When we left Australis II in Borneo in November we noticed that a lot of of other yachts in Kota Kinabalu had wrapped their props in thick black plastic bags. They all swore by it as a sure way to prevent coral growth if the boat was being left in the pen for a while. The idea is that with no light, no coral growth can occur.
By this stage we had locked Australis up and were on the jetty with all our bags packed ready to catch a cab to the airport to fly home. I figured we were not back aboard until mid Jan so it might be worth trying it out. To my good lady's horror I dropped my dacks, grabbed a bag and dived in with a couple of cable ties and a big black plastic shopping bag.
I'm going up there again next week so I'll let you know if it made any difference although if I do it again next time, I'll do it before we pack and lock everything up - a 9 hour flight back to Oz with damp jocks is not the most comfortable flying attire