Davit arm design

[Roger2]

I have tried to write a spreadsheet from the calcs given in Pressure Vessel Design Manual by Deniss R Moss. It seems strange that for the curved davit as Type 3 if the wall thickness is increased the stress in M2 increases* M1 remains the same!!! Also if the radii of the arm is reduced* again the stress goes down* dont get it! is not M1 and M2 the same?
Any comments welcome.

[techwarrior08]

Dear Roger2*
Are u referring to the curved arm davit design as per Type B in Design Manual by Moss. Type 1/2/3 refers to the different types of loading whereas Type A/B refers to the configuration of davit arm.
In case of curved arm design* M1 & M2 are different as they act at different locations.
If u take summation of forces about davit support u will get M1 whereas u have to take summation of forces about the Start of davit arm to get M2.
Hope it helps.