The steel chocks under the main engine have become loose, requiring frequent retightening of the holding-down bolts. Possible reasons:

1. The chocks were not correctly fitted/seated: if the chocks do not have full face contact with the bedplate and the foundation, they can settle and become loose.
2. The chocks are too thin or the material is not suitable: steel chocks that are too thin can deform or the contact pressure can cause them to yield.
3. The holding-down bolts were not correctly tensioned initially, or the tension is lost due to the engine settling.
4. Vibration and thermal cycling: the engine's vibration and the thermal expansion/contraction can cause the chocks to work loose and the bolts to lose tension.
5. The foundation/bedplate is not rigid enough, or the hull is deflecting, causing the chocks to move.
6. Corrosion or fretting between the chock and the bedplate/foundation.

Re-chocking using a different material (e.g. an epoxy/cementitious chocking compound instead of steel) might reduce the incidence because:

1. Epoxy chocking compound is poured in place and cures to give full, uniform face contact with the bedplate and the foundation, eliminating the high spots and the settling that occurs with steel chocks.
2. The epoxy compound has a high compressive strength and does not deform or settle, so the holding-down bolts maintain their tension.
3. The epoxy compound is resistant to corrosion and fretting, and it bonds to the surfaces, preventing movement.
4. The epoxy chocking distributes the load evenly over the full area, reducing the local contact pressure and the risk of the chock becoming loose.
5. The epoxy chocking is easier to fit accurately and does not require the precise machining of steel chocks.

So re-chocking with an epoxy compound provides a more stable, full-contact support that maintains the bolt tension and reduces the need for retightening.

If the loose chocks and the loss of bolt tension are allowed to continue unchecked, the consequences could be:

1. The engine bedplate can move/vibrate excessively, causing misalignment of the crankshaft and the shafting, leading to bearing wear and damage.
2. The holding-down bolts can fail (fatigue or over-stress) due to the repeated loading, allowing the engine to move.
3. The engine can become misaligned, causing the crankshaft deflections to go out of limits, leading to main bearing failure and crankshaft damage.
4. The vibration can damage the engine and the ship's structure, and cause noise.
5. In severe cases, the engine could shift on its seatings, causing catastrophic damage to the engine and the shafting.

The loose chocks must be rectified (re-chocked) promptly to prevent serious damage.