Fishing Craft Technology

Unit 4 - Boat building materials and construction of boat

4.9.Construction of aluminium boat
Fabrication of aluminium hulls is carried out in the same manner as for steel construction. Forming and shearing of plate are carried out with presses and sheers as for steel, while cutting is accomplished with saws in a similar manner to wood, although knife blades and saws require special setting and teeth with gullets to clear chip dust. Bend radii are higher than those for steel and for most marine applications range from 2 to 5 the thickness of the plating depending on the alloy and temper used.
The keel is made of mild steel and over this a rubber coating is needed. As per the template design, Aluminium magnesium alloy pipes are fixed over the keel as a mould station (skeleton). The space between the pipes covered with aluminium magnesium alloy sheets by using argon arc welding unit. Te sheets that are attached to the framework should always overlap one another.
Two welding processes are used for the joining of aluminium such as the MIG (Metal Inert Gas) process and the TIG (Tungsten Inert Gas) process. This inert gas, shielded-arc processes are used exclusively for non¬ferrous metal fabrication. Small boats are usually constructed upside down over jigs with the relatively lightweight of the material facilitating the turn over process for outfitting and completion. Larger vessels are built upright and jigs can be used to facilitate the fitting and welding of hull plate:
Painting is not essential and hulls of fishing vessels are frequently left unpainted except for underwater, antifouling to prevent marine growth, aluminium to steel or wood joints for increased resistance to electrolytic corrosion, non-slip paint on decks, and internal surfaces in accommodation for aesthetic reasons. Where painting is required, the alloy surface is etched primed and painted with zinc chromate or chromate-phosphate chemical conversion coatings as a base coat. Selection and application of antifouling paints require special care. Anti fouling paints containing mercury in any form must not be used.