Guidelines for U-Boat spacing is as follows:
When Joist Spacing is 24” o.c.*, U-Boat spacing should be 16” o.c. along the joist minimum and not to exceed 24” o.c.
When Joist Spacing is between 12”-16” o.c., U-Boat spacing should be 16” o.c. along the joist minimum and not to exceed 32” o.c.
Most (>99%) of applications will work fine with 16” o.c. spacing of U-Boats along the joist. Spacing further apart will improve low frequency isolation below 40 Hz. However, spacing should never exceed 32” o.c.
*o.c. refers to “on center” and represents measuring from the mid-point of a joist or U-Boat to the mid-point of an adjacent joist or U-Boat.