One problem I have with boats is that there aren’t many places to put cups in the cockpit when at sea. However with some scrap wood or plastic, thin rope and a spare snap shackle or hook you can easily make a swinging cup holder.
Most cups on boats are stackable however every type of cup will work. First I measured the diameter of two points in the cup. I luckily had access to a laser cutter at school and made a CAD of my cup holder. My design has a hole in the middle for the cup to partially fit through and 4 holes for the rope to go through round the outside of the holder.
However, a laser cutter is not essential, the holder can just as easily be made by cutting a large hole through a piece marine grade wood or plastic and drilling 4 holes around the side.
You need to make two of these rings with different sized holes through the middle so that they sit at different places on the cussp.
Next is the difficult part, you must pass some thin rope through the cup holder and tie stopper knots just below where each of the rings go. Make sure that both the rings are tight around the cup so it does not rattle.
Lastly tie the end of the ropes to a small snap shackle, carabiner or even a hook so that the cup holder can easily be attached to the guardrail.
If your cups are not stackable or you want to use mugs instead place the top ring lower down the cup and don’t cut a hole in the middle of the bottom piece and rest the cup on top of the bottom piece.
These cup holders can be easily placed anywhere where there is a horizontal wire or rope and are perfect for small cockpits because it stops them being cluttered.