# Trim and roll (or heel) for submersibles

Hey guys,

Im studying submarines and I was wondering when discussing buoyancy changes for submersibles what is meant by "changes in trim and roll or heel". What is trim/roll/heel? How should I picture it?

Thank you!

anorlunda
Staff Emeritus
Hey guys,

Im studying submarines and I was wondering when discussing buoyancy changes for submersibles what is meant by "changes in trim and roll or heel". What is trim/roll/heel? How should I picture it?

Thank you!

It has to do with whether the sub sits level or tilts in one of the three possible axis. I usually hear the three described as pitch, roll, and yaw.

Cars go down the highway in the direction the wheels point (unless they are skidding.) Boats and airplanes do not necessarily move the same way the nose points.

tech99
Gold Member
It has to do with whether the sub sits level or tilts in one of the three possible axis. I usually hear the three described as pitch, roll, and yaw.

Cars go down the highway in the direction the wheels point (unless they are skidding.) Boats and airplanes do not necessarily move the same way the nose points.
Yes, also I think heel is roll induced by a sail or by cornering force.
Yaw is rotation about a vertical axis, as when steering.

CWatters
Homework Helper
Gold Member
When a submarine is on the surface heel can cause the centre of buoyancy to change in a way that reduces heel, eg contributing to stability. This doesn't happen when the submarine is submerged because the hull is surrounded by water.

olivermsun
When a submarine is on the surface heel can cause the centre of buoyancy to change in a way that reduces heel, eg contributing to stability. This doesn't happen when the submarine is submerged because the hull is surrounded by water.

Are you saying that heel can lead to a shift in the center of buoyancy that opposes further heel?

CWatters
Homework Helper
Gold Member
Yes. But only when on the surface.

olivermsun