I have only seen the Swinge once - I was on a Sigma 38 motoring with tide (spring I think) after the St Peter Port JOG race to Alderney where we had an important appointment in the First and Last. Conditions a bit like your picture and we saw some breaking water ahead as we motored towards the SW corner of Alderney. Gosh we thought 'that must be the Swinge everyone says you should avoid at all costs!' Cue lots of country accents and dire warnings along 'we're all doomed' basis.
Anyway perfectly safe but the overfalls are big even in practically no wind - some disappeared below as I don't think there was time to get oillies on before we were in it and the rest of us hudled standing round the backstay. 15 mins later we were in Braye thinking that would be really awful in any wind!
So if in doubt go to the east of Alderney is my tip.
The only time Ive ventured down the Swinge was after leaving Braye, just before HW, so as we started to head south the ebb had just got under way. With no wind we motored with an increasing ebb beneath us, lots of upwellings but nothing that would stop me doing it again in similar conditions.
Jimi, that nasty unmarked rock at the end of it is Gurnsey and it is marked, I'm sure the locals would be very offended by you ignorance! /forums/images/graemlins/wink.gif