Paul, we use 'Safe Boat Skin' on our RIBS which are afloat in Dinorwic virtually all year
During the Summer Months, ie May- Sept we do, when time permits whip em out an wipe em!
I must admit, during this period they are used very regularly which also helps to keep the shiot at bay
Hastily bunged some on the Aircraft (for the first time) when we launched in Sept
Brought the boat out in Dec and just hosed the hull etc and it all came off lurrverley and we will recoate this week just before we launch
We have used it on our plastic boats too
But as I said we do whip em out during the Summer 'growth' period about every 6 weeks just to make sure all is smooth on their bottoms.
I,ve had boats off the Gazelle over the years , it's a very 'lively' place ref weed growth etc etc, I know where you are coming from, or-- where you aint going, wot with the snot I saw on yer rib last year!!
I just looked back on previous posts about SBS, it seems there were a few folks who didn't rate it etc, just saying it works for us
Getting back to the Menai
In my experience of the place, no matter what you coat yer bum or tubes with you will get growth about the waterline, there is so much life in there.
Must say Ive never put antifoul on tubes so I can't comment there
Had a 5 metre by the slip in Menai years ago, just used to retrieve every couple of months and jet wash it in Brittania garage