Description
BoatInertia is a relatively simple utility plugin to enable the modification of maximum boat speed. After spending too much of my time looking for something that could do this, I gave up and just did it myself.

Installation

Download the latest release from my GitHub repo
Download ProtocolLib - this is a required dependency
Drag both jar files into your plugins folder
Let the server run once to generate config and readme files
Edit BoatInertia config to slow down or speed up boats

Notes

BoatInertia 1.2 was built on ProtocolLib Build #546 / 4.8.0-rc2
Tested on Purpur 1.18.1 but should work on any Bukkit fork that ProtocolLib supports
NO, there are no commands yet. Just one simple field in the config file
The lack of a functioning Bukkit/Spigot API for boats made this challenging - as a result, I had to rewrite the entire boat movement/physics engine. Boats may behave slightly different because of this. See below to report issues

Support
I recommend using the GitHub repo's issue tracker to report issues. Be sure to include server/environment information and respective error logs. I have to recreate the problem in order to fix it, so the more details, the better.

Thanks for trying it out, have fun!