Man-Hrs for Steel Hull Construction (part 2)
Now picture building the single-chine hull shells in a the 'frameless' construction method, Ie,....'plate first, frames second' pictured here:
This should be even easier with the 'coaster style hulls', ...certainly even easier than the multi-chined sailboat hulls being built in these photos.
Mike Kasten presents a pretty clear explanation of the pros and cons of the frameless metal hull construction here:
Frames First or Plating First...?
For purposes of this estimate lets specify 6-mm hull plating of pre-primed steel for both the bottom and the topsides. The steel topsides will be extended up to just above the deck level, and there it will transition into honeycomb composite panels for the 'topsides railing' around the vessel. The upper edges of the steel hull-shell will provide a steel ledge all-around to support the composite main deck. The steel hull-shell will also provide supports for the tubular verticals that support the outer edges of the upper deck (saloon roof). Those details are yet to be specified, but hopefully will be relatively simple in design.
STRINGERS (& Fuel Tanks)
There should be 2 major stringers running about 2/3 the length of the vessel, from under the fwd stateroom aft to the bulkhead below the end of the saloon (just before the lazarette). These stringers will provide support for the single main engine and the generator unit.
There should be 2 each minor stringers to each side of the principle engine stringers. These minor ones may not be 'continuous' by their nature, as I anticipate two sizable internal fuel tanks to be built-in at the beam sides about midway of the hull's length.The inner vertical walls of these fuel tanks will act as stringers, and furthermore some internal baffle plates will act as hull-plate stiffeners also.
There should be 5 full bulkheads positioned down the length of the vessel. They should look something like this....
...with cut-out lightening holes and top flanges to support the composite deck panel. These bulkheads backup the stringer system, support the main-deck/ floor, and help maintain the firm width of the hull-shell at deck level.
Unlike the the Fla Bay Coasters & the Great Harbor Trawlers, this vessel will be a single-engine vessel with a single keel and a single rudder fashioned in a standard manor.
CNC CUT STEEL
All of the steel work will be pre-cut from computer files, and be of the pre-primed nature. The steel hull fabricator does NOT have to include the cost of this steel material in his estimate to 'construct' the hull-shell. BUT it would be VERY helpful if he could supply some estimates of this material costs based upon his past experiences?
As noted above the steel will come to the builder in a pre-primed condition rather than raw mill steel.
The hull fabricator will NOT have to be concerned with any type of finishing (painting, priming, etc) of the 'exterior' surfaces of the hull-shell,....other than touch-up priming of those spots he 'disturbs' when he tack-welds the hull plating to the jig support fixture.
However the fabricator will be responsible for the interior surfaces of the hull-shell. We seek to provide a really durable, easily maintained surface to bilge areas, the internal steel hull plating and framing. Its been recommended that all 'mating' pieces of steel (ie, stringers to hull plating, stringers to bulkheads, etc), be sealed with a polyurethane chalking such as Sikaflex or equivalent, to prevent moisture and air from getting at the undercuts, etc that might not be so easily coated with the final primer and epoxies that will be applied to these bilge areas.
The hull fabricator will be responsible for this full coating of primer and epoxy coating of the interior surfaces of the hull-shell, and shall also coat the interior surfaces of the built in fuel tanks and baffles prior to placing a top on them.