Customer always right?

Updated: May 11, 2019

Some time ago I smoothed the surface of a small hard chine hull. The company for which I did this work was engaged in the release of working documentation for this vessel. In the original version, the bottom surface was made developable. Project designer rejected this option and insisted that all bottom frames should be strictly straight. Explain this by the fact that the design will use panels with ribs in the plane of frames. Since I had no direct contact with the project designer and had no opportunity to discuss this problem, I agreed to change the surface. Making the frames straight is the simplest solution. The hull of the vessel was aluminum and assumed the deformation of the metal when bending sheets of plating, so I agreed to such a decision. At the same time, I did not have much choice when changing the shape of the surface - I did not have the opportunity to deviate a lot from the original shape of the boundary curves. The smoothed body was approved by the customer and was used for the release of working documentation.

When the working documentation for the most part of the hull was already made and deliver to the shipyard, it turned out that the fore ship bottom shell plate unfolds with errors - the lengths of the development shell plates edges do not correspond to the shell plate edges in 3D. At first, we thought it was a bug in the program that was used for the production of the working documentation. I unfolded the same shell plate in ShapeMaker and also got an unsatisfactory result. I spent quite a lot of time trying to split this plate to get a more or less correct result. As a result, I had to split it into four plates.

Front view. Bottom surface with straight frames.

Since the original shell plate was triangular at once it was not obvious why it does not unfold. After a more thorough analysis of the surface, it became clear that the frames were twisted relative to each other. Just as if you fixed opposite edges of a sheet of paper with rulers, making them strictly straight, and twisted the rulers one relative to another. At the same time, a sheet of paper cannot take any form and is deformed in an unpredictable way.

Twisting paper sheet plate in real life.

This is what happened with our shell plate. Of course, splitting a plate gave a positive result, but it only minimized the error.

3D View. look how simple this surface...

This is a good example of how a designer’s reluctance to delve into problems in the release of workshop documentation leads to problems when building a case. Perhaps it was the result of the fact that I did not have a direct connection with the project designer. As a rule, I work with companies that produce workshop documentation. In any case, I got a good lesson. Next time, if the requirements of the designer will be so tough and contradictory, it is better to abandon their implementation. So, the rule under which the customer is always right is not always really working.

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