However, the practice is now becoming fashionable with some open-water divers who want to use two tanks. Not least of the reasons for this is that you can easily access your tank-valves at any time, neatly avoiding those shut-down drills that so many divers find difficult, if not humiliating.
They also enjoy the unencumbered feeling that side-mounting imparts in the water, especially with aluminium tanks and a wetsuit.
When out diving from an inflatable, the side-mounted diver can hitch his tanks on in
a moment once at the dive-site, and avoids either wearing a twin-set during what might be a lumpy journey, or having to heave one up onto a tube to climb into it.
I’m even beginning to see single tanks side-mounted lately. The Hollis SMS50 is the latest side-mounting wing to come my way.

The Design
I loved the earlier Hollis SMS100 side-mounting wing, and would have used it far more if not for its weight of up to 4kg, which made me baulk at packing it for long-haul trips.
For diving with a pair of standard aluminium tanks I didn’t need so much lift either, so when the SMS50 was announced at the last DEMA show, I put my name down for one.
It is similar to the SMS100 in many ways but has a smaller (10kg lift) buoyancy cell, large outstanding rings instead of rails on the beaver-tail, and a clean back with no facility to mount tanks there.
The rings have two positions pre-drilled with eyelets, and I found that the default lower position was the best for a tall diver in a drysuit with steel cylinders.
Used with aluminium cylinders, three weight-pockets are strategically placed, one at the top and two either side, although disappointingly the side-pockets were too small to take a standard 1kg block weight.
The dump-valve and the corrugated hose for direct-feed or oral inflation are at the lower, wider part of the buoyancy cell, indicating the absolute imperative to keep the body horizontal when ascending.
You might even need to go bottom-up – not recommended in a drysuit.
The corrugated hose comes with a cord and clip that engages at the sternum-strap so that it doesn’t float about wildly and become hard to find. I would have liked a dump-valve at the top, too.
It all looks rather glittery at first, but there is only the minimum number of stainless-steel
D-rings. The two at the upper shoulder take the valve end of the tanks, and the ones on the beaver-tail take the main body of the tank-clips with cambands.
I confess that I discarded the Hollis cambands, because they were about as malleable as a sheet of steel, making them hard work to fit on smaller tanks. I substituted much nicer Buddy cambands and fitted the Hollis H-clips and piston-clips instead.
It proved to be a bit of a workout merely adjusting the webbing of the harness to fit me.
There are a couple of small D-rings along the bottom edge of the buoyancy cell on which to clip a reel or suchlike.
The harness is almost one-piece, in that there are no usable breaks, and of course it is long enough to go around a very large burger-eater. If I have a criticism, it’s that Hollis is too generous to its overweight clients! I tucked most of the surplus webbing away to stay sleek in the water.
There are two moveable D-rings on H-clips that can move around the waistband, but I left them where they were at the hips in case I needed to re-rig the aluminium tanks as the gas was breathed and they became lighter.
Then there are the elasticated straps that terminate in a piston-clip hooked on a top D-ring. These are passed around the tank-necks to pull them in close to the body.
I managed to use sling-tanks for deco and rebreather bail-out for years without ever needing this feature, and I am still in two minds as to whether it’s worth the bother.
I saw a Uruguayan diver called Juan using an SMS50 in Egypt, and he had replaced the straps with simple bungee cord instead. When I came to try the SMS50, I realised why he had done this.
The straps are too short, and with the limited number of options as to where to clip them provided by the SMS50, I found that they pulled the tanks under my arms in such a way that the tank-valves became inaccessible under my armpits.
I and a group of other divers who had gathered to inspect the rig tried lengthening the shoulder-straps to lower the top D-rings a little, but to no avail.
Like Juan, I would prefer to fit my own longer bungee straps.

In the Water
Hollis supplies a short direct-feed hose, but I was inclined to use a flexible lightweight braided hose instead, just as I did with the two regulators I used.
Apeks makes a side-mounting kit composed of regulators with short hoses too (see next page) but I found that by using flexible hoses and identical gases, I could dispense
with the idea of a separate octopus rig.
It is normal to have one long hose and one short hose on the second stages, both
on a necklace.
As an underwater photographer with a complicated camera rig, I find that necklaced regulators get in the way, and I often get the hoses tangled with the long arms of my flashguns.
It’s not in any book, but I prefer to bungee the hoses and pull out the one from which I choose to breathe.
I’m probably not using my camera by the book either, but I get results.
I normally dive headfirst into the sea from the boat, dipping my camera rig in first and following it.
You can’t do that when side-mounting unless you want to get a clout from a tank, so I resorted to conventional giant-strides or backward rolls, depending on my starting point.
I don’t know if side-mounting actually streamlines you, but with light aluminium tanks it certainly feels less restrictive.
I used this rig in the open ocean, so the effect amounted to having twice the normal
gas supply for a leisure dive, and no stressed back when getting ready to dive on the boat.
Now that I have the Hollis SMS50, I’ll probably be side-mounting far more often.

Comparable side-mount rigs to consider:
Hollis SMS100, £662
Dive Rite Nomad XT, £650

PRICE £582
DRY WEIGHT 2.8kg without tank-bands and clips
DIVER GUIDE width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100%