Man B&W L35MC6-TII User Manual

MAN B&W 17.06
Page 2 of 2
MAN Diesel
198 42 269.2MAN B&W MC/MC-C/ME/ME-B/MEC/MEGI engines
When running undercritical, significant varying
torque at MCR conditions of about 100150% of
the mean torque is to be expected.
This torque (propeller torsional amplitude) induces
a significant varying propeller thrust which, under
adverse conditions, might excite annoying longi-
tudinal vibrations on engine/double bottom and/or
deck house.
The yard should be aware of this and ensure that
the complete aft body structure of the ship, in-
cluding the double bottom in the engine room, is
designed to be able to cope with the described
phenomena.
Overcritical running
The natural frequency of the onenode vibration
is so adjusted that resonance with the main criti-
cal order occurs about 3070% below the engine
speed at specified MCR. Such overcritical con-
ditions can be realised by choosing an elastic
shaft system, leading to a relatively low natural
frequency.
The characteristics of overcritical conditions are:
• Tuningwheelmaybenecessaryoncrankshaft
fore end
• Turningwheelwithrelativelyhighinertia
• Shaftswithrelativelysmalldiameters,requiring
shafting material with a relatively high ultimate
tensile strength
• Withbarredspeedrange,EoD:407015,of
about ±10% with respect to the critical engine
speed.
Torsional vibrations in overcritical conditions may,
in special cases, have to be eliminated by the use
of a torsional vibration damper.
Overcritical layout is normally applied for engines
with more than four cylinders.
Please note:
We do not include any tuning wheel or torsional
vibration damper in the standard scope of supply,
as the proper countermeasure has to be found af-
ter torsional vibration calculations for the specific
plant, and after the decision has been taken if and
where a barred speed range might be acceptable.
For further information about vibration aspects,
please refer to our publications:
An Introduction to Vibration Aspects
Vibration Characteristics of Two-stroke Engines
The publications are available at
www.mandiesel.com under
‘Quicklinks’ → ‘Technical Papers’
Critical Running

Man B&W L35MC6-TII Specifications

General

Brand	Man
Model	B&W L35MC6-TII
Category	Engine
Language	English