In the course of its life the Alma Doepel has been modified to suit the operations requirements at the time. Some of these modifications were major and resulted in the complete reconfiguration of the vessel into the one you see now. Other modifications were more subtle.
The proposed fixes were the modification of main weights to remove loading from the ends of the vessel, the addition of additional supporting structure and the refastening/recaulking of the entire vessel.
The Proposed Fixes
Modification of main weights
It can be quickly seen that removing excess weights from the ends of the vessel and relocating them closer to the centre, where the centre of buoyancy of the vessel is located will reduce the bending moment that causes the hogging deformation.
In practice this is not an easily implementable option. Major weights include the propulsion engines, gensets and bow thruster. Whilst the main engines could be replaced by smaller, lighter units of similar power, they cannot be moved. Similarly, for the generator sets and the bow thrusters.
Tanks contribute a significant proportion of the point weights loading this structure. The installation of a water-maker would allow for smaller amount of water to be stored aboard. Similarly smaller diesel engines and a more limited operational program may allow for smaller amounts of fuel oil to be stored.
The effects of these changes were made to the point weight distribution and to the input loads into the FEA. This has been quantified in the chart below which can be compared to the original point load input chart – Ship mass distribution. If this comparison is made it can be seen that the changes in the distribution are not dramatic. This lack of substantive change may preclude this modification from having significant effects on hogging alone.
Additional Supporting Structure
A visual inspection of vessel indicates that some structural elements tying the deck to the hull have been removed. It seems this may have been done to ‘open up’ the accommodation areas making access easier.
However it is considered that the removal of these ‘props’ or vertical pillars joining the hull and deck does effectively reduce the shear connection between the two vessel elements. An effective shear connection is required for global and local vessel stiffness and will help the vessel withstand the bending load that is currently resulting in hogging.
Areas were identified where props could be added without undue difficulty and without compromising the function of the vessel. These are shown below in red.
Refastening & Recaulking entire vessel planking
The restoration of the main structural elements of the vessel to their original condition is a normal and fundamental part of any vessel restoration program. Significant reductions in the stiffness of the main hull timbers and their connections to each other were factored into the analysis of the vessel in its current state.
The importance of refastening the vessel cannot be overstated. All the fastenings in the vessel are iron, a material prone to degradation due to rusting. This rusting process also degrades locally the timber it is in contact with. These two factors significantly deteriorate the structural stiffness of hull planking. As a consequence refastening has a significant impact on the ability of the vessels structure to withstand global bending loads.