583
1 INTRODUCTION
Theobjectiveofthepresentpaperistodeterminethe
windimpacttoavesselinteractingwithseaice.Here
weconsidertwoshipice‐stickingeventsonwhicha
sufficientdescriptionisavailable.
TheGulf of Finlandhas a special combination of
intense winter shipping and extensive seasonal ice
cover.TheGul
fofFinlandisice‐coveredinnormal
andseverewinters[1].Strongwindsblowofftenon
theGulfofFinland.Thewindgeneratesicepressure
andalsoitimpactsdirectlyonavessel.Avesselhull
appears to the wind as a sailing.Maximum day‐
averagewindspeedstayedbelow15m/sinthewinter
seasons1971‐2005 [2]. In severe winters strong
winds blow from N and NE. In mild winters SW
windsdominateintheGul
fofFinland[3].
The ice‐sticking of ships causes a tremendous
economic loss. The ship loses its speedor even
sticksinice.Inthemodera
tewinter2009/10about250
entrapment events are reported. According to the
data, the ships spent in ice‐catch totally 67 days [4].
Theneedfordetours toavoidhard‐iceareasraisesthe
trip duration. Vessel hull may get damage when
sailinginice.49shiphulldamagestookpla
ceinthe
GulfofFinlandintheseverewinter2002/03[5].
The ice pressure is rarely measured on the GoF.
TukkerandPerovich[6]goticestressupto350kPain
packiceintheArcticarea.Thischaracteristicdepends
on the lot of fact
ors: the ice thickness and
concentration,icetypeanditsshape,windspeedand
direction.Theicepressurevariesgreatlyalongarea
andtime.
2 CASEDESCRIPTIONS
We observe the two ice‐sticking events on which a
sufficientdescription(thelocation,timeandtheevent
recordinthelogjournal)isav
ailable.
2.1 Case1:Nordlandia,29thJanuary2010
TheferryNordlandia,153mlong,ca40mhighwith9
decks.UsuallyitgetsfromHelsinkitoTallinn(Fig.1
and2)in3.5hours.ButontheJanuary29th2010the
voyage took 10 hours as the vessel got stuck in the
A Case Study of the Wind Impact on Ship Ice-sticking
J
.Rjazin&O.Pärn
TallinnUniversityofTechnology,Tallinn,Estonia
ABSTRACT:Inthepaper,theimpactofwindonaferrysailinginicefieldisdescribedandanalysed.Twoice‐
stickingeventsontheGulfofFinlandaretakenforthecasestudy.Thewind,especiallyitsdirection,isstatedas
animportantfactortoentrapavesselintheice.Thewindblowing acrossthevessellongit
udeaxiscausedboth
theshipstostick.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 10
Number 4
December 2016
DOI:10.12716/1001.10.04.06
584
ice[7]. The ice condition during the event: the area
100% ice‐covered, ice thickness 0.05‐0.25 m, ridge
fraction10%.
Figure1. Wind force acting on the ferry Nordlandia. The
shipis(A=100%)surroundedbyice(photo:vastavalo.fi).
Figure2. The FMI ice model product for the ice
concentration and drift. The ice drifted to the NWW. The
location of Nordlandia is shown by the black item with
white inscription. The red colour indicates the full (100%)
icecoverinthearea.
Figure3. The wind directions on the 29th Jan. 2010. The
wind changed its direction on the dawn 30 th Jan. thus
enablingtheferrytomove.
Atthisentrapmentevent,thewindblewfromthe
East (Fig. 3) all the day with the speed 8 to 18 m/s
(Fig. 4). Thus the wind blew across the ferry
movementdirection.
Figure4.ThewindspeeddurigtheNordlandiaevent.
2.2 Case2:Saxen,7/8
th
january2003
The tanker Saxen, 99.6 m long, was sailing from
Tallinnto Porvoo (Fig. 5). It was caught in ice for 5
hours. Its hull got damage[8]. The ice condition
during the event: the area 100% ice‐covered, ice
thickness0.3‐0.4m.
Duringtheentrapmentevent,the
windblewfrom
NNWandWwithspeed5‐9m/s.Thusthewind blew
almostacrossthelongitudinalaxisoftheship.From
theshiplogjournalweknowthatsometimelaterthe
windchangedindirectionandthentheshipgotfree
fromtheicestick.
From
Tallinn
to
Porvoo
5 m/s
wind
Figure5.ThelocationwheretheSaxengotstuck.Theblack
arrows show the winds directions and the blue arrow
depictsthevesselmovementdirection.
585
3 THEWINDIMPACTANALYSISONTHESHIP
HerewereconstructtheNordlandiaice‐stickingevent
with respect of the wind blowing on the ship. Also
thiseventiscomparedheretotheSaxencasebecause
the circumstances are similar enough at the both
events.The ice covered 100% the
ship vicinity in
both the cases. At both the events the wind blew
almost across (assumed orthogonally for the
reconstruction)theshiplongitudinalaxis.
Thewind‐generatedforcesimpactontheshipgot
intouchwiththeiceisconsidered.Thewindpushes
the ship against the ice (Fig. 6)
whereas
underpressure takes place on the other side. We do
nottaketheimpactoftheiceinfrontoftheshipinto
account here. Here we consider neither the ice
pressurenortheimpactofunder‐icecurrents.
The ship area with respect to the wind is ca
5000
m
2
whereas we do not take the ship geometric
shape into account.A force acts to the ship by the
windblowingorthogonallytotheshiplongitudinal
axis.Thewindforceisdescribedbytheformula:
2
/2
wind to ship a ship d
FUCA
(1)
where
a
isairdensity,Uiswindspeed,
d
C isdrag
coefficient(3.5fortheopenaironsea).
In the Nordlandia case the wind blowing with
speed 8 m/spushes the ship with force600 kN.
Then the ship impacts on the side ice with the
pressure 15 kPa (Fig AS). We estimate how much
engine power is needed
to keep the ferry speed 20
knotsinspiteofthefrictionforceprovidedbyice.
The necessary power is characterised by the
formula
wind to ship
WF v
where F is the side wind
force, v is the ferry speed and
is the friction
coefficientbetweensteelandice.ThusW=180kWis
calculatedbytheformula.Thus,toovercometheside
ice friction force, the ferry engine has to develop
W=180kWadditionallytothepowerneededtosail
in free water. For a comparison, typical
27 m long
ferry‐boathastheenginepower220kw.
Wind force
S
hip pressure to ice
S
hip area about 5000 m²
Ice h=0.25m
Figure6.Theforcesactingonthevessel.
4 CONCLUSIONANDDISCUSSION
Stickingtheshipintheiceisaresultofafewnatural
factors acting together. In this paper we focus on
windactingtovesselsailinginice,ontheexampleof
twoentrapmenteventsintheGulfofFinland.Inthe
bothstudiedcasesthe
naturalfactorssufficedtostick
thevesselsintheice.
The wind‐generated pressure resists the ship
movement as the wind is blowing across the vessel
longitudinalaxis.Atboththeentrapmenteventsthe
wind blew so. Sticking is probable when the cross‐
wind is accompanied by ice pressure and
under‐ice
currents.
WeevaluatedthewindimpacttotheNordlandia.
Inthiscasethewindprovidedpressure15kPa.This
pressure caused an additional friction between the
hull and the ice.To overcome the side ice friction
force, the ferry engine has to develop power
additionaltothepowerneeded
tosailin freewater.
Typical 27 m long ferry‐boat commonly has the
enginepower220kW.
The present study belongs to the research area
aiming to determine the necessary and sufficient
conditions of sticking a vessel in the ice. Knowing
these conditions enables to avoid navigating ships
frombeingcaughtinice.
ACKNOWLEDGMENT
This work was supported by institutional research
funding IUT 19‐6 of the Estonian Ministry of
EducationandResearch.
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