Moby Duck Tours
Letter Mail Controlled 04/17/2000 4:26:27 PM MC# 2000546 1. Please accept the enclosed letter from our naval architects as our formal response to your correspondence of 2-18-00:
(John W. Gilbert Assocs. On behalf of Moby Ducks, wrote):
It is our opinion, based on over 35 years of experience designing U. S. Coast Guard certified passenger vessels, that the NTSB has rushed their recommendations out to the industry without proper consideration of the different types of amphibians in operations, the practicality of installation of the recommendations, and even the possible conflicts of their recommendations with existing safety regulations.
The U. S. Coast Guard determined in their Marine Board of Investigation Report that the World War 11 era-built DUKW "Miss Majestic" sank in Arkansas in May, 1999 due to a specific flaw in the vessel's drive shaft sealing system. Contributing to the sinking and loss of life was the failure of the vessel's main bilge pump, distraction of the vessel operator by tour-guide duties, lack of required bilge-level alarms, lack of positive flotation or watertight bulkheads, and entrapment of the passengers under the awning and windshield after the vessel sank.
The U. S. Coast Guard Marine Board of Investigation produced a 13 item list of recommendations dealing with improvements to the DUKW'S, modification to inspection procedures, requirements for further crew training, possible requirement for an additional crew member, and possible requirements for new regulations governing awnings on small passenger vessels.
The NTSB has recommended in their February 18 letter that all passenger-carrying amphibious vessels be fitted with watertight bulkheads or built-in flotation "without delay."
The NTSB, in their report claims that "no other U. S. Coast Guard inspected vessels rely upon an active system to ensure their ability to remain afloat in the event of flooding". THIS STATEMENT IS NOT TRUE, AND HAS UNDOUBTEDLY LED TO THE NTSB'S RECOMMENDATIONS.
In fact, watertight bulkheads are not required on my U. S. Coast Guard inspected passenger vessel less than sixty-five feet long and carrying 49 or fewer passengers in U. S. waters. This regulation is contained in the U. S. Code of Federal Regulations, Title 46, Subchapter T.
There are literally thousands of U. S. flag passenger vessels less than sixty-five feet carrying 49 or fewer passengers that do not have watertight bulkheads or fixed flotation. All of these vessels rely on active means to remain afloat after flooding, despite the NTSB's letter.
In any case, watertight bulkheads would not be effective in a DUKW, LARC or other small passenger vessels unless the bulkheads were spaced such that flooding in one compartment would not sink the vessel down to its deck edge. Once a vessel's deck is immersed, stability is quickly lost, and capsizing would occur.
At the present time, the NTSB has not released its full report or the report prepared by the "recognized naval architectural firm" which apparently concluded that addition of watertight bulkheads and foam flotation to the DUKW was "practical and cost-effective."
We have conducted preliminary studies involving the installation of watertight bulkheads or foam in the "Moby Duck" LARCS.
In order to float the vessel, passengers, crew, and fuel, the LARC would need 392 cubic feet of foam to be installed in the hull. Our calculations show that there is room for only 290 cubic feet of foam in the vessel, and this assumes a very high fill ratio, which might not be possible due to the presence of structure and machinery in the hull space. Additionally, the 392 cubic feet of foam would add approximately 600 pounds to the displacement of the vessel, equal to the weight of four persons and costing one-half inch of freeboard by itself.
The Coast Guard generally discourages the use of foam for flotation in passenger vessels, in any case. The regulations do allow the use of foam, but its approval is done on a case-by-case basis. Foam installed in passenger vessels is required to pass flammability test requirements if installed in spaces with possible sources of ignition. Foam is at best flame-retardant, and at worst highly flammable. All foams used for flotation will bum to some extent, and will emit heavy smoke and gases when burning. The NTSB's recommendation to install foam in a gasoline-powered DUKW seems to be questionable. Since the LARCs are diesel powered, this would be slightly less of a problem, but would defeat some of the advantage the LARCs have over the DUKWs lower risk of a fire.
Installation of foam in a DUKW or LARC also presents another problem not addressed by the NTSB's recommendations. The foam installation would block access to the structure and shell plating of either vessel. It is important, especially for DUKWs to have access to the shell plating for inspections of the structure. The shell plating of DUWKs is very thin sheet steel, and has had problems with wastage over the 55 years they have been in service. The LARCS, on the other hand are manufactured of corrosion-resistant welded aluminum, but it is still not recommended practice to block access to the structural frames and shell plating.
Improper distribution of positive flotation in a vessel can also lead to transverse or longitudinal capsize after flooding. The flotation must be arranged to float the vessel upright and to provide sufficient stability to allow the vessel to be evacuated or await rescue by other craft. Prior to the installation of flotation, a stability study should be conducted to ensure satisfactory stability characteristics after flooding.
Our preliminary analysis of the installation of watertight bulkheads in the LARC does not look promising. The vessel would need four watertight bulkheads, one of which would need to go right through the center of the main engine, in order to meet the requirements for a one compartment standard of flooding. We do not see any advantage to the installation of bulkheads unless they would allow the vessel to meet the one-compartment standard. Once a vessel suffers deck immersion from flooding, sinking or capsizing is inevitable. We cannot do an analysis of watertight bulkheads in the DUKWs due to our lack of access to plans, but it does not seem likely that it would result in a better outcome than the LARCS, since they tend to have slightly less freeboard and less reserve buoyancy.
The NTSB recommendations, in our opinion, have been applied hastily to all types of passenger carrying amphibious vessels without due consideration to the differences between the various types, particularly between the DUKWs and LARCS. The DUKWs were created at the height of World War II using a standard GM truck enclosed in a watertight shell of thin sheet steel. Due to the time constraints and wartime pressures, the DUKWs had to be manufactured using available parts. The LARCS, on the other hand, were designed from the ground up to be true amphibians, and extensive design and testing was done by the Army Materiel Command to develop the best possible vessel. The LARCs were manufactured specifically to replace the DUKWS, and were designed to be more mechanically reliable, more stable, capable of carrying heavier cargoes, and be resistant to corrosion in a marine environment.
It should be noted that the LARCs were rated by the Army for the carriage of I 0,000 pounds of cargo, versus a rating of 5,000 pounds for the DUKWS. As passenger vessels, the DUKWs are usually certified to carry 30 passengers, each assumed to weight 140 pounds, for a total of 4,200 pounds. The Moby Duck LARCs were tested by our office-with a load of 30 persons weighing 165 pounds each, for a total of 4,950 pounds. Therefore, while the DUKWs are pushed fairly close to the Army limits, the LARCs are well below their rated limits.
The Arkansas DUKW was equipped with four bilge pumps, one of which was chain driven by the main engine. When the Arkansas accident happened, the engine-driven pump was inoperative, due to a broken key in the pump shaft. The three electric bilge pumps together were capable of pumping 34 gallons per minute at the most. The Moby Duck LARCs have been re-equipped with three electric bilge pumps each capable of pumping 62 gallons per minute, for a total of 186 gallons per minute. The pumps operate independently of the main engine and have capacities far in excess of the 20 gallons per minute required by the Coast Guard.
The Coast Guard determined in their investigation that the windshield and side curtains, along with the awning and support structure trapped many of the passengers on the Arkansas DUKW when it sank. The Arkansas DUKW, in particular, had extensive side curtains and awning extending from the windshield all the way to the stem. In addition, vertical supports for the awning left spaces of only 24 inches by 36 inches for escape along the sides of the vessel. The DUKWs normal escape route is aft, over the raised deck via a ladder, and then over the stem via another ladder. The Moby Duck LARCs are fitted with vinyl side curtains, but they have been redesigned this year to attach only with Velcro, on the outside of all supports and can be pushed out from inside the vessel easily. The awning supports have clear openings of 60 inches by 40 inches, providing easy escape. There is also no windshield fitted on the Moby Duck LARCS. The normal escape route is through a gate in the side of the bulwark, right in the passenger seating area.
The Coast Guard determined that the operator of the Arkansas Duck was distracted from her duties by the requirement to be a tour guide as well as a vessel operator. The Coast Guard felt that if a second crew member had been on the vessel when it started to take on water, that the discharge from the aft bilge pumps would have been noticed and some action could have been taken to abandon the vessel or move it into shallow water before it sank. THE MOBY DUCK LARCS HAVE ALWAYS BEEN OPERATED WITH TWO CREW MEMBERS ABOARD, ALTHOUGH COAST GUARD REQUIREMENTS ONLY CALL FOR ONE CREW MEMBER. The driver/captain operates the vessel, and the second crew member acts as the tour guide. This arrangement provides a margin of safety beyond the usual DUKW operation.
A major finding from the Coast Guard investigation of the Arkansas DUKW sinking was that required high level bilge alarms had not been installed in the vessel. This requirement was added to the passenger vessel regulations, to be complied with prior to March 11, 1999. Had the bilge alarms been installed, the Coast Guard believed that the vessel would have had time to turn around and make it back to the shore before sinking. Moby Duck LARCs are all equipped with the required bilge alarms, and were before the March, 1999 deadline.
In conclusion, we believe that the NTSB hastily concluded that the amphibious vessels were operating at a lower level of safety than other small passenger vessels, based on a mistaken belief that all U. S. passenger vessels had positive flotation or met a one-compartment standard of subdivision. While the accident in Arkansas may point out a need for a change in the regulations for all small passenger vessels, the NTSB's narrow focus on one solution to the problem ignores other safety issues and unfairly targets one position of the small passenger vessel industry.
We would advise that operators of LARCs not undertake installation of watertight bulkheads or positive flotation until final engineering studies are completed showing that it is feasible to provide upright, stable flotation characteristics after flooding. We also believe that the normal rule making procedure be followed by the Coast Guard, so that all portions of the industry have a chance to comment on proposed regulations, and so that new regulations do not conflict with other existing regulations.