Quote:
Originally Posted by leopold
The pictures of barges on the river usually shown here are somewhat misleading , since the barges shown are fully loaded (for obvious economical reasons and since there aren't any big waves in the rivers).
However the typical hull dimentions of a barge are above 3 meter high ,
(See the link : http://www.barges.us/bargedrafttable.html)
therefore if it's only ~ 50% filled it'll be :
a) 1.5-2 meters above the waterline. (Reasonably close to the landing craft used on D- Day)
b) Have a significant spare buyoncy for the intake of occasional wave that crosses its gunwale.
(Again - I think there were better ways to make the Sealion work than the barge fleet, but let's not get too nasty on the good old barges...) |
The problem here is one of metacentric height in addition to simple freeboard and bouyancy. The barges were designed to haul a substancial load of heavy bulk material on inland waterways. Using them as landing craft presents two naval engineering problems:
The first is that the new craft will not be hauling a heavy load but rather one that has considerable space requirements, eg., men. The vehicles again take up alot of space with respect to their weight. This leads to the second problem: Metacenter.
Metacenter in simple terms is a mathematical model of the ship's stability. It is measured as the difference between its center of gravity and its center of bouyancy. While a light load gives the barge better bouyancy it also raises its metacentric height considerably. On a smooth river this is of little concern. At sea what it means is that the barge bobs around like a cork. The Germans tried to fix some of this by adding concrete ballast. But, only so much could be added before they ran out of space.
So, the choice is do the barges rock and roll like corks in a toilet bowl or do the Germans load them down for stability and take chances with low freeboard? Of course, if the first course is taken the passengers are likely to not be in great shape by the time of the landings also.