Weight and Buoyancy

[MasterBurte]

I always felt that the system how UAD calculates ship weight distribution is off. Currently we have for/aft weight offset, left/right weight offset, roll and pitch. Structures and guns that are placed further away from the center have more negative impact on roll and pitch characteristics than put closer to the center. Placement height doesn't seem to affect things.

To make it more realistic we need to understand how balance really works in ships (see pictures). What matters is the center of gravity and the center of buoyancy. When the ship tilts the center of buoyancy shifts and creates a leverage that helps pushing the the ship back in the upright position. When we add weight on top of the ships hull we increase the height of the center of gravity which results in a smaller leverage to upright the ship. As long as the ship is in balance regarding to the weight offset (left/right or front/back) it doesn't matter where the each single structure or gun is placed.

You could for example add 100t of weight at the centerline of the ship or or two times 50t evenly far away from the centerline and on the same height on to the left and one to the right. Both variants would result in the exact same center of gravity. On the other hand if you instead increase the height the weight is placed (for example a gun on a barbette with imaginary 0t weight) the center of gravity would change.

This is what i would call static balance. But ships are also dynamic as they have to absorb forces from gunfire, waves and maneuvering.

When we look at the dynamic forces we have to talk about momentum and rotational energy. If a ship steer to one side due to it's momentum a higher center of gravity results in more leverage and therefore more tilt. Everytime the ship is beeing rotated energy is converted into rotational energy. Guns fire a broadside and induce roll and pitch dependend on the force vector direction and position. Everytime a wave hits the ship the same happens. If we have to identival ships with the only difference beeing that the first has more mass near it's center of gravity and the second has its mass more spread out the second ship would be the more stable platform due to more rotational energy needed to achieve the same indused pitch and roll angle.

As an example you could think of a canoe steering into the waves. One time with one adult of 70kg sitting in the center and another time with two kids each 35kg sitting the bow and rear. It's the same fundamental physics that are used by ice skaters or tightrope acrobats.