Yeah that would be super realistic to be able to swim in heavy armor. (sarcasm).
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yes and no. EVA suit a desinged for Walk so they have to be able to hold a constant pressure against the Vacuum in space, so it like a foce that try to tear the Suit apart. How ever if you want to go for a dive in your see next door it should be no big deal for your suit, but lets say thats not enought we want to visit sponbob on the bottom of the sea. so see there or we have to go deep and now you can see that every 10 meter (about 33 feet) we adding 1 bar about 1 atm. now your suit what is desinged against the force which was tearing now have to work aginst a force that are try to press you suit togather. I guess would cause some Problems. how ever i am no Spacesuit scientist and if someone know better i would really like to correct me here
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I dive for a living and I can tell you that so long as you have air to breathe and you are suitably insulated with regards to temperature, you can spend as long as you want at 40 meters or less. That said, you will develop significant nitrogen saturation in your blood stream and this will lead to nitrogen narcosis (essentially being high at the bottom of the ocean (this is a VERY bad thing)) and/or requiring such a massive decompression schedule to surface safely that you may as well stay down there (seriously, I've spent 45 min on deco for 15 min of bottom time, now imagine you've been down there for three hours or more).