Hand line frame
An oval frame with a rounded rim and a hook park, sized so the line does not set into permanent coils.
The problem
The hand lines in the shops are thin injection-moulded plastic that cracks in the cold, and the rim is sharp enough to mark the line. The hooks have nowhere to go, so they catch on everything else in the box.
The fix
The frame is 180 mm across with a rounded rim, printed in PETG with four walls. The rim is what decides it: a sharp edge puts a kink in the line at every turn, and after a season those coils are there for good. One end carries a TPU insert slotted for the hook and a hole for a lanyard.
Inside is a sealed chamber so the frame floats if it goes over the side. That depends on the walls genuinely being watertight, and printed parts are unreliable there — water creeps in between the layers. So the chamber gets five walls, and every frame spends a day submerged and is weighed afterwards before anyone calls it floating. Handheld gear is what recreational fishing in the Oslofjord runs on in practice now, but the rules change and have to be checked.
The rules for recreational fishing change, and they are not the same everywhere. Check what applies where you intend to fish before you go out.
More ideas
A hook guard that actually stays on
A soft TPU clip that snaps over treble hooks and jigs so they stop catching nets, clothing and fingers.
A rod holder that fits your rail
A parametric holder printed for the exact tube diameter your boat has — not a standard no boat actually follows.
Gear tags for nets and pots that last
Name, phone number and registration embossed into the tag itself — not written in marker that vanishes in three weeks.