Helicopters and cruise ships - Page 2 - Ships Nostalgia
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Helicopters and cruise ships

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  #26  
Old 13th April 2019, 15:18
John Rogers's Avatar
John Rogers John Rogers is offline  
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Quote:
Originally Posted by tony Allard View Post
very interesting read guys, yes it does raise a few questions.
so helicopters and fighter jets on carriers suffer from sea spray badly i hear, so what do they do exactly when they land and shutdown and go back in the hangar?? they wash them down with clean water and say a salt dissolver to break down sea spray?? thats one thing id like to know more about.

helicopters can be very noisy i was once at a airport with the rural fire brigade and we were back up water supply to the urbans if a plane caught alight or crashed, but by the end of that day i had the worst damn headache from the noise but mainly from the jetfuel its ok at first but damn its smelly after a while and strong.

Things to keep in mind in the case of aircraft are:
1) They are made from Different alloys of aluminum. 3 of the most popular alloys are 2024, 6061, and 7075. All three have different corrosion potentials. Now to complicate things, you can heat treat them to different hardnesses or heat conditions. These hardnesses will impart different corrosion rates to the individual alloys. Finally, many aircraft manufacturers will use Al-clad aluminum sheet for the exterior of an airframe. Al-clad is a coating of pure aluminum on the alloy sheet. The pure aluminum is much more corrosion resistant then alloy. But many times it is only on the exterior of the sheet, not both sides. So, you can have two different corrosion rates for the same sheet.
2) Anodize finishing - Most, but not all, exterior aluminum will get an anodize coating. The main types of anodize are (best to worst for corrosion) Hard Coat Sulfuric, Sulfuric, Chromic Acid, Phosphoric Acid. Another anodize is Boric Sulfuric Acid anodize, but it has only been around since the early 90's and would not be on a historic aircraft yet and Phosphoric anodize is used chiefly for bonding.
The corrosion rates between all of these differ greatly and some manufacturers, Boeing, do not use any anodize on exterior surfaces. Boeing likes Al-clad.
3) Primers and Paints - Just about every aircraft since the late 30's has gotten some type of chromate primer on the interior. Up to the mid-late 80's Zinc Chromate was a favorite Since then Epoxy chromates are used. Almost any time you see an aircraft painted it will have some type of chromate coating.
Now put all this into salt water add corrosion modifiers for temp and galvanic effects and you have only a basic guess as to what the actual rates will be. Not to mention what corrosion may have occurred prior to loss of the aircraft.
So, any real rates will be individual to the aircraft type and manufacturer.
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  #27  
Old 13th April 2019, 18:23
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Originally Posted by Spiralling Steel View Post
It strikes me that the debate regarding having helipads on ships is, or should be, redundant. To my simple mind the attachment of lifeboats to ships, and the requirement for passengers to undertake lifeboat drills suggests that they are the principal method of evacuation. Or are lifeboats another conspiracy to lull the general populous into a false sense of security. If, as I suspect, in a real emergency they are of little use, having been told, on two occasions on, one cruise that the tenders could not be used due to a 5 metre swell it begs the question what would happen in the event of problems in really high seas. Perhaps it is time for shipping world to waken up to the fact that helicopters have limitations in terms of payload and operating conditions and that evacuating the mega cruise liners of today is simply a maritime disaster waiting to happen.

Using the tenders in a 5 metre swell would be a total disaster -- can you imagine trying to get in and out of a tender in those conditions? It would be a very dodgy situation to have to use them as lifeboats where everyone is embarked from the Prom deck and you only have to worry about letting go the falls at the right moment. The ship really was in a terrible position to try launching her lifecraft so close to a rocky shore in that kind of sea state?
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  #28  
Old 21st April 2019, 09:38
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oh i never thought of the different types of aluminum used and the effect the coatings have on corrosion.
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