Aluminum Hull

[chicopee]

Is aluminum a good material for a gun boat hull? Wasn't that type of material used on a British gunship sunk by the Argentinian Air Force during the Falklands Island dispute?

 

[IRstuff]

Depends on what you want to do with it, and what the design requirements are. There are certainly civilian boats made from aluminum. One big issue will be corrosion.

As for the HMS Sheffield:

http://en.wikipedia.org/wiki/HMS_Sheffield_(D80)#The_sinking_of_HMS_Sheffield

At least, here, the implication is that aluminum was not involved.

TTFN

FAQ731-376

 

[ornerynorsk]

Aluminum is a good material for any type of boat hull. As is steel, wood, FRP, etc. It's just that the weight savings is not as important in marine applications, and maximum speed is not necessarily a function of less weight unless it's a hydrofoil or other surface effect design. I believe the United States was/is aluminum hulled, as are a lot of coastal patrol and rescue boats. A steel hull is more forgiving of the paint or bottom coatings, whereas aluminum needs more prep and THE correct paint. There are a hundred factors to consider. Corrosion is definitely a major one, as IRStuff, mentioned.

Are you mainly concerned about aluminum regarding its resistance to munitions, or some other specific criteria?

 

[IRstuff]

For gunboat, the best defense is a good offense. We used to market a fiberglass hulled Magnum with a 30-mm M230 chain gun.

The stand-off distance was at least 1.5 km, ensuring that only cutters and larger would be a threat, and at that point, you're better off bailing than fighting.

TTFN

FAQ731-376

 

[MadMango]

Most warships in the US Navy are aluminum-hulled. The newest coastal littoral warfare ships will be/are steel-hulled though not exactly sure of the reasons for the switch.

"Art without engineering is dreaming; Engineering without art is calculating."

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[KENAT]

MM, are you sure about that I thought it was the other way round, most ships steel a few newer ones al? Or did you mean some 60's/70's ships had Al superstructures?

http://www.defensenews.com/story.php?i=4446438

Anyway, there were indeed reported problems with the aluminum structure on some Royal Navy Vessels in the Falklands war. Though at least some of these appear to have been discredited. Look up Sir Galahad & Sir Tristram - the latter was severely damaged and when rebuilt it was done with steel instead of Al.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA133333&Location=U2&doc=GetTRDoc.pdf

page 57

http://www.seaotterboats.co.uk/english/aluminium.php

USS Belknap is one poster child of aluminum fire damage concerns.

http://en.wikipedia.org/wiki/USS_Belknap_(CG-26)

There's a lot of information on the web about this, though you need to sort through the military fan sites etc.

http://files.harc.edu/Projects/BlueWater/CaseHistories/WeldableAluminumAllows.pdf

http://www.google.com/url?sa=t&source=web&ct=res&cd=10&ved=0CCcQFjAJ&url=http://

http://www.usna.edu/Users/naome/phm...w5nHDw&usg=AFQjCNEwFarYqSCRLQqptsrhWZRgh10AbA

Al was originally used on military ships to save top weight. I'm not sure why it wasn't used more for Mine Counter Measures Vessels where GRP seems more popular. Being non magnetic should be an advantage it shares with GRP though being conductive I wonder if Al hulls are prone to still setting up electro magnets.

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[mauner]

MadMango,

KENAT is correct. Most US Navy ships do not have aluminium hulls. I think composites will be the material of choice for future ships.

 

[boo1]

The excellent corrosion resistance of the 5XXX alloy is one of their most important characteristics. They are resistant to marine atmospheres and can be used in these environments without additional protective measures such as painting or sacrificial anodes.

However, under certain conditions of elevated temperature exposure, alloys containing higher amounts of magnesium (>3%Mg) may become susceptible to intergranular forms of corrosion (i.e. intergranular corrosion, exfoliation, and/or intergranular stress corrosion cracking). Exposure to certain unsuitable combinations of time at elevated temperature (>150 degrees F) either during the fabrication of the sheet and plate products or in service can cause precipitation of the b-phase (Mg2Al3), which forms preferentially on the grain boundaries. The b-phase precipitate is electrochemically more active than the aluminum matrix and the susceptibility of the 5XXX materials to intergranular forms of corrosion increases with the continuity of the grain boundary precipitation.

Require producers to perform nitric acid mass loss testing (ASTM G67) to verify that the material is resistant to intergranular forms of corrosion. Consider using hull material Aluminum Alloy 5083 and Aluminum Alloy 5454 for higher temperature compartments .