Sidemount basics? Just some simple questions

[Wheeler925]

Good day. I know these are dumb questions. I'm not a sidemount diver, and probably wont go that route for quite awhile yet, but I find it intriguing and from zero experience, it looks like a better option than back mounted doubles. I Just have some simple questions as I think about things.

I see a lot of talk about LP85s and such.. why? Is there a reason to avoid standard AL 80s or some other, larger volume tanks?
Does each tank get its own first/second stage? I'd guess yes is the obvious answer
What about an octo? Just using the second tanks second stage in case of emergency?
Left/Right balancing - Assuming all of the above is true, do you switch off breathing from one side to the other occasionally to balance the weight distribution?

Any other simple, stupid questions you'd like to answer, would be appreciated. At this point its really just a curiosity for me.

 

[Rollin Bonz]

Better buoyancy characteristics. AL 80s typically get floaty as they get empty. Several ways to deal, one of which is use tanks that stay negative, like steel tanks. LP85s are somewhat of the GOAT SM tanks for many. I've been unable to aquire a set, so I can't confirm. You can still use AL80s, just use a method such as sliding D rings for the lower attachment point, or just moving the lower attachment point to a snother fixed D ring closer to the front.

Yes

No octo needed, you have 2 separate redundant air supplies which is even better than a single tank with an octo. If you have a buddy that runs OOA, you donate your long hose (then find a better buddy).

Yes, you will alternate from your left to your right tank periodically to maintain balance. 500 psi, 1000 psi, whatever keeps you balanced out.

When SM is good, it's AWESOME, but it can be very finicky and difficult to dial in.

And getting it dialed in today, doesn't mean it'll be 100% dialed in next dive. Sometimes it seems like something as simple as passing gas between dives will throw your trim to $#1t.

 

[Mobulai]

I see a lot of talk about LP85s and such.. why?

Seems like a cold/fresh water preference tank

there a reason to avoid standard AL 80s or some other, larger volume tanks?

well to expand on the 1st question:
AL80s behavior is a bit unique; -ve buoyant when full, +ve when below 100bars
And they are bigger for tgeir volume (so that they can withstand the pressure as AL is weaker than steel)
Their advantage is in salt water, as they need less “TLC”
Steel OTOH, is extremely -ve when full; lightly -ve when empty — an advantage for cold water divers that need more weight to go down (I’m oversimplifying)
Steel tanks can also get “cave fill” (over-pressured) and carry more gas — I doubt aluminum can

Does each tank get its own first/second stage? I'd guess yes is the obvious answer

Correct

What about an octo? Just using the second tanks second stage in case of emergency?

yes (to the lack of octo); if you get a freeflow for example you switch off that tank and use the other one — decoupled redundancy

Left/Right balancing - Assuming all of the above is true, do you switch off breathing from one side to the other occasionally to balance the weight distribution?

switch every 10-15bars

 

[pdwh]

I just finished my recreational sidemount class. It's a LOT of fun and for anyone with joint/back issues, a lot less stress on the body. Switching regs isn't too bad - I recommend a dive computer that flags when to switch and transmitters on both tanks, but that's my preference. I've got a buddy who did the class with me that never uses transmitters (but he also seems to make air underwater).

Getting the connections correct is a lot of work up front, and I can already tell it'll be a constant bit of adjustment, but maintaining trim was so much easier, and knowing that I'm carrying a fully redundant air supply is nice too.

 

[Wheeler925]

I just finished my recreational sidemount class. It's a LOT of fun and for anyone with joint/back issues, a lot less stress on the body. Switching regs isn't too bad - I recommend a dive computer that flags when to switch and transmitters on both tanks, but that's my preference. I've got a buddy who did the class with me that never uses transmitters (but he also seems to make air underwater).

Getting the connections correct is a lot of work up front, and I can already tell it'll be a constant bit of adjustment, but maintaining trim was so much easier, and knowing that I'm carrying a fully redundant air supply is nice too.

I've got a peregrine tx which says its sidemount support with switching alerts, so that parts already covered

 

[pdwh]

I've got a peregrine tx which says its sidemount support with switching alerts, so that parts already covered

That's what I have. I set up the two customizable sections at the bottom with 3 values each. I put tank 1pressure, tank 2 pressure, GTR, TTS, and clock time on there. When it's time to switch, the label for the tank pressure turns a different color (mine's set to green) to remind you which one to breath off of. Of course, if you need the numbers larger, you can just put a single vale in each box and skip the extra data, if you'd prefer.

GTR - Gas Time Remaining - in sidemount mode, it uses both tanks for this.
TTS - time to surface from your current depth (at a safe rate)

I love the computer. I've used several others in single tank back mount, but this is by far the best of the ones I've used.

 

[Underwater Tourist]

I see a lot of talk about LP85s and such.. why? Is there a reason to avoid standard AL 80s or some other, larger volume tanks?

It depends where you dive, in Mexico 100% of SM dives are done using AL80s. They do get floaty as they get empty, but as was already mentioned, a 5$ sliding D-ring fixes the problem, so its not an issue at all.

Does each tank get its own first/second stage? I'd guess yes is the obvious answer

Yep

What about an octo? Just using the second tanks second stage in case of emergency?

Yep, if you get an OOA buddy, you share your long hose from the right tank.

Left/Right balancing - Assuming all of the above is true, do you switch off breathing from one side to the other occasionally to balance the weight distribution?

Yeah you will start doing that on autopilot after a couple of dives. Often people recommend to switch every 20bar or so, but personally I switch every 40-50 bars and have zero issues with weight distribution. I dive AL80s and can always trim the tanks with the sliding D-ring so everything looks nice and sexy.



For SM, the single most important thing is to get a good instructor, because SM can turn into a **** show if you get taught by an idiot

 

[grantmac]

In warm water AL80s are great and what you are likely to find. A sliding D ring such as the superb ones offered by SumpUK makes handling them easy.

That said LP85s/50s are fantastic to dive because they are thin and don't really get floaty until they are nearly empty.

 

[pdwh]

It depends where you dive, in Mexico 100% of SM dives are done using AL80s. They do get floaty as they get empty, but as was already mentioned, a 5$ sliding D-ring fixes the problem, so its not an issue at all.


Yep


Yep, if you get an OOA buddy, you share your long hose from the right tank.



Yeah you will start doing that on autopilot after a couple of dives. Often people recommend to switch every 20bar or so, but personally I switch every 40-50 bars and have zero issues with weight distribution. I dive AL80s and can always trim the tanks with the sliding D-ring so everything looks nice and sexy.



For SM, the single most important thing is to get a good instructor, because SM can turn into a **** show if you get taught by an idiot

I second the good instructor comment. Not only was mine good, he was also diving the same BC as everyone in the class (by accident, not design). Made it really easy to get ideas on how to tune the gear. Hollis Katana 2.

 

[ps444mike]

one of the pros i see is my dive buddy.. she can get in with one tank or none and we can add tanks to here. while in the water (shes Handicap)