Richard,
Re my post of yesterday.
I was alerted this morning to the fact that my Mk4 has turned turtle overnight. I’m now awaiting assistance to have the boat righted and taken to shore. The weather yesterday and overnight was very benign and rainfall was very light. It would appear that the weight of the outboard on the offset mount has caused the starboard duct to settle below the waterline and the transom flap has proved totally ineffective. I’m now seriously thinking of never using an outboard on the dinghy again and taping up the ducts!