I believe it`s just to stop Jack or Royal going out through the back!
That`s a fine looking RIB, wish I`d know it had been for sale in Cornwall, I could have gone round and kicked the tyres, at least, do you mind me asking how much it cost you?
Link to mine in the gallery below if your interested.
http://rib.net/forum/showthread.php?...=jenny+haniver