MOD2 what to prepare/know?

[beldridg]

What's in the 2 80s? One with trimix and one with o2 or 'shallow mix'?

Assuming your deep bailout is different than your diluent, you would likely have either 21/35-ish or 18/45-ish for your deep bailout and 50% for the rich mix. Different people and instructors feel differently about the PO2 max of bailout at depth (and certainly, how long you would be on that mix -- e.g., penetration).

If you are on a unit that uses the same gas for Diluent and Deep Bailout (e.g., the popular Choptima with twin LP50s for bailout/dil), then it might be different.

I have no idea what the agency standards are and don't teach so take it with the proverbial grain of salt. But, generally, for most MOD2 (60m/200') dives I do, I feel comfortable with two bailout cylinders with 70-80 cf each.

Your instructor should definitely prep you for gasses you will need based on your unit, dive conditions, etc.

- brett

 

[berndo]

If you are on a unit that uses the same gas for Diluent and Deep Bailout (e.g., the popular Choptima with twin LP50s for bailout/dil), then it might be different.

I have no idea what the agency standards are and don't teach so take it with the proverbial grain of salt. But, generally, for most MOD2 (60m/200') dives I do, I feel comfortable with two bailout cylinders with 70-80 cf each.

One deep dil/BO and one shallow tank leaves you without any redundancy and when the 1 stage craps out or a hose blows at depth you'll have a problem. I'm surprised that an agency would see this as a prudent approach.

 

[BlueTrin]

One deep dil/BO and one shallow tank leaves you without any redundancy and when the the 1 stage craps out or a hose blows at depth you'll have a problem. I'm surprised that an agency would see this as a prudent approach.

Sorry if that’s a silly question but what’s the correct solution in your opinion in terms of setup.

 

[Tribal]

I only dive on CCR for 3 years, so it’s only thinking out loud here and definitely not advising.
If you don’t have a separate DIL bottle I would assume you need 2 DIL\BO bottles, like the D7 on the GUE JJ’s?
Isn’t it otherwise like diving with a single 20L for example instead of a D12 in OC?

Some redundancy is needed, with onboard DIL you have a separate BO.

 

[beldridg]

One deep dil/BO and one shallow tank leaves you without any redundancy and when the 1 stage craps out or a hose blows at depth you'll have a problem. I'm surprised that an agency would see this as a prudent approach.

Just to be clear, I didn't answer the question for a setup with a combined Dil/Bailout. Your question wasn't specific and was just "which gases in the two cylinders."

My Onboard Dil and Deep Bailout are _completely_ different systems. They don't share anything.

That is why I started my reply with "Assuming your deep bailout is different than your diluent..." and why I specifically mentioned it "might be different" for systems that use a combined Dil/BO.

I have no idea what an agency or instructor recommends for a system that uses combined Dil/BO for a MOD2 course. For a MOD2 course with a back mounted rebreather with a separate onboard Dil bottle, I'm pretty sure that the instructor and/or agency would recommend/require 2 bailout cylinders (one deep with Trimix, one shallow likely with Nx50).

- brett

 

[BlueTrin]

Sorry for the confusion, should have added, I dive a JJ in standard configuration.

 

[beldridg]

Sorry for the confusion, should have added, I dive a JJ in standard configuration.

No worries.

Obviously check with your instructor once you find one and decide to take the course, but it is a reasonably good assumption that they will require 2 x AL80/11L (or similar) bailout for your configuration.

In terms of your original question, I think making sure you can hold a deco stop is probably a really good skill to develop before you take a MOD2 class and something you can practice on every dive you do.

For example, practice doing a "fake" deco profile on your current dives. Just write on a slate (50' 1min, 40' 2 min, 30' 4 min, 20' 8 min) -- well, for you, metric equivalent -- and then see how you do on your post-dive profile.

Do that a bunch and then, if you can, do it with 2 x AL80 cylinders.

You can also practice hitting a run-time target with those simulated deco profiles. I.e., assume your dive run-time needs to be 70 minutes include deco stops with a 15 minute deco profile. Can you start your ascent on time and end up surfacing at 70 minutes?

If you don't have any open circuit Trimix classes or knowledge, then you will have to learn some of that, but if you can master handling two 11L tanks and doing a simulated deco profile, it will go a long way.

Regards,

- brett

 

[grantctobin]

Sorry for the confusion, should have added, I dive a JJ in standard configuration.

1) all of the usual fundamental skills such as trim, holding stops, free ascents, gas sharing, etc that should have been covered in MOD1
2) smooth and easy bailout ascents. you can simulate bottle rotations with your current MOD1 gasses
3) if you're sidemounting your bailouts, ensuring you can still perform a clean gas verification procedure

Edit: Brett beat me to it

 

[BlueTrin]

Thanks guys, I am gonna focus a bit on the free ascents without DSMB and improve my stability ant shallow stops and try with two stages.

I think I am generally comfortable with the other things.

 

[beldridg]

Thanks guys, I am gonna focus a bit on the free ascents without DSMB and improve my stability ant shallow stops and try with two stages.

I think I am generally comfortable with the other things.

The great news is that you can practice it on every pretty much every dive you already do.

MOD2 is such a great course and opens up so many different dives and doesn't add a massive amount of complexity (vs MOD3). It really starts to let you take advantage of what a rebreather system can offer. My favorite dives are generally in the MOD2-ish range.

IMO, it is definitely worth pursuing if you are serious about rebreather diving.

Regards,

- brett