Are you serious Marty about the ships?

YEP 100%....back in the days of full steel ships (titanic, bismark etc etc) where ships are riveted together, the banging of the steel walls (facing north/south) changes the steel's magnetic properties since it's in the north/south (magnetic) earth axis...
ALL ships were later made east/west to minimise magnetic offsets within the ship, obviously this is a big prob with the onboard ship compass etc...

No doubt it's all on google somewhere :-)

For the home experimenter, go grab an old steel spanner or length of steel rod, even a screwdriver shaft (preferably it's already non-magnetic) and lay it on the ground facing true north/south....then bash it with a steel hammer (not sure how many times or how long this takes) but the spanner should then become magetic.
( i think it has to be pure steel and not a forged cast spanner etc?? )


MM