Aluminum to Steel

[Dawktah]

Hello!

I am new to the board and looking for some advice. I am considering buying our own 119cf steel tanks, cleaned and used for Nitrox. In order to keep down the confusion we are, EANx, recreational advanced divers who dive quite regularly in the Virgin Islands. I am not acquiring the tanks to increase bottom time but to save space aboard a small boat, two tanks instead of four. Looking to get two dives out of one tank. I am acquiring a 15' RIB. The tanks are described as being similar in size to an Aluminum 80, the size we commonly rent in the V.I. Other than removing weight from belt what else can I expect? I am 210 lbs. 6'0" but my soon to be wife is only 130 lbs. 5'6". Our routine involves doing our safety check at the dock and then putting on weight integrated BCDs in the water at dive site. There are only two Nitrox fill sites in V.I. One on St. Thomas and the other on Virgin Gorda. One tank each will also mean one evening trip to fill station

Is this a logical approach? Anybody using the 119cf tank? Are any steel tank brands better than others? Other than clean and dry and not letting it get completely empty anything to be careful of?

--Chris

 

[PerroneFord]

Sounds pretty reasonable. Of course, I don't know your breathing rate, so only you could answer whether you'd get all the time you require off one 119cuft tank. If you can get the shop to put 3000psi in it, you should be golden!

The 119 is a pretty common size. Different manufacturers tanks have different buoyancy characteristics, so be aware of that. Be aware of what valve comes in it. I'd probably get one of those DIN valves with a yoke adapter that can screw into it.

 

[scubadobadoo]

Your soon to be wife will likely be able to get away with using one tank for two dives assuming you aren't diving deeper that 50 or so feet for most of your dive. You however may have an issue but I almost weigh the same and do it with my steel 100 on shallow dives frequently in cooler waters. The concern when doing this is not will you have enough air for a normal or shallow dive, but will you have enough air in an emergency at the end of that second dive for both you and your partner.

The main concern here that you may have overlooked is that your wife may end up being over weighted in warm waters with a steel tank. My wife is the same exact size and if she used a steel tank in warm waters she would have to add major air to her BC to compensate and that isn't good as you should already know. Good luck! Decent idea but it may not work ideally.

 

[Damselfish]

was just going to say the same thing, depending what your wife2be wears for a suit and how much weight, she might find she's overweighted with just that tank and no additional weight. I know I would be.

 

[The Kraken]

Your wife, if she selects to use the 119, may want to consider an alternative flotation device. I elect to disagree with the term "overweighted" with respect to gas.

If one wants "x" amount of gas, then it will require a tank that can contain that amount. That is the tank with which you dive. If breathed down to 500 psi the steel 119 will be ~ 3 pounds negative at the end of the dive.

Keep in mind that it is at the end of the dive where one's proper weighting is determined. Does one have sufficient weight to be able to hold a safety stop at 15' with an empty BC and some residual gas?

It is a good possibility that she may be just perfectly weighted at the end of the dive with a steel 119. It's really one of those things with which one must experiment a bit in order to come up with the proper weighting combination.

I dive steel HP 119's and love them. With my SAC rate and doing an average 65' rec dive on EAN36 my NDL and gas consumption just about come out at the exact same time.

As to the length of the tanks, they're 24" long and would be a perfect length for her. No "bump the butt" during the dive, if you would.

the K

 

[mark99]

For you, I would consider getting a steel HP-130 tank. If you are considering the 119 then you are already OK with the larger diameter (8" rather than 7.25). Given your height and weight, I don't think you'd have any trouble with the larger size, and likely you have a greater SAC, you'll appreciate the extra air. You should consider the availability of HP fills at your destination, because if you get HP tanks and you can only get 3000 psi-200 bar fills, you have to consider the volume of air at that pressure. My HP-120 has only 107 cf at 3000 psi.

If I were you I'd carefully look at both your SAC's, prospective dive profiles, and possible underfilled tank volumes to make sure 2 dives per tank is do-able.

 

[Dawktah]

Thanks for the quick repsonses. We dive 3mm two piece suits. I hadn't thought about getting a 130cf for myself.

 

[J75]

If your wife is diving in a 3mm suit, with a steel 120', she's likely not giong to need any weight at all. You might want to think about a 130' for yourself and maybe a steel 85' for her.

 

[SteveAD]

another thing you might consider if you have significantly different SACs is swapping tanks between dives; she has more air left so you take her tank she takes yours for the second dive.

 

[Damselfish]

If breathed down to 500 psi the steel 119 will be ~ 3 pounds negative at the end of the dive.

at the end of the second dive.