Boatnerd Discussion Forum

The hull designs of the Maritimer ships of 1943 were tested at the David Taylor Model Basin in Carderock, Maryland with the hull form developed by a young naval architect, Kent Thornton.

Pittsburgh Steamship Company approached American Ship Building in 1947 for the design of a new ore carrier that would be 70 feet wide, 647 feet long, coal fired and a 4,500 horsepower steam turbine. Hull form was derived from the Maritimers. With the design and specifications completed Pittsburgh Steamship decided not to proceed with the project.

Walter C. Cowles in the Fall 1989 issue of Inland Seas in an article titled "A Decade of Great Ships: 1948-1958" wrote the following on page 195, "It should be noted that the proportions of Great Lakes ships are such that they fall outside all reference parameters available for both hull form and structural design. Little scientific work had been done on hull for and structural design for Lake type vessels and design was based largely on experience. Certain major structural criteria were covered by Classification Society rules but most design critetia were in the records of the shipyards and the minds of their technical personnel.."

After the Wilfred Sykes was completed Pittsburgh Steamship decided to proceed with their construction plans, this time with an increase in horsepower and oil firing. The AAAs had a hull form similar to the Sykes, but with improved hull form at the stern based on extensive testing at the David Taylor circulating tank. (The Wilfred Sykes had very severe vibrations when operating at normal speeds in deep lake waters early in her career.)

The AAA hull form was certainly not tested in a wave tank, cavitation and hydrodynamics were not analyzed to any detailed extent, and machinery was selected quite differently than today.

I'm not so sure. The Department of Naval Architecture at the University of Michigan operated a test basin at Ann Arbor since 1904, and, recently remodeled, is still in use. The late Dr. Harry Benford of the Michigan faculty worked regularly with regional naval architects in its use, particularly in conjunction with American Great Lakes hull forms, to optimize the economic efficiency of hull design. The famous David Taylor, head of naval construction for the government, began earnest investigations into cavitation at least as early as 1905 at the U. S. Model Testing Basin, and there is a vast literature, empirical and theoretical, on that subject from this nation and Great Britain from even before that era to this day. Machinery selection is another subject, though, the province of maybe professional marine engineers but probably parsimonious owners.

A guest wrote:

GuestfromEU wrote:Remember, when the AAA class was built, there were no computer calculations, only slide rules and "let's try this out". It is quite impressive how advanced the technology was for the time, given the resources.

Far far from "let's try this out". Designs prior to computers came from concepts, solid knowledge, calculations and a host of other factors. Computers are simply an additional tool in today's process.

Well, knowledge from experience certainly played a factor, but I am referring more to how today's ships are designed. The AAA hull form was certainly not tested in a wave tank, cavitation and hydrodynamics were not analyzed to any detailed extent, and machinery was selected quite differently than today. These were all aspects that were not known, or the technology was not available at the time. Though too often today, the "human experience"...what works best, design changes better for operations, etc...are taken less into account than in days past. Shipyards have catalogs of designs from which customers are given to select, with change orders only adding to the cost. Today, ships are built for maximum efficiency at the lowest overall cost. Small modifications are always made, but rarely are input from experienced crew taken to heart. If a ship's crew was allowed to design a ship, it would be a dream to work on, and would last 100 years, but the cost would be unimaginable.

Not sure where you would find one today but at one time I saw a book put out by Pittsburg Steamship Co (USS) that showed what different boats of a certain class had different components. Might be different buckets on the prop. different type of engines, etc. This was back in the day where every few years they would contract for a few more bottoms. Heard from one engineer in the Cleveland office who going thru old files where Someone in the office would just call one of the shipyard and tell them to start ordering enough steel for two/three boats and they would sign the paperwork on a later day. The book I am referring to was just trash that we were tossing out of the pilot house at fit out one spring. Seems to me there was upwards of 30 boats listed. To me they were trying to see what worked best in what situation. I asked the book seller in Port Huron about obtaining one from him and he said he had seen one many years before but had sold it....

Thanks everyone, for the info !

GuestfromEU wrote:Remember, when the AAA class was built, there were no computer calculations, only slide rules and "let's try this out". It is quite impressive how advanced the technology was for the time, given the resources.

Far far from "let's try this out". Designs prior to computers came from concepts, solid knowledge, calculations and a host of other factors. Computers are simply an additional tool in today's process.

Kort Nozzles are sometimes mistaken for a similar arrangement, where a ship is fitted with a rotating propeller on the vertical axis. Thus, the propeller is contained in a nozzle, and the nozzle turns, eliminating the need for a rudder. This requires a controllable pitch propeller. More moving parts means more expenses in initial building and ongoing maintenance. The benefits are increased low-speed maneuverability and a shorter propulsion arrangement (without a rudder, the stem can be placed further aft, bringing the entire machinery space aft, increasing cargo hold space.

Ducted Propeller utilize a traditional propeller/rudder arrangement, with either a full-surround shroud around the propeller, or half-circle appearing ducts placed on the hull forward of the propeller. This guides the water flow into the propeller at more efficient paths. This is quite common on large ships, even up to today.

Azipods and Azimuth Thrusters (a more advanced design of the first paragraph) are increasingly being used, particularly on cruise ship and Dynamic Positioned vessels.

Remember, when the AAA class was built, there were no computer calculations, only slide rules and "let's try this out". It is quite impressive how advanced the technology was for the time, given the resources.

In the late sixties some lakers were built with a cort nozzle through the next 40+ yrs some had nozzles some not question being you would think the way it makes ships handle better they would be standard but they weren't, was it not a great system or ust cost prohibitive?

Direct link to the page RTNerd mentioned below:

https://books.google.com/books?id=nj1RW ... se&f=false

The answer can be found on page 431 of the book "Basic Ship Propulsion" by J. P. Ghose, available on Google Books. The diagram on pg 432 (for a modern ship without a shoe) shows the change in hull shape just forward of the prop. The hull is twisted above and below the stern tube to impart a swirl in the flow to the propeller. This counters the rotation of the flow induced by the propeller. The rudder stock is on center but the sides are split at the propeller centerline and the portions above and below are slightly twisted in plan about the stock one to port and the other to starboard. There is a horizontal plate closing and connecting the sections at the height of the prop which gets wider toward the trailing edge. These designs were employed to improve efficiency. The AAA's, early 50's Manitowoc boats, C4s and Liberty ships were built this way but these designs fell out of favor in the later 50's probably due to the higher cost of construction. The AAA's were fitted with conventional rudders when they were replaced with larger units for the lenghtening projects. Propeller rotation should not be changed on a ship with an asymmetrical stern as might be considered when repowering and changing to a controllable propeller which is usually left-hand rotation.

The fleet gallery describes improvements in hull design this way:

"Water flow to the propeller was improved by the asymmetrically designed hull by the stern. The rudder was offset slightly to function more efficiently in the flow of water back from the prop."

Can someone explain how the stern would be asymmetrical and the rudder offset and how these would improve water flow ?

TIA