MultiSurf – relational geometry

MultiSurf is AEROHYDRO’s advanced marine design application, a parametric 3D, relational surface design program. It enables you to design any kind of boat, yacht and ship, from hard-chined dinghy to big sailing and motoryacht, cargo vessel, multihull ferry, offshore patrol craft, etc. If you can draw it, you can model it - in MultiSurf .


MultiSurf – precise control of complex geometries

One of the unique aspects of MultiSurf is its support of a variety of different point, curve, and freeform surface types. This variety gives you wonderful freedom to pick the right tool for each job.


MultiSurf – complete and flexible design

Due to the wide variety of curve and surface kinds you can create models with unlimited depth of detail and complexity, while at the same time maintaining relational editability and bi-directional associativity. If you can draw it, you can model it in MultiSurf . Traditional longkeel hulls, stepped bottoms, vanishing chines, "constant radius" hulls, multi-chine hulls, decks, superstructure, keel, rudder, internal structure, tanks, rigs and so on. You, the designer, decides, if hollow waterlines in the bow are intentional, not the program with the one surface type available.


MultiSurf – design iteration by Relational Geometry

Design is a complex iterative process with many cycles of visual evaluation and refinement. This process is made much easier with the relationships between entities that you can establish in MultiSurf with its unique system of Relational Geometry (patented).

Moving a single point moves the entire frame, which adapts to the cross section shape while maintaining its principal dimensions.

Change the hull shape and all frames adapt automatically

  • MultiSurf is parametric: by variation of few parameters a family of geometric similar forms is created. A concept is fast to modify, without requiring that the whole model must be rebuild from the beginning.
  • MultiSurf is associative: by changing a supporting point or curve all dependent points, curves and surfaces are automatically updated.
  • MultiSurf is relational: defined relations between entities are maintained throughout editing
    • absolute und proportional spacings
    • angular positionings
    • mirror and rotational symmetry (design one side of the ship, or one propeller blade)
    • constraint of points to lie on curves or surfaces
    • constraint of curves to lie on surfaces (design prominent curves directly instead as intersection of two sur faces)
    • accurate, durable watertight joins between surfaces
    • automatically maintains specified relationships throughout the design cycle



Change your mind at any time

Everything is editable. Every entity depends on other entities. Points define curves, curves define surfaces, surface define solids. When you change an underlying entity, the entire model is automatically updated.

For example, when you drag a defining point of the stem curve of your hull, then the hull shape is changed immediately, also the cross section, the waterlines, buttocks. You can see directly the change in displacement, the shift of the longitudinal center of bouyancy and so on. In short time you can try many design variations to achieve a better result.


27 m passenger vessel with hull and deckhouse structure. Changes to the geometry envelope are possible with Relational Geometry even in the late design stage. (by courtesy of CL Shipdesign)


MultiSurf – Procedural Curves and Surfaces

MultiSurf offers procedural curves and surfaces as user-defined entities. You create one typical point (or curve) of the procedural entity and MultiSurf repeats the creation procedure for all positions of the parents.

Rudder design with Procedural Surface – the moving curve in spanwise direction is a Naca section, defined by cutting the trailing edge, leading edge and thickness distribution curve. The cutting plane is normal to a guiding curve that accounts for the change of inflow direction near the bottom of the hull. Thus the local water flow “sees” true Naca foil sections.



Procedural Surface construction:

Deck with constant radius deck beams (thus a single jig will be required when laminating beams)

The moving curve is part of the camber template, cut off at the local sheer position.




Procedural Surface construction:

Deck with constant camber deck beams

The moving curve is an arc; its camber is a user specified percentage of the deck width at the local sheer position.



In MultiSurf you can create curves on surfaces - for example to serve as paths for longitudinal frames. Using Procedural Curves a path can have a fixed distance to a surface edge or to other paths, or the surface can be equally divided automatically.

When you change the surface, the absolute and proportional spacing is maintained, thus the longitudinal frames adapt automatically - no need for re-arrangement and correction.



Clinker boat hull – plank lands defined by Procedural Curves, a fast and effective way to achieve constant width of lands.



MultiSurf – Formulas and Variables

MultiSurf features variables and formulas for powerful applications – define dimensions of entities, user defined foil sections, check geometry against class rules, show main dimensions, etc.

Example: define rig and sail dimensions by variables and see how sail areas, centroids, lead will change, when dimensions are modified.


Or use Hydro Reals formulas and MultiSurf will balance weight and bouyancy with free trim at given heel.

So while you shape the hull form, you can see heeled waterlines with the true flotation waterline. Also convenient for checking transom immersion.



MultiSurf – Components

Portions of a geometry model can be saved as component and inserted into other models for re-use.


MultiSurf – OLE Automation Server for macro programming

MultiSurf exposes its objects through OLE Automation to provide the advanced user with very powerful capabilities. Program macros enables to:


MultiSurf – Marine design tools

  • Mass Properties - tabulates areas, centers of gravity, and moments of inertia for surfaces; arc lengths, centers of gravity, and moments of inertia for curves and contours
  • Weight Schedule - total weight, centers of gravity, and moments of inertia for model (calculated from unit weights you assign to objects)
  • Hydrostatics - upright hydrostatics (dimensions, displacement, water plane, wetted surface, coefficients) from input of specific gravity, ZCG, sink, trim, and heel
  • Ship Lines - body plan, plan, and profile views of model; six layouts
  • Offset Table - standard offset table in decimal units or feet-inches-eighths through the ExportOffset Table utility.


MultiSurf is supplemented by further AeroHydro programs:


MultiSurf module structure:

The basis program is MultiSurf Solo. With C-spline- and B-spline-surface for free-forming, true developable surface, ruled surface, rotational surface, translation and swept surfaces the most often used point, curve and surface types are available. Further hydrostatic and weight calculation, offset table output and ship lines are supported. The upgrade modules Advanced Modeling (providing the full set of point, curve and surface type, for example procedural curve and surface), Hydro (hydrostatics und intact stability), Flattener (expansion of compound curved surfaces and true developable surfaces) and SolidWorks Integration make it possible to put together the most convenient configuration and extend it.