WÄRTSILÄ 46F Series, Product Manual

Page: 163 / 208

15. Foundation
Engines can be either rigidly mounted on chocks, or resiliently mounted on steel spring
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 should not extend under the reduction gear or generator, if 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 should be integrated with the engine foundation.
15.2 Engine mounting
The mounting arrangement is similar for diesel electric installations and conventional propulsion.
15.2.1 Rigid mounting
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. Bolts number two and three from the flywheel
end on each side of the engine are to be Ø46 H7/n6 fitted bolts. The rest of the holding down
bolts are clearance bolts.
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 appear from the foundation drawing. 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 a 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
the free 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.
DAAB605814 15-1
15. Foundation Wärtsilä 46F Product Guide