Surface float with hang tank

[nv]

All,

I would like to know if anyone does the following and/or their recommendations:

I have a surface marker and been thinking of connecting a hang tank to it at approximately half the max distance I will be diving. I tend to do deeper dives on private boats and thought this might be a pretty good idea/safety precaution.

Thanks in advance

 

[rongoodman]

I think you'd be better off planning your dive and gas consumption in advance, and then sticking to the plan. If you still want a redundant gas supply, sling a 30 or 40 cubic foot tank which you can access when you need to, rather than having to get back the the hang tank.

 

[nv]

I think you'd be better off planning your dive and gas consumption in advance, and then sticking to the plan. If you still want a redundant gas supply, sling a 30 or 40 cubic foot tank which you can access when you need to, rather than having to get back the the hang tank.

I say it more for the group in general. I have the gear for it. I usually dive with 4-5 people. More of an "oh shoot" situation safety practice.

 

[Peter69_56]

If you do tech training they will advise carrying all the required gas. You may not be able to get back to the float thus the gas is of no use to you. Even if its there as backup, it isn't a backup if you cant get it.

In saying that I usually hang a cylinder under our boat with deep dives. It doesn't come into any gas planning at all and is simply there for an emergency and is usually 50% Nx. I carry all my required gas for thirds diving gas rule, and usually have more than enough for the deco.

 

[rambaldi]

One of the charter operations I often dive with does this. It is usually for dives on a wreck where it is much easier to find your way back to the anchor etc. Instead of hanging the bottle at 1/2 depth they hang it at 6m to ensure people can sit on it for their safety stop. They can do this with out having to take it off the line or deal with it in any other way. They have it hanging there charged but turned off so it doesn't all leak away.

 

[Peter69_56]

Yes usually on rec diving where there is a possibility of divers not being diligent enough to ensure they have enough air to do a safety or potential deco stop. Not there as a requirement, rather as an emergency supply if all else fails.

 

[supergaijin]

Sounds like a good way to lose a tank. Hang tanks can be very useful but require a solid shot line. Normally a 'surface marker' has very thin line.

I'd seriously consider slinging a pony for those 'Oh shoot' moments.

 

[Peter69_56]

Sounds like a good way to lose a tank. Hang tanks can be very useful but require a solid shot line. Normally a 'surface marker' has very thin line.

I'd seriously consider slinging a pony for those 'Oh shoot' moments.

Good point, silly how we (me) miss the bleeding obvious. Agree, an SMB line is a bit on the thin side, shot line required, and how do you propose to stop the SMB (assuming it will take the weight) from drifting away?

If you are going to hang a tank, just hang it from the boat on a shot line, (normally) at 5m or so, line charged but turned off to prevent a free flow.

I would sling the cylinder on me so I can't lose it.

 

[DevonDiver]

I don't see any logic in hanging a tank 'half-way'. Either carry it, or hang it at stop depth.

It's a relatively common practice for charter boats to deploy a 'hang tank' down at 5m on a shot line; to ensure divers returning from deeper dives have sufficient gas to conduct safety or emergency deco stops. It's not common to use nitrox mixtures (especially above 40%), as this might entail legal liability if/when divers aren't trained/qualified to use that.

If the plan isn't to come back to a shot line, or there is reasonable doubt that you might do so, (as your question seems to indicate), then the gas should ideally be carried throughout the dive. A slung tank is the generally preferred method. The dive leader carrying that tank does not preclude it being handed over to any other group member who might subsequently require it.

There's really no excuse for running low on air, even more so in conjunction with overstaying NDLs and accruing deco obligation. If this were a serious possibility with a given group of divers, then the prudent option would be to avoid taking those people on deep dives in the first place - rather than trying to plan contingencies for the predicted screw up...

 

[AfterDark]

Olympus dive op uses 2 tanks on board the boat one port one starboard with 25' hoses which puts 2 2nd stages right at SS depth. The very 1st time out I used that rig! My PDC battery went dead during the dive. I had been playing the bottom time and depth, reducing depth every time I got close to the NDL. I decided to do a long SS really a deco stop of 15 minutes. I didn't have the gas for that long of a stop, but thankfully they did! I don't know what you use for your float line. I use 1/4" braided line which will hold a small boat. Back when I started diving hanging tanks (from the boat) was as common as slinging them is today. If I understand you correctly the tank is not only for you but for anybody in your party that needs gas. IMO it's not a bad idea.