Well, I can only overwrite

common/src/main/java/io/github/xiewuzhiying/vs_addition/mixin/valkyrienskies/MixinShipInertiaDataImpl.java

@@ -0,0 +1,38 @@
+package io.github.xiewuzhiying.vs_addition.mixin.valkyrienskies;
+
+import com.llamalad7.mixinextras.sugar.Local;
+import com.llamalad7.mixinextras.sugar.ref.LocalRef;
+import org.joml.Vector3d;
+import org.joml.Vector3dc;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+import org.valkyrienskies.core.impl.game.ships.ShipInertiaDataImpl;
+
+@Mixin(ShipInertiaDataImpl.class)
+public abstract class MixinShipInertiaDataImpl {
+    @Shadow public abstract Vector3dc getCenterOfMassInShip();
+
+    @Inject(
+            method = "addMassAt",
+            at = @At(
+                    value = "INVOKE",
+                    target = "Lorg/joml/Vector3dc;z()D",
+                    ordinal = 1,
+                    shift = At.Shift.AFTER
+            ),
+            remap = false
+    )
+    private void fix(double x, double y, double z, double addedMass, CallbackInfo ci, @Local LocalRef<double[]> var9) {
+        Vector3dc position = new Vector3d(x, y, z);
+        Vector3dc center = this.getCenterOfMassInShip();
+
+        double new_x = position.sub(center, new Vector3d()).x;
+        double new_y = position.sub(center, new Vector3d()).y;
+        double new_z = position.sub(center, new Vector3d()).z;
+
+        double[] inertia = var9.get();
+    }
+}