Pony Bottle setup

[Michael_Lambert]

When you buy the tank you need or want, just make sure you buy it with a 200 BAR DIN valve.. it would come with the screw in adapter. At least all mine have

 

[AndyNZ]

So, I will consider to buy 2 different bottles (13 shallow shore, and bigger then 13 for deeper boat dives)

If you can, try and get hold of a larger tank first - preferably borrowed - and try it on a shore dive.

You may find that the extra size doesn't cause you any problems, in which case you can just buy one!

 

[elan]

But more weight and more complexity!

Not necessarily true, with our cold waters I calculated my dry weight was the same between double HP100 and single HP100 + 30cuf + all the lead

I actually found it less complex.

 

[hudson]

First, I want thank you all for excellent suggestions.

1. I am planning to use it up to 90feet depth NDL single tank dives and only for emergency bailout or looking for my buddy. But most of my dives is shallow shore dives (<70feet) and "dry" weight is consideration to me. So, I will consider to buy 2 different bottles (13 shallow shore, and bigger then 13 for deeper boat dives)

From experience, this would be unnecessary, unless you want maximum ease of carrying for travel/flight. In the water, there is no difference in ease of handling between a 13 and 19, I've slung both. Even on the surface the difference is minimal.

For refilling, you need to figure out your SAC - then google Rock Bottom Calculator for a spreadsheet that'll tell you how much gas you'll need for an ascent from 90ft. You can allow for a fast ascent rate to ~40ft and slower after that, and also minimize the safety stop duration with minimal increase in risk of DCS, and you'll see 13cuft is sufficient from an ascent from 90ft, even including ~200psi for gauge error, ~100psi for minimal gas to breathe and another ~200 psi for fudge factor or surface breathing.

However this would require a refill after losing only a few hundred PSI from the AL13. With the AL19 you can have the cylinder 2/3 full and still be ok. Download the spreadsheet and run your own numbers.

Regarding total rock bottom, you only really need to reserve enough rock bottom for one diver to ascend in your backgas, not two. The reserve for the second diver is in the pony.

 

[AndyNZ]

I actually found it less complex.

Try dealing with a manifold or first stage failure, then compare it with dealing with issues whilst either sidemounting or using a slung pony. Being able to see what you are trying to resolve is inherently more simple than trying to work out what is going on behind your head!

 

[diverrex]

I have a 13 cu ft pony. That was a mistake. A 19 is only slightly bigger but has 50% more gas. A 13 is much better than a spare air but I'd never recommend one to anyone, a minimum of a 19 is what I recommend.

 

[Nitroxnut01]

I don't normally post but since I used to sling on my left side a 19 cuft bottle when doing deeper then 80 ffw dives figured I'd post. I used to dive deep with a 19 until I found the article by NWGratfuldiver (nwgratefuldiver.com/articles/gas.html) on gas management. I figured my bailout and found that the 19 was to small but ended up going doubles anyway. The first question you had, any dive shop worth their salt should have a din to yoke fill converter. I ran a yoke on mine but have since going to doubles changed just about everything to din. The second question you had, filling it. What i did was check the tank to see if it was at 3000, if it wasn't because I'd used it to practice with or just from checking it I'd fill it. The 3rd question, I started with a button gauge then moved to a larger one because I couldn't see it. But with mounting it behind you it doesn't matter the size because you will not be able to see it during the dive. With the stage and deco bottles I use now, i have a small brass gauge on a 6 in hose. As for the size of the tank run the numbers from the article. I did some quick back of the page math from what info you have given. For a bailout at 90 ft :
Assess the problem and change to bailout
2 x 3.72 x 1.5 = 11.25
Assent to 20 feet for stop at 30 ft per minute
3 x 2.67x1= 8.01
Stop at 20 feet for 3 minutes
3 x 2.81 x 1 = 8.43
Assent to the Surface at 30 ft per minute
1 x 1.20 x 1 = 1.2
11.25+8.01+8.43+1.2 = 28.89 or 29 cuft

So a 19 would not do it for you and a 30 might cut it close. Other posters have pointed out that your buddy should be there and have enough gas for you and him to get to the surface. But if you don't know the buddy or if the buddy sucks down his air might not have enough for both of you. The nice thing about a slung tank is, if they are OOG and you don't have enough to safely take both of you to the surface, a slung bottle can be handed off. That is my 500 psi on it.

 

[Doc Harry]

Try dealing with a manifold or first stage failure, then compare it with dealing with issues whilst either sidemounting or using a slung pony. Being able to see what you are trying to resolve is inherently more simple than trying to work out what is going on behind your head!

Since you guys are "Down Under," aren't you also doing it upside-down?

 

[Diverpro1]

This chart may be helpful.

 

[Druid]

I change the gas in that tank once a year, assuming of course that I haven't used the tank.

I top off my pony every time I fill my tanks......I take a few breaths of the tank on each dive to check it works and practice deploying it.......so I loose a bit every dive......

My LDS tops them off for free, so it is no big deal........

This is my biggest issue with pony cylinders - people buy one because it provides "redundancy" but they never actually practice using it. So when the **** does hit the fan and they need the pony, they forget they have it/don't use it correctly/otherwise **** up and they slide deeper into the incident pit*. A pony is a good idea for no deco dives under 30m/100ft, but you need to practice its use regularly. Start at 6m and work your way down to the maximum depth you dive to, switch to your pony and ascend, doing any safety stops required. Jorgy is making some effort, but I would suggest making a habit of ascending on the pony from depth on say 1 dive in 10.




*There was a well publicised incident in the UK of a fairly experienced diver who failed to surface from a dive a couple of years ago. When his body was recovered his pony was empty, but his main cylinder was still full. It is believed that he began the dive breathing off his pony, when he drained it he spat out the reg, found his pony reg and put that in his mouth. Of course, the pony was empty and he was inside a wreck at 25m...