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 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.
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 type of resin and the require-
ments of the classification society. It is recommended to select a resin type that is approved by the relevant
classification society for a total surface pressure of 5 N/mm
2
. (A typical conservative value is Ptot 3.5
N/mm
2
).
During normal conditions, the support face of the engine feet has a maximum temperature of about 75°C,
which should be considered when selecting the type of resin.
The bolts must be made as tensile bolts with a reduced shank diameter to ensure a sufficient elongation
since the bolt force is limited by the permissible surface pressure on the resin. For a given bolt diameter
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Product Guide Wärtsilä 34DF - 3/2012
Product Guide
15. Foundation
