Ships inevitably get heavier and become less stable during their usually long operational lives as new kit and systems added above center of gravity, its naval architectural practice for naval ships to be designed with built in displacement margin for this future weight growth so as not to exceed the ships design weight and stability limits. The normal cheap fix is to add lead/pig iron ballast to restore ships stability.MikeKiloPapa wrote:
I wonder if the 6900t figure is lightship or standard displacement ? .....as for the Hunters 8800t , that is supposedly its mythical End Of Life displacement , which IMO is a bit of a bollocks term anyway ( Full load is full load....ie the maximum displacement of the design....it doesn't change unless you lengthen the hull) , but in the case of the Ozzies/RAN ,they are known for cramming their ships full of new heavy equipment when upgrading and modernizing and thereby sacrificing seakeeping and stability,. Which means the Hunter class will probably end up weighing 10kt but only be able to sail in sea state 2
The USN had standards, but these days more ignored than honoured, as can see from table with the actual LCS figures and the new FFG(X) capability only spec'd at 5%.
Ship type----------------------------------------------Weight(%)------------------------------------ Vertical centre of gravity
Surface Combatants-------------------------------------------10.0------------------------------------------12"/0.30m
Aircraft Carriers--------------------------------------------------7.5------------------------------------------30"/0.76m
Amphibious warfare ships (large decks)---------------------7.5------------------------------------------30"/0.76m
Amphibious warfare ships (other)----------------------------5.0-------------------------------------------6"/0.15m
Auxiliary ships---------------------------------------------------5.0-------------------------------------------6"/ 0.15m
Special ships and craft-----------------------------------------5.0-------------------------------------------6"/0.15m
LCS requirements---------------------------------------1.4 to 1.6-------------------------------------------6"/0.15m
Re the Hunter I'm guessing the 8,800t EOL displacement quoted reflects 8,000t FLD on entry into service with 10% weight growth designed in.