54
INTERNATIONAL
ANDSPECIALIZED TRANSPORT
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APRIL 2015
THEKNOWLEDGE
aswell.Knowing that the transport of the
windgenerator components often requires
less thanhalf of thiswidth it becomes
apparent that anarrowgauge track crane
wouldbe cost effective for the civilworks.
SeeFigure4.
One can imagine, however, thatwhen
a crane’s stabilitybase is reduced from
12 to6m, the stabilityof the crane
becomes questionable. For this reason,
when transporting a crane innarrow
gauge track configuration, outriggers are
used toguarantee the crane’s stability.
Theseoutriggers, however, areoff
thegroundor only slightly touching the
ground. Theybearno loadduring the
transport unless the crane starts leaning.
Leaning canoccurdue to anunevenor
out of level road surface, slight settlement
onone sideof the road andweather
conditions such as rain,wind etc. This is
anunwanted situation as leaningwill have
tobe counteredby ‘pushing’ the craneback
using theoutrigger stroke.
Secondly,when the crane starts leaning,
thepressureunderneath the trackon the
sideof the lean rapidly reaches extreme
values and it can easily take70 to80%of
the totalweight of the crane.As a result,
the roadneeds tobe able towithstand
thesepressures and shouldnot cave in
or sink.
When thishappens theoutriggerwill
not beofmuchhelp. It canpush the crane
backbut avoidwill appearunder the track.
Narrowgauge track cranes are cost-
effective anduseful, as longas theyareused
with caution.
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tower adapter can copewith all of these
variables, andmore. Transporting a tower
sectionwith a tower adapter is similar to
transportingwith turntables or bolsters.
The front and rear transporter canpivot
under the adapter support point. The tower
adapter allows the tower tobekept close
to theground as it hangs inbetween the
front and rear transporter; this reduces
theoverall transport height to the largest
towerdiameterplus thebolted rimof the
adapter. The tower section can alsobe
raised; the tower adapter allowspivotingof
the adapter arms bymeans of ahydraulic
cylinder. SeeFigures 1a and1b.
The tower adapters comewith twomore
advantages. First, no crane is required for
the loadingof the tower section.When
they areproperly laidout the truckwith
adapter can simplyback-up against the
tower section and the securingbymeans
of bolted connection and, or, hydraulic
clamping canbedone. Secondly, once
the tower section isdelivered to site, the
front and rear adapter canbe connected
and returned to the loading facility as
one transport combination. There isno
need for a second truck to return the rear
transporter. SeeFigure2.
Overcoming issues
Nacelles, specially thebigger ones, have
threedrawbacks. They areoversized, heavy
and awkward shapes. Theoversize aspect
can create a situationwhere,when the
nacelle ispositionedon a trailer, theoverall
height becomes toomuch for the route.
Similar to the tower sections, the solution
is tohang thenacellebetween a front and
rear transporter andkeep it as close to the
ground aspossible. The awkward shape
of thenacelle,which isdifferent for each
manufacturer andoften for eachmodel,
makes anacelle adapter a trickydesign.
This isworkedout between the
manufacturer of thenacelle andof the
transporters by a templatedesign that fits
on theone side to the tower adapter andon
theother side fits thenacelle. The adapters
aredesigned for a certainmaximumweight
and, as the tower sections aregenerally
lighter inweight than thenacelle, not
all nacelles canbe transported in this
manner. SeeFigure3. In addition, a crane
isunnecessary for loading thenacelle and
both transporters canbepulledback to the
loading facilitybyone truck.
The transport startingpoint is often
similar tootherheavy andoversized cargo
and isusually aport facilityor a factory.At
somepoint, the transport leaves thepublic
road and continues on a temporary road
that is solely constructed for thepurposeof
mobilising thewindgenerator components
and for the crane to lift the components.A
well compacteddirt roadmaybe just fine
for the jobbut it is important tounderstand
what forces are imposedon these roads.
Transport equipmentmanufacturers
havedesigned some clever adapters and
features asdescribed above to aidproject
execution.Cranemanufacturershave also
comeupwithnew solutions.We all know
that crawler cranes are a common sight on
wind turbine erection jobsdue to the ease
ofmoving them fromone lift pad to the
nextwhile (nearly) fully assembled.One
of thedrawbacks of crawler cranes is the
wide tracks; 12 to15m is common for the
large capacity crawlermachinesused for
wind turbine jobs.As a result, the approach
road to the lift padneeds tobe thiswide
Figure2
Figure3
Figure4
