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from the everyone's-a-superhero-everyone's-a-captain-kirk dept.
David Sharp reports at the Boston Globe that the the futuristic 600-foot, 15,000-ton USS Zumwalt, the largest destroyer ever built for the US Navy is heading out to sea for the first time for sea trials. The ship has electric propulsion, new radar and sonar, powerful missiles and guns, and a stealthy design to reduce its radar signature. Advanced automation will allow the warship to operate with a much smaller crew size than current destroyers. ''We are absolutely fired up to see Zumwalt get underway. For the crew and all those involved in designing, building, and readying this fantastic ship, this is a huge milestone,'' says the ship's skipper, Navy Capt. James Kirk. With an inverse bow jutting forward to slice through the waves. and sharp angles to deflect enemy radar signals, the Zumwalt-class destroyer looks like nothing ever built before. The Zumwalt — which will receive its "USS" designation when it is christened — also is to be a test-bed for one of the Navy's most futuristic weapons, an electromagnetic rail gun under development by the Office of Naval Research. It uses electromagnetic pulses to launch projectiles at Mach 7, or seven times the speed of sound, at targets up to 110 miles away.
However critics say the ''tumblehome'' hull's sloping shape makes it less stable than conventional hulls, although it contributes to the ship's stealth and the Navy is confident in the design. Doubts about the radical hull form emerged as soon as the shape was revealed in the competitive stage for what was first called DD-21, then DD(X). Ken Brower, a civilian naval architect with decades of naval experience says the ship will capsize in a following sea at the wrong speed if a wave at an appropriate wavelength hits it at an appropriate angle. "The trouble is that as a ship pitches and heaves at sea, if you have tumblehome instead of flare, you have no righting energy to make the ship come back up. On the DDG 1000, with the waves coming at you from behind, when a ship pitches down, it can lose transverse stability as the stern comes out of the water — and basically roll over."
(Score: 4, Informative) by Runaway1956 on Thursday December 10 2015, @03:13PM
Not my expertise, Bubba. I had no idea that an iron hulled tumblehome ever existed, until I went in search of information. I've read many real expert's opinions, as well as engineering arguments against tumblehome.
Conventional hulls have built in "righting arms" - that is, when a ship rolls off of upright, physics exert measurable force to bring that ship back upright. Generations of architects have strived to maximize those forces.
The Zumwalt simply DOES NOT have the righting arms that any US destroyer has had in the past 100 years and more.
http://www.dept.aoe.vt.edu/~mccue/papers_archive/bassler_etal_stab07.pdf [vt.edu]
For corresponding wave conditions, a
significant difference can be observed between
the flared and tumblehome hull forms, at
similar KG values. For the worst-case sea state
8 conditions, the number of capsizes for a
given KG value is much greater for the
tumblehome topside when compared to the
flare topside geometry. From this plot, it can be
observed that the tumble
home topside requires
about a 1m-1.5 m increase in KG (thus GM) to
achieve a number of cap
sizes similar to the
flared hull topside hull form.
http://www.phisicalpsience.com/public/Tumblehome_Hull_DDG-1000/Tumblehome_Hull_DDG-1000.html [phisicalpsience.com] [phisicalpsience.com]
"The righting moment (GZx) displacement being greater for the flare hull (blue curve) having nearly 2.5x times more resorting moment at ~41o degrees than the tumblehome hull and over 3x times the restoring moment at the curve's maximum value of ~59o degrees. In addition, the ONR flare hull possesses greater angular restoring range prior to experiencing pure loss of stability with a value of ~109o degrees, besting the value of ~93o degrees for the tumblehome hull (red curve)."