I would stay tied tight to the dock under those conditions. It's not just the swell height time factor, it's also the effect of a 12' swell as it approaches the bar. If you need to cross a bar to get to the ocean those 12' swells will be a lot taller at the bar. Be a good idea to check the tidal exchange, which is very important information on a bar crossing. What port are you thinking about using or is this a general question?
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