CMC provided Naval Architecture support to Detyens Shipyards, Inc. (DSI)  for the overhaul of USNS APACHE (T-ATF 172).  Tasks included drydocking calculations and pumping plans using the floating drydock, new as-built drawings for a Doppler Speed Log and Echosounder installation, and technical support for replacing a significant amount of steel hull and support structure around the rudder post carrier.


Inspection of the hull steel structure revealed hull plating, tank top, transverse frame, and longitudinal girder structure that needed to be replaced.  It became apparent that special precautions and a detailed ripout and welding sequence procedure was necessary in order to minimize deflection of the vertically aligned carrier for the rudder post bearing.

Exterior view of starboard rudder, nozzle and hull fairing
Carrier looking outboard above tank top structure
Autocad Model of Carrier and Surrounding Structure

CMC worked closely with the DSI Hull Department to coordinate the desired degree and sequence of hull structure removal and installation in order to minimize distortion of the carrier.  MSC tasked CMC to perform a Finite Element Analysis (FEA) of the entire structure in the area in order to provide a conservative determination if excessive deflections would occur at any point throughout the repair process.

CMC used FEMAP with NX NASTRAN FEA software to perform the linear static analysis of the structure.  The following screenshots and animation show the model and results.  The shipyard was able to proceed with the repair as outlined in the sequence procedure with a high level of confidence that the carrier alignment would not be adversely impacted by the steel repairs.  This is a great example of how FEA can assist a shipyard with major steel repairs.

This view shows structure in red that needed to be replaced. The carrier is in blue
NX NASTRAN FEA Model both sides shown for visualization. Only stb side was analyzed.
FEMAP Deformed plot (exaggerated view) looking inboard
FEMAP deformed plot with contours of deflection values, looking inboard/fwd
FEMAP deformed plot with contours of deflection values, looking inboard
Exaggerated Animation of Structure Deflections

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