I noticed that in versions of the plugin for 1.12 and earlier versions, the ships move instantly with each click, no lag no matter how big the ship is. In post-1.12 versions, the ship can take several seconds to fully load in after being moved. Is this a constraint of the post-1,13 code changes or something that could possibly be changed?

Explanation

Back in 1.12 when ships moved they did create lag on the server, in particular drop the TPS down to single digits. This is why when ships was rewritten from the ground up for 1.13+ one of the focus improvements was to stability.

This resulted in what you have experienced, community named it the "fizzle effect" it was designed to move a small amount of blocks no matter how big the ship was resulting in no TPS loss.

how to go back to the old ways

I knew the fizzle effect takes a while to process and can be undesirable. So i allowed the ability for the old Ships 5 to be applied

The easiest way to apply it is to simply run the following command

/ships config set config advanced.block.movement ships:movement_ships_five

To reset back to Ships 6 (1.13+) then run this command

/ships config set config advanced.block.movement ships:movement_ships_six

Hope that helps