Decks are very similar to transoms in that a deck also closes the hull. Usually in Maxsurf you do not want to model a fillet radius between a deck and the hull (that is unnecessary detail for hydrostatic calculations) and therefore a deck is added to a model using trimming in most cases.

One of the advantages of using trimming when adding a deck is that the deck can be shaped completely independently from the hull and have completely different properties (i.e. stiffness). If you were to use bonding the deck and the hull would have to share the same degree of stiffness in the longitudinal direction (you will learn this later). Some examples of a deck that has been added using trimming:

The deck of this bulker has several step ups at the poop deck and F’castle. Several hatch coamings, cranes and a superstructure have also been added and are also trimmed to the deck.

The deck of this sailing yacht has camber in transfers direction and has a cockpit opening trimmed out as well as a coachroof on top of it. All this is very easy to do with trimming.

In the previous section you learnt how to use trimming to trim the hull to a transom. In this section we will practice what you have learnt and insert a deck surface as well as bowthruster.

A bowthruster is a cylindrical opening in the hull. A bowthruster can be modelled for different reasons:

1.      Realistic rendering or image of the design. Use highest precision to get best rendering results.

2.      The production geometry. In particular the intersection line of the cylindrical bowthruster surface and the hull.

3.      Hydrostatic volume of the hull. The volume of the bowthruster is not part of the buoyant volume of the hull. Hydrostatic calculation software, such as Hydromax, use transverse sections to calculate the volume of the hull. The volume of the bowthruster is calculated using the same transverse sections as for the hull. Since the hull is generally much bigger than the bowthruster and the spacing of the transverse sections is dependent on the length of the hull, the bowthruster volume can not always be calculated accurately because there are only a few sections intersecting the bow thruster.

200 transverse sections along the length of this Containership.
Only a few intersect the bowthruster.

The curve of areas only uses up to 36 transverse sections.  The volume of the bowthruster can not be seen in the curve because none of those sections intersect the bowthruster.

When an accurate hydrostatic volume is required, it is recommended to model the bowthruster as a non-buoyant volume compartment in Hydromax rather than using trimming to create an opening in the hull.

In this section of the training document we will insert a cylindrical shape that consists of two half-cylinders. Then we will trim that to the hull and visa versa in order to get a produce a rendering of the hull.

 View a video that shows you how to quickly model a step in a deck surface, insert a bowthruster and use right click trimming. [Web | Disk]

Ø  Use the model from the previous section or open MyFirstDesign_TrimmingTransom.msd

Ø  Save the model as MyFirstDesign_TrimmingComplete.msd

Ø  In Profile view, lock all surfaces, display Buttocks and switch trimming on (Display | Trimming | Trim Invisible).

You should see something like this:

Start with adding a deck surface:

Ø  Surfaces | Add Surface | Waterplane

Ø  Using the Assembly Pane (View | Assembly) rename the Waterplane à Deck

Ø  Use a Selection box and drag the control points down

Ø  After dragging them down (1), Move the aft edge of the Deck well Aft of the transom (2) and extend the fwd edge of the Deck beyond the bow (3)

Ø  Insert two rows of control points

Ø  Model the Deck surface so that it looks like this. Keep using the Selection box every time you move the control points, else it will become a mess quickly!

Ø  Display intersections

Ø  Switch to Plan view:

Ø  Drag the outer edge of the Deck surface well beyond the maximum beam of the hull. Tip: Use a selection box and hold the shift key down while dragging outwards so that the control points do not move fwd or aft unintended.

Deck surface extended well beyond Hull surface to form a closed intersection.

You are now ready to trim the Deck surface to Hull and Transom, the Hull to the Deck and Transom, and the Transom to the Deck and Hull.

Ø  Use Plan view to trim the Deck

Ø  Use Body Plan view to trim the transom

Ø  Use Profile view to trim the hull

Ø  Use Perspective view to check your work:

The black lines along the edges of the Transom and Deck become visible when the surfaces are unlocked.

Ø  Save your design

We are going to insert a cylindrical bowthruster with a 1m radius (not very realistic, but makes it more visible) and then trim the hull to the bowthruster and visa versa. Rather than creating a cylindrical surface ourselves, we’ll use the inbuilt shapes generator in Maxsurf:

This dialog automatically generates a cylindrical shape of any size in any orientation.

Ø  Lock all surfaces, Hide intersections

Ø  Surfaces | Add Shape | Cylinder

This brings up the dialog above.

Ø  Set the Orientation to Transverse, specify a 6 m length, a 1m radius and tick the Symmetrical half model on Centreline model option. You do not need to close the ends of the bowthruster.

Ø  Click OK

More information on the Add Shapes command can be found in the Surface Operations section in the Maxsurf manual. It is not necessary to read that at this stage.

Ø  In the Assembly Pane, rename the assembly called “Transverse Cylinder” à “Bowthruster”.

Ø  Open the Bowthruster assembly folder and notice that there are 2 surfaces in there:

Ø  Making sure you have the Net displayed and using a selection box, drag all control points to the bowthruster position (use your own creativity, but preferably below the waterline).

We’ll now use perspective view to trim both surfaces to each other:

Ø  Switch to Perspective view, rendering off, hide buttocks, display intersections

Ø  Lock the Bowthruster assembly using a right click command:

The Assembly tree allows you to lock groups of surfaces.

Ø  In Perspective window, zoom in to the bow and rotate your model so that you can clearly see the intersection line and the bowthruster surface edges:

Ø  Now select the Hull-Bowthruster intersection line with your left mouse button and then use right click trimming on the Intersection line:

Right clicking on the intersection line is a quick way to trim both surfaces

Ø  Trim the Hull, the Cylinder Top and the Cylinder bottom surface

Trimming the hull by clicking inside the Intersection region with the bowthruster

When you are done trimming, your model should finally look like this in Rendered Perspective view:

You may notice some rectangular rendering around the cylindrical opening. This is purely a rendering/drawing artefact and nothing to worry about; it will not influence any calculations.

Ø  Switch to highest precision to improve the quality of the rendering.

Ø  Save your design as MyFirstDesign_TrimmingComplete.msd

Finished!

Continue with the section on When Not to Use Trimming.