Tug Madeline - Lofting and Creation of Parts and Plates

In the fall of 2006, Bay Marine, Inc., in Barrington, RI, hired Oak Hill Marine Design to provide CAD data for the detail design of an 80' tug. The hull design incorporated several chines, a large skeg, and twin Z-drives aft. The superstructure consisted of a deck house with a faceted pilothouse.

Wilmington Tug MadeLine Wilmington Tug's MadeLine - The finished vessel underway. (Photo by Thomas Birk)

Working with AeroHydro's MultiSurf and an included macro, we translated the original designer's AutoCAD-format 2D lines into plan, profile, and section line-strings in MultiSurf. We then matched these with 3D B-spline curves, using those as edges for the hull, skeg, and main deck surfaces. The resulting lines were checked and approved by the designer.

With the basic shape of the hull model modeled, we created the internal structure, including sections for transverse bulkheads and frames of differing thicknesses, longitudinal stiffeners and girders, and angled stiffeners and frames. Skeg diaphragms were also modeled, with one side of each trimmed to accept a flat bar for plug-welding the plating.

Since the vessel would be built in modules, break lines and extended plate edges were added to the model. These, along with structure molded lines and reference water lines were exported on the expanded plate shapes, which went to Bay Marine as CAD files to be detailed for CNC cutting.

Hull Plates Hull Plates - Expanded surfaces of the hull plates. All include provision for corner-to-corner joints, butts, etc., so edge trimming is minimal.

Structural sections, along with plan, profile, and fore and aft views of plates in place were sent to Bay Marine for use in construction drawings.

The vessel's fore and aft decks had to be cambered fore and aft, as well as port to starboard. Each deck was modeled in MultiSurf as a continuous surface, then individual plates were laid out on each surface. Wherever possible, these plates were dimensioned so as to be 20' x 8' after expansion with AeroHydro's FlattenerTM application. The deck plates varied in thickness, but this was automatically taken into account in the plate expansion.

Deck Plate Arrangement Fwd Deck Plates Fwd Deck Plates Mid Deck Plate Arrangement Fwd, Deck Plates Fwd, and Deck Plates Mid

The aft deck not only had plates of different thicknesses, but it also had insert plates for additional strength. All plate outlines were overlaid on the basis surface then, exported as expanded surfaces, complete with frame and longitudinal molded lines.

Deck Plate Arrangement Aft Deck Plates Aft Deck Plate Arrangement Aft, Deck Plates Aft

The superstructure consisted of a deck house with pilothouse above. The deck house front had angled corners and inward sloping surfaces above the window line. It also had internal ducts and stairwells which required modeling, as they were all part of the deck house structure.

Deck House Wireframe Deck House Wireframe - A view of the 3D deck house model, showing the angled surfaces on the front, sides, and rear, intakes, and internal bulkheads. Deck house structure is also shown, including tees, flat bars, and cut plates.

The pilothouse front, sides, and rear sloped outward from bottom to top, then sloped inward toward centerline for an upper set of windows. Aft, the plating was framed with flat bar and cut plates; tee stiffeners were installed forward, located on the plate intersections. We modeled the plate shapes, exporting them for CNC cutting, as well as the tees. The latter provided us with cut lengths and angles for the builder.

Pilothouse Wireframe Madeline Pilothouse Pilothouse Wireframe, Madeline Pilothouse

As usual, we provided Bay Marine a wireframe model for hydrostatic analysis, and offset tables of the hull and superstructure for the builder's use when erecting the frames.

Background photograph by Alison Hudson