TRY IT OUT: LESSON 2/ MULTIMEDIA HANDOUT

Unit Three: In foul weather!

SNAPSHOT: 

http://www.metacafe.com/watch/1068104/storm_with_force_10_by_beaufort_scale_in_atlantic_ocean/

STORY:

1) The wind has now reached force 10. The seas are already very high with white crests and the air is white with spray. Captain James has been through many storms. He knows that he will need all his skill and experience to save the ship from damage or loss. There are many important factors to consider - the wind direction and force, the course being steered, the height of the sea, and whether the sea is short or long. In a strong headwind the vessel will pitch. When the wind is abeam the ship, we say that she is rolling. Not only the height but the length of the seas is important.

2) Stability is the ability of a vessel to endure high winds and seas and resist capsizing even if she heels over (or lists) heavily in the wind. Adding weight above a vessel’s centre of gravity will change its stability. If the centre of gravity is raised too much, the vessel will become unstable. As a result, less tilt is needed to capsize the vessel. Removing weight from below the centre of gravity also decreases stability. When the Marina was loaded, the Chief Mate was careful to see that the loading did not decrease the stability of the Marina. If much of the cargo weight is at the bottom of the holds, the centre of gravity is low, and the ship is said to be stiff. The breaking waves then strike the ship’s hull with force and in some cases the hull might even be damaged. On the other hand, if too much cargo has been placed in the ‘tween decks or on the decks, the centre of gravity is high. This makes the ship tender, and she will roll freely and rapidly. Cargo might shift and the ship might start listing. She may then be unable to recover from a roll and capsize.

3) Both wind and sea are now abaft the starboard beam of the Marina, which is rolling heavily in the high seas.

Captain: I think we ought to reduce speed to half speed.

Chief Officer: OK, half speed.

Captain James has reduced speed to save the Marina from being hit too violently by the waves. The storm is now becoming increasingly violent and the Marina is pounding heavily.

Captain: We shall have to heave to. We’ll take her bow to the sea. Hand steering on!

Chief Officer: Very well, hand steering!

Captain: Stand by Engine Room control!

Engine Room Control: Standing by.

Outside there is only the roaring of the wind and the fierce beating of the seas, which are now mountainous, - wind, air and water. Inside the navigating bridge there is only the monotony of the orders to the Engine Room and the strained concentration of the two men.

Captain: Dead slow ahead.

Chief Officer: Dead slow ahead.

Captain: Hard a starboard.

Chief Officer: Hard a starboard.

Captain: Full ahead.

Chief Officer: Full ahead.

Captain: Stop her.

Chief Officer: Stop her.

Captain: Dead slow ahead.

Chief Officer: Dead slow ahead.

Captain: Is she answering the wheel?

Chief Officer: Yes, she is.

 

PRESENTATION

The Beaufort Scale is an empirical measure for describing wind speed based mainly on observed sea conditions. Its full name is the Beaufort Wind Force Scale.

The scale was created in 1806 by Sir Francis Beaufort, an Irish-born British admiral and hydrographer who succeeded in standardizing the scale based on his observations of the wind behaviour at sea.

Here you will find Admiral Beaufort constructing the scale:

http://littleshopofphysics.wordpress.com/2009/10/23/wind-segment-7-historical-scientist-francis-beaufort/

As we have seen before, the Beaufort Scale standardizes the wind speed into 12 categories, from milder to stronger. To see how the wind affects land installations, visit the following website:

http://www.mountwashington.org/education/center/arcade/wind/wind.html

 In terms of the effects on the sea, check the following chart:

 

Beaufort number	Description	Wind speed	Wave height	Sea conditions	Land conditions	Sea state photo
0	Calm	< 1 km/h	0 m	Flat.	Calm. Smoke rises vertically.
		< 1 mph
		< 1 kn	0 ft
		< 0.3 m/s
1	Light air	1.1–5.5 km/h	0–0.2 m	Ripples without crests.	Smoke drift indicates wind direction, still wind vanes.
		1–3 mph
		1–2 kn	0–1 ft
		0.3–1.5 m/s

2	Light breeze	5.6–11 km/h	0.2–0.5 m	Small wavelets. Crests of glassy appearance, not breaking		Wind felt on exposed skin. Leaves rustle, vanes begin to move.
		4–7 mph
		3–6 kn	1–2 ft
		1.6–3.4 m/s
3	Gentle breeze	12–19 km/h	0.5–1 m	Large wavelets. Crests begin to break; scattered whitecaps		Leaves and small twigs constantly moving, light flags extended.
		8–12 mph
		7–10 kn	2–3.5 ft
		3.4–5.4 m/s
4	Moderate breeze	20–28 km/h	1–2 m	Small waves with breaking crests. Fairly frequent white horses.		Dust and loose paper raised. Small branches begin to move.
		13–17 mph
		11–15 kn	3.5–6 ft
		5.5–7.9 m/s
5	Fresh breeze	29–38 km/h	2–3 m	Moderate waves of some length. Many white horses. Small amounts of spray.		Branches of a moderate size move. Small trees in leaf begin to sway.
		18–24 mph
		16–20 kn	6–9 ft
		8.0–10.7 m/s
6	Strong breeze	39–49 km/h	3–4 m	Long waves begin to form. White foam crests are very frequent. Some airborne spray is present.		Large branches in motion. Whistling heard in overhead wires. Umbrella use becomes difficult. Empty plastic garbage cans tip over.
		25–30 mph
		21–26 kn	9–13 ft
		10.8–13.8 m/s
7	High wind, Moderate gale, Near gale	50–61 km/h	4–5.5 m		Sea heaps up. Some foam from breaking waves is blown into streaks along wind direction. Moderate amounts of airborne spray.	Whole trees in motion. Effort needed to walk against the wind.
		31–38 mph
		27–33 kn	13–19 ft
		13.9–17.1 m/s
8	Gale, Fresh gale	62–74 km/h	5.5–7.5 m		Moderately high waves with breaking crests forming spindrift. Well-marked streaks of foam are blown along wind direction. Considerable airborne spray.	Some twigs broken from trees. Cars veer on road. Progress on foot is seriously impeded.
		39–46 mph
		34–40 kn	18–25 ft
		17.2–20.7 m/s

9	Strong gale	75–88 km/h	7–10 m	High waves whose crests sometimes roll over. Dense foam is blown along wind direction. Large amounts of airborne spray may begin to reduce visibility.	Some branches break off trees, and some small trees blow over. Construction/temporary signs and barricades blow over.
		47–54 mph
		41–47 kn	23–32 ft
		20.8–24.4 m/s
10	Storm Whole gale	89–102 km/h	9–12.5 m	Very high waves with overhanging crests. Large patches of foam from wave crests give the sea a white appearance. Considerable tumbling of waves with heavy impact. Large amounts of airborne spray reduce visibility.	Trees are broken off or uprooted, saplings bent and deformed. Poorly attached asphalt shingles and shingles in poor condition peel off roofs.
		55–63 mph
		48–55 kn	29–41 ft
		24.5–28.4 m/s
11	Violent storm	103–117 km/h	11.5–16 m	Exceptionally high waves. Very large patches of foam, driven before the wind, cover much of the sea surface. Very large amounts of airborne spray severely reduce visibility.	Widespread damage to vegetation. Many roofing surfaces are damaged; asphalt tiles that have curled up and/or fractured due to age may break away completely.
		64–72 mph
		56–63 kn	37–52 ft
		28.5–32.6 m/s
12	Hurricane-force	≥ 118 km/h	≥ 14 m	Huge waves. Sea is completely white with foam and spray. Air is filled with driving spray, greatly reducing visibility.	Very widespread damage to vegetation. Some windows may break; mobile homes and poorly constructed sheds and barns are damaged. Debris may be hurled about.

 

 Now that you already know all about Beaufort Scale, let’s take a look at the following announcmeent:  http://mvvaldivia.glogster.com/accident-glog/

TRY IT OUT: LESSON 16/MY WIKI PROJECT

 

In the link below, I have left an open question for my students to investigate and to contribute. They would have to research on different causes causing vessels to capsize. Once they determine the cause, they would have to illustrate it with one example, indicating why, when, where, what type of cargo/vessel it affected, etc.

 

http://imoteacher.pbworks.com/w/page/32879449/capsizing