WÄRTSILÄ WARTSILA 20, Руководство по эксплуатации продукта

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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.
Prior to installation the shipyard must send detailed plans and calculations of the chocking
arrangement to the classification society and to Wärtsilä for approval.
The engine has four feet integrated to the engine block. There are two Ø22 mm holes for M20
holding down bolts and a threaded M16 hole for a jacking screw in each foot. The Ø22 holes
in the seating top plate for the holding down bolts can be drilled though the holes in the engine
feet. In order to avoid bending stress in the bolts and to ensure proper fastening, the contact
face underneath the seating top plate should be counterbored.
Holding down bolts are through-bolts with lock nuts. Selflocking nuts are acceptable, but hot
dip galvanized bolts should not be used together with selflocking (nyloc) nuts. Two of the
holding down bolts are fitted bolts and the rest are clearance (fixing) bolts. The fixing bolts
are M20 8.8 bolts according DIN 931, or equivalent. The two Ø23 H7/m6 fitted bolts are located
closest to the flywheel, one on each side of the engine. The fitted bolts must be designed and
installed so that a sufficient guiding length in the seating top plate is achieved, if necessary
by installing a distance sleeve between the seating top plate and the lower nut. The guiding
length in the seating top plate should be at least equal to the bolt diameter. The fitted bolts
should be made from a high strength steel, e.g. 42CrMo4 or similar and the bolt should have
a reduced shank diameter above the guiding part in order to ensure a proper elongation. The
recommended shank diameter for the fitted bolts is 17 mm.
The tensile stress in the bolts is allowed to be max. 80% of the material yield strength and the
equivalent stress during tightening should not exceed 90% of the yield strength.
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.
Wärtsilä 20 Product Guide - a13 - 6 September 2016 15-1
15. Foundation Wärtsilä 20 Product Guide