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Ship’s Girder Deflection

Ship's Girder Deflection & DWT Gain/Loss Software - Introduction

According to International Standards, hull girder deflection is limited to 1 mm per meter of ship length. As per the classification rules, no specific limits on hull girder deflections are given explicitly, but the L/D ratio on the design stage is related to the criteria which allows safeguarding against excessive deflection. It is appreciated that the deflection, hence stiffness against bending, depends upon both geometry (moment of inertia, I) and elasticity (E).
Maximum Deflection values depend on the distributions of the maximum bending moment and the moment of inertia as obtained by the second integration of the Bending Moments divided by the moment of inertia curve.
It is expected the maximum value of the deflection to correspond to the maximum value of the bending moment at the cross section.

Which are the main data input?

At the top of the main Ship’s Girder Deflection screen, if “Given Draft Mark Readings” tab is selected,
input of the Draft Aft, Amid and Fwd at both Port and Starboard Side at Mark Readings, shall be inserted
at the respective fields.

Next, if thermal deflection needs to be determined, you may input data for Air Temperature and
Seawater Temperature for Thermal Deflection Calculations, in order to find the total Deflection at
Midship and eventually the total DWT Gain/Loss.

Otherwise, you may select the tab “Given Draft Amid and Deflection”, if deflection at Midship can be
already determined from existing instruments onboard. In that case the Draft Amid (Loading
Instrument) and Deflection at Midship shall be inserted at the respective fields.
Also, Sagging or Hogging Condition shall be defined.

Likewise, if thermal deflection needs to be determined, you may follow the above steps as being
described in “Given Draft Mark Readings” steps.

How the results are illustrated?

The calculated Deflection and the Deadweight Gain or Loss are displayed in the Table Results for both

At the bottom of the Table results screen, the Thermal Deflection at Midship and the total Deadweight
Gain or Loss are illustrated.

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Ship specific approvals since 1986 granted by
Classification Societies