Heavensent is made of a material called Pykrete. The wood pulp binds the ice in such a way as to keep it from smashing. I first heard about it in this short story.

Seeds–

�We have a block of cells on this level. But mostly it is just for stores.�

�Cells?�

�Heavensent avoided the major trade routes, but still came across the occasional boat or castaway. They were questioned, then kept in their cells.�

�It would be more efficient to kill them.� Reed suggested.

�That would be against the mariners� code, apparently.� Serena shrugged, �And none of them were combatants. They will be released when the mission is over.�

�How far down are we?� Jay asked, �We must be under water by now.�

�Almost certainly. Most of Heavensent is below the waterline. Because of the way it was built, every block is different. It is hard to estimate how far down we have actually gone.� Serena�s tour had gone on for a long time. They were now beyond loosened up and into footsore. �Below here are the engine rooms and refrigeration plant. You would not be interested in those. I know I am not. Come, your quarters should be ready by now.�

�The refrigeration units keep the ice frozen?� Jay had found an exposed piece of wall and was scraping off frozen mush. �And that is all this ship is? Ice and wood pulp.�

�That is all. It is almost indestructible, unsinkable- obviously- and even without the refrigeration units it would take an age to melt.�

�You know an awful lot about the vessel.�

�I had a meal with the inventor. The other officers say he just came out of the forest one day with this plan and a manner that had everyone believing him.�

�A holy man?� Reed wished the awe in his voice hadn�t been so obvious.

�Yes. I did not believe in them either. I thought it was just a cult drawn around the occasional genius. But, no, holy men exist.�

�The Silver Tower?� asked Jay.

�He would not talk of it, but I believe the Silver Tower is real as well.�