To solve this problem, we need to understand the concept of fresh water allowance (FWA) and how the change in water density affects the vessel's draft.
The fresh water allowance is the extra depth a vessel will sink when transitioning from salt water to fresh water, due to the difference in water density.
Given:
First, calculate the ratio of the densities:
The vessel will sink deeper in fresh water because fresh water is less dense than salt water. We need to determine how far below her marks the vessel can be loaded in fresh water to just float at her marks when she moves to salt water:
Given that the total change in draft (FWA) is specified in inches:
This means when the vessel transitions from fresh water to salt water, it will rise by 8 inches. Therefore, we need to calculate how much deeper it can be loaded in fresh water to maintain the correct draft in salt water.
Since the question asks for "how far below her marks the vessel may be loaded," we need to use the density ratio calculated earlier to find the movement caused by the density change:
For saltwater:
This means the vessel will sink by 8 inches more in fresh water than in salt water, so when it floats in salt water, it will rise by 8 inches.
Thus, the answer is: D) 8.0 inches
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