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Performance of merchant vessel in ice in Baltic

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jonna nevalainen

on 26 November 2014

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Transcript of Performance of merchant vessel in ice in Baltic

Ice resistance
Ship performance in ice directly related to propulsion power.

Formulations for:
- Level ice
- Channel resistance
- Ice ridges
Analysis of ship measures a merit in ice
Influence of ice conditions
Ship performance in Ice
Performance of merchant ships in ice in the baltic.
Level ice resistance
Main variable ice:
- Ice thickness hi
- Ice strength
- Density
- Friction

Lecel ice resistance variables:
- External properties
- Ship's shape
- Ship's size

Breaking ice flows from intact level ice field.
Enkvist 1986
Channel ice resistance[1]
Due to moving of brash ice

Proposed formula based on work from Englund(1996), Wilhelmson(1996) and Malmberg(1983).
Differences in
Resistance due to ice ridges
Not a design criteria because it's difficult to determine, since resistance is strongly affected by the probabilities of size and occurrence.

Channel ice resistance[2]
Speed dependency according to Wilhemson(1996) and Vance et al. (1981).
Hf describes the brash ice layer moving along the ship from bow to midship.
For Bm> 10m and Hm>0.4m
First part is the ship moving the ridge. It may be taken as a point force applied at the ship's shoulder.
With C1=7.5 kN/m³
The second part is about the friction along the ship's parallel midship.
C2= 172 kN/m³
Integration of the ridgeprofile over the ship's profile.
Performance of merchant vessel in ice in Baltic
Ship performance requirements in ice
Ship performance requirements in ice dictated by the ships ice class.
Currently divided into 4 classes:
IAS (unescorted navigation in channel)
IA (escorted navigation in channel)
IB (escorted navigation in channel)
IC (escorted navigation in channel)
IAS and IA intended for year-round navigation.
IB and IC reserved for early winter or for lakes.
Powering based on escorted navigation in channels
Ship performance requirements in ice (2)
Powering requirement formulated based only on brash ice resistance.
Although open water is right behind escorting ship, nevertheless, some ship lengths away channel is closed again.
Bow waterline and stem angle values are taken at B/4.
The average value of the angles over the bow would give more accurate resistance estimates, however, it is to complicated to take into account.
Powering based on independent navigation in channels
Ship performance requirements in ice (3)
Powering requirement consists of two parts:
Resistance in channel brash ice
Resistance due to consolidated layer of ice in channel
Consolidated layer part of the resistance is described by level ice thickness equations at an assumed speed of 5 knots.
Design thicknesses and final power formulations
Ship performance requirements in ice (4)
Maximum design thickness for channel ice (class IAS) was chosen based on north Bothnian bay.
Consolidated layer was chosen as 0.1 m
The values show in the above table are inserted into level ice thickness and channel ice resistance equations.
This further simplifies the equations and the channel ice resistance can be expressed as follows:
Constants related to consolidated layer of ice in channel
where Ke is dependent on the number of propellers and their type and Dp is the propeller diameter

The power requirement expressed in kW for all ice classes is as follows:

ice condition
Traffic control
ship operational mode
power requirement
Encounter ice conditions and operational modes in winter 1994
Lehtinen, 1994
Aim of study
Good ice performance

is a ability to proceed in ice
Low ice resistance
High propulsion efficiency and thrust
economically profitable
Crew experience
Ice class
Traffic restriction
Icebreaker escort
Navigation system:
Individual ship perspective:
System perspective:
Measuring good ice performance of ship by:
A good ice going ship :

P/DWT ratio versus ship speed in Raahe channel
Pöntynen, 1992
Transportation efficiency:
Navigational modes of ship:
Escorted in an old channel after icebreaker
Independently in an old channel
Escorted in ridged field
Independently in ridged field
Power requirement based on ice resistance:
The performance in terms of propulsion power
Propulsion can be found via pollard pull!
Full power,speed is 0 knots:
equal with
Pollard pull
In open water:
Tnet=total thrust- Row
Min speed require for ship navigating independently in ice =5 knots
By using relationships between Tnet and Tpull, in 5 knot speed
Propulsion power in ice is:
The power requirement based on ice resistance in two operation modes of old channel conditions:
ICE RESISTANCE formulation were modified
for present purposes
to ensured fluent and continously proceeding behind icebreaker in channel

Ship performance requirements in ice (5)
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