This section covers the construction of the aluminium hull and deck, starting with the fabrication of the frames.
The frames were built by welding pre-bent aluminium T extrusions into CNC-cut floors.
Each frame was manufactured on top of a full-scale drawing on a table with a precision tolerance better than 1 millimetre.
T extrusions were too strong to be rolled successfully. Instead, custom tooling adapted to a hydraulic pipe bender allowed shaping them.
Each frame was designed to interlock with the longitudinal girders like a giant jigsaw puzzle.
The cockpit was folded and assembled early to form the backbone of the stern module. More frames are awaiting to be installed to the bottom girders of the main section to form the next module to be connected. The bow section formed the last module.
Setting up must be performed with the utmost accuracy. Laser levelling with reference lines on each frame was used.
The roof top was plated first, holding the centreline of the frames into position, then the side-decks. Deck stringers were cut and added incrementally.
The composite bulkheads, pre-manufactured on a flat table, were inserted into place before hull stringers were added.
Plating proceeded fairly swiftly, starting from the areas without significant compound curvature, progressing symmetrically throughout. Plates are put into place, incrementally welded to the frames first and their edges finally trimmed and tack-welded from the outside. The butt seams are then fully welded from inside as the job advances.
Having a second set of hands on the job would have allowed working with one person welding inside the hull and another holding the plate in position from outside. The gain in efficiency would have been nothing short of phenomenal.
Nearly all plates were wheeled. Heat-treated marine-grade aluminium sheet is too stiff and strong to be pulled into shape on the framing. Most plates were half-a-sheet wide, or about 900mm.
The short curve is the most important one to obtain by rolling; the long curve can be progressively forced in to some extent, taking advantage of stress relief when welding. While somewhat crude, the wheeling machine was invaluable. Don’t even think about plating a round-bilge hull without forming the plates, or by using rollers and plating diagonally, as it was sometimes suggested to me.
Plating continued into the areas of heavy compound curvature – the turn of the bilge near the main beam – and the tight spot where the bottom meets the stem, using smaller, more manageable plates.
Staying on top of the job is essential as the slippery slopes become more pronounced! The ground is a long way down.
The bottom of the forebody was plated using a single piece, no seam on the centreline, one of the most difficult plates to shape and get into place, but still achievable as a one-man job.
The hull plates hang below the deck edge. After a lot of overhead welding, the toe rail was built by boxing between the deck and the hull plating with aluminium angle.
Finally, all the plate seams are gouged back from outside to reach the root of the inside run and flush-welded, resulting in a full thickness weld with a bead inside. MIG is the only suitable process for welding an aluminium hull due to limited heat input. While most photos were taken in daylight, a lot of the work took place late at night like here.
The open transom was the main access way to get in and out for welding. It was left open for as long as practical. I must have gone through literally hundreds of times while manufacturing the shell.
Filling and fairing is a dusty job and a good workout. It followed sandblasting and sealing the metal using an excellent anti-corrosive high-build epoxy primer. Epoxy resin and glass epispheres were used as low-density filler below the waterline, phenolic resin microballoons in the topsides as they were supposedly easier to sand. There was no difference sanding either filler and epispheres were a much better and cheaper product.
Fairing amounted to an average of 2-3 millimetres. No sandblasting photos as there isn’t a minute to waste between blasting and sealing the surface.
A startling amount of high-build epoxy primer was literally poured out of the spray gun onto the faired hull to encapsulate the filler. The bottom was then sanded again smooth, primed with more high-build epoxy and a single thin tie-coat of hard antifouling was sprayed on. There is nothing worse than having to sand a hull from underneath. This approach ensured that the antifouling would later be able to be sprayed following a simple high-pressure wash.
The last task before turning the hull over is test-fitting the hollow keel foil into its slot. It is much easier to play with the 200kg foil up there while trimming the slot than repeatedly raising and lowering the entire shell over the keel later.
First look down-below, into a little world now upright for the first time. The hull was rolled over in slings between chain blocks. One of the first tasks coming up was now etching and painting the bilge plating up to the waterline with high-build epoxy primer. All alloy vessels should have painted bilges, even more so commercial workboats that are seldom as dry and clean. It saves having to deal with pitting issues down the track.
Some areas of the roof were not able to be plated until now, as steel supports were coming through from the ground. It was also good to be able to close this deep hole before falling into it. Later, I instead elected to fall through a large hatch opening covered by a tarp – without much in the way of adverse results.
The roof sides can now be plated. At first, the roof was plated to hard edges, but the seams were not welded.
Finishing involved re-cutting the edges in place and forcing in a split section of pipe to achieve radiused corners and soften the shape. Windows were cut and frames added, the sliding hatch constructed, hatch openings cut… At this point, a lot of the deck hardware needs to be available already in order to be fitted.
Building good sliding hatches is a renewed challenge each time. The hatch must be able to resist considerable flooding from above, operate well and ideally never wear out its slides.
Completed deck plane. Cleats were anchored through the deck into the frames and machined stanchion bases welded in. There is nothing worse than through-bolted stainless steel stanchion sockets on an alloy boat. The roof top hand-railing is also integral to the construction.
Construction of the appendages is described here.