Going to Cozumel first itme in Aug, next month. I very, very rarely dive warm water.
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So, for those who have sidemount dove [anywhere but maybe know cold water gear] and been to Cozumel...or if you just want to comment some pearls of wisdom...what would you do?
I would never dive sidemount in Cozumel. I suspect some people do these days, but I would absolutely just use a single tank like everyone else on the boat, mounted on a BC on your back. It will be MUCH more comfortable and practical both for the boat exit/entrances and for the diving itself.
I've been to Cozumel at least 20 times, and I dive sidemount in the caves on the Mexican mainland. It's very easy to do both on the same trip. Here's how I do it:
In addition to the cave stuff, I bring a compact BC (I use a freedom plate and oxycheq 18lb wing, but anything small and simple will do fine), a 5ft hose, a 20" BC inflator hose, and a 24" HP hose, and a small adjustable wrench and a 4mm allen wrench. When I want to switch from SM to single tank backmount, I just take the left 1st stage, replace the 6" LP inflator hose with the 5ft regulator hose, put the 2nd stage from my right tank on it. I leave the short hose regulator (24", bungee necklace) in place. Add the 20" LP inflator hose to one of the LP ports, remove the SPG, put the 24" HP hose in it's place, and put the SPG on it. The whole process takes well under 5 minutes, and the only extra stuff to bring is 3 hoses. Two could work if you were willing to use the 7ft hose on a single tank. I don't like to do that and so I use the 5ft hose. Others might prefer a 40" hose, using the right angle adapter that's on the other 2nd stage.
Point is, it's just switching a few hoses around. This is a small price to pay for much easier and enjoyable diving. There is zero reason to dive with 2 tanks on the Cozumel reefs; the small boats are poorly equipped, and the dives are single tank dives. If you're ultra paranoid about your ability to manage gas and/or deal with instabuddies, you can sling a small pony; a 13cft or 19cft would work fine. I occasionally see people doing that on the boats, but I wouldn't bother. I'm a safe diver and a good dive buddy, so I'm fine diving with a single tank like 99% of the people who have been doing these dives safely every day for decades do.
There are two other small issues; DIN vs yoke tanks and appropriate fins. Most of the dive ops these days on Cozumel use tanks with convertible valves, so you can simply remove the DIN plug and use your DIN regs. For the occasion that's not possible, you can use a DIN-yoke adapter. I have never had to. Regarding fins, my favorite fins for Coz are full foot avantis that are small, lightweight, and neutral. Back when I was using jets in backmount twins for cave, I would try to bring the other fins as well, but now I'm using eddy fins in sidemount, and they are close to neutral so they work fine for me in single tank.
These days many people are fascinated with sidemount and so maybe that inspires them to try to use it for diving where it just doesn't make sense.
