# Safety Assessment for Upper Part of Floating Crane Considering Minimum Luffing Angle
## 2 Minimized Design of Luffing Angle
### Target Crane and Additional Consideration by Minimized Luffing Angle  
The length overall of the floating crane barge being developed in this study is 63.125 m, and the breadth, depth, and draft (DLWL, Design Load Waterline) of the barge is 24, 3.8, \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Bridge Name** & **Bridge Type** & \
\begin{tabular}{c} **Min Span Length** \\ **(m)** \\ \end{tabular} &
\begin{tabular}{c} **Clearance under** \\ **Bridge (m)** \\ \end{tabular} \\ \hline Youngiong & suspension & 300 & 40 \\ Seohae & cable stayed & 470 & 62 \\ Mokpo & cable stayed & 500 & 53 \\ Machang & cable stayed & 400 & 64 \\ Kwangyang & suspension & 1545 & 75 (85, center) \\ Bukhang & cable stayed & 540 & 60 \\ Ulsan & cable stayed & 560 & 60 \\ Geoga & cable stayed & 470 (main) & 52 \\ Incheon & cable stayed & 230 (sub) & 36 \\ Incheon & cable stayed & 800 & 70.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specifications of major domestic marine bridges. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Capacity** **(ton)** & **Min. Luffing** **(deg)** & **Boom Height** **(m)** & **Back Tower** **Height (m)** & **Remark** \\ \hline
120 & 50.5 & 50 & 22 & \\ \hline
600 & 40 & 38 & - & Sako Co. \\ \hline
1200 & 30 & 41.8 & 36.5 & Sako Co. \\ \hline
2000 & 35 & 48 & 40 & Haekwan \\ \hline
2200 & 40 & 56.1 & 34.5 & Kumyong \\ \hline
3000 & 40 & 76.6 & 45 & SHI * \\ \hline \hline \end{tabular}  
* SHI: Samsung Heavy Industries, Ltd.  
\end{table} 
Table 2: Specification of major domestic floating cranes. and 2.5 m, respectively. Figure 2 shows a part of the general arrangement (G/A), and the main materials used are AH32 and AH36 with the modulus of elasticity of 206 GPa and Poisson's ratio of 0.3. The reason of being unavailable to decrease the luffing angle of previous floating cranes to very low angle is that it is not possible to increase the luffing angle again if the luffing wire is lowered to less than the minimum angle of the boom. Accordingly, most previous floating cranes have the minimum luffing angle in the level of 30\({}^{\circ}\) to 40\({}^{\circ}\), as shown in Table 2.  
This floating crane is designed so that the boom can go down to the same level as the height of back tower. In this case, the luffing angle of a boom can be adjusted up to 10\({}^{\circ}\). For this purpose, four hydraulic cylinders were installed between the boom and the structure of attached support. These cylinders help the luffing wire and luffing of the boom when the boom is recovered to the luffing angle under the service condition, namely, when the boom is lifted higher. Figure 2 shows the side shape of the developed model for a floating crane along with the descriptions of major specifications mentioned in Table 2. The boom will go down to the level of the back tower. In addition, the figure also displays the positions of added hydraulic cylinders. The crane developed in this study belongs to a relatively small class with a scale of 250 tons. Recently, ultra large floating cranes with a rated capacity exceeding 10,000 tons have also appeared. SSCV Sleipnir is the largest crane vessel in the world after being built in 2019. She is a semi-submersible crane vessel (SSCV) owned and operated by Heerema Marine Contractors. The vessel is equipped with two evolving cranes, each with a capacity of 10,000 tons, and the main cranes can be operated in tandem to jointly lift 20,000 tons [24]. However, these ultra large floating cranes are not intended for offshore work adjacent to land, as they are manufactured for the purpose of installation and rescue work of very large heavy objects at sea. Estimating based on statistics related the crane vessel [25], the maximum capacity of the crane vessel for offshore work adjacent to land is expected to be 4000 tons. The general feature of the crane of 4000 tons or higher is that the lower hull is not the barge or a monohull. Their lower hulls are multi-hull or a semi-submergible structure.