Alum vs. Steel

[DA Aquamaster]

I have a couple sets of double X7-100s and they work well at about 33 lbs and 24" in lenght.

E7-120's are about 4 inches longer and 5 lbs heavier.

LP 104's are about 13 pounds heavier than the 3442 psi E7-100 or X7-100.

Both the LP104 and the E8-130 are very similar in dimensions and the LP104 is about 2 lbs heavier and 2 lbs more negatively bouyant when empty. So for the size and weight of a 104 you can get a 130. If you live in north florida the LP 104 will get filled to similar pressures and volumes but for the rest of the world, the 3442 psi E8-130 is the way to go.

 

[lamont]

Of course, this scenario could NEVER happen with AL80 doubles if we stuck to your Rock Bottom philosophy, right? Here's a quote from the Rock Bottom web page: The rule of thumb is that you should not dive to a greater depth in fsw than your tank capacity in cu ft. This works reasonably well for most beginning and intermediate recreational divers and caps the depth that an Al80 should be dove to to 77 fsw (Al80 == 77.4 cu ft). Since double Al80s have a tank capacity of only 154.8 cu ft our depth limit would be 154'-155'...barely beyond recreational limits in the U.S. and just a few feet beyond recreational limits in the UK (BASC).

That's a rule of thumb for single tank recreational divers. I don't know how you could overlook all the qualifications that I wrote around that rule of thumb and how it should be applied and assume I meant it applied to technical diving. The audience for that whole web page is recreational divers, not technical ones. We keep having fatalities here of recreational divers who simply run OOG and were never exposed to any ideas on gas planning beyond "be on the boat with 500 psi" and that is what that webpage was written in response to.

 

[rjack321]

While I use a 7mm wetsuit for cave diving in MX, I can't imagine using one at any substantive depth (MX caves are really shallow, max 65ft for me). The compression just adds a huge bouyancy swing and really adds up. If you want to deep dive in anything colder than 3/2mm or skin type temps you need a drysuit. Seems odd I know but that's life for 100+ft dives in less than ~82F water (really really warm, warmer than FL)

 

[k-valve]

Thanks guys for all the good input. Most of the local debate seems to be one group trying to one up the other with no real factual information coming from either side.
Most of the diving I'm interested in will be in the 100-200 ft. range. I had already, pretty much, made up my mind on a set of HP STL 100, alum 40 for O2 and alum 80 nitrox mix. HP STL 100's are about the limit for this old back. LP95's or LP104's seem to be so much heavier than the HP100's or is this just my imagination? The dry suit for plan B situations is the reason I'm trying to find the proper glue for my dry suit seals.

That's a nice set up you're considering. The only two things you might consider...which you may have already...is LP85 doubles and a smaller EAN32 deco bottle. Most of the time a 40cf stage is plenty for your EAN32 mix and a 30cf is plenty for your O2 or EAN80 mix. Those smaller bottles are a little easier to learn with. The LP85 doubles are about the same size as the HP100s. You can get more gas in them with an overfill...if your LDS will do that for you. It's hard to get a complete 3500 psi fill in HP tanks sometimes, much less an overfill. That depends on where you dive though. My tech instructor has HP100 dbls and often wishes aloud that he had LP85s.

Good luck with your diving!!

 

[fweber]

To the OP: Without considering all the lp95,104, wet vs dry, etc discussions. And comparing more or less apples to apples, al80 vs lp85/hp100. Why would you want to stap on the essentially unditchable lead(if going into deco) required by the al80's? I started with twinned al80's and eventally moved to light steels for the reason of weight. By moving to light steels we dropped 8lbs of lead, and approximately 6lbs of tank weight, for a net loss of 14lbs less weight while standing on the swimplatform, equal bouyancy characteristics and a rig that can still be swum up, because the light steels are no more negative than the weight of gas in them at any point in the dive(same as the aluminum if the lead isn't considered ditchable because you may have to hold deco stops).

 

[MattL]

so what it realy comes down to is if your diving wet you go with al tanks if you dive dry then steel are what you like to dive.
THIS IS A DIR ANSWER!

 

[k-valve]

so what it realy comes down to is if your diving wet you go with al tanks if you dive dry then steel are what you like to dive.
THIS IS A DIR ANSWER!

First off this is not a slam, sarcasm, etc, but an honest question:

Why would one want to dive deep with (for example) a set of al80 doubles and a 7mm wetsuit? It seems to me that bouyancy swings are going to be a huge problem with this setup between compression factors of the 7mm and the positive bouyancy of the al80s. Sounds like a disaster waiting to happen to me. You'd be way overweighted at the bottom or way underweighted at the surface.

 

[lamont]

First off this is not a slam, sarcasm, etc, but an honest question:

Why would one want to dive deep with (for example) a set of al80 doubles and a 7mm wetsuit? It seems to me that bouyancy swings are going to be a huge problem with this setup between compression factors of the 7mm and the positive bouyancy of the al80s. Sounds like a disaster waiting to happen to me. You'd be way overweighted at the bottom or way underweighted at the surface.

Steel doesn't change anything in your analysis compared to aluminum. The only real additional safety issue with steels is if you cannot take off enough weight with highly negative steel doubles so that you are still overweighted at the surface with empty tanks (for me, diving in fresh water with double-130s and my 200g DC thinsulate undergarmet and my trilam drysuit i'm still pretty negative even when the tanks are empty with an Al backplate and no weight -- with a 3mm wetsuit or something like that i'd be severely overweighted throughout the dive).

Beyond that its just the buoyancy shift from consuming the gas, and the buoyancy shift of the wetsuit compression with depth.

So your question is really why anyone would want to dive deep with a 7mm wetsuit? Either way with 160 cu ft of gas and 7mm of wetsuit that gets crushed the buoyancy shift is going to be the same. Doesn't really matter about the tank material holding the gas. Doesn't matter that "aluminum is buoyant" since you'll just wind up offsetting that with a 10# v-weight or something like that anyway.

 

[MattL]

First off this is not a slam, sarcasm, etc, but an honest question:

Why would one want to dive deep with (for example) a set of al80 doubles and a 7mm wetsuit? It seems to me that bouyancy swings are going to be a huge problem with this setup between compression factors of the 7mm and the positive bouyancy of the al80s. Sounds like a disaster waiting to happen to me. You'd be way overweighted at the bottom or way underweighted at the surface.

If your overweighted then you need to get a biger wing I like to have a wing thats 10 more lbs then what I need for min lift so this is how I add it up my tanks are 2.5 neg each and manfould bands and other hardware is 3 lbs neg can light is 2.5 neg backplate is 6lbs neg and a 2 lbs tail weight so thats 17 lbs neg and I need 16 with out stages that are pos so I need no wight this is for a drysute.This is tanks at 300 psi so when there full there more like 10 to 11 lbs neg and thats the weight you need to figer left for your wing. When I dive wet i need its the same for me some peaple are less or more so if im at 150 and my wing fails how am i getting up thats why i say to dive wet with als becouse you have weight on your hip that you can drop to make you not as neg at deapth and kick your way up.

As to the question say you live in truck were you can dive a 3mm to 200 and not get cold why spend 2k or more on a drysuit when diving wet with stages gives you just as much gas as steel 130s.

Now I have a question of my own and i know its off subject a little bit but I want to know what are the best over all tank i had guys today tilling me that hp100s are when i was looking at 130s and i asked why they said that your can cary a stage for the other 60 cuft and not have 20 more lbs on your back so how do you guys feel about tank size for over all diving ps i have a set 2 set of hp100 sorry for getting of topic but on the same lines