The fact that your barnacles are concentrated where they are in that photo tells me two things:
1. It doesn't appear that your shaft strut got any bottom paint love when the bottom was painted last - the hull pressure washed clean, but the shaft strut has hard growth all over it. Easy enough to fix when you repaint.
2. I've tried two methods to discourage growth on the running gear - bottom paint and zinc paint. Ablative seems to wear off too quickly - I mean, it IS running gear, so that makes sense. You could try the expensive treatments that require exacting prep or they fail - or they fail anyway (see Kappykaplan's post above), but I've had luck with the zinc paint. You can buy it in its "marine" form from Pettit (Pettit Prop Coat in spray or liquid paint $35-$109), or you can get virtually the same thing from home Depot (Rust Oleum Cold Galvanizing spray paint - $8). Its not magic - nothing on running gear is - but in the brackish water of the Chesapeake it seems to do a decent job, and other than a few lucky barnacles my running gear comes out looking like my ablative bottom paint when pressure washed at the end of the season. Unfortunately I wasn't there when I was hauled out so I don't have any photos, but it didn't look anything like kappykaplan's prop from Lusby - not far from me in Deale. Can't tell you why - maybe use? i dunno.
At any rate, the Rust Oleum Cold Galvanizing on my prop shaft and prop seem to work pretty well - especially for $8. I give it at least two coats after a good sand to rough everything up, and then some acetone to clean it. If you're in true salt water (we're technically in brackish) I can imagine you'd need regular bottom cleanings, so may not be of any help. Couldn't tell where you are from your post.
Good luck.