Stuart on DDG-51's Full Waterplane Hull Design

[MKSheppard]

Uh oh.

More than a dozen Arleigh Burke-class destroyers have suffered “significant” structural damage in rough seas because designers didn’t account for the effect of “bow slams” on the ships’ hulls, Navy documents said — and they said fixing the problem could cost almost $63 million.

A Navy PowerPoint presentation, obtained by Navy Times, confirmed a report Thursday in the British defense publication Jane’s revealing the design problems in the Burke class.

Support beams and other structures inside the destroyers warp so much from the stress of withstanding high seas that they must be cut out and replaced, even in new ships — the destroyer Gridley, commissioned in February, already underwent repairs in September. The report described the damage common to 13 ships, in both “Flight I” and “Flight II” variants of the destroyer. Later Flight II ships have their own helicopter hangars and slightly different weaponry than earlier destroyers in the class.

“Damage ranges from local buckling of deck transverse beams and shell web frames and shell longitudinals resulting in several inches of permanent deformation,” said one slide in the presentation.

Internal structure warping is not uncommon among surface warships; the Navy’s cruisers and frigates have gone into shipyards for hull stiffening repairs.

With each ship designed to serve for around 35 years, the Burkes are the Navy’s only destroyers in service. The first ship was commissioned in 1991, and shipyard Bath Iron Works of Bath, Maine, announced it has started work on the last, DDG 112, expected to join the fleet in 2011.

Re: the 35 year service life - normally, I'd expect that they'd be retired long before then so the USN could build new ones and sink the DDG 51s to the bottom of the sea or some such egregious waste, but what with tightening budget belts and the rising costs of weaponry, I reckon the DDG 51s might actually live out their entire lives.

Provided that this buckling doesn't impact their service life, of course.

Re: the 35 year service life - normally, I'd expect that they'd be retired long before then so the USN could build new ones and sink the DDG 51s to the bottom of the sea or some such egregious waste, but what with tightening budget belts and the rising costs of weaponry, I reckon the DDG 51s might actually live out their entire lives. Provided that this buckling doesn't impact their service life, of course.

First the buckling. The Arleigh Burkes have a different hull form from most previous US Navy warships. They have continuous flare along the whole of their length (in other words, the hull sides continue to slope outwards along all of their length; in previous US Navy ships, the hull sides are essentially vertical after the bow flare and before the stern transom.

That new hull form has a number of advantages. It increases deck area proportional to displacement, it makes the ships drier in rough weather and (very significantly) it increases tolerance to flooding. That's because the outward flare of the ship's hull means that the waterplane area (the area of the hull at the actual waterline) increases as the ship sinks deeper into the water. The rate at which a ship sinks is determined by tons per inch immersion, the weight of water required to make the ship sink one inch. The tpi rating is determined by waterplane area so, if the rate of flooding is constant, the increasing waterplane area will mean the ship sinks more slowly.

Obviously, nothing comes for free. The Arleigh Burke hull form (its called a Full Waterplane Hull by the way) has significant disadvantages. It's heavier and more expensive to build. It's harder to dock and easier to damage when docking. It is also inherently more susceptible to slamming and under conditions where slamming is a problem, the effect occurs along the whole of the ship's length rather than just at the bows. This effect was noted when the Arleigh Burke made her maiden voyage and hit heavy weather, she needed serious repair work (somewhere floating around in the Navy is a 1991 memo from me pointing out that the hull form of the destroyer is inherently susceptible to damage from slamming). The hull form has some other problems as well but they're the obvious operational ones.

Why does the Arleigh Burke have a full waterplane hull? Primarily because when she was designed, there was a strong school of thought that Russian ships of similar size were "more advanced designs" than existing warships (Sprucans) and their hull form was better suited to modern conditions. So the Burkes were designed ina ccordance with that school of thought. One of the interesting things is that our experience with the Burkes taught us a lot about the shortcomings of that generation of Soviet ships.

Basically, these problems are nothing new, they've been known about for a long time and they're not that serious. Nor are they unique to the Burkes or indeed to the US Navy. The British had a lot of problems with the Leanders and the Type 22s from similar causes and the Type 21 problems in the same department were so bad they required major surgery (look at pictures of the ships, now in the Pakistan Navy and you can see the long reinforcing bar that had to be welded to the hulls in order to strengthen them). So this is basically no big deal.

Navy Times is a people newspaper. It's primary focus is on personnel issues and their grasp of technical matters is slight at best. They're nota reliable source for this sort of information.

OK. Disposing of ships. Sinking them is not "egregious waste", its the cheapest way of getting rid of a worn-out ship. The days when we could sell a ship for scrap are gone. If we compare scrap steel prices with American labor costs, scrapping a ship is a sure and certain way of losing money - and that's before we start to count in things like environmental considerations and the cost of disposing of toxic and otherwise undesirable waste. The only way to make ship scrapping profitable is to do what the Indian and Pakistanis do - run the ships onto a beach and use local people to cut them up, in the hope that the accident rate inherent in using unskilled labor to cut up ships will reduce the wages bill still further.

So, the U.S. Navy actually pays people to scrap surplus ships. I't's cheaper to sink them, either as live-fire target exercises (from which we learn a lot) or to create artificial reefs which is very good for marine wildlife.

35 years is pretty average for US Navy warship. We build them tough.

I know the reasons why they're sunk instead of scrapped, I just still find it a waste of a perfectly good warship. Just look at the Spruance DDGs. They certainly didn't live out their service life before they started being sent to the bottom, unfortunately.

They had actually. The first Sprucan entered the fleet in 1975 and the last in 1983. That mostly made them 25 - 30 years old when they were pulled from service. That means they had around 5 - 10 years of hull life left (actually quite a bit less since they were worked very hard). That meant modernizing and rebuilding them simply wasn't economic - why spend large sums of money on a ship that is nearly worn out.

The catch was that keeping them in the fleet meant they needed a rebuild. They were dedicated ASW ships with very little capability outside the ASW role. The first to go were the ones that hadn't been refitted with VLS systems forward. They were absolutely ASW ships and really had no role in the modern fleet that demands multi-role combatants. The VLS equipped ships had a vistigial multi-role capability but it wasn't that great. In addition, the ships' had seriously outdated electronics, their comms facilities were below par, they were very expensive to run and in an environment where the submarine threat is pretty limited, they just weren't needed.

So it made good economic sense to get rid of them. The things that were needed, they couldn't do, the things they could do, an FFG-7 could do cheaper. So why keep them?

Note, we tried to give them away, nobody wanted them.

Why does the Arleigh Burke have a full waterplane hull? Primarily because when she was designed, there was a strong school of thought that Russian ships of similar size were "more advanced designs" than existing warships (Sprucans) and their hull form was better suited to modern conditions.

Norman Friedman's latest US Destroyers (the revised edition) goes into this, many captains had the experience of seeing russian ships exibiting better seakeeping characteristics (in their opinion) in rough seas than their own ships, and of course, they wanted this in our next destroyers; instead of a hull form more optimized for calmer waters.