Why was the sheer lowered?


TitanicNerd

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I remember looking at a list of refits of the Olympic, and one of them says: Sheer line (Yellow line on hull) lowered. So why was it? Originally, it was above the black hull. But after the refit, Olympic had her sheer line lowered to on the black hull. Many other WSL ships also had the refit. Why was this??
 
Mar 18, 2008
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I remember looking at a list of refits of the Olympic, and one of them says: Sheer line (Yellow line on hull) lowered. Originally, it was above the black hull. But after the refit, Olympic had her sheer line lowered to on the black hull.

Which refit do you mean?

It was done to go along with the yellow line on the other WSL ships.
 
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Jim Currie

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The sheer of a vessel is not a line per se but it is the rise of deck from midship to bow and stern. It provides more buoyancy to the ends where it is most needed. See here:

Sheer line 3.jpg

By raising (Increasing) the sheer, they can increase the vessel's end buoyancy. If they lower it, they make the deck nearer horizontal from end to end and decrease the ends buoyancy.

Jim C

Sheer line 3.jpg
 

PITAI

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Olympic Paint Stipe on Hull

'ullo again!

I've been looking at a few images of Olympic. At some point in her life, she acquires a stripe of paint a few feet below the white paint of her superstructure. It's very apparent in the footage of her going to the scrapyard. I was curious when exactly she got this stripe.
 
Mar 18, 2008
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The merger with Cunard was in 1934.

As I stated above it was always there and lowered a few feet about 1922 to go confirm with the other ships of the Line.
 
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Alex Clark

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I thought the sheer was the outward flare of a hull to the sides, rising from the waterline. The sort of thing you'd see when looking bow or stern on. Is there a name for this design feature?

Regarding the fore and aft rises, I suppose it would take getting used to the sloped decks in those areas. Wouldn't want to drop any marbles on the deck in one of the forward alleyways. :)
 
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Traditionally, the "sheer" is the fore-and-aft line of the hull at the main deck. It is a physical element in the construction of the vessel. Until the recent monstrosities of cruise liners it had a sweet upward curve toward both the bow and stern. Typically, the rise was 2 to 4 percent of the length of a merchant vessel, or about 0.6 to 0.7 percent of a passenger ship or large yacht. In a seaway, this upward curve maintained the freeboard as the hull pitched (bow up and down). It also gave strength of shape to the hull.

The "sheer line" is the fore-and-aft curve of the rail or decks which follow the sheer of the deck.

The "sheer stripe" or on yachts "cove stripe" is a decorative line which echoes the sheer but at a slightly lower level. It serves two purposes. One, it makes the sweet line of the sheer more obvious. And, two, it breaks up the expanse of the topside making the vessel appear longer and more sleek. The term "cove" comes from inscribing the line of the stripe into the hull. Typically, a rounded gouge would be used to cut what wood butchers called a "cove" in the sheer plank. Painters used this longitudinal cove to guide the painting of the line.

The "boot stripe" is a decorative stripe covering the area where the topside paint meets the bottom paint. In former years it covered the area between the light and load waterlines. It also has multiple purposes. One is to cover the "joint" where the topside and bottom paints meet to prevent bare skin which could cause corrosion. Older bottom paints lost their anti-fouling properties if they dried out, so boot topping was applied over the bottom paint to keep it active even when the ship was unloaded. The boot topping also allowed painters to cover up any mistakes or wanderings in the meeting of the two main paints with a smooth line. Another purpose is to work in tandem with the sheer stripe and make the hull appear longer. Curiously, a boot stripe appears of even width to the eye even though it is considerably wider in the bow and stern where the topsides curve outward instead of being vertical.

"Flare" is the outward curve of the topsides usually seen in the bows. It helps deflect spray from the decks and also increases the reserve buoyancy against pitching into head seas. Flare seldom extends aft more than a quarter of the ship's length.

In the stern, the flare is usually quite pronounced and so deserves a name of its own. Titanic had a "counter stern" which was also known a "schooner stern." This type of stern provided lots of reserve buoyancy necessary in sailing ships running before the sea on passages like rounding "Cape Stiff" (Cape Horn). Overtaking waves would lift the stern rather than simply was over the ship. Some waves were too large and ships did get "pooped." That was the term for a wave washing over the poop deck. Often as not it would take sailors with it, usually the men at the wheel of an old square rigger.

Many vessels had topsides that curved inward toward the sheer. This was most often called "tumblehome," although shipbuilders also used the term "flam."

In addition to the curve of the sheer, decks on ships traditionally have "camber." This is a slight tathwartships curve with the high point along the vessel's centerline. It helped water run off the decks and also gave strength of shape to the hull.

Next time we'll talk about catharpins and baggywrinkle.

-- David G. Brown
 
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