Hullspeed Slender Body Plots

Hi
Does anyone else out there have trrouble getting sensible contour/render plots from hullspeed's slender body method?
Mine are all fine up to Fn = 0.4, but after that there always seems to be a discontinuity around the end of the "virtual appendage"
Have tried without it, but the model generally sh*ts the bed.
I perhaps have falle short a little bit on iteration cycles - I haven' had the patience to stick around whilst it does the maximum 5000001 - perhaps this would help.
It makes for a particularly dodgy looking broad immersed transom - i.e. the virtual appendage is approaching the length of the vessel.

Any feedback gratefully recieved

Dan