Nobody knows better than the boys (and girls) at the Seaway Tower. Ring the bell one day and ask them if they can give advice. They still might let people up to get a bird's view of the the seaway and surrounding banks (chocolate helps). The seaway can be easily crossed in most conditions but if in doubt, don't go.When heading out firstly sit in the seaway for at least 5 mins to become familier with the conditions and what it's doing on the day. Wear jackets if wary. Pick a slot between sets (if any swell) and go for it. Don't try turning around in the middle, just point nose into the swell and keep a steady speed. Head out past the south wall and in a SE direction once past initial swell. Crossing on a rising or still tide is much better than a falling so time your return during these times (especially during big tides). Any strong winds with a bit of East in them can make it messy at times but the seaway is the safest bar at most times.
If in doubt, don't go.
Cheers, Jay