Stage 1 · The Tank
Most homemade lures roll over and die.
Build one out of blocks. Every material has a real density, the lip makes real drag, and the balance between weight and buoyancy decides whether you get an action or a very expensive piece of skating firewood.
Coarse by design — grid cells, not millimetres. It models the couplings that decide whether a bait works (mass against buoyancy, lip against righting moment, tie position against action), not the exact depth a given bait runs. What the model does and does not do.