Foundation; Steel Structure Design; Mounting Of Main Engines - Wartsila ?31DF Series Product Manual

Wärtsilä 31DF Product Guide
15.

Foundation

Engines can be either rigidly mounted on chocks, or resiliently mounted on rubber elements.
If resilient mounting is considered, Wärtsilä must be informed about existing excitations such
as propeller blade passing frequency. Dynamic forces caused by the engine are listed in the
chapter Vibration and noise.
15.1

Steel structure design

The system oil tank may not extend under the reduction gear, if the engine is of dry sump type
and the oil tank is located beneath the engine foundation. Neither should the tank extend
under the support bearing, in case there is a PTO arrangement in the free end. The oil tank
must also be symmetrically located in transverse direction under the engine.
The foundation and the double bottom should be as stiff as possible in all directions to absorb
the dynamic forces caused by the engine, reduction gear and thrust bearing. The foundation
should be dimensioned and designed so that harmful deformations are avoided.
The foundation of the driven equipment must be integrated with the engine foundation.
15.2

Mounting of main engines

15.2.1 Rigid mounting
Main engines can be rigidly mounted to the foundation either on steel chocks or resin chocks.
The holding down bolts are through-bolts with a lock nut at the lower end and a hydraulically
tightened nut at the upper end. The tool included in the standard set of engine tools is used
for hydraulic tightening of the holding down bolts. Two of the holding down bolts are fitted
bolts and the rest are clearance bolts. The two Ø43H7/n6 fitted bolts are located closest to
the flywheel, one on each side of the engine.
A distance sleeve should be used together with the fitted bolts. The distance sleeve must be
mounted between the seating top plate and the lower nut in order to provide a sufficient
guiding length for the fitted bolt in the seating top plate. The guiding length in the seating top
plate should be at least equal to the bolt diameter.
The design of the holding down bolts is shown in the foundation drawings. It is recommended
that the bolts are made from a high-strength steel, e.g. 42CrMo4 or similar. A high strength
material makes it possible to use a higher bolt tension, which results in a larger bolt elongation
(strain). A large bolt elongation improves the safety against loosening of the nuts.
To avoid sticking during installation and gradual reduction of tightening tension due to
unevenness in threads, the threads should be machined to a finer tolerance than normal
threads. The bolt thread must fulfil tolerance 6g and the nut thread must fulfil tolerance 6H.
In order to avoid bending stress in the bolts and to ensure proper fastening, the contact face
of the nut underneath the seating top plate should be counterbored.
Lateral supports must be installed for all engines. One pair of supports should be located at
flywheel end and one pair (at least) near the middle of the engine. The lateral supports are to
be welded to the seating top plate before fitting the chocks. The wedges in the supports are
to be installed without clearance, when the engine has reached normal operating temperature.
The wedges are then to be secured in position with welds. An acceptable contact surface
must be obtained on the wedges of the supports.
15.2.1.1 Resin chocks
The recommended dimensions of resin chocks are 150 x 400 mm. The total surface pressure
on the resin must not exceed the maximum permissible value, which is determined by the
DBAE248994
15. Foundation
15-1