Oysters do block inlets – I know!
I read with interest your article about oysters being introduced to MDL marinas in the Solent (Jul 17). However, the assertion that oysters will not block boats’ through-hulls is untrue. A few years ago I changed my saildrive's gaiter. On splitting the leg I found a live oyster across the engine cooling pipe. It was blocking half the cross-sectional area of the pipe and, if left, would have grown to block it completely. Located about 250mm up inside the leg, it was almost impossible to detect or reach. It was so strong and well attached that I had to use a long steel drift and a hammer to remove it.
I recommend that all cruisers inspect and clear possible blockages during the annual lift out. The Volvo saildrive has a 15mm diameter (approx.) hole in the bottom. I poke a 13mm diameter wooden dowel (500mm long) up the hole to the top of the waterway. The inside surfaces should be straight and smooth so guiding the dowel tip up each side of the pipe will detect any oysters. A steel rod and hammer may be needed to remove an oyster as they have very strong shells and cement. The wooden dowel will smash mussel shells, which can be washed out. Chris Mardon