North Stradbroke island is about 40-50km from Brisbane CBD and it'll take about 2 hours to get there including the ferry ride. The best time to head to straddie is when it's blowing from north to north east as this will give you a good onshore breaze between amity point and cylinder beach.
When it's blowing between south and east, go to to frenchmans bay or main beach. These two spots are facing the open sea and it will get choppy. If you're keen for a downwinder, get someone with a 4wd to drop you off upwind of main beach.
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Point Lookout is a east facing beach and is usually quite choppy. It's a good spot for downwinders if you can get someone to drop you down south of the point.
Cylinder Beach
Cylinder beach is north facing beach and protected from the open sea. This spot is great for wave surfing. It's a patrolled beach and so keep away from any swimmers.
Adda Rock
Adda Rock, just a few km west of Cylinder is also a north facing beach but with long stretch of beach.
Frenchmans Bay
Frenchmans Bay is a east facing beach and is usually slightly less choppy than Point Lookout. The bay is protected by north and south rocks but the swell can get pretty big. If you head out behind where the waves are breaking, be careful of the rocks that sometimes submerged (switch the map above to satellite and you'll see).