Distorted ship's hull steel panels

Not just ships but aircraft also, if you get up close to a USAF Boeing B52 bomber (there is one on display at Duxford) the body skin is wrinkled vertically along the full length of the aircraft. Quite normal apparently, the body skin is thin alloy to keep the weight down on such a large aircraft. The wrinkles come about from the stresses and strains of flight and is said to cause no problems in flight performance or the service longevity, the B52 has been around for donkeys years and they are still in service so the wrinkling is not detrimental.

Edited By Ron Laden on 13/04/2021 16:06:35

Yes, but most of the energy in a guided missile is explosive, not kinetic. The explosive in an Exocet warhead weighs 165kg compared with 24kg in a Japanese 18" Armour Piercing Shell plus it has more zip because it doesn't have to withstand the shock of being fired from a gun. And as the rest of the missile is mostly propellant, any unburned when the target is struck adds to the devastation.

The maximum range of the Japanese 18" shell was about 42km and at that distance a 9 shell salvo would be dispersed over 600m. In comparison, the Exocet is good for up to 120km and unless disrupted it will hit the target.

The other problem with big guns is their weight. Breech and barrel of an 18" gun, 180 tons. Three guns in a turret, with all the gear needed to fire them, 2700 tons, about the same as the total weight of a Tribal Class frigate. Pretty clumsy compared with a pair of missiles fired from an aircraft.

Dave

The buckling of relative thin plating, when subjected to shear loads, is called Wagner tension field. Although the plating is continuous, for shear forces it acts like a lattice girder with tensile and compressive forces at +/- 45 degrees. The parts in compression tend to buckle and produce the effect mentioned. It is very noticeable on large helicopters. It is not detremental. Apparently the same effect is used in the garment industry, although they call it drape.

Impressive as their engineering was, I wasn't trying to make a case for the reinstatment of dreadnought gunnery.

But it does seem to me that the light construction of modern warships reflects the demise of armoured ships, and has progressed in tandem with it. As currently constructed, most antiship missiles can't penetrate armour of any substance, less still explode behind it. Adding a shaped-charge pre-warhead wouldn't help in any obvious way, as the hole it would make wouldn't normally be big enough to pass the rest of the weapon.

The logical outcome is what has actually happened - naval designers have concentrated on detecting and attacking incoming weaponry in the hope of preventing hits. Given comparable accuracy, the belligerent capable of launching the greater number of threats will have the better prospect of saturating their opponents' defences. That bit was also true back in the day.

Edited By Mick B1 on 13/04/2021 17:38:15

The epoxy compound is only used below the waterline. It is purely functional, it reduces hydrodynamic drag and it reduces and homogenises hull generated noise, aesthetics are not a factor.

Attempting to predict the ultimate shape of the hull and rolling the shell plating so that welding induced distortion is eliminated would probably be theoretically possible but almost certainly outside any cost budget.

It wasn't only the non slip floor coatings that burned and gave off toxic fumes, it was mattresses, bedding, even the sailors clothing was polyester so it burned and melted onto the skin. Horrible.

Performance of a modern warship can be fairly spectacular. Again I was told by someone who would know that HMS Broadsword would accelerate from 0 to 30mph faster than a sports car. I always assumed this was an MG Midget type sports car, not a 7 litre AC Cobra type of sports car!! Certainly being on a launch alongside when she did a standing start sprint, was very impressive.

cheers

Bill

Some hours later I have just realised that I had "hydrodynamic", "homogenises" and "aesthetics" all in the same sentence. Obviously I was sleepwalking and snacking on a thesaurus.

apologetically

Bill

If Broadswords top speed was only 30 knots, how was its acceleration quite so good??

**LINK**

The MoD when publishing data about HM ships, they can be a little coy about some information. For instance regarding top speed all they say is "...in excess of 30 knots" In Broadswords case it was well in excess of 30 knots.

cheers

Bill

Thank you all for joining the chat. But I still cannot see why, when they build a big Naval ship, the plates (panels?) all appear indented at launch.

>>>> Trust me Norm, it's the welding of the frames and bulkheads and longitudinals to the shell.

Bill kindly explains the welding might pull in the centres, but that seems odd - couldn't they design the ribs to match the planned curvature in all places?

>>>>The primary consideration is what the sea "sees", that is the actual part of the shell that gets wet. Predicting what the shell is going to do post welding, is certainly possible, however, the shell plating is distorting between the frames/bulkheads and longitudinals.

A big ship like a liner with heavy plates has them all rolled to match the curvature; I don't think the same plate distortion is seen. So, are we thinking that the Naval ships are made with much thinner plates, to make a lighter and faster ship, and try as they might they cannot make them neatly curved all over, and have to resort to seven tonnes of epoxy filler?

>>>Some plates are flat others are rolled to shape, it depends on where they are destined for. Once again, the seven tonnes of epoxy is there for hydrodynamic reasons only. The epoxy is applied only below the waterline. Whether or not the below waterline aesthetics are improved or not is irrelevant and as such not a consideration

So why can't thin steel panels be rolled to a correct curve, and welded to the curved bulkheads and ribs, so that it all looks neat? There is something we are not understanding, and that was the whole point of my first question

.>>>The shell plating is rolled to the correct shape, the plating is distorted by the welding. No doubt it would be feasible to go over the entire above waterline area of the shell and carefully heat and dress the distorted panels flat, so the ships side presented a pleasing appearance to the tax paying population. This however might render the ship rather expensive.

My guess is that localised heating and cooling of the skin from the sun leads to expansion that either has to pop in or out, and standard practice says to make them all pop in. I wonder if this is why the same panel distortion is seen in welded locomotive tenders?

>>> The distortion is not caused by the sun.

But, if the panels are flexing in and out with sun heating, how does the seven tonnes of epoxy stay in shape?

>>> The epoxy is only below the waterline. The sun does not cause the shell plating to "pop" in and out.

italically yours

Bill

Thank you Bill for kindly addressing the points in my ramble.

I will stop my worrying and accept that it is welding distortion, inevitable in large panels tacked to widely spaced frames

And the Royal Navy does not waste taxpayers' money making the hull above the waterline look like a thing of beauty

If I recall correctly I had seen an episode of Extreme engineering about the construction of a US carrier where the hull was dressed with sledgehammers.