This is Witchfinder's annual weekend out of the water.

Attached to the hull on either side of the top of the rudder are two plastic flaps. They are pretty flimsy and I suspect are there either to shape the flow over the where the rudder post enters the hull or to stop free floating bits of weed getting caught in there.

Well, they both now have tears in them. How to I replace them? I can't recall ever seeing such things in chandlers. Would the material that poly bottles are made of be adequate?