Incline Experiment

The incline experiment calculates the most critical number for ship stability:  vertical center of gravity (VCG).  The VCG of the light ship sets the baseline for your ship stability.  

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Over the lifetime of the ship, small changes alter your ship’s lightweight and VCG.  Remember that fresh coat of paint from a few years back?  That altered your ship weight.  Eventually, the small changes add up and you need to recalculate the VCG with a stability test.

With only a 2% change in light ship weight, a stability test may become necessary.  For many vessels regulated by the US Coast Guard, it becomes required, see MTN 04-95.

The incline experiment is the second half of a stability test.  In the incline experiment, we shift weights transversely across the deck to heel the ship.  Those shifted weights generate a heeling moment.  After each weight movement, we measure the resulting heel of the ship.  By comparing the measured heel and the known heeling moment, we can calculate the ship’s VCG.

An incline experiment requires coordinating many factors.

  1. Submit test procedure for approval.
  2. Coordinate with regulatory witness
  3. Locate suitable incline weights
    1. Check that the weights do not exceed load limit of the deck
  4. Crane to move the weights
    1. We can use the vessel’s own crane if available
  5. Suitable location to perform the experiment
  6. Consider weather conditions on the planned test date
  7. Perform a deadweight survey

An incline experiment requires extreme accuracy.  Imagine weighing a single sewing needle, and then using that to predict the total weight for a whole crate of sewing needles.  Plus, the crate has some straw thrown for extra complications.  Incline experiments present a similar challenge.

The challenge of the incline experiment is the accuracy.  The vessel heels by only 2-4 deg, barely detectable by the eye.  But from this tiny movement, we calculate one of the most critical numbers for your ship.  Scientific discipline becomes essential.  Of course, a working ship is not the ideal setting for high caliber scientific experiments.  Skilled engineers at DMS employ their experience to anticipate all the potential problems with the incline experiment.  We check our results during the experiment and provide immediate feedback after completing the experiment.  You get preliminary results on the day of the test.

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