Detailed design and considerations for marine rubber fender system

Detailed design and consideration for marine rubber fender system

For the selection of a rubber fender, the design of parts such as fender panels, chains and fixings is required for the fender system. In particular, in the case of rubber fenders with panels, the design of these parts is a valuable aspect that determines the final size, rubber grade and cost. After the selection, based on the effective berthing energy, if the design of a fender panel or chain for the selected rubber fender is not suitable, the designer may overlook the inherent hazards of the system. It is necessary to perform the design appropriately in accordance with the engineering principle and confirm the results with the purchaser. The actual design calculations may be left to manufacturers because the details of these design procedures vary by type, size, and manufacturer. Therefore, the basic concepts of the fundamental balance of forces and moments are presented here.

(1)Allowable hull pressure

The fender panel should be joinable with the rubber fender body, and its size should be larger than the required contact area for the allowable average hull pressure. The average hull pressure P on the panel is determined by dividing the design reaction force by the effective panel area, as shown in equation (below), to determine the size of the fender panel. 

where

P : Average hull pressure (kN/m2 = kPa)

R : Design reaction force (kN)

A : Effective contact area of fender panel (A = WFe x HFe：m2 )

Hp : Allowable hull pressure (kN/m2 = kPa)

WF : Width of fender panel (WFe = Effective width：m)

HF : Height of fender panel (HFe = Effective height：m)

Above presents the values of the maximum allowable hull pressure recommended for each type of vessel in the PIANC Guidelines  amended with an example of the domestic results. According to the Technical Standards and Commentaries of Ports and Harbour Facilities , the recommended hull pressure is 200 to 400 kN/m2 on the premise of the frame (ribs) coming into contact on the vessel side. The effective width and effective height of the fender panel may not include the oblique chamfer portion of the end in the area but may include the gaps between the resin pads. This configuration is shown in below figure(Effective size of fender panel).

Although the hull pressure is restricted by the strength on the vessel side, the hull pressure is not uniform because the reinforcement on the hull is not uniform. The allowable hull pressure is the average face pressure, used as a standard for determining the size of the fender panel. However, in certain locations, the pressure is higher than the average hull pressure at the reinforcing rib of the vessel side. Furthermore, the contact pressure is zero on the indented area. In addition, in the case of angular berthing, the contact of the panel in the initial stage of berthing is a point or line contact, and the contact area cannot be calculated. Although the hull pressure is usually referred to as the contact pressure, here, it is termed as the average hull pressure to distinguish it from the local contact pressure. Moreover, since this pressure has a large value in a rubber fender without a panel, the panel is often required when the hull pressure is limited. 

(2)Load cases for fender panel

The bending moment applied to the fender panel should be carefully considered according to the manner in which the berth force is applied, as shown in below Fig. .

1) Point load: Corner contact at the initial stage of berthing, etc.

2) Line load: Angular berthing, contact of hull flare, etc.

3) Two line loads: Contact of vessel with belted hull

4) Central line load: Contact with the centre of two or more vertical fenders

5) Distributed load: Full contact or partial contact with fender panel

(3) Design Considerations

When designing fender panels and chains, the berthing and cargo handling operations can affect the durability of fenders and the safety of operations. Some representative examples are as follows:

①Prevention of breakage due to hooking of mooring ropes

②Preventing hooking on the hull belt

As shown in the right figure in below figure, if the vessel has a belt that extends from the hull,installing a wing to prevent hooking by producing an inclined portion at the upper and lower ends of fender panel is effective. In addition, if such a protrusion is present on the vessel side, the resin pad on the surface of the panel may be damaged rapidly; thus, a resin pad should not be used when constantly receiving loads such as those of a ferry