There are a good few songs called Molly Bawn or Molly Ban. Never seen it spelled "Bonn", mind you. The song you want was posted here last March (text only); see this discussion:
Even if you are unsure of a title, you can generally find things here via the excellent onsite search engine, which you will find on the main Forum page: use a short phrase from the bit of text you remember. In this case, boating on Loch found it.