Trimming a transom

Trimming a transom – Concepts

A transom can be added to a design in two ways.

§   Bond the transom to the hull

§   Intersect the transom with the hull and trim the surfaces

 

The recommended method is dependent on the shape of the transom and the transom-hull transition. For example:

 

 

The transom is blended into the hull with a fillet radius. In this case it is impossible to use trimming and you should use bonded surfaces.

 

The transom on this ship almost literally cuts off the hull. In these cases trimming is recommended.

 

In some of the sample designs supplied with the program, you will see examples of ships that have no transom at all. A model does not “need” a transom when:

- the model is used for hydrostatic calculations

- transom shape is planar
- transom orientation is vertical and orthogonal to the centreline.

 

In general it is good practice to close the model completely (adding a transom and a deck to make it a “closed box”).

Trimming a transom – Video

* View a video that shows you the use of trimming after inserting a transom surface. This video also shows how the trimmed surfaces automatically update to changes in surface shape or position. [Web | Disk]

Trimming a transom – Procedures

In this section you will insert a 2nd surface in your MyFirstDesign model and use that as a trimming surface to trim the hull to a transom.

Ø  Open MyFirstDesign.msd and Save it as MyFirstDesign_TrimmingTransom.msd

Ø  Lock the Hull surface

Ø  In Profile view window, Insert a Section plane surface from Surfaces | Add Surface:

Ø  Change the name of the Transverse surface to “Transom”

Ø  Show the Net, Hide all Contours except edges,  and Display | Contours | Intersections or use the  toolbar button

Ø  Drag the control points to as displayed in the image below:

You may have noticed that there are two corner control points directly behind each other in Profile view and thus they appear to be only one control point. Use the selection box to make sure you select both:

Ø  In Plan view, drag the outer column further outwards:

You can see the intersection line (red in the image above) dividing the hull into two separate regions. This means you are now ready to trim the hull. If you refer back to the Trimming – Concepts

Trimming Sequence on page 18 you’ll see the steps we have to take:

Ø  Step 1: Switch trimming on: Display | Trimming | Trim Invisible

Ø  Step 2: Select the Surface to trim. There are several ways to do this, but the fastest way is probably by right clicking on the intersection line and select Start trimming Hull:

This will highlight the currently visible (read: “untrimmed”) regions of the selected surface. There are 2 regions separated by the Intersection line.

Ø  Step 3: Select trimming region: Click inside area 1. This will hide this area (read: “this will trim away this area”).

Ø  Step 4: Trim the Surface: There are also many different ways to do this step, but probably fastest is to either hit “Ctrl+T” on your keyboard or right click anywhere in the screen and select “Trim (Ctrl+T)”.

Ø  Switch to Rendered Perspective view to check your work:

The transom is not making the model look very nice at the moment. You can trim away the surface completely:

Ø  This time Right click on the Transom surface in the Assembly tree and select “Start Trimming”:

Ø  Go through steps 2, 3 and 4 to completely trim the Transom away.

Note: You may have noticed that you could not select different regions on the transom. This is because the intersection line does not form an enclosed region. Trimming the Transom only “hides” the trimmed region of the Transom. The surface is still there and the trimming can be undone at any point.

 

Now let’s make the shape of the transom a little bit more interesting:

Ø  In Body Plan view select this control point:

 

And then insert a Row of control points here:

The reason for first selecting the control point in the Right Top corner is that otherwise you may get unexpected results when inserting this row such as:

Ø  Switch to Profile view and drag the control points backwards:

Ø  Check again in Perspective view:

Notice that the shape of the trimmed hull has automatically been updated to the new shape of the Transom. As long as the intersection line between the surfaces remains intact (read: closing off the trimming regions) you can make changes to both the hull and the transom and the trimming will automatically update.

Ø  Try moving the Transom Fwd and Aft and check that the trimming is updated continuously. The best way to do this is probably in Profile view with Buttocks displayed.

 

 

 

 

The advantage of using trimming is that you can fair the hull surface and model the shape of the transom completely independently. This gives you a great freedom of what shape you wish to make the transom. It does mean that you have to extend the hull aft of the transom. For example if you wish to model a 40 m yacht, you will have to model a hull of 41 m long and insert a transom surface 1 m fwd of the Aft Extremity of the hull.

 

Congratulations! You have performed your first trimming operation. In the next sections we will practice this some more by also inserting a deck surface and a bowthruster.

 

Continue with the next section Trimming a Deck and a Bowthruster.