FreightWaves explores the archives of American Shipper’s nearly 70-year-old collection of shipping and maritime publications to showcase interesting freight stories of long ago. In this edition, from the May 1975 issue of American Shipper, FreightWaves revisits a detailed account of an experiment on the seas.
The cushioned ride of a skewed propeller
First American O/B/O ships used to test a new propeller concept. The Ultrasea broke a blade somewhere between Hamburg and Galveston but the crew never knew it until they arrived in port. Seen as boon to containerships with vibration problems.
The sister ships Ultramar and Ultrasea are as similar as two peas in a pod until you look closely at their sterns.
There, tucked out of ordinary view beneath the fantail and behind the rudder, the Ultrasea displays a sharply pointed propeller which bears more resemblance to a set of cowboy spurs than it does to the fulsome curves associated with most ship propellers — including that of Ultramar.
The wheel on the Ultrasea does, in fact, spur the ship along at a speed one knot faster (at 950 RPMs) than the Ultramar and saves the operator as much as $250,000 a year in fuel costs to boot.
Furthermore, the new propeller — officially described as “highly skewed propeller” — does its job with such quiet perfection that vibrations aboard ship are reduced to a surprising minimum. This point was all the more surprising to the crew when the ship arrived at Galveston last fall and personnel ashore reported one blade of the propeller was broken and missing. With any other propeller, the crew would have known the instant the mishap occurred and would have endured the vibrating misery of the missing blade until the voyage was completed. The ship itself would have suffered and finely calibrated instruments would have been shaken out of adjustment, fittings loosened, and shaft and engine parts worn down before their time.
The Ultrasea and Ultramar are “test tubes” in a large-scale experiment undertaken by naval architects, marine engineers and the Maritime Administration to improve operating efficiency of ships. MaRad has yet to report its formal conclusions, but there can be little doubt when one spends a few minutes talking with men aboard the ships and officials of the company who operate them.
They know, and the answer is “Right On!”
The basic problem
As ships become larger in order to lower the cost of shipping, so must the power plants that move them. For economic reasons, most of the larger vessels are single screw. With such large power on a single propeller, difficulties have occurred because of cavitation and ship vibration.
The forces acting on the propeller as it turns in the water vary. This weakens the metal in the propeller and is transmitted to the ship as vibration.
By using larger propellers which turn more slowly, cavitation can be reduced. Also, hull vibrations can be reduced by use of special structural designs, clear water sterns, fine hull lines and large propellers; however, the effects of such methods are limited and not always satisfactory.
One experimental method of reducing the problem is the highly skewed propeller which reduces cavitation and vibration by equalizing the forces acting on the propeller.
The first test of a highly skewed propeller on a large vessel is being conducted by MaRad on the Ultrasea and Ultramar, owned by Aries Marine Shipping Company and the United States’ first Ore/Bulk/Oil (O/B/O) carriers.
The two vessels are 875 ft. long, 105 ft. wide and operate at draft up to 45.9 feet. The vessels displace 98,855 tons each and are powered by identical power plants which generate 24,000 horsepower. They were built by National Steel and Shipbuilding Company (NASSCO) in San Diego, California.
The first step in MaRad’s test program began before the two O/B/Os were constructed. Hydronautics, Inc. was designated to design and test a conventional propeller for the existing model of the San Clemente Class O/B/O, under all possible operating conditions.
At the same time the Naval Ship Research & Development Center (NSRDC) was designated to design and test a model of a highly skewed propeller for the O/B/O. The two propellers were designed with five blades and a diameter of 26 feet.
The first two O/B/Os were chosen for the test, the Ultramar being equipped with a conventional propeller and the Ultrasea with the highly skewed blade. Because the ships are almost identical in every detail, they were ideal for a comparison study.
Full-scale test
It was then decided to test a large skewback blade on a full scale application.
Finally a design was selected for the skewed propeller with a skew angle blade tip of 72°, and Ferguman Propeller of New Jersey was contracted to build the propeller while instruments were designed for the vessels to measure the effect of the propellers on the vessels.
The Ultramar went into service in the summer of 1973 and the Ultrasea in March 1974.
As evidence to possible savings, before the Ultrasea was put into service, one blade on her highly skewed propeller was damaged and restored by the electrical conduction method. This method, which weakens the blade, is not practical on a conventional propeller because the normal cavitation would cause the blade to break almost immediately.
The blade finally broke on the vessel’s last voyage before being laid up but according to Peter Constans, vice president of Aires Shipping, the vessel’s crew was unaware the blade was broken until they reached port and there was no noticeable decrease in operating efficiency with half of one blade gone as there would have been if the blade were equipped with a conventional propeller. According to Constans, the highly skewed propeller is performing much better than the conventional propeller.
Savings
In addition to savings in maintenance, Constans said that the increased operating efficiency of the Ultrasea resulted in fuel savings of $800 a day. With its highly-skewed propeller, the Ultrasea averages one knot better than the Ultramar at 950 RPM which translates into approximately 10$ fuel savings.
Constans estimated that over a period of twenty years, the owners would save a million dollars on maintenance cost.
Views of captain
According to Captain Louis Kingma of the Ultramar, “We get about 1.7 miles to a barrel (of BunkerC), same as the Ultrasea, but with our conventional propeller we do have a lot more vibration which can affect the calibration of the electronic equipment in the engine room.”
Of the skewed propeller, Captain James D. Bennett aboard the Ultrasea said, “It’s a real fancy blade. The thing that is amazing is that the propeller’s been damaged and one-half of one blade is missing and I can see no change in the performance. We can not detect any change in the vibrations in the ship as far as the shaft and what have you is concerned.”
Captain Bennett said that even though they knew the blade was broken somewhere between Hamburg, Germany, and Galveston, Texas, on their last voyage, they do not know where because the break was not discovered until they reached Galveston.
Joseph Bond, chief engineer on the Ultramar, was on board when the Ultrasea went on her sea trials and was surprised at the lack of vibration in the ship.
In a report to MaRad on the first phase of the test, NASSCO reported, “The primary advantages of the highly skewed propeller are the reduction in unsteady bearing forces and moments; and reduction in unsteady pressure forces. These Advantages are shown to be achieved without an adverse effect on the ahead or backing efficiency.”
Additional advantages reported were improvements in habitability because of the reduction in noise and the considerable reduction in vibration of machinery with the highly skewed blade. This reduced vibration, according to the report, will have a great effect in reducing machinery maintenance.
Cost of vibration
Another indirect advantage is an improvement in the vessel’s cost/benefit analysis as a result of savings because of reduced vibration. The study reported that the new American fleet of large merchant vessels could recognize considerable savings through use of highly skewed propellers. In 1972 the additional expense of vessels with vibration problems runs an average of $250,000. In the container vessel fleet, of which 63% of the vessels have vibration problems, the potential savings could come to $125,000 for every vessel in the fleet.
The ships are now laid up in Jacksonville. Before they go back into service they will both undergo drydocking at Jacksonville Shipyards, Inc. The Ultramar will be equipped with the skewback blade and the Ultrasea with a conventional blade to verify the results of the study.
Their voyages
The Ultrasea, which arrived in Jacksonville toward the end of January, had made only four voyages since launching nearly a year ago.
On her maiden voyage she carried grain from Vancouver to Bangladesh. She then picked up a cargo of bauxite in Grove, Australia, and delivered it to Rotterdam.
On voyages three and four she carried grain from New Orleans to Hamburg. It was while returning from voyage four that the ship’s blade was broken.
The last grain shipment was delivered in December and the vessel then sailed to Rotterdam for bunkers before sailing to Galveston, where she lay at anchor awaiting orders.
The two ships have a grain capacity of 3,217,510 cubic feet and a liquid cargo capacity of 561,549 barrels.
The Ultramar, in over 18 months of service, has made only seven voyages. The voyages were from Rastanura, Saudi Arabia, with 553,494 barrels of crude oil to Naples, Italy, and Sete, France; from New Orleans to Rotterdam with 63,510 tons of grain; from New Orleans to Rotterdam with 62,644 tons of grain; from Sept-Iles, Quebec, to Ijmuiden, Holland, with 79,200 tons of Iranian oil; from Norfolk to Fanakawa, Japan, via the Panama Canal with 55,719 tons of coal and then from Hay point, Australia, to Ijmuiden with 77,970 tons of coal; from Norfolk to Kakogawa, Japan, with 59,350 tons of coal; and finally, from the Persian Gulf to Delaware with 471,763 barrels of crude oil.
The last cargo was delivered on Feb. 1, 1975, and the vessel sailed directly to Jacksonville for lay up.
Cargo preference
Both captains agreed that if the bill before Congress passes, which would allocate 30% of oil supplies coming into the United States to American Flag vessels, it would definitely be of benefit to their ships.
According to Captain Bennett, “Anything that is going to increase the amount of oil that’s brought into the country in American Flag tankers is going to increase the profitability of many ships under the American flag capable of hauling oil, and we can haul oil. You might call this a baby supertanker if she were in oil.”
The Ultrasea has yet to carry oil but according to Captain Kingma, the Ultramar, which has twice handled oil, can carry oil without any special preparations.
The ships were built to carry any cargo which can be handled in bulk and, according to Captain Kingma, their competition is coming from foreign flag vessels.
Both vessels cruise at a speed of 16.5 knots and consume approximately 1.7 barrels a mile, which, according to Captain Kingma, is an excellent consumption rate.
In addition to low fuel consumption, the vessels are fully automated and carry a crew of only 26 compared with a crew of 48 for Victory tankers only a seventh the size of the OBOs.
The ships are also the largest permitted through the Panama Canal and can pass through the Suez Canal if it is again opened. For steering, the large ships have oversized rudders and maneuver very well, according to Captain Bennett.
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Source: Freight Waves
