I use 2 coats of soft and slip every 18 months, usually only slime build up not many barnacles.
Using soft also reduces build up of AF.

I don't beleive hard performs well on slow moving boats. I use it on the alloy saildrive/ prop and they are always covered in barnacles after 18 months.

Intervals depend on your location this will even vary from bay to bay in the same waterways. Best solution is talking to people moored close to you.

Crusoe said..
What sort of life do you get out of each?

It's going to depend on the brand and the batch. A lot depends on the bloke making it on the day. I have had Jotun that lasted 3 months and other times it's gone to 2 years. I tried the new Hempel and that was very disappointing but someone here raved about the same product. I still have a tin but will use that as a primer coat under Micron next time. There seems to be very little difference in time between hard and soft in the same brand and price range. I just like soft because it does not have the build up. Pressure wash and re coat.

I've always asked those around me as to what they put on their bottoms. What works in some places won't work in others. A lot of course depends on usage, if you have a mooring minder then....