Sailing a classic dinghy

We have booked a day on a classic dinghy in The Broads. I'm just want to do it. It's my mid-life Swallows and Amazons thing, apparently. We will be taking out a Waveney Class boat, 20' of solid wood and rope and gunter-rigged sail.

I am nervous about it. How do you tack on a narrow river with hoardes of plastic hire boats all over the place? How can you keep the damn speed down when running on said narrow rivers with a huge sail. I'm already checking the weather forecast with unnatural frequency: it's due to be WSW, 15 knots.

Funnily enough, Griff Rhys-Jones was on The Broads last night in the latest edition of his TV series "River"; wonderfully evocative and he managed to get his boat, a bigger cabin yacht, under Potter Heigham Bridge.

It's a dilemma: I'm nervous but looking forward to it all so much. Just wish it was longer.