FEA Large Displacement Error - Marine Knuckle Boom Crane - Help Required

Hi,

I hope you can help me with a recurring excessive displacement error.

I am trying to run a FEA study on a marine knuckle boom crane (see attached for model and mesh) - I have run FEA studies before with success, but I am having issues with FEA for this design, perhaps it is because this design consists of thin sheeted parts comprising a box-type cross section, DH36 steel. 

So far I have significantly defeatured original model to allow for meshing; there is a fixed fixture at pedestal base along with pin connectors elsewhere, piston and cylinders are rigid, with 1.5T load at end of jib arm. FEA solver wishes to change to sparse Intel before displacement warning, perhaps FEA solver does not like the sharp edges or internal T plates?  

Perhaps as opposed to a vertical load I should model the loading via the hoisting cable housing.  

Any advice or suggestions would be greatly welcomed, I have troubleshooting the gravity check with soft spring and according to resulting displacement plot the top plate is failing.

Best wishes,