I say 50F because of the fact that if I go any deeper without a drysuit on, it gets all the way down to 38F because 50F is RIGHT above the thermocline, so I don't usually go down that far because I don't own a drysuit 
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So the 144 IP should be fine for my average temp? I'm doing a polar bear dive in December and another one in January. You think those will be fine, too? Or should I have it detuned a bit?

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So the 144 IP should be fine for my average temp? I'm doing a polar bear dive in December and another one in January. You think those will be fine, too? Or should I have it detuned a bit?