3.1.1 The
shaft alignment calculations required by Vol 2, Pt 5, Ch 4, 2.1 Documentation - Shaft alignment calculations 2.1.2 and Vol 2, Pt 5, Ch 4, 2.1 Documentation - Shaft alignment calculations 2.1.3 are
to be in accordance with the requirements of Vol 2, Pt 5, Ch 4, 3.1 Design calculations 3.1.2 to Vol 2, Pt 5, Ch 4, 3.1 Design calculations 3.1.5.
3.1.2 For
the purpose of the calculations, the following assumptions are to
be made:
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The shafting base
line, to which all slopes and deflections are to be referred, is to
be taken as the nominal centreline of the shafting as shown on the
shafting arrangement plan. This is to be established as the line of
sight on the vessel.
-
The centreline
of the shaft at the mid-length of the bearing adjacent to the propeller
lies on the nominal centreline of the shafting.
-
The centreline
of the shaft at the mid-length of each of the other bearings lies
initially on the nominal centreline of the shafting.
-
The propeller
and shaft masses act at right angles to the nominal centreline.
-
The propeller
and shaft weights are reduced due to immersion in water and oil as
applicable.
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The load distribution
in the outboard bearings and sterntube bearings is not uniform along
the bearing length.
-
The load on each
plummer and bulkhead bearing is concentrated at the mid-length of
the bearing.
3.1.3 The
bearing loads corresponding with the shaft centreline at each bearing
lying on the nominal centreline of the shafting are to be calculated
together with a set of influence coefficients for each bearing. The
set of influence coefficients for one bearing is to show for a downwards
vertical displacement at that bearing of 0,25 mm, the change in load
upon it and upon each of the other bearings.
3.1.4 If the
distribution of the bearing loads corresponding with the shaft centreline
at each bearing lying on the nominal centreline of the shafting is
not acceptable, a satisfactory distribution of load is to be obtained
by introducing vertical offsets of the bearings upwards or downwards
as necessary.
3.1.5 In some
arrangements, the disposition of the main gearbox relative to the
nearest plummer block may result in an excessive bending stress in
the shaft unless the main gearwheel shaft bearings are assumed to
carry the weight of the part of the intervening shafting in addition
to the weight of the gearwheel and its shaft. In such arrangements,
offsets for the main wheel bearings are to be selected to provide
a distribution of load on the main gearwheel forward and aft bearings
acceptable to the gearing designer.
3.1.6 Using
the selected bearing offsets, the bending moment and deflection diagrams
are to be drawn and the slopes through the sterntube and bracket bearings
relative to a defined datum established both for as new and for maximum
weardown of outboard bearings.
3.1.7 To ensure
that the shafting system will be supported at the slope and heights
calculated, allowance is to be made for:
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Bearing clearances.
-
Compression of
bearing materials under load.
-
Expansion of bearing
material due to immersion in water.