full filled from 33 FSW after the bag hits the surface. Many 6' tall SMBs are rated ~30 Lbs so the bag would be about half full. It would be about 27 Lbs when inflated at 66 FSW.

Unless I am orally filling deeper than about 60', I try to get two lung-fulls in the bag. Here is the sequence that is working for me.

1. Blow a little into the bag to make it unfurl and stand upright for easier handling.
2. Get the reel and line sorted out and exhale a large lung-full into the bag.
3. Replace regulator but breath shallow
4. Dump gas from the BC and/or drysuit until neutral holding the bag with a large lung full of air.
5. Blow the second lung-full into the bag
6. Replace regulator
7. Release the bag on the reel before sucking in too much air

This technique gives me an essentially full bag shot from 33'+. It also leaves me heavy as I am winding the reel up towards a stop, which I find easier with a little tension on the line. Of course, the other downside of a 6'+ bag is figuring out how to carry the beast due to the significantly larger size.

DAN is advertising, but not yet delivering, an updated version of their 6' bag with light reflective strips down both sides and an imbedded radar reflector. It will be interesting to test the effectiveness of the radar reflector. A friend has a radar equipped boat and an old DAN SMB for comparison. Detectable distance will vary a lot based on radar quality and operator skill, but I will post my impressions when I get them. It would sure be nice if the new SMB really lights up the blip.

 

[mweaver40]

It does appear the fault is mine and I am inflationally challenged LOL I bought the small skinny halcyon tube and it seems I am no better off then with my 6 foot wider tube and $100 poorer The water was a little on the cool side about 50 but I would probably have trouble if it was 70. Just can't seem to get the air in the tube and not out the side of my mouth. I think I ill spend some pool time on this and if that doesn't work I may be headed for a semi closed SMB. Thanks for all the good advice it is interesting to see how much thought goes into what seems such a simple task.