Shelli, there are as many possibilities as there are artists. I did not find any practical way to paint while underway. There is simply too much motion in too many directions. At anchor
there can be moments of stability interspersed with rocking and rolling. Also not good. (Perhaps that is how cubism got started?) In a slip you can wedge your easel or tie it down. A table top easel can sit nicely on a cockpit
table or saloon
Of course you can carry your painting gear
ashore and paint plein air. If you are using oils you will have to figure out how to store wet canvases onboard. You might find a dry medium more useful such as colored pencils, pastels or high quality markers.
I wish I could tell you that I found a good solution but after carrying and storing onboard my easel, paints, papers, canvases, brushes
, solvents, oils, etc. for over a year I concluded to separate my passions and I took them all off the boat. Now I take a camera
onboard and paint on shore.