Just now realized why righting arm diagram from the CG MSC report looks the way it does:
This is what a typical righting arm looks like. The report calls it a curve for a notional vessel
This is the righting arm CG-MSC generated using a computer model.
I don’t recall seeing a graph like this before but If I understand it correctly theses curves are the residual righting arm which would be the top graph more or less minus the energy created by the turning of the ship.
The MSC ( Marine Safety Center) stability report is #83 in the docket: NTSB Docket - Docket Management System
Looks like I didn’t (or don’t) understand the graph in the last post. This one shows the righting arm with and without a turn.
There is an interesting tidbit in the the CG stability report wrt to the forces in a turn.
In a turn when the rudder is put over, say to starboard as in this case; before the vessel heels to port due to centrifugal force there will be a slight, temporary heel to starboard. On a vessel in tender condition and at speed this shift, first to starboard then over to port can be easily felt.
Section 4.3.3. of the report Stability During a Turn goes into detail on the phenomena.
If the vessel heels over excessively in a turn to starboard then giving opposite rudder to port actually makes the problem worse.
According to the report; in this case not significantly worse because at high heel angles the rudder had little turning power.
