Building a ship is a very long and expensive process. You can’t wait until the ship is built and at sea to find out if the hull is strong enough or streamlined enough to perform as expected. Finding the best design for speed and strength cannot be a trial and error process. How can the design be tested and optimized?

Ship designers use models and a long towing tank to simulate the final design. A model of the ship hull is instrumented and then towed through water at simulated speeds and sea conditions. By measuring the stress levels in the model, changes in the design can be made at a very early level, before the expensive process of building the full-size ship.

To determine stress levels in a ship model, strain gages are affixed to the key structural elements. Strain gages sense the force applied and produce a very small change in resistance. Strain gages require signal conditioning: they must be given excitation current, be wired as a Whetstone bridge (using completion resistors), and the small changes in signal due to stress amplified for data logging as the ship model is towed through the water. Because the tow tanks are often several hundred yards long, a self-contained signal conditioning and data acquisition system is used.