diff --git a/CMakeLists.txt b/CMakeLists.txt
index c0bb271..72ff2e7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -183,13 +183,18 @@ if(SEASTACK_ENABLE_CHRONO)
             "  (or /usr/local/opt/libomp on Intel Homebrew).")
     endif()
 
-    # If Chrono set HDF5_DIR, retry the find
+    # If Chrono set HDF5_DIR to NOTFOUND (common when Chrono itself found HDF5
+    # via module mode, not hdf5-config.cmake), clear it so later FindHDF5
+    # module-mode discovery (e.g. Ubuntu libhdf5-dev) can succeed.
     if(NOT HDF5_FOUND AND DEFINED CACHE{HDF5_DIR})
         if("${HDF5_DIR}" MATCHES "NOTFOUND")
             unset(HDF5_DIR CACHE)
             find_package(HDF5 CONFIG QUIET)
         endif()
     endif()
+    if(SEASTACK_ENABLE_HYDRO_IO AND NOT HDF5_FOUND)
+        find_package(HDF5 QUIET COMPONENTS CXX)
+    endif()
 
     # Use same C++ standard as Chrono for ABI compatibility
     if(DEFINED CHRONO_CXX_STANDARD)
diff --git a/adapters/chrono/CMakeLists.txt b/adapters/chrono/CMakeLists.txt
index 46f30a5..ae95378 100644
--- a/adapters/chrono/CMakeLists.txt
+++ b/adapters/chrono/CMakeLists.txt
@@ -24,19 +24,25 @@ target_include_directories(seastack_chrono_adapter
 
 # Chrono MBS YAML registers TSDA/RSDA force functors without copying damping onto the link;
 # simulation_export reads damping_coefficient from model YAML when GetDampingCoefficient()==0.
-find_package(yaml-cpp CONFIG QUIET)
-if(NOT yaml-cpp_FOUND)
-    find_package(yaml-cpp QUIET)
-endif()
-if(TARGET yaml-cpp::yaml-cpp)
-    set(_seastack_yaml_cpp_target yaml-cpp::yaml-cpp)
-elseif(TARGET yaml-cpp)
-    set(_seastack_yaml_cpp_target yaml-cpp)
-elseif(TARGET Chrono::yaml-cpp)
-    # Chrono's config often provides yaml-cpp as an imported target without a system package.
+#
+# Prefer Chrono's bundled yaml-cpp when available so that the yaml-cpp headers
+# (which come from Chrono's chrono_thirdparty/yaml-cpp/include via Chrono::Chrono_core)
+# match the linked library. Mixing a system libyaml-cpp.so with Chrono's headers can
+# produce link errors against internal symbols (e.g. YAML::FpToString, YAML::Emitter::Write).
+if(TARGET Chrono::yaml-cpp)
     set(_seastack_yaml_cpp_target Chrono::yaml-cpp)
 else()
-    message(FATAL_ERROR "yaml-cpp not found (required for Chrono adapter).")
+    find_package(yaml-cpp CONFIG QUIET)
+    if(NOT yaml-cpp_FOUND)
+        find_package(yaml-cpp QUIET)
+    endif()
+    if(TARGET yaml-cpp::yaml-cpp)
+        set(_seastack_yaml_cpp_target yaml-cpp::yaml-cpp)
+    elseif(TARGET yaml-cpp)
+        set(_seastack_yaml_cpp_target yaml-cpp)
+    else()
+        message(FATAL_ERROR "yaml-cpp not found (required for Chrono adapter).")
+    endif()
 endif()
 
 target_link_libraries(seastack_chrono_adapter
diff --git a/adapters/chrono/src/simulation_export.cpp b/adapters/chrono/src/simulation_export.cpp
index 5e7a60c..c9e55c2 100644
--- a/adapters/chrono/src/simulation_export.cpp
+++ b/adapters/chrono/src/simulation_export.cpp
@@ -1082,13 +1082,18 @@ void SimulationExporter::RecordStep(::chrono::ChSystem* system) {
     }
 
     // ── Generic joint reactions (level-gated) ───────────────────────────────
+    // GetReaction1/2 and GetFrame1Abs/2Abs are virtual on ChLinkBase, so they
+    // work for every concrete joint type (ChLinkLock, ChLinkUniversal,
+    // ChLinkRevoluteSpherical, ...). Previously this code dynamic_cast<>'d to
+    // ChLinkLock* only, silently writing zeros for every other joint type --
+    // including the ChLinkUniversal joints used by the 5SA articulated WEC demos.
     for (auto& j : impl_->joints) {
         auto* L = j.link;
-        if (auto* lock = dynamic_cast<::chrono::ChLinkLock*>(L)) {
+        if (L) {
             try {
-                auto w1 = lock->GetReaction1();
-                auto F1 = lock->GetFrame1Abs().TransformDirectionLocalToParent(w1.force);
-                auto T1 = lock->GetFrame1Abs().TransformDirectionLocalToParent(w1.torque);
+                auto w1 = L->GetReaction1();
+                auto F1 = L->GetFrame1Abs().TransformDirectionLocalToParent(w1.force);
+                auto T1 = L->GetFrame1Abs().TransformDirectionLocalToParent(w1.torque);
                 j.react_force_b1.insert(j.react_force_b1.end(), {F1.x(), F1.y(), F1.z()});
                 j.react_torque_b1.insert(j.react_torque_b1.end(), {T1.x(), T1.y(), T1.z()});
             } catch (const std::exception& ex) {
@@ -1098,9 +1103,9 @@ void SimulationExporter::RecordStep(::chrono::ChSystem* system) {
             }
             if (!is_compact) {
                 try {
-                    auto w2 = lock->GetReaction2();
-                    auto F2 = lock->GetFrame2Abs().TransformDirectionLocalToParent(w2.force);
-                    auto T2 = lock->GetFrame2Abs().TransformDirectionLocalToParent(w2.torque);
+                    auto w2 = L->GetReaction2();
+                    auto F2 = L->GetFrame2Abs().TransformDirectionLocalToParent(w2.force);
+                    auto T2 = L->GetFrame2Abs().TransformDirectionLocalToParent(w2.torque);
                     j.react_force_b2.insert(j.react_force_b2.end(), {F2.x(), F2.y(), F2.z()});
                     j.react_torque_b2.insert(j.react_torque_b2.end(), {T2.x(), T2.y(), T2.z()});
                 } catch (const std::exception& ex) {
diff --git a/data/demos/run_seastack/5sa/bimodal/5sa_bimodal.hydro.yaml b/data/demos/run_seastack/5sa/bimodal/5sa_bimodal.hydro.yaml
index 32569c1..1159c59 100644
--- a/data/demos/run_seastack/5sa/bimodal/5sa_bimodal.hydro.yaml
+++ b/data/demos/run_seastack/5sa/bimodal/5sa_bimodal.hydro.yaml
@@ -1,20 +1,31 @@
 hydrodynamics:
   bodies:
+    # Surge/sway/heave/roll/pitch/yaw damping mirrored from the spreading
+    # case. The bimodal swell + wind sea combination contains spectral
+    # energy near the chain's heave natural frequency, and with zero
+    # linear and quadratic damping in heave/pitch/yaw the rigid-body
+    # heave mode runs away after ~200 s of accumulation (body z-position
+    # exceeded 10 m above SWL by t=280 s in the previous configuration).
     - name: body1
       h5_file: ../assets/hydroData/5sa_directional.h5
-      linear_damping: [0, 100000, 0, 500000, 0, 0]
+      linear_damping:    [20000, 80000, 80000, 500000, 200000, 200000]
+      quadratic_damping: [10000, 40000, 40000, 250000, 100000, 100000]
     - name: body2
       h5_file: ../assets/hydroData/5sa_directional.h5
-      linear_damping: [0, 100000, 0, 500000, 0, 0]
+      linear_damping:    [20000, 80000, 80000, 500000, 200000, 200000]
+      quadratic_damping: [10000, 40000, 40000, 250000, 100000, 100000]
     - name: body3
       h5_file: ../assets/hydroData/5sa_directional.h5
-      linear_damping: [0, 100000, 0, 500000, 0, 0]
+      linear_damping:    [20000, 80000, 80000, 500000, 200000, 200000]
+      quadratic_damping: [10000, 40000, 40000, 250000, 100000, 100000]
     - name: body4
       h5_file: ../assets/hydroData/5sa_directional.h5
-      linear_damping: [0, 100000, 0, 500000, 0, 0]
+      linear_damping:    [20000, 80000, 80000, 500000, 200000, 200000]
+      quadratic_damping: [10000, 40000, 40000, 250000, 100000, 100000]
     - name: body5
       h5_file: ../assets/hydroData/5sa_directional.h5
-      linear_damping: [0, 100000, 0, 500000, 0, 0]
+      linear_damping:    [20000, 80000, 80000, 500000, 200000, 200000]
+      quadratic_damping: [10000, 40000, 40000, 250000, 100000, 100000]
 
   # Bimodal sea state: swell along +X, wind sea from beam (90 deg).
   waves:
@@ -42,6 +53,11 @@ hydrodynamics:
           type: cos2s
           s: 8
 
+  # Bimodal sea: swell and wind-sea have different headings, so excitation
+  # must be evaluated in the frequency domain (matches spreading case).
+  excitation:
+    method: frequency_domain
+
   radiation:
     method: rirf_convolution
     smoothing:
diff --git a/scripts/unix/build.sh b/scripts/unix/build.sh
old mode 100644
new mode 100755
index f0170f8..4cfbf31
--- a/scripts/unix/build.sh
+++ b/scripts/unix/build.sh
@@ -318,14 +318,15 @@ else
   USE_VSG=0
 fi
 
+# HydroIO / HDF5:
+# Do not force HydroIO OFF merely because build-config.json leaves HDF5Dir empty.
+# On Ubuntu/Debian, libhdf5-dev is discovered by CMake FindHDF5 (module mode)
+# without a config-mode HDF5_DIR. Passing -DHDF5_DIR is optional; Chrono's
+# ChronoConfig may even set HDF5_DIR to NOTFOUND when it used module-mode HDF5.
+# Only --no-hydro-io disables HydroIO here. If CMake cannot find HDF5, configure
+# fails with a clear FindHDF5 error instead of a later missing-header failure.
 if [[ -z "${SEASTACK_HDF5_DIR:-}" && "${NO_HYDRO_IO}" -eq 0 ]]; then
-  echo "   [WARN] HDF5 not found; HydroIO will be disabled." >&2
-  if [[ "${USE_CHRONO}" -eq 1 ]]; then
-    echo "          If Chrono was built without HDF5, set HDF5Dir in build-config.json." >&2
-  else
-    echo "          For Chrono-free builds, set HDF5Dir or use --no-hydro-io." >&2
-  fi
-  NO_HYDRO_IO=1
+  echo "   [INFO] HDF5Dir unset; HydroIO left ON for CMake HDF5 discovery (module/config)." >&2
 fi
 
 if [[ "${MOORDYN}" -eq 1 && ! -f "${REPO_ROOT}/extern/MoorDyn/CMakeLists.txt" ]]; then
diff --git a/scripts/unix/ctest_suite.sh b/scripts/unix/ctest_suite.sh
old mode 100644
new mode 100755
diff --git a/scripts/unix/run_benchmarks.sh b/scripts/unix/run_benchmarks.sh
old mode 100644
new mode 100755
diff --git a/scripts/unix/run_chrono_free_tests.sh b/scripts/unix/run_chrono_free_tests.sh
old mode 100644
new mode 100755
diff --git a/scripts/unix/run_comparison_tests.sh b/scripts/unix/run_comparison_tests.sh
old mode 100644
new mode 100755
diff --git a/scripts/unix/run_regression_tests.sh b/scripts/unix/run_regression_tests.sh
old mode 100644
new mode 100755
diff --git a/scripts/unix/run_seastack_demo_smoke.sh b/scripts/unix/run_seastack_demo_smoke.sh
old mode 100644
new mode 100755
diff --git a/scripts/unix/run_unit_tests.sh b/scripts/unix/run_unit_tests.sh
old mode 100644
new mode 100755
diff --git a/scripts/unix/run_verification_tests.sh b/scripts/unix/run_verification_tests.sh
old mode 100644
new mode 100755