I was recently asked about the use of the VRML model created via MapIt and the PictSolid representation of the hull as tools for verifying the acceptability of the SHCP hull form offset surfaces you are creating/examining.  Let me say right up front: Those two surface oriented representations of the SHCP hull SHOULD NOT be used to verify the proper construction of your hull offset surfaces.  There are several reasons for this but suffice it to say that these surface models are only intended to help the user better visualize the model as it has been constructed.  The Picture wire-frame model representation is sometimes difficult to interpret and the surface conversions via VRML and PictSolid help ease this viewing problem.

How Should I Verify My SHCP Offset Surfaces?

The tools you need for verification are all available via SHCP graphics themselves.

1. We assume you have built the offset surfaces according to the SHCP rules.  The Picture program will help you visualize how well you are doing as you are building your station based surface.  It is more forgiving of mistakes that occur during development.  The EditSect software will also help you build, modify and check your station data.
2. Once you are ready to verify your surfaces, build your SHCP input file, turn on the body plan and isometric plots, add HYDRO drafts from low to high to cover the entire draft range of your surface(s).
3. Turn on waterlines, composite sectional area curves, and hydrostatics plots in the HYDRO module.
4. Run SHCP and review the plotted results.
5. The body plan plot shows you how well your stations represent the stations you wanted.  The isometric plot shows you how well you have located your stations to accommodate areas of substantial  vertical and horizontal change longitudinally in your hull surfaces.  But a good looking body plan and isometric plot are not (typically) sufficient to verify correct construction of your offset surface model which are typically comprised of multiple offset surfaces.
6. Review the waterlines, composite sectional area curves, and hydrostatics plots created via the SHCP HYDRO module.  The waterline endings for ‘inside’ and ‘outside’ surfaces should match.  The composite sectional area plot (not just the sectional area plot of the main hull) should show the same or increasing volume (area under the curve) for the entire longitudinal extent of each curve.  There should be no higher draft curves dropping below previous draft curves.  None of the curves should show any negative values (all curves above the horizontal axis).  There will be regions of no increase when a part becomes fully submerged.  The plot of hydrostatic values should look reasonable.  Be careful NOT to specify HYDRO draft values exactly at heights where the surfaces are flat (flat of bottom, flat aft sections, flat well decks, etc.).  Instead, specify drafts just below and just above these flat spots.  In this way you will capture the effects of the rapid waterplane transition without confusing SHCP.

If everything looks good, then you are ready to proceed with the next part of your data creation or analysis.