How to create curves when block modelling and using references?

Hey,

So this is my first (real) attempt at using a reference image to model an object. What’s the best way to create those curved surfaces (see below) on the underside of this craft?

Thanks for the help!

Take a look at the bevel tool (CTRL+B) in edit mode, it seems to do what you need.

Thank you! I was trying to play around with modifers and wasn’t getting anywhere.