«Final May 20, 2000 Introduction Most boats have compartments inside their hull that serve to capture rain and seawater entering the hull of the boat. ...»
A review of the performance of bilge socks proposed for use in
Buzzards Bay recreational boats in response to a request for
proposals issued by the Buzzards Bay Action Committee and the
Town of Dartmouth
Joseph E. Costa, Ph.D.
Buzzards Bay Project National Estuary Program
May 20, 2000
Most boats have compartments inside their hull that serve to capture rain and seawater entering
the hull of the boat. These compartments also capture fuel and engine oil that may leak within the boat. Boats with fuel compartments, inboard engines, and drive shafts are far more likely to leak oil into these compartments. Maintenance of inboard engines can also result in spills into the bilge. Many bilges can drain automatically when a boat is in motion, but almost all boats have pumps to evacuate the bilge compartment to prevent boats from swamping. These pumps often turn on automatically when water levels rise too high in the boat. The pumping of bilge water laden with fuel and oil is an important source of oil to the marine environment and is often the cause of the oily sheen seen in some harbors or near some marinas.
In the fall of 1999, the Buzzards Bay Action Committee (BBAC) received a grant from the Massachusetts Coastal Zone Management office, through its Coastal Pollution Remediation Program, to provide free bilge oil absorption devices to recreational boaters in Buzzards Bay.
These devices are generally referred to as "bilge socks", "bilge pads", or "bilge pillows" depending on their shape. The purpose of this initiative was to raise the awareness of the boating community as to the significance of oil and fuel inputs from boat bilge compartment discharges.
Additionally, this initiative was meant to encourage boaters to use oil-absorbing bilge socks to capture this oil and fuel before it is discharged to the marine environment. The grant also provided funds for towns to pay for the establishment of collection sites for the bilge socks, and to pay for their disposal. The Town of Dartmouth, on behalf of the Buzzards Bay municipalities, administered the BBAC grant.
Most boats are expected to require one or two bilge socks during each boating season to capture oil and fuel leaking into their bilge compartments. While each boater would get their first bilge sock free through this program, the expectation is that when boaters see the value of the bilge sock, they will continue to purchase and use them on their own. Although it is believed that bilge socks are not widely used by Buzzards Bay boaters, their typical retail cost of $7 to $12 is not viewed as an impediment if their utility and value is recognized and understood. Another benefit of this program is that Buzzards Bay municipalities and private marinas will continue to provide disposal services for bilge socks.
At the request of the Buzzards Bay Action Committee, the Buzzards Bay Project provided technical assistance in the development of the request for proposals and the testing of the bilge socks. A foremost goal of the BBAC was to implement an easy, clean, and cost effective process for recovering bilge oil. Because of concerns about maintaining recycling equipment, OSHA requirements on operating recycling equipment, and permitting and liability issues that would be involved with keep used oil drums on docks, the use of reusable bilge socks was rejected.
Instead, single use socks that could be incinerated at conventional waste disposal facilities was the preferred type of product.
Besides desiring single use disposable socks, the BBAC had interest in a "no-mess" product that physically or chemically bound the oil so that when the sock was removed and transported by the boater, or when dozens of the socks were deposited in storage drum, oil would not seep from the
Response to Request for Bids Eleven companies submitted bids, but 3 of the companies did not submit products.
Based on the literature on the products provided, these products all appeared to be made of polyethylene adsorptive fibers. Of the remaining eight companies, several offered more than one product so that altogether 21 products were submitted. One of the products (a pad) was rejected outright because it did not conform to bid specifications, so that altogether 20 products were tested.
Of the twenty products tested, nine socks consisted of polypropylene fibers, two socks tested (actually one product in two sizes) contained a hydrocarbon absorbing foam, one product contained cellulose, four contained a plasticizing polymer, two had a plasticizing polymercellulose blend, and two socks (one product in two sizes) contained emulsifiers with purported bacterial treatment.
Evaluation Criteria To meet the performance goals identified by the BBAC, the Buzzards Bay Project proposed the
following design and performance criteria:
1) The absorbent device must be able to pass through a 3 1/2" inch diameter hole with a 12-inch clearance below the hole. This was meant to simulate small bilge compartments on some boats.
2) The device must have a rope with loop to enable its attachment and removal from within bilges, and to prevent the device from blocking bilge pumps.
3) The device must have a 1.5-quart hydrocarbon capacity.
4) The device does not drip or release oil under moderate pressure.
The manufacture also had to confirm that the product was of a material that would be accepted at conventional waste disposal incineration facilities in Massachusetts.
Materials and Methods The Town of Dartmouth and Buzzards Bay Action Committee performed tests with technical support and guidance from the Buzzards Bay Project. Len Gonsalves, Executive Director of the
A bilge compartment port size-test device was constructed as shown in the plans in Figure 2. The purpose of this device was to ensure that the product could be retrieved from boat bilge compartments with 3.5" openings after becoming saturated with hydrocarbons.
To evaluate hydrocarbon uptake capacity, one and a half quarts of hydrocarbons composed of 3 cups of engine oil (10W30) and Socks being placed in bins.
3 cups of diesel fuel were added to 10-gallon bins containing 7 gallons of fresh water. The bsorbent device was added to the bin and left for 3 days with 1 minute of stirring each day. The bins were kept in an unheated garage. Ambient temperatures in the garage during the test period were approximately 40-50 degrees F. The test site was kept locked and secure.
The device was retrieved after three days and any remaining oil was observed. After the three-day period, the device was evaluated if it passed the three performance tests (absorb 1.5 quarts, pass through the hole, drip test). To evaluate whether the devices released oil under moderate pressure, the absorbent device grasped firmly with two hands and was attempted to be twisted 180 degrees by hand. The individual performing this "twist and squeeze test" applied firm but not too exertive effort, so that even if the device became rigid and could not be twisted 180 degrees as attempted, it would receive about the same pressure as the other devices.
3 Results Table 1 summarizes the results of all tests. Five products overtly failed the 1.5-quart hydrocarbon absorption test.
Three of these conspicuous failures appeared to be the result of the fact that the products appeared undersized to adsorb the 1.5-quart oil-fuel mix volume. The two emulsifier socks failed to absorbed oil to any appreciable degree as claimed.
The manufacture of these products claim that the emulsifiers in the sock break down the oil into smaller droplets, and this oil is then broken down by bacteria in the sock so there is no waste oil to dispose of. The results of this test did not support these claims. Because of these overt failures, these products were not tested further.
Most of the remaining socks appeared successful in removing the 1.5-quart fuel-oil mixture.
There actually was some variability in oil uptake final performance in the form of some droplets at the surface, but these proved very difficult to quantify or characterize. The volume of this very small amount of residual oil could have also been influenced by the amount of mixing time and exposure to the sock. Because the remaining 15 socks did not overtly fail the 1.5-quart test, and could be judged to have taken up 95% of the oil, it was determined they passed the hydrocarbon absorption test.
Of the 15 absorbent devices that passed the hydrocarbon uptake test, only one did not pass the hole test. This device, a 4-inch foam cube (5.6" diagonal) could not pass through the 3.5 inch hole. This device also failed the squeeze test.
Of the 14 absorbent devices passing the hydrocarbon absorption and hole tests, 11 failed the twist and squeeze test. In particular, any bilge sock filled exclusively with adsorptive materials like polyethylene or cellulose easily failed the squeeze test. In fact, many of these products dripped a milky water-oil immersion when lifted from the test bins or when placed in trays. The two devices that were composed of polymer-cellulose mix did well in oil uptake, however, they still released oil in the twist and squeeze test. Only three devices passed the twist and squeeze test, and these were the only ones composed exclusively of plasticizing polymer compounds that physically or chemically bound the oil.
Conclusion and Discussion Only three devices passed all tests and criteria outlined in the Request for Bids. These bilge socks were the only ones composed exclusively of plasticizing polymer compounds. These
In presenting the findings of this study, the Buzzards Bay Project is not endorsing or recommending against any of the products tested.
Furthermore, the results of these tests should not be considered as invalidating the utility of any products tested in this study, or other comparable devices on the market. The test results in this report were developed to address some very specific needs identified by Buzzards Bay municipalities. For example, many of the oil adsorptive materials and bilge socks composed of polyethylene or other materials can be wrung out and recycled. Thus, these products, which tend to be cheaper than socks containing polymers, can be recycled and reused, and are cheaper for the consumer. If adequate recycling facilities are available, and if properly handled and bagged by the consumer, these products can have utility in many situations.
The only class of products evaluated in this study that have been found by others to be of questionable efficacy in protecting the environment are those products that contain emulsifiers.
Although some of these products are composed of natural plant-derived soap-like products, and are themselves biodegradable and non-toxic, their ability to emulsifier oil into small droplets may make the oil more harmful to marine life. In fact, the US Coast Guard and the US EPA expressly prohibit the use of soap products, like dishwashing liquid, to disperse oil spills.
Although some of these bilge products contain bacteria that purportedly digest the oil, there has been no independent substantiation of the decomposition of oil in the hours, days or weeks that oil may remain in a bilge compartment before it is pumped overboard. Some government agencies and environmental organizations have questioned the utility of emulsifying products in bilges. For example the Coast Guard and Fisheries and Oceans Department of Canada goes so far as to state "Bilge cleaners, even the biodegradable ones, merely emulsify or break down the oil into tiny, less visible droplets. This process spreads the fluids over a greater volume of water and severely inhibits all forms of marine life from mammals, to fish, to plants, to algae" (http://www.pacific.ccg-gcc.gc.ca/Epages/offboat/pae/bilges.htm).