We kept our last boat on a Dry Stack system in Poole and never antifouled it. The boat was regualrly in the water (ie at least every other weekend) for 3-4 days. At times it spent upto 2 weeks in the water.
Over time the hull WILL discolour, especially around the waterline...it will go a horrible yellow.
However, this can easily be removed with Starbrite Hull Cleaner which is just brilliant stuff, wipe it on with a sponge, leave for 3 minutes and rinse it off... you will literally watch the staining disapear.
After 5 years the hull of the boat still looked line new....
For the period of time you are talking about there is absolutley nothing to worry about. If you think there is some slight staining then get a bottle of the Starbrite stuff
You have all been great with the advice and can now finalise the Skandia Cowes week jaunt with a relaxed view that it will be ok! Will be trying out that Starbrite cleaner though as even after a day in the water it can get a bit dirty.
Hope to see a few of you out there (or in the pubs?!)
Antifoul only stops it getting fouled, as far as I am aware it doesn't add any protection to the grp. With the new boat scrubbers being installed around the Solent some boats aren't antifouled at all and kept in the water 24/7/365 with no problems. Antifoul does what it says on the tin.