Ask An Expert- Naval Forces

[zraver]

This is a thread for members to ask specific questions of the experts who will then reply if the question is in their specialty. Non-expert members may not answer, I will delete them.

Opsec is in effect- don't ask for classified information or trade secrets.

Follow on questions may not be rebuttals of the answer provided, but you may ask for clarification.

question format (sample)

Field- small/medium warships

Question- Generally, how rough can the seas be and still permit helicopter landings/takeoffs?

[Dreadnought]

*USS Independence LCS-2
General Dynamics Littoral Combat ShipThe General Dynamics LCS concept features an innovative, high-speed trimaran hull that delivers one of the largest useable payload volumes of any US Navy surface combatant afloat today. Its very large and stable flight deck that rests higher above the water than any US Navy surface combatant will support near-simultaneous operation of two SH-60 helicopters, one H-53 helicopter or multiple unmanned aerial vehicles. Coupled with the inherent stability of the trimaran hull form, the ship is capable of conducting operations in Sea State 8 conditions and performing full flight operations through Sea State 5.

[eocoolj]

I was browsing the ol' wikipedia recently, and ended up comparing the specs of the new America Class LHAs to the Essex Class carriers, particularly in their Vietnam-Era spec. Can anyone comment on their similarities and differences? They look to be roughly the same size. If an America were to dispense with the helicopters and carry only F-35s, how would its air wing compare (in numbers, not capabilities) to a Vietnam-era Essex?

Also, the America looks like it is significantly slower than the Essex. Obviously I'm assuming this is be design. Why design a ship to be so much slower than ships of WWII vintage?

[gunnut]

Essex, even in WW2 layout, was designed as a fast carrier. She needed the speed in order to generate the head wind to launch fixed wing aircraft.

America LHA is an assault carrier. Her airwing is comprised of helos, Harrier, and F-35B. They don't need much head wind to help with take off.

Slower speed means less machinery and more room for stuff. It's the major knock on LCS...too much speed taking up too much room for needed machinery.

[tmasi]

Field - Warship maintenance

Question - What are the key tests/metrics that the Navy uses to evaluate whether a warship is still considered fit for service? I'm asking purely about tests of "wear & tear", not determinations of design or mission obsolescence. Is it as simple as looking for holes in the hull?

[RustyBattleship]

Field - Warship maintenance

Question - What are the key tests/metrics that the Navy uses to evaluate whether a warship is still considered fit for service? I'm asking purely about tests of "wear & tear", not determinations of design or mission obsolescence. Is it as simple as looking for holes in the hull?

Thorough inspections are made of the hull plating, hull stifferners, main machinery foundations, weather decks and most importantly the bulkheads around fuel tanks.

The general rule-of-thumb is if one-quarter or more of the plate's orginal thickness has been lost due to corrosion, it needs to be replaced. Ultra-sound equipment is used to determing the thickness. Did that for several days in the fuel tanks of the USS Cacapon (AO-52). Instead of taking a lot of time to erect staging in all of the tanks, steel rafts were built for us to ride on while the tank was being flooded to the next level up for inspection.

The webs of the Tee-Bar stiffeners of the hull plating are also inspected for excessive corrosion. Any areas that have rusted all the way through the thickness of the web, those sections plus one-foot at each end, is replaced.

If there are dents in the shell plating caused by tugboats, or mooring accidents they also need to be inspected. However, if the stiffeners around the shell plate dent are not bent or warped, the dent is passed off as cosmetic damage only. But if any of the stiffeners are bent or warped then that section of shell plating and damaged stiffeners are replaced.

Corrosion pitting on the hull below the waterline is treated depending upon the type of ship, the original thickness of the shell plating and the type of steel used for the shell plating.

On thin hulled ships, such as Destroyers, fall under the "Loss of one-fourth the original thickness" rule. Thick hulled ships such as the Battleships are inspected for the depth of pitting. Because of the enormous size and square footage of such a ship, to weld over all the pits would take far too long and require enormous numbers of workers and amounts of cost to repair. Therefore, any pits less than 1/8" are disregarded. Pits at least 1/8" deep or more must be welded up. But to ensure 100% weld penetration, the pits have to be "drilled" out with a countersink drill bit. This allows a funnel shape so the first pass of the welding rod gets all the way to the bottom of the pit.

[tmasi]

Thanks for the answer. Sounds like an inspection takes months. For hull pitting, the inspection is entirely visual? I imagine that you need to be fairly close up in order to see the hull pitting.

[RustyBattleship]

Thanks for the answer. Sounds like an inspection takes months. For hull pitting, the inspection is entirely visual? I imagine that you need to be fairly close up in order to see the hull pitting.

Hull pitting can be quite deceiving to the eye. Therefore when we had to do a lot of pit repair to the hull of one of the BB's, we used a simple gauge to check for depth of the pit. It was just a piece of flat metal a little larger than a business card. Attached with a screw to the plate was merely a strip of steel about 3" long with a hook sticking out on one end. Radial gauge markings were photo-etched on the plate.

You would merely set this simple gauge on the hull plating with the hook over the pit. With your thumb you pushed the hook into the pit. Then the top edge of the strip would identify the depth of the pit on the photo-etched gauge markings.

It really only took a few seconds to read the depth of each suspicious looking pit. If it was over 1/8" deep, a felt point pen was used to circle the pit for the drillers and welders to follow up on its repair.

Some "pitting" however wasn't small but spread over a wide area. Some were so large they didn't look like pits at all but like a chunk of the plating had been eaten away by acid. THAT took a lot of clad welding.

Most was HTS plating (High Tensile Steel) and the welding rod required was fairly easily ground down flush with hand-held stone grinders. Some plating was STS (Special Treated Steel) that had to be welded with stainless steel rod. THAT is really a beast to grind down.

By the time we got that ship ready to go back out to sea, our Pneumatic Tool Operators (PTO's) who did all the grinding had arm muscles to put The Terminator and Rambo to shame.

[tmasi]

Sounds like some pretty rough work, Rusty.

How long would it take for an Iowa or South Dakota class vessel to get the point where it needed that sort of treatment? Is that something done every two years or every five? Or after 10 years of service?

[Ytlas]

Sounds like some pretty rough work, Rusty.

How long would it take for an Iowa or South Dakota class vessel to get the point where it needed that sort of treatment? Is that something done every two years or every five? Or after 10 years of service?

Luckily most ships never get in that situation......

[RustyBattleship]

Sounds like some pretty rough work, Rusty.

How long would it take for an Iowa or South Dakota class vessel to get the point where it needed that sort of treatment? Is that something done every two years or every five? Or after 10 years of service?

Ytlas is correct. Dry docking of ships for hull cleaning and painting was every 3 to 5 years. However, the corrosion problems on the ship I referred to was due to two factors:

One being that the Passive Cathodic Zinc pattern installed was only designed for 3 years before replacement of zinc anodes. But the ship's tour was extended to 5 years.

Secondly was that hull cleaning by divers was done 4 times a year instead of only once or twice. Worse, the the cleaning machines used wire bristles instead of fiber. There were areas of the ship where the paint had been COMPLETELY wire brushed off down to bare metal.

[tmasi]

I see. So if, say one the Ayatollah-class destroyers that the Taiwanese have, were to be inspected, you just wouldn't find that sort of pitting or hull thinning even though the ship is 25+ years old because of the on-going maintenance that was done.

I get interested in this topic because I look at the way budgets are going and I just hate to see the U.S. not get the most of its ships knowing how hard its going to be to fund future replacements. Plus I believe that the Navy's role in keeping America on top is very under-appreciated. I believe that without a strong/dominant surface fleet to influence political events, the U.S.'s control over its own destiny becomes much less secure.

Thanks for your answers, guys.

[RustyBattleship]

I see. So if, say one the Ayatollah-class destroyers that the Taiwanese have, were to be inspected, you just wouldn't find that sort of pitting or hull thinning even though the ship is 25+ years old because of the on-going maintenance that was done.

I get interested in this topic because I look at the way budgets are going and I just hate to see the U.S. not get the most of its ships knowing how hard its going to be to fund future replacements. Plus I believe that the Navy's role in keeping America on top is very under-appreciated. I believe that without a strong/dominant surface fleet to influence political events, the U.S.'s control over its own destiny becomes much less secure.

Thanks for your answers, guys.

Actually, those 4 ships are around 30 years old. It was in November of 1980 I was on an inspection team to Pascagoula, Miss to see how they were adding armor plate to the ship superstructures. (They depended a lot on sandwiching Kevlar in between the bulkhead with aluminum "armor" over it. I'm not much of a fan of Kevlar for stopping steel fragments and designed the armor for the rest of the Spruances out of solid aluminum).

Actually, since those ships were to be built for the Shah of Iran, precise fitting and quality control of fitting the bow mounted SONAR dome was very well done as the Shah wanted real quiet ships to patrol for submarines and mines.

As for the hull plating, all of the Spruances and Tycos were built of Carbon Manganese Steel, a commercial equivilant to the Navy's HTS (High Tensile Steel). It holds up pretty well against corrosion and if you have Impressed Current Cathodic Protection (vs. Zinc anodes) you can keep the hull pretty well intact.

[Tarek Morgen]

How does a sea quake affect submarines that are caught in the area?

[blidgepump]

How does a sea quake affect submarines that are caught in the area?

The impact on a submarine would be minimal, unless it was tied up to a pier.

Any lurkers that could offer pictures of museum ships in the quake zone would be interesting.