A typical holding down bolt (fitted type) is shown in the figure below. The holes in the tank top are screw cut and the studs are screwed down, until the conical face, at the lower end of the enlarged part of the stud, seats on the tank top to form a water tight joint with the Grommet as shown. Holding down bolts for modern main propulsion slow speed engines are of the ‘long sleeve’ type, and are hydraulically tensioned. Owing to its greater length, it has greater elasticity and is less prone to cracking, than earlier bolts.

The holding down bolts can only withstand tensile forces, and must not be subjected to shear stresses.

Reference and Images

“Marine Engineering Practice” by Vikram Gokhale and N. Nanda