AL tanks and diving wet

[Cthippo]

I've been told, mostly on this board, that aluminum tanks are not really suitable for diving with a wetsuit, especially in colder water. My understanding is that this is because of the net positive buoyancy of an empty AL tank needing more lead to counteract. That makes sense up to a point, but is it really enough to not dive the most common tank on the market because I use a wetsuit? It seems like both a steel and AL tank will lose the same amount of weight as the air is released and from the tank data I have seen the difference is less than 5 lbs.

 

[Boarderguy]

I still dive my 2 AL 80s with my hollis semi dry. 22 lb of lead, 13 cu pony, go pro camera rig. I'm close to being too light at the end of my dive though.

 

[inquis]

I think you may have misunderstood. Many people dive AL tanks with a wetsuit. You're correct that the change in buoyancy due to the air is 5 lbs for an AL80.

You actually have to be careful diving some heavy steel tanks with a thinner wetsuit, because you can be substantially negative. Maybe that was what you were remembering?

 

[azstinger11]

I think you may have misunderstood. Many people dive AL tanks with a wetsuit. You're correct that the change in buoyancy due to the air is 5 lbs for an AL80.

You actually have to be careful diving some heavy steel tanks with a thinner wetsuit, because you can be substantially negative.

I would say that in colder climates it is recommended when possible to dive to steel tank over AL due to the net positive buoyancy. Seeing as OP is Washington State steel tanks over aluminum tanks would be the prevailing wisdom.

But your point is absolutely correct regarding steel tanks and thin wet suits.

 

[inquis]

With thicker wetsuits, it's possible your integrated weight pockets cannot carry all the lead you need. This mandates putting some on a weightbelt or, as @azstinger11 indicates, using a steel tank in lieu of some of the lead.

 

[Boarderguy]

I wear a 12lb seasoft belt and have 10-12 lbs in my bc depending on the gear I have with me and an AL80

 

[Ski_Lounge]

It's hard to make a true apples-to-apples comparison, because the most common steel tank alternative, HP-100, while similarly sized to the AL-80, gets you 25% more air. I have not seen HP-80's much, so let's ignore that.

A steel HP-100 is about 6lbs more negatively buoyant than an AL-80, so that's 6lbs less of weight on your back. Likely you're driving a thicker wetsuit in cold water, so you probably still need some weight. In my 7mm wetsuit, with my steel backplate (6lbs), I only need to carry an additional 4lbs of lead weight. The HP-100 in particular also trims out quite well, more so than the AL-80.

 

[ColoDale]

Tons of people in Cozumel dive AL80s with wetsuits and they may be using more lead. Don't know. An AL100, which I use, is going to be more positive at the end than the 80. I use 14 lbs with a 3 mil jacket and neoprene weight belt. I drop down to 6-8 lbs with steel 120's. A DM I go with in the winter in Cozumel wears a 3 mil full wetsuit and 3 mil shorty with a beanie, uses AL80s and uses little weight. Anecdotal stories aside, a few pounds extra if you need it is not that big a deal.
I have not seen alot of posts saying AL80s are not suitable with wetsuits but plenty of posts about on SB about tank capacity, displacement and weighting.
You mention cold water so maybe you are talking about much more neoprene (7 mil ?). If I have that much buoyancy from wetsuits then I would prefer steel over AL instead of more lead with AL80s.

 

[kinoons]

All of my diving has been with AL80s. Tropically I usually use a 2/3 full body suit as I run a little cold. I use 10 lbs of weight.

I dove blue hole in NM a month ago. Also AL80 and a 7mm wetsuit with beanie and gloves. I had 10lbs and that was a little light. 12 lbs worked okay but I did have to kick down a little to get the 7mm compressed.

 

[TMHeimer]

I have only 4 AL80s since selling my 2 steel tanks years ago. I dive wet in Nova Scotia and use 40 pounds with my 7 mil farmer john. No problems in my 17 years diving. Dealing with an AL tank that may have less than 500 PSI near the end of a dive should be no problem for anyone except maybe a newly certified diver.