Introduction:

“At nightfall rocks and shoals were seen ahead… at supper she (HMB Endeavour) went over a bank of 7 or 8 fathom water which she came upon very suddenly: this we concluded to be the tail of the Shoals we had seen at sunset and therefore went to bed in perfect security, but scarce were we warm in our beds when we were called up with the alarming news of the ship being fast ashore upon a rock, which she in a few moments convinced us of by beating very violently against the rocks.” Joseph Banks, HMB Endeavour, 11 June, 1770.

The Endeavour had just struck the Great Barrier Reef, which Captain Cook did not know existed. He was quite sure he had struck a reef, but had no idea it was a reef to the extent of the Great Barrier Reef, running for hundreds of miles along the east coast of Australia. The Reef managed to tear a melon-sized hole in the underside of the ship. A clever sailor rigged a makeshift sling from a sail, dragging it into place over the hole, plugging the leak. The Endeavour managed to sail to the next harbor for repairs, even though she was taking on water.

Upon entering the shallow coastal waters near the mouth of what Cook called the Endeavour River, he reports that he ran the ship aground twice before dropping anchor. Upon ‘careening’ the ship (rolling her over to repair the leak), the sailors found the rock still embedded in the underside of the ship. Had it been removed prior to finding shallow water, it was large enough to have sunk His Majesty’s Barque, Endeavour!

“In this situation all the sails were immediately taken in, and the boats hoisted out to examine the depth of water round the ship…the vessel had been lifted over a ledge of the rock, and lay in a follow within it…in some places there was from three to four fathom, and in others not so many feet.” James Cook, HMB Endeavour, 11June, 1770.

As the Endeavour was being made seaworthy once again, Cook ordered the recently discovered harbor to be examined. Much knowledge of the underwater terrain must be identified prior to their departure to avoid any more collisions with the reef system. Cook reports in his journal, “ I sent Master again out to sound about the shoals, the account which he had brought me of a channel being by no means satisfactory.”

What does the floor of the ocean look like? Is it flat and sandy or perhaps, like the surface of land? As Cook and crew came to realize, the ocean has geography similar to the land above water, containing underwater mountain ranges and valleys. Coral reef systems dot the ‘landscape’ and as Cook discovered, have to be reckoned with. Knowledge of what lay just below the surface of the water was critical.

It was common practice to take soundings the closer to shore a ship traveled. A sounding line was lowered overboard to chart the ocean floor in shallow areas. The sounding line consisted of cone-shaped weights attached to knotted ropes. The knots marked fathoms, a measure of about six feet. Usually a lead line was 40 fathoms in length. (What is its length?)

After the Endeavour’s repairs were made and she was ready to depart the harbor, Cook once again relied on a sounding rope to chart the way. They could not afford more encounters with hidden reef systems!

Excerpts from his journal describe Cook’s procedure for departure: “…the pinnace (small boat used to transport from the ship to shallow waters) went ahead, which was ordered to keep sounding continually.”

History records they made safe passage through the Great Barrier Reef through a channel known today as ‘Cook’s Passage!"

Vocabulary:

• soundings (measurements taken of the ocean floor)
• fathoms (linear nautical length of six feet)
• shoals (shallow water)
• channel (passage way through a reef system)

Materials:

• dishpan or bowl at least 15” in diameter
• unopened 1-pint carton of milk/juice
• marbles or comparable size rocks for weight
• pencil
• scissors
• ruler

Preparation:

• Create cooperative groups to discover the principle of displacement as you observe two model ships in the water.
• Groups will test the ship design. Offer suggestions as to safer design features for ships sailing in shallow waters.

Procedure:

• Without opening the carton, measure 2 inches from the bottom. Draw a line around the carton.
• Poke a hole on the line and empty the contents of the carton. Cut around the line to make two separate pieces.
• Fill the dishpan with 2 inches of water. Float each half of the carton in the water.
• Add weights (marbles, etc.), one at a time, to the triangular-bottom half (simulates the underside of the Endeavour). Keep track of how many weights it takes to make the ship hit the bottom.
• Put the same number of marbles into the flat-bottomed ship. Does the ship sink when you reach the final weight?
• In journals, record your ideas to the following:

If you were Captain Cook, how would you have tried to sail the ship off the reef?

If you were a ship builder in the time of Cook, how would you make your ships safe for island exploration?

Analyze and Conclude:

• Were you able to construct ‘boats’ to test the displacement theory? Could you draw reasonable conclusions as to which boat design would be more effective in shallow water travel?
• Did you accurately record information and observations as you conducted the displacement experiment?
• Does your student journal reflect an understanding of the data gathered from the experiment?
• Student journal entries should provide information for island/coastal exploration, i.e.take soundings to determine ocean terrain; ship design to accommodate coastal exploration, and ideas of ocean floor geography.

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