The final Boat Manufacturing NESHAP regulates fiberglass boat and
aluminum recreational boat manufacturing operations. The emissions
from these boat manufacturing operations and processes are fugitive
in nature. Fugitive emissions result from HAP evaporating from the
resins, gel coats, solvents, adhesives, and surface coatings used
in these processes.
See the Highlights
Fiberglass Boat Manufacturing Operations
Thousands of products are manufactured from reinforced plastics.
Examples include hulls for recreational and commercial watercraft;
bodies for recreational vehicles; building panels, sporting equipment,
appliances, and power tools; bathtub, shower, and vanity installations;
automotive, aerospace, and aircraft components; and structural
components for chemical process equipment and storage tanks. The
fiberglass reinforcing in these plastic products improves their
structural strength and rigidity, as well as providing high heat
resistance and nonconductive properties.
The U.S. boat manufacturing industry produces a wide range of
boats, from small canoes and kayaks to large luxury yachts. Basically,
the boat manufacturing industry can be divided into eight separate
boat segments according to boat size and location of the engine.
They are:
Outboard Boats:
Small to medium-sized boats, powered by a self-contained detachable
engine, which is attached to the transom at the stern (rear)
of the boat. This category of boats includes most runabouts,
bass boats, utility boats, offshore fishing boats and pontoons.
Personal Watercraft (PWC):
Small boats (most under ten feet long) powered by water jets
instead of by an open blade propeller, on which the rider
stands or sits (as on a motorcycle).
Inboard Runabouts:
Mid-sized boats powered by an attached engine located inside
the hull at the middle or front of the boat, with a prop
shaft running through the bottom of the boat. Over 90% of
the boats in this category are tournament ski boats.
Jet Boats:
Small to mid-size boats powered by water jets rather than a
gas or diesel motor. The jets can be located at either the
stern or inboard.
Sterndrives:
Mid-sized boats powered by an attached inboard engine combined
with a drive unit located on the transom at the stern (rear)
of the boat. Also known as inboard/outboards or I/Os.
Canoes:
Small boats powered by hand-held paddles.
Inboard Cruisers:
Large boats powered by one or more inboard engines. Two engines
are found in over 95% of these boats.
Sailboats:
This category of boats includes all sizes of boats powered,
at least partially, by wind-driven sails. This category includes
both nonpowered sailboats and auxiliary-powered sailboats
that include a motor.
Fiberglass boats are built from glass fiber reinforcements laid
in a mold and saturated with a polyester or vinylester plastic
resin. The resin hardens to form a rigid plastic part reinforced
with the fiberglass. The resin is mixed with a catalyst, as it
is applied, that causes a cross-linking reaction between the resin
molecules. The crosslinking reaction causes the resin to harden
from a liquid to a solid. Fiberglass manufacturing processes are
generally considered either ‘‘open molding’’ or ‘‘closed
molding.’’ In open molding, fiberglass boat parts are
built ‘‘from the outside in’’ according
to three basic process steps:
The mold is sprayed with a layer of gel coat, which is a pigmented
polyester resin that hardens and becomes the smooth outside surface
of the part.
The inside of the hardened gel coat layer is coated with
a ‘‘skin
coat’’ of chopped glass fibers and polyester or vinylester
resin.
Additional layers of fiberglass cloth or chopped glass fibers
saturated with resin are added until the part is the final thickness.
Open Molding
In the open molding process, the surface of the mold is polished
and coated with a wax, which allows easy removal of the finished
product from the mold after curing. Next gel coat, consisting of
unsaturated polyester resin, catalyst, and pigments, is sprayed onto
the waxed mold. This forms the outer, visible surface of the boat.
After the gel coat is fully cured, fiberglass reinforcing material
saturated with catalyzed polyester resin is applied over it. Two
common methods of application are:
Chopper gun (spray coat) - the resin, catalyst and fiberglass strand
are fed into a gun, and the fiberglass is chopped into short segments
and sprayed with the resin into the mold;
Hand layup - the resin is catalyzed, then brushed on to layers of
glass mat or roving which have been hand fitted into or over the
mold.
Air bubbles and other imperfections are removed by hand with rollers.
Tools are cleaned periodically of resin, using acetone or a substitute
cleaner before the resin begins to polymerize.
Styrene is emitted both during the application stage when gel coat
or resin material is applied to the mold and during the post-application
period when the material cures. Most boat building facilities use
high ventilation rates to ensure that styrene levels are below the
100-ppm worker exposure limit established by the Occupational Safety
and Health Administration (OSHA). Dilution increases the volume of
contaminated air and, because the cost of an add-on emission control
system is a strong function of the total air flow, these diluted
air streams are more costly to control.
Some facilities designate certain areas for gel coat or resin spraying
to reduce the contamination of plant air. In these cases, a spray
booth equipped with a dry filter medium may be used to reduce particulate
emissions, but diluted styrene emissions are typically vented directly
to the atmosphere. Spraying emissions can be controlled through spray
gun pressure calibration, operator training and overspray containment.
To review, some of the major steps in making open mold-based products
are:
In closed molding, the resin is applied to fabric placed between
the halves of a two-piece mold. Three basic types of closed molding
used in boat manufacturing are resin infusion molding, resin transfer
molding, and compression molding with sheet molding compounds.
Emission Considerations
The polyester and vinylester resins that are used in fiberglass
boat manufacturing contain styrene as a solvent and a cross-linking
agent. Gel coats also contain MMA (methyl methacrylate) as a solvent,
and styrene. Styrene and MMA are HAP, and a fraction evaporates
during resin and gel coat application and curing. Resins and gel
coats containing styrene and MMA are also used to make the molds
used in producing fiberglass parts.
Mixing is done to stir the resin or gel coat and promoters, fillers,
or other additives before being applied to the parts. Some HAP
from the resin and gel coat are emitted during the mixing process.
Resin and gel coat application equipment requires solvent cleaning
to remove uncured resin or gel coat when not in use. The resin
or gel coat will catalyze in the hoses or gun if not flushed with
a solvent after each use.
Organic vapors consisting of volatile organic compounds (VOC)
and HAPs are emitted from fresh resin surfaces during the fabrication
process and from the use of solvents (usually acetone) for cleanup
of tools, molds and spraying equipment. Organic vapor emissions
from fiberglass fabrication processes occur when the polymerizing
agents and solvents contained in the liquid resin mix evaporate
into the air during resin application and curing. State-of-the-art
techniques can economically recover solvents in concentrations
above 70 ppm through activated carbon adsorption. However, styrene
can polymerize on the carbon and deactivate the adsorber. When
solvent vapor reclamation is not feasible, thermal oxidation of
the solvent emissions can be conducted with an oxidation efficiency
exceeding 97 percent, although the cost per ton of VOC is quite
high. There also may be some particulate air emissions from automatic
fiber chopping equipment.
Fabric and Carpet Adhesive Operations
The interiors of many types of fiberglass boats and aluminum recreational
boats are covered with carpeting or fabric to improve appearance,
provide traction, or deaden sound. The material is bonded to the
interior with contact adhesives. These adhesives often contain
HAP solvents, such as methylene chloride, toluene, xylenes, and
methyl chloroform (1,1,1-trichloroethane). The solvents evaporate
as the adhesives dry.
Aluminum Boat Manufacturing
Aluminum Recreational Boats Surface Coating
Aluminum is also used in manufacturing a large portion of smaller
boats, such as rowboats, canoes, and freshwater utility and fishing
boats. Aluminum is used because it is lightweight, durable, and
low maintenance. Steps in manufacturing process may include:
Parts cutting and bending
Metal part assembly
Surface preparation
Surface coating
Flotation foam pouring
Carpet installation
Final assembly and rigging
Aluminum recreational boat hull topsides and decks are painted
with coatings applied with spray guns. These coatings may be high-gloss
polyurethane coatings or low-gloss single-part coatings. These
surface coatings often contain HAP solvents, such as toluene, xylenes,
and isocyanates.
Thousands of products are manufactured from reinforced plastics.
Examples include hulls for recreational and commercial watercraft;
bodies for recreational vehicles; building panels, sporting equipment,
appliances, and power tools; bathtub, shower, and vanity installations;
automotive, aerospace, and aircraft components; and structural
components for chemical process equipment and storage tanks. The
fiberglass reinforcing in these plastic products improves their
structural strength and rigidity, as well as providing high heat
resistance and nonconductive properties.
Fiberglass boats are built from glass fiber reinforcements laid
in a mold and saturated with a polyester or vinylester plastic
resin. The resin hardens to form a rigid plastic part reinforced
with the fiberglass. The resin is mixed with a catalyst, as it
is applied, that causes a cross-linking reaction between the resin
molecules. The crosslinking reaction causes the resin to harden
from a liquid to a solid. Fiberglass manufacturing processes are
generally considered either ‘‘open molding’’ or ‘‘closed
molding.’’ In open molding, fiberglass boat parts are
built ‘‘from the outside in’’ according
to three basic process steps:
Styrene is emitted both during the application stage when gel coat
or resin material is applied to the mold and during the post-application
period when the material cures. Most boat building facilities use
high ventilation rates to ensure that styrene levels are below the
100-ppm worker exposure limit established by the Occupational Safety
and Health Administration (OSHA). Dilution increases the volume of
contaminated air and, because the cost of an add-on emission control
system is a strong function of the total air flow, these diluted
air streams are more costly to control.
Organic vapors consisting of volatile organic compounds (VOC)
and HAPs are emitted from fresh resin surfaces during the fabrication
process and from the use of solvents (usually acetone) for cleanup
of tools, molds and spraying equipment. Organic vapor emissions
from fiberglass fabrication processes occur when the polymerizing
agents and solvents contained in the liquid resin mix evaporate
into the air during resin application and curing. State-of-the-art
techniques can economically recover solvents in concentrations
above 70 ppm through activated carbon adsorption. However, styrene
can polymerize on the carbon and deactivate the adsorber. When
solvent vapor reclamation is not feasible, thermal oxidation of
the solvent emissions can be conducted with an oxidation efficiency
exceeding 97 percent, although the cost per ton of VOC is quite
high. There also may be some particulate air emissions from automatic
fiber chopping equipment.