Giant battleship question

[Simon_Jester]

Exactly how absurd was the Habbakuk proposal, anyway? Was there a catastrophic, inherent flaw along the lines of "Pykrete won't work as a building material," or was it just an unreasonably expensive way to solve a problem that could be dealt with more efficiently by other means?

[Sea Skimmer]

Pykrete is like concrete, it’s very strong in compression but it has little tensile or shear strength so when you start building a large hollow object like a ship its going to tear apart easily. Wave action makes any large ship flex a considerable amount; they have to have expansion joints in the decks to allow it. Pykrete wont flex, it will crack.

The design did call for a fair bit of steel reinforcement, but it’s likely that by the time sufficient reinforcement was added to the design it wouldn’t even float. We are talking about over three times the mass of the largest steel supertankers ever built, even with all steel it would be hard to make a ship that big.

The question of how to keep a 2 million ton ship frozen during construction, and then frozen at sea is also daunting. You’d need a pretty epic anti freeze piping system to do that.

[CaptainChewbacca]

The problem with Habbakuk was it was supposed to fulfill the function of a floating island/carrier but do it with cheap materials. The problem is the freezing plant needed to keep it cold required more steel than an aircraft carrier.

[Sky Captain]

When Mythbusters tested the properties of original pyckrete it was fairly durable when subjected to bending loads. However ship made from it could only function in very cold waters like in North Atlantic during winter and would still need an extensive cooling system to prevent meltdown.

[Simon_Jester]

I've heard good things about pykrete's melt-resistance (some of the showy demonstration stunts involved dropping it in a steaming bathtub)... but I can't really see it being all that much better than normal ice over the long run. The Second Law of Thermodynamics plays no favorites, after all.

[lord Martiya]

A 1000 t prototype in Patricia lake took three summers to fully melt, but I don't know if they kept the freezing motor active.
But that's not my problem. My problem is: how do you LIVE on that thing without freezing to death? Or you have a heating system for the living quarters? I think this one would create some problem controlling the melting...

[Raxmei]

A 1000 t prototype in Patricia lake took three summers to fully melt, but I don't know if they kept the freezing motor active.
But that's not my problem. My problem is: how do you LIVE on that thing without freezing to death? Or you have a heating system for the living quarters? I think this one would create some problem controlling the melting...

Part of pykrete's durability is that as it melts it creates an insulating layer of wood pulp on its surface that reduces heat transfer. The ship was also planned to include a lot of fiberboard insulation. People can and do survive sleeping in igloos and other snow and ice based structures.

[Sea Skimmer]

I saw that. The problem is they didn't test piece's large enough to be very relevant to shipbuilding, nor did they test any means of joining the piece's to form an object 4,000 feet long. The plan was to freeze Habbakuk in a series of blocks as much as 30 feet thick, and joining them is no minor task.
Nor did they as far as I recall conduct any long term tests, which would demonstrate a really annoying property of ice, it still flows. That means the whole ship would slowly be squishing under its own two million ton weight. To a certain extent that can be tolerated, and deep freezing can slow the process down, but a ships hull creates concentrations of stress and those areas are going to deform rapidly.

It might be possible to build Habbakuk and keep her frozen next to a pier in a sheltered port, but no way was that thing going to cruise through a North Atlantic winter storm under power.

Mythbusters also showed you could make a boat out of frozen newspaper, but anyone think that'd scale up to making a destroyer?

[CaptainChewbacca]

The artist's renderings for HMS Habbakuk are pretty impressive:



Of course, some people took 'Giant aircraft carrier made of ice' rather literally

[Simon_Jester]

Yeah. It looks great. I don't really expect it to work, but it sure looks great.

Thanks for addressing my questions about the concept, people.

[Sky Captain]

Another problem would be when the ship is under way it would generate continuous water flow over the hull which would apply heat and also erode the pykrete, wave action would probably wash away the melted wood pulp continuously exposing fresh layers of pykrete to relatively warm ocean water.
At least Mythbusters frozen newspaper boat started to delaminate and leak fairly quickly even in cold water. A ship made of pykrete would probably require some sort of durable insulation material where hull comes into contact with water.

[Sea Skimmer]

Another problem would be when the ship is under way it would generate continuous water flow over the hull which would apply heat and also erode the pykrete, wave action would probably wash away the melted wood pulp continuously exposing fresh layers of pykrete to relatively warm ocean water.
At least Mythbusters frozen newspaper boat started to delaminate and leak fairly quickly even in cold water. A ship made of pykrete would probably require some sort of durable insulation material where hull comes into contact with water.

Yeah, and that raises the question of how do you attach the insulation? Drilling into the ice to use thousands of bolts is a non starter (this would provide melting paths deep into the ice), so you'd have to do something like wrap cables around the entire hull to hold it on. That could be possible though since the ship is already going to be very slow and drag wouldn't really matter.