
Old Registry Tonnage
I had asked several times about the old formula for Registry Tonnage, & there have been several discussions about it. I ran across the (or a?) formula in "The History and Archeology of Two Civil War Steamboats: the Ironclad Gunboat USS Eastport and the Steamer Ed. F. Dix", prepared for the USA CofE by Coastal Environments Inc. It is stated there that the formula from 1789 until 1864 was (length x 3/5 beam) x (beam x 1/2 depth) divided by 95. " No uniform method for taking the measurements was mandated, such that considerable variations could occur in the tonnages of nearly identical vessels." Based on the tonnage figures I've encountered, considerable variation could also occur when the same vessel was meaured by different inspectors. The source for this formula is given as (Gibson and Gibson 1995a.xxxii) The copy I have does not include the references cited section, so I am unsure of the source refered to.

The source is probably Gibson & Gibson's "Dictionary of Transports & Combatant Vessels, Steam & Sail, Employed by the Union Army, 18611868"

The rules for admeasurement of boats and ships are designed for cheating. Each nation aims to favor their own ships and penalize those of other lands. Each owner wants to reduce the tonnage as much as possible to avoid fees and charges. Every naval architect wants to satisfy the owners. Every nation wants to collect as much in duties and taxes as possible.
As a result a confusing and inaccurate system of admeasurement has grown, like a virus, with traditional, not written, exceptions and exemptions of great complication. Variations in conformation of the ships and boats create variances.
For example, seagoing vessels store cargo in the hold (as a general rule) while steamboats carry it on deck. According to most rules the deck is not suitable. Western rivers steamboats frequently had capacities of double their admeasured tonnage because the space above deck was not admeasured.
Today we have the phenomenon of containerization. Do the inspectors admeasure the ship only? Or do they admeasure the containers? If so, how?
You have opened a can of contrary and lively worms.

?
Here is Moorman's Formula to approximate register tonnage under any proposed dimensions: Let L = length on upper deck [of hull] from plank at bow to plank at stern. Let B = inside main breadth from ceiling to ceiling [side lining to side lining]. Let D = inside depth from upper deck to ceiling [planking on top of beams] at timber strake. Then the register tonnage of any ship will be equal to L x B x D/100 multiplied by the factor opposite the class in the table below. Sailing ships: cotton and sugar ships, old form, 0.8. Ships of present form [1879], 0.7. Steam vessels and clippers, 0.65. Ships of three decks, 0.68. Yachts, vessels above 60 tons, 0.5. Vessels, small, 0.45. This is accurate to within 2.5%
My comment: this is as close as any other guess.
Last edited by Alan Bates; 06172006 at 11:38 AM.
Reason: misspelling

Today's rules may be found in 46, Code of Federal Regulations, Subchapter G. This is about 110 pages of rules for measuring, lists of exemptions and exceptions, etc. In addition the admeasurer's office has cabinets full of files listing decisions affecting the above, most of which are aimed at reducing the tonnage.
Tonnages include: deadweight tonnage, gross registered tonnage, net registered tonnage, under deck tonnage, between deck tonnage, light ship tonnage and others. I quote from the Society of Naval Architect and Marine Engineers book, PRINCIPLES OF NAVAL ARCHITECTURE. "They are archaic rules written in antiquated language, requiring unnecessarily complicated calculations which result in tonnages not truly representative of either the size or the earning capacity of the ship. There is extreme difficulty of interpretation leading to inconsistent results within and between countries. The lack of logic in the rules leads at times to tortured interpretations, made more to fit the words of the regulations than the intent of the rules or the circumstances of the particular case."
Now, Hank, tonnage is a meaningless description of any ship or boat. Those of us who had to deal with it cheated to the extent we could. The examiners who checked our work did so with tongue in cheek, knowing we were cheating. Everybody involved, owner, architect and examiner knew all of this, had another drink, thanked eah other profusely after the admeasurement, and then had a farewell drink at the owner's expense.

A while back I tried to calculate the BARBARA H's true tonnage by determining the approx. cubic feet of water displaced by the hull. I have the hull drawn to scale in my CAD software, so the cubic feet should be pretty close. I came up with 107 short tons, or about 96 long tons. The Coast Guard has the tonnage at only 44 net and 55 gross. I guess the lower numbers are a good thing as far as licensing requirements are concerned.
Alan, what is the BELLE's documented tonnage, and what do you think its actual tonnage is? Does the CG go by long or short tons?

Steve, the USCG goes by long tons only for displacement and stability calculations. What you calculated is displacement tons. A registered ton is 100 cubic feet and is not a measure of weight. Gross registered tonnage is the space theoretically available for cargo. Net registered tonnage is gross tonnage less certain exceptions and exemptions. I'll be glad to lend you my Subchapter G if you want to go into it more thoroughly, but I warn you(!) that word "theoretical" applies.
In your instance (if memory serves me reasonably well) you should measure the length between the after edge of the stempiece and the forward edge of the transom framing to get "L". Measure the breadth between the inside faces of the side frames to get "B". Measure from the top of the bottom frames to the underside of the main deck to get "D". To do the job right you would be obliged to apply Simpson's Rules for Irregular Areas to account for the rakes and bends in the sides. Then measure the total space in the cabin because tonnage applies to the first deck above the main deck. After all of that you would deduct the space occupied by the engineroom and stairways, the after machinery space and maybe the crew and cooking spaces. The pilothouse would not count because it is above the first deck above the main deck. Other exemptions are mentioned in Subchapter G based on sizes of doors, locations of skylights and ventilating spaces, and so on, and on, and on...on...and...on. If you come up with any number remotely resembling 96 tons of 100 cubic feet you win the leather medal.
The Belle's gross registered tonnage is marked on the main beam, which is just aft of the collision compartment and it is 360 tons. I know because my license is for Inland Waters, steam or motor vessels, not exceed 360 tons with an operator's endorsement for western rivers.

Simpson's Rule, as used for determining volumes for admeasurement works this way:
Determine the length. Divide it into any convenient even number of equal spaces. The dividing points between spaces are called stations. If you make ten spaces you will have eleven stations numbered 0 through 10. This must be done both horizontally and vertically. Each space length is called "s". Measure the breadth at each station. These breadths are multiplied by factors as follows:
At station 0, multiply by 1. At station 10, multiply by 1. At even numbered stations, multiply by 4. At odd numbered stations, multiply by 2. Add all breadth times factors together. Multiply the sum by the length of the spaces between stations and divide by 3. Lo! you have the area. You the do the same thing for height. Multiply the height answer times the length answer and you will have the volume. Divide the whole weird mess by 100 and you will have gross tonnage. Buy a double roll of wallpaper for these calculations.
I am not being smartalecky. I am trying to show the absurdity of the entire tonnage admeasurement system. This sort of thing is the reason why we cannot depend on tonnages to gauge the size or capacity of ships and boats.

Alan,
Thanks for that info on gross and net tonnage. Subchapter G sounds like real exciting reading material (??). If they have a "Subchapter G For Dummies" book, I could probably figure it out, otherwise it sounds like another career. I guess knowing what the boat really weighs (displacement tonnage) is of more interest to me. Wonder why they don't document actual displacement tonnage for vessels, along with all of the theoretical net and gross tonnage?

Thanks for the info, sir. I'm well aware that registry tonnage is a legal fiction, but from the standpoint of historical research, it's useful for know what the fictions of the era were.
Posting Permissions
 You may not post new threads
 You may not post replies
 You may not post attachments
 You may not edit your posts

Forum Rules