The first blog post of this seawater-oceanic shipping series deals with an introductory classroom activity that challenges students to predict how the composition and temperature of seawater influences a ship's buoyancy. Student predictions are based on three observations and the conclusions they draw from them.

The second classroom activity, discussed below, begins with three questions related to each of the three observations described in the introductory activity. Pictorial summaries of each observation are below. The three 'starter' questions follow the summaries. The purpose of the 'starter' questions is to gauge, before launching into the 'nuts and bolts' of the second activity, student understanding of what was learned in the introductory activity. Any misunderstandings then can be addressed at that moment before moving onward.

**Summary of Observations 1-3:**

**Observation 1:** The correct order of the five water types on the International Load Line (ILL) symbol on merchant ships. Typically, a merchant ship's hull is painted a different color above and below the **S** water type line.

**Observation 2:**

**Observation 3:**

### 'Starter' questions:

Determine if each *italicized* statement below is **TRUE** or **FALSE**. If **FALSE**, rewrite the statement so that it is true.

*For Observation 1 according to the International Load Limit (ILL) the buoyancy and hence maximum load capacity of a ship depends on the type of water a ship is sailing through. A ship is most buoyant and hence sits highest in water type W whereas the same ship is least buoyant and hence sits lowest in water type TF.*

*With respect to Observation 2 it can be concluded that water of a given composition is less dense at the lower temperature than it is at the higher temperature.*

*According to Observation 3 saltier water provides more buoyancy than freshwater at a given temperature.*

Answers: Top to bottom: **TRUE**, **FALSE** (change* less* to *more*), **TRUE**

The three italicized TRUE/FALSE 'starter' questions above allow the instructor to address any deficiencies in understanding 'in the moment'.

As in the introductory activity this second classroom activity employs mJiTT (modified Just in Time Teaching) and Think-Pair-Share (TPS). See the introductory activity for a brief description of each teaching approach as I use it. The second classroom activity starts with the addition of a fourth observation, followed by questions that challenge students to apply conclusions drawn from Observations 1-4.

**Observation 4:**

Q1 (version 1): Which graph below, if any, qualitatively represents an object's buoyancy in water of different densities? **Choice (7) = none of the choices**. Compare your choice with another student with a different answer. Reconcile, if possible, any differences. Did you change your mind after discussing?* x*-axis: water density; *y*-axis: buoyancy of object

Q1 (version 2 = additional information in first sentence; the rest of the wording is the same): The height of the bobber above the liquid is directly proportional to its buoyancy. Which graph below, if any, qualitatively represents an object's buoyancy in water of different densities? **Choice (7) = none of the choices.** Compare your choice with another student with a different answer. Reconcile, if possible, any differences. Did you change your mind after discussing? *x*-axis: water density; *y*-axis: buoyancy of object

Answers: **Graphs (3) and (6)**. Both show a direct proportionality between water density and an object's buoyancy. The more dense the liquid, the more buoyant the object in that liquid, the higher it floats in the liquid. Whether the relationship is linear (**choice 3**) or non-linear (**choice 6**) I do not know. To me it does not matter if it is linear or non-linear as all I care about is that students have figured out that the relationship is direct.

### A Quick Primer on Ship Anatomy:

Before applying the principles learned in Observations 1-4 to ships, a brief mJiTT on ship anatomy and terminology helps out. The image below and a bit of time for students to study the image and terminology are all that is needed before moving onto the questions below the drawing.

Q2 (version 1): Below right is the International Load Line (ILL) symbol located amidships on both sides of the hull of merchant ships. Based on what you learned and conclusions drawn from Observations 1-4 (and any prior knowledge), which choice below, if any, is true when a loaded merchant ship travels initially from water type **W** to **S** and so on until ending up in water type **TF**. **Choice** **(9)** **= none of the choices**

Compare your choice with another student with a different answer. Reconcile, if possible, any differences. Did you change your mind after discussing?

↑ = increase, ↓ = decrease, ↔ = no change

Answer: **Choice (5)**. As a merchant ship sails through water of decreasing density (per question, W → TF), it responds by floating lower in the water (= is less buoyant).

Q2 (version 2 = three columns of variables + 3 more choices; same wording for question): Below right is the International Load Line (ILL) symbol located amidships on both sides of the hull of merchant ships. Based on what you learned and conclusions drawn from Observations 1-4 (and any prior knowledge), which choice below, if any, is true when a loaded merchant ship travels initially from water type **W** to **S** and so on until ending up in water type **TF**. **Choice (12) = none of the choices**

Compare your choice with another student with a different answer. Reconcile, if possible, any differences. Did you change your mind after discussing?

↑ = increase, ↓ = decrease, ↔ = no change

Answer: **Choice (9)**. As a merchant ship sails through water of decreasing density (per question, W → TF), it responds by floating lower in the water (= is less buoyant). Floating lower in the water means the distance between the water line and the upper deck, aka the freeboard (see **Ship Anatomy** drawing above), decreases.

Q2 (version 3): Below right is the International Load Line (ILL) symbol located amidships on both sides of the hull of merchant ships. Based on what you learned and conclusions drawn from Observations 1-4 (and any prior knowledge), determine how each of the variables below change, if at all, when a ship travels initially from water type **W** to **S** and so on until ending up in water type **TF**.

Compare your choices with another student with a different answer or answers. Reconcile, if possible, any differences. Did you change your mind after discussing?

↑ = increase, ↓ = decrease, ↔ = no change

Answer: **See Q2, versions 1 and 2**.

### What did you get? Let's talk:

Before revealing the answer and for any version of any question type above, an option to encourage student-to-student discussion is to have students first compare their answer with other students (employment of the TPS teaching approach). Maybe with discussion some will change their mind, maybe not. As much as possible I like for students to practice defending their conclusion. [Drawings below in reference to Q2 (version 1).]

Another option is to have students assemble in 'Choice groups', that is students who answered Choice (1) get into a group, those that answered Choice (2) get into a group, and so on. Students in one 'Choice group' discuss the reasons for their choice with another 'Choice group'. Allow students to move between groups if they change their mind after discussing with another group. Did any students move from one 'Choice group' to another on account of the discussion? How many groups, if any, increased/decreased in number?

The third blog in this series will look at sea surface salinity data and students will apply salinity data and the principles learned previously to how a ship's master must account for the variation in ocean salinity so as to not compromise the ship's stability (buoyancy) and hence, tens if not hundreds of millions of dollars of cargo.

Thanks for reading...sjd