Unfort divemaster doesn’t mean anything in terms of overhead environment or technical training. I’d argue that on average it’s a net negative. Poo on SDI for allowing limited penetration at the recreational level with a single tank. Unequivocally f that.
Let’s assume that you’re in a drysuit and drygloves with a large amount of undergarments to loft (as you really must be in this area to do any extended range diving). Let’s also assume the local levels of sidemount training and backmount training available to you are on par with one another (they’re not).
In doubles, gearing up is as clean as sitting on the bench, necklacing your reg, connecting your suitgas, and routing your long hose. Stand up, fit through the gate, and jump off the boat. Deco bottles either tied to a down line or clipped onto you either by yourself or by crew depending on your strength level. Either way, the deco bottles are not really part of the ballast equation and at most, are ~5lb negative (50%/70’ AL80 bottle) so clipping them onto yourself at 10’ or 20’ is of no concern if they’re on a downline. There’s never a point when you’re in the water when all of your ballast is not on you. The general choice in the area are HP100s/LP85s (less so bc the Midwest doesn’t really cave fill), HP119s/LP95s. This helps alleviate the need of a massive amount of weight stored somewhere. While I think AL80 doubles are great wetsuit tanks, they’re not my top choice in a drysuit.
In sidemount, there’s three ish ways to get your bottles to you. Having them passed to you from someone on the boat, a downline, or by clipping them onto your harness while on the boat. Option 1 is pretty reckless and even worse with steel cylinders, so we’ll skip that. Option 2 involves one cylinder being clipped on while on the boat and one on a down line. Doable in aluminum cylinders, more difficult or reckless with steel cylinders. Now you need to add whatever portion of your ballast the down line cylinder accounted for onto your harness and are overweighted. Clipping bottles off with drygloves underwater is a pain depending on the harness/glove/attachment point/boltsnap combination and if you accidentally drop one, it’s gone. Connecting a wing inflator across your chest in dry gloves with 1-2 pairs of liners is difficult at best and a fools errand at worst.
Which brings us to option 3, or attaching your SM cylinders while on the boat. You’ll likely need to add leashes to the top of your cylinders to avoid stretching the bungee. So now, to get geared in, you need to put your harness on (with light can, whatever necessary weight, suit gas, suit heater...and finding a place for all of that). Clip in one bottle top and bottom, connect the bungee, run the necklaced reg around your neck, connect your wing. Then, now 50% wider than you were prior, you need to do the same on the other side. Cool taken care of. Sweet, you’ve done your modified S drill, gas is on, and you’re ready to stand up. Except now you’re taking up twice the bench width of your compatriots. If you’re out of Hammond and diving the Hume, it’s nbd if the boat isn’t full. Full boat or one of the corner seats, you’re either in the way of other divers or the last off the boat because of the amount of help and space you need. The Alma out of MKE has more space on the bench but it’s difficult to sit down effectively to put your fins on with sidemount cylinders clipped on in general. Now, you just have to jump off. Ouch, the forward gates on the Seaquest aren’t wide enough to do a giant stride safely so you need to fall in half sideways. The rear isn’t that much wider. Same story with the gate on the Molly V or the Alma, though iirc the Alma is slightly wider and might work if you’re naturally narrow and with 7” cylinders. Can’t easily clip on SM deco bottles hunched over (because you’re main bottles are already on and you can’t sit straight) and being hinged over with your primary bottles on covers where those deco bottles should be getting clipped.
Sweet, now you’re in the water and diving. All is well. Wait, is the wreck upright? Hallways work better in backmount if they are. But now you’re in sidemount and swimming canted. Admittedly nbd if the wreck is on its side. Dive comes to an end. Ah poo now you need to get out. Did you unclip your leashes in water and now need to reclip them? (hint leave them clipped). Are your deco bottles as cleanly doffed underwater as they are in backmount? No, not if they’re laying where they should be. It’s even more difficult when you have a 70-100mm dry glove ring in your way. Storm rolled in and now you’ve got 3’+waves and you’re less balanced and trying to fit in a smaller pocket/gate relative to your girth than your backmount friends. Smack goes the SM cylinder against the gate or the ladder or the rack. Wait I thought sidemount was supposed to make maneuvering on the surface easier? Once the process of getting you in a seat is finished, most people seem to need help unclipping themselves from their gear.
TL
R
Cold water sidemount is a burden on the crew, your body, and the boat. There’s a small number of people that manage it, but for most it’s a pis poor idea. Learn SM when you actually need it and tip real well on those boats if you don’t need it but think it’s cool.
