
Class	BUG
Severity	1
Status	ready

Models: Cable/LumpedMass

Found: 2026-09-30 review of f42360e..a6492d6 (four parallel correctness reviews)

Decision needed: —

Evidence

The wet-fraction-dependent mass (CalcFoundation → CalcMassAndWeight, continuous since R65/R66) is copied into the end-node inertia only by UpdateInertia() (src/cable/subroutines/InternalCable.cpp:750-760), which runs in UpdateCable() before AddEndForces in CalcOutput/OdeFcn; the stability factor m_eFactor is computed only when the length changes. Suspected by reading; not run.

Effect

Near the surface the node inertia is that of the previous evaluation: a small, step-size-dependent inconsistency, larger with a coarse step in waves. It was a discrete switch before, so less visible.

Possible fix

Update the inertia after the foundation is computed for the current state, in the same evaluation.

Test that would prove it

An end node crossing the surface with a finite-difference check of the acceleration against the current mass; or two runs at step h and h/2 that should agree to the integrator's order.

Risk

Low: a small result change for cables crossing the surface.