Comment by tokenadult | Hacker News Reader

Comment by tokenadult | Hacker News Reader

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This brief article about current uses of wood pulp reminded me of something I read in a book back in the 1970s about a proposal to build an aircraft carrier during World War II (when there was a shortage of steel) out of a mixture of wood pulp and water ice. That material was called "pykrete," after the name of its inventor, Geoffrey Pyke. The shortage of steel was alleviated, and plenty of aircraft carriers constructed of conventional steel, before this idea was implemented. In actual use, such a ship would have had to have been continuously refrigerated, perhaps a greater drain on scarce materials than building a ship out of steel.

Sure enough, there is a Wikipedia article about the material,

http://en.wikipedia.org/wiki/Pykrete

which reports that the Discovery Channel popular science program Mythbusters made ship models to test out the idea.

Wikipedia

http://en.wikipedia.org/wiki/Project_Habakkuk

and the Royal Naval Museum

http://www.royalnavalmuseum.org/info_sheets_Habbakkuk.htm

have websites about the frozen aircraft carrier project that relate more details, citing sources other than the book I read decades ago.

AFTER EDIT: I think the book I read about this plan was Of Spies and Strategems by Stanley Lovell,

http://www.amazon.com/Spies-Stratagems-Stanley-Lovell/dp/B00...

although a Google Books search doesn't show the keyword I'm looking for in that book.

I can't find footage, but Mythbusters had a pretty impressive episode where they tested various formulations of pykrete. Jamie's newspaper-based one seemed to be the strongest. A smallish piece of it held a pile of lead, plus Adam's entire weight, while he smacked it with a hammer repeatedly. They built a little boat out of it which disintegrated pretty quickly. The idea that you could build an aircraft carrier was deemed "plausible but ludicrous". http://mythbustersresults.com/alaska-special-2

You have to remember that surface area increases with the SQUARE of size, but volume by the CUBE. So scale it up by a factor of 10 and you have 100x the surface and 1000x the volume, so it will melt much slower.

Scale it up by ANOTHER factor of 10, and it'll melt another factor of 10 slower, and possibly more. Building-size blocks of ice take months to melt, even in warm temps.

That helps if your aircraft carrier is a solid block...

It applies regardless of scale. The proposal had internal refrigeration, and air is a very poor conductor of heat - most of the heat transfer would occur with the water, not the air, even if the air was 10-20 degrees warmer, maybe more.

Here are some clips from the episode:

http://www.youtube.com/watch?v=UMKis4FPykw

http://www.youtube.com/watch?v=uQO4FDuW3PI

I would consider "plausible" and "ludicrous" to be mutually exclusive.

There are many things that are possible, but never the optimum solution to any real engineering problem. Mythbusters has a long track record with that sort of thing, probably most notably their functional lead balloon.

Militaries have a way of combining them. For example: "normal" aircraft carriers.

"plausible but ludicrous" can be parsed as "probable [that it would work] but ridiculous"

While they didn't build battleships out of Pykrete they did build fuel tanks out of laminated paper and plastic. (An early form of fibre glass, using paper instead of glass.)

(http://www.ww2aircraft.net/forum/other-mechanical-systems-te...)

(http://home.earthlink.net/~charlesfelton/id19.html)

Anyone who has been around a university physics lab will easily recognize linen (as well as paper) phenolics which are typically used as insulators and occasionally for mechanical parts. They used to be pretty popular for gaskets as well.

In general, paper based phenolics were used for tons of things, and if you have anything around that looks like hard plastic that was made before the 70s you've probably encountered it as well (buttons, knobs, etc...). The trade name Bakelite was a general term to denote a paper/linen/cotton based thermoplastics.

http://en.wikipedia.org/wiki/Bakelite

http://en.wikipedia.org/wiki/MythBusters_%282009_season%29#P...

That's really fascinating. The boat sounds almost like a mobile version of the huge wall of ice in Game of Thrones. I could see this used to construct space stations and vehicles, to be used where the vacuum of space prevented thawing.

If I recall my science correctly water ice would sublimate in the vacuum of space: http://askville.amazon.com/water-evaporate-vacuum/AnswerView...

In fact, this is pretty much what constitutes a comet's tail.

Vacuum doesn't prevent thawing. Vacuum is an insulator against mechanical heat transfer, but it doesn't do anything against radiative heat transfer. Better not bring that pykrete hull anywhere closer to the Sun than, say, Mars.

Also, cellulose is harder to find in space than carbon, iron or aluminum, currently.

>it doesn't do anything against radiative heat transfer

That's easy: put Multi-layer insulation between you and the sun, and install radiators on the shaded side.

http://en.wikipedia.org/wiki/Multi-layer_insulation

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/1971001...

I remember reading this many years ago. I don't think it is mentioned in the wikipedia article but a further benefit of pykrete was that it would make an aircraft carrier almost immune to torpedo attacks. I didn't see any backup to this but I seem to remember that the aircraft carrier would have a hull of pykrete 14 foot thick, which judging by the bullet tests mention in the article, might have made it exceptionally strong.

I am going on memory on this so happy for someone to correct me.

This sounds unlikely. From what I understand, torpedoes do most of their damage by causing hull flexion of the target ship by exploding underneath rather than punching a hole in the hull itself. An incredibly heavy, inflexible hull seems like it would be easier to crack as opposed to some material that has the ability to bend and absorb shock.

I'm not an expert either so hopefully one of our naval folks will come in and clear it up.

This is true of modern torpedoes, but was not true of WWII vintage torpedoes, which generally smacked into the side of the hull and blew up.

Ahh, thanks for the clarification.

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