You can tweak most speed and movement aspects for ships in this powerful mod. I don't know what half the variables do, and I haven't even built a raft yet, but this was by request, so here you go:

It is a powerful mod that lets you tweak most speed and movement aspects for ships. You can use it for free and try it out.

The first thing you need to know is that you will need to install it in order to use it. You will need to make sure that you have the latest version of it.