When I was making the title image for this site I started with the idea of a swish - those wave shapes above. Initially I tried drawing by hand with the pencil tool but even with a tablet my drawing was too shaky. It would have taken a lot of node editing to get that looking even slightly smooth. Next I tried using Bezier curves to construct the shape but after joining all the lines it just looked kind of of messy.

To get a smooth looking shape I needed a more simple approach. So here’s how I ended up with a smooth shape.

The shape is basically a triangle - thick at one side and tapering into a point. So start by drawing a triangle with the polygon tool.

Next you’ll need to edit the triangle’s path to create the curves, but before you can edit the path you’ll need to change it from an object to a path. Path>Object to Path will do this. Choose the Edit Paths by Nodes tool and select the image to see the nodes.
Stretch the triangle out so it forms the basic shape of the wave you’re making. It will probably look something like this now:

To create the curves start by working on the nodes that lie between the base and the tip of your triangle shape. You can tell by the sharp angles between the lines that these are corner nodes. To smoothen that, out make the node symmetric.

You can see the angle has been smoothed out into a curve. Repeat with the node below.
Now you can move your curved areas around to make the beginnings of a wave. In the picture below I’ve moved the top node up and left slightly and the lower node up and right. I’ve tilted the curve by moving the Bezier handles up and down until I’m happy with the shape. You’ll also notice the top right-most node has been moved down to make the base of the shape more narrow.

To add another curve I add two nodes (top and bottom) between the curve and the point and repeat the process to create the new curve. To add more nodes shift-click on the two nodes you wish to add a node between and click the Insert Node button.
In the same way as you did above, play around with positioning the nodes and moving the Bezier handles until you end up with a curve you like. Here’s a pic showing the position of each node’s handles.

And that’s it - a pretty easy way to get a smooth curved shape.

If you give this a try please comment below and let me know, or if you have an alternative method I’d love to know.