You are on a vessel with a 30' mean draft....

You are on a vessel with a 30' mean draft. While maneuvering away from the dock at slow-speed the vessel grounds near the bow area on hard sand. In order to achieve an additional three foot of trim by the stern, you need to shift ballast from the forepeak, which is full, to the after peak, which is empty. Your ballast pump for this operation has a capacity of 85 tons per hour. How much tonnage needs to be shifted and how long should it take?

🔍 Key Concepts

• Trim and change of draft: how shifting weight forward or aft changes draft at bow and stern • Moment to change trim (MT1 or MTI) and how moving a weight through a known distance affects trim • Pump rate and time: using ( \text{Speed} = \frac{\text{Distance}}{\text{Time}} ) logic to relate tons to hours and minutes

💭 Think About

• First, think about how you normally calculate the weight required to change trim by 1 foot, then scale that to a 3-foot change at the stern. • Next, consider that the weight is being shifted (not added or removed). How does the distance between the forepeak and after peak factor into the trim calculation? • Once you have the total tons to shift, how do you convert that to time using the given pump capacity in tons per hour?

✅ Before You Answer

• Be sure you are using trim, not overall mean draft change, in your calculation. • Check that your units are consistent: feet vs inches of trim, tons vs tons/hour, hours vs minutes. • Verify that the required shifted weight is physically reasonable when compared with the likely capacity of a forepeak tank on a vessel of this size.