Wednesday, April 11, 2007

Tumblehome Troubles

Originally via Murdoc, concerns were recently raised over the stability of the DDX hull form.

One former flag officer, asked about DDG-1000, responded by putting out his hand palm down, then flipping it over. “You mean this?” he asked.

Ken Brower, a civilian naval architect with decades of naval experience was even more blunt: “It will capsize in a following sea at the wrong speed if a wave at an appropriate wavelength hits it at an appropriate angle.”



I believe the technical term is "ewww".

Despite the non-ridiculousness of the idea that modern naval architects might utterly screw something up...I'm slightly skeptical

The article makes a lot of he demise of French and Russian Battleships which used a tumblehome hullform around the turn of the century.

The shape was popular among French naval designers in the late 19th and early 20th centuries, and a number of French and Russian battleships — short and fat, without any wave-piercing characteristics — were put into service. But several Russian battleships sank after being damaged by gunfire from Japanese ships in 1904 at the Battle of Tsushima, and a French battleship sank in 90 seconds after hitting a mine in World War I. All sank with serious loss of life. Both the French and Russians eventually dropped the hull form.

However, there are a few problems with this...
The UK's pre-dreadnaughts starting with the Royal Sovereigns and Majestic's also used a tumblehome hull form albeit less pronounced than the French.

These battleships, designed by Sir William White, were the most successful and prolific series of battleships of their day and some served into the '20s. Indeed, the Japanese battleships that slaughtered the Russian BB's at Tsushima were built in UK yards to UK designs. The Fuji was a modified Royal Sovereign and the Shikinshima's improved Formidable's.

The French/ Russian designs, like some early US designs greatly exaggerated the tumblehome form to facilitate a good (theoretical)end on fire of secondary armaments. See here....the French built Russian BB Tscharevitch which was the only Russian heavy unit to survive Tsushima...is illustrative of the extremes this was taken.

The Russian Borondino class that was so annihilated at that battle was a Russian built version of this ship, but without the torpedo defense and in many ways inferior, especially regards topweight . Poorly trained, worn out crews, poor discipline, bad tactics, a very incomplete damage control system and little DC training coupled with the superbly trained IJN and their extremely destructive shells and expertly used torpedoes ended these ships.

If a tumblehome hullform contributed it was likely due to the extremely exaggerated nature of that feature in these ships.

The French BB lost in 90 seconds was even less useful a case study. The Bouvet was old poorly maintained, and hit a WW1 mine far more powerful than any contemplated when she was constructed in the 19th century. Reportedly her counterflooding arraingements did not work and when she was brought out of mothballs (she had been discarded as obsolete years earlier) her watertight doors were so rusted they would not close.

Now this does not mean that the Navy has not made an error here...a good argument can be made that the whole DDX program is a bit muddled, but the idea that because poorly handled, designed and maintained ships with a very exaggerated version of a hullform used by a 20th century ship got sunk is hardly compelling. In fact, using that logic we can make a good argument that this is a cool idea.

In 1917 the aformentioned Tscharevitch and her Borondino class half sister Slava (completed too late to get sunk at Tsushima) despite being utterly obsolete, fought off several modern German Dreadnoughts at the battle of Moon Sound....both survived considerable damage though Slava had to be scuttled as she drew too much water to return to port after battle damage.

This isn't compelling either.

It is quite possible that in an attempt to achieve stealth the Navy has compromised seakeeping.

Flair, the opposite of tumblehome, has certain advantages in damage control....as the ship gets lower in the water the Surface Area increases somewhat mitigating buoyancy loss.

But as this DID article points out, the jury is still out.

I'm not a fan of the DDX program, and I'm certainly not a naval architect, but I am, again, somewhat skeptical of this story....

.....but not exactly dismissive either.

1 comment:

Wonderduck said...

“It will capsize in a following sea at the wrong speed if a wave at an appropriate wavelength hits it at an appropriate angle.”

I'm no sailor, but couldn't the same be said for just about any ship?