What's that Book? Based in Australia, kids on a steam boat. Fire or explosion involved

My friend has searched years for this book!

There was a paddle steamer and something about renovations and a family with a shop who then had a shop on the paddle steamer.

They went down the river selling things. There was a group of kids, one was a cousin who was part of the friend group.

At some point the paddle steamer caught or there was an explosion or something

Sorry that's I've got!

He read it in German but its based in Australia.

It isn't River Boy by Antony Hill (Really thought I had it with this one!)