Steel HP100 or HP120 and reserve air in tank?

[Flashgun66]

Look up Minimum Gas or Rock Bottom. My reserve is tied to my depth (among other things). Also consider what you need the reserve for (e g., is entanglement likely where you dive).

Thanks I'll check it out

 

[Flashgun66]

Hey guys - so after all the gas calculations are done for depth, plus air to surface, including safety stop and possible emergency air needs for a specific dive .... I'm wondering do you guys still surface with an additional 1/3 air volume remaining in your tank/s? (Not including pony air as just for emergencies). So I'm hung up on rule of 1/3's. If I dive and surface with 1/3 left in my tank, I'm needing more air than my al80. That's why I've been using the backmounted 30 attached to the 80.

How much air volume relative to tank size (not including pony) do you surface with in your tank at the end of a dive?

 

[lowwall]

What does rule of thirds have to do with OW diving?

As has been suggested, look up rock bottom aka minimum gas and build your plan with that in mind. Here's a thread to start with: diving thirds vs rock bottom

There may be better threads, I grabbed the first one that looked reasonable.

 

[Flashgun66]

What does rule of thirds have to do with OW diving?

As has been suggested, look up rock bottom aka minimum gas and build your plan with that in mind. Here's a thread to start with: diving thirds vs rock bottom

There may be better threads, I grabbed the first one that looked reasonable.

Thanks for sending this thread, a good read and I appreciate your comment.

 

[inquis]

No, just a single reserve for the ascent. Rule of thirds is one way to compute it. Minimum Gas is another. The point is to get home after terminating the dive. For recreational profiles, Thirds typically reserves more gas; arguably, more than necessary.

That said, you might apply Thirds for other purposes -- in addition the above amount you've reserved for ascent. For example, say you really want to get back to an anchor line before terminating the dive. Let's say you've worked out the Min Gas amount to be 800 psi. You just descended the line and now have 2300 psi, which gives you 1500 psi to burn. You might take a third of that to go away from the line and a third to come back, leaving 500 psi to hopefully cover any delay or increased usage in returning.

This secondary reserve really speaks to risk assessment. (How likely would you be delayed AND need to share on the ascent?) If delays are likely, you might even use "Fourths" instead of Thirds for this phase. OTOH, is getting back to the line really necessary or just a nice to have?

 

[Flashgun66]

What does rule of thirds have to do with OW diving?

As has been suggested, look up rock bottom aka minimum gas and build your plan with that in mind. Here's a thread to start with: diving thirds vs rock bottom

There may be better threads, I grabbed the first one that looked reasonable.

Thanks Iowwall – after more in-depth reading of the 8 pages of the thread you suggested I feel I have a much better understanding.

As mentioned I was hung up on the Rule of 1/3’s, as that was one aspect of my training, but can see now this originated in cave diving. As I’m an OW solo shore diver 99% of the time (1% future boat diving - still OW), I really like the Rock Bottom method. I like that it actually tells me the minimum gas I’ll need from depth to get out of a jam and make it to the surface. I think it’s great that during a multi-level dive this RB value is changing, and I can follow a specific RB /depth that reduces as I go up to the next level of the dive. And I like that I can dive using more gas in my tank.

I see that Rock Bottom was designed for two divers but this seems like an advantage for me specifically, as I’m a conservative diver. Also, I’ve been on a lower vis shore dive where I was passed by a buddy team and one buddy really wasn’t paying attention and saw me in his peripheral vision and thought I was his buddy. A short time later he lifted his head in astonishment looking at me, then swung his head left and right looking for his buddy only to dart off in the direction he thought his buddy was travelling. My worry is that as a solo shore diver I could easily be approached by an OOA diver separated from their buddy. If I follow the Rock Bottom method and assume the worst SAC rate for the OOA diver then we can both make it to the surface without having to rely on the 40ft3 slung pony. This scenario may never happen and if that’s the case I’m fine with that as I’m a conservative diver, and will have some extra air at the end of the dive over and above Rock Bottom values for a solo diver. Just my thoughts on this anyway.

 

[uspap]

I personally dive a steel 120 with a back mounted 19cf pony. I'm 5'11" and it has never bothered me. I do photography also and for me, having a slung 40 would be a pain. My 120's are Worthington's and they have close to the same profile as an AL80. I think the newer 120's are a bit longer now.

I've never had an OOA diver come up to me, solo or when with a Buddy. I have had people freak out because I'm lying still on the bottom trying to get a shot.

 

[tursiops]

I've never had an OOA diver come up to me, solo or when with a Buddy.

What is your point? Are you suggesting it never happens?

I have had people freak out because I'm lying still on the bottom trying to get a shot.

So much for not touching the bottom.

 

[uspap]

Not interested in a debate. I'll leave now.

 

[InWay2Deep]

You should try and borrow a 120 and dive it some first. I have a 100 and a 120, i hate the 120, way to long and heavy. I love my 100 is crazy how different they are.