Talk:Builder's Old Measurement

Creation of New Article
I have created this new article from my references and notes over several years while researching a sailing ship model. I have tried my best to be accurate and to respect what has already been written in Tonnage.

I am relatively new at doing this.I would appreciate any comments, whether as to the style, accuracy or adherence to Wilipedia's quidelines. I have not yet figured out how to make the references behave according to the guidelines. Feel free to fix that, or let me know how.Tvbanfield 02:47, 23 April 2007 (UTC)
 * I formatted the citations. There is a textual formula following the In 1678 . . . phrase which you may want to reformat to make it consistent with the others.  Kablammo 16:29, 23 April 2007 (UTC)
 * Thank you, I've reformatted the formula as you recommended.Tvbanfield 22:25, 23 April 2007 (UTC)

How is length measured?
I have often tried to calculate displacement and/or tonnage of old sailing ships while researching model ships or while trying to determine if a stated displacement or tonnage is correctly stated. It rarely works very well. One of the reasons is not using the correct "Length." In some sources the stated length is the overall length, counting the extentions such as the bow sprit and spanker boom. The length correctly should be the waterline length since the BOM formula is based on the weight of water the ship displaces. However, the length at the waterline is rarely stated. I am well into the research of this question and plan to add a paragraph explaining length measurement. I invite comments on this discussion page.Tvbanfield 22:25, 23 April 2007 (UTC)Tvbanfield 15:41, 25 April 2007 (UTC)
 * I'm afraid this is totally wrong, except the statement that BOM is based on the length of the ship's keel (and the breadth of the ship, as well). But IT IS NOT repeat NOT based on the weight of water displaced; in fact BOM is nothing whatsoever to do with weight. BOM is a measure of cubic capacity. Rif Winfield (talk) 19:46, 6 February 2012 (UTC)

Burthen ~ mass?
To centralize discussion:

A site of Steamship Mutual suggests that burthen is a way of approximating a meaure of weight. It says that the calculation used draught.

This cite, at the foot of the present article, suggests otherwise: It states that burthen uses depth, not draught. Other sources state the same.
 * Burthen, or Burden, William Falconer's Dictionary of the Marine, 1780

If calculations of burthen used depth rather than draught, how could anything related to displacement be measured by it? Kablammo (talk) 14:22, 9 February 2012 (UTC)


 * No, the Steamship Mutual article does not talk about BURTHEN, it talks about "Tonnage measurement of ships," and it says "'Tonnage' broadly is a measure of a ship's size which can be expressed in terms of either volume or weight.--Tvbanfield (talk) 15:55, 10 February 2012 (UTC)
 * The 1678 section is the confusing part, in that it uses displacement, draught, and block coefficient, which of course are related. But at the time burthen was the calculation commonly used, was it not?  Certainly in 1780 that was the case.  And burthen (and BOM) uses depth, not draught.  Kablammo (talk) 20:32, 10 February 2012 (UTC)

To Rif Winfield & Kablammo

Is BOM weight based or volumetric?

Please see my response to Rif on his talk page. My conviction that BOM is weight based is largely in reliance on my Steamship Mutual citation. Rif has changed the article taking the position that BOM is volumetric, contrary to the current citation and without any citation to support his position. In coming up with a method to measure tonnage, a problem arises because it is difficult for a port authority to board a new ship and measure its displacement, with or without cargo. Therefore, all methods in history are based on simplifying assumptions and measurements that can readily be made (without sending down a diver, for example) making it difficult to analyze.

Faulkner’s Dictionary defines BURTHEN or BURDEN and describes a calculation method. It does not refer to BOM. per se.

As to when the BURTHEN method was in use, The Oxford Companion to Ships and the Sea makes the point that BOM “…gradually replaced the burthen method of calculating a ship’s carrying capacity…”, however its description does not make it clear whether “ ½ the beam” serves to replace “draft” or whether it serves to replace “depth of the hold.” Nor does it explain the origin of the divisor of 94, or what its units are.

Given these uncertainties, and lacking proper citations, I think the BOM Article should be revised eliminating statements or references as to whether it is a volumetric or weight based measurement. The essential fact is that the BOM formula was how tonnage was measured then, never mind whether it was a volumetric or weight based measurement. This approach serves to make the WIKI article more encyclopedic.

What do you think?--Tvbanfield (talk) 04:54, 11 February 2012 (UTC)


 * It looks to me like the Steamship Mutual site defines a method used by shipbuilders on the Thames to approximate the deadweight portion of displacement. But nothing in that site says that it is Builder's Old Measurement or "burthen".  So I think we are talking about two different things, just as today gross tonnage is different to displacement or deadweight.  In other words, the Steamship Mutual site may be correct as far as it goes, but it does not mention BOM or burthen. Kablammo (talk) 20:00, 12 February 2012 (UTC)


 * I have written to the head of Research and Publications of Steamship Mutual inquiring about the relationship between the 1678 Thames shipbuilders measurement and BOM. Hopefully their response will help us. I'll let you know.--Tvbanfield (talk) 15:44, 13 February 2012 (UTC)
 * Thanks for doing this. Kablammo (talk) 00:20, 14 February 2012 (UTC)


 * As Rif has mentioned, we need an article tracing the historic development of the concept of tonnage. Perhaps that should be in the Tonnage article, or a daughter article of it, viz. History of Tonnage or something akin.  Kablammo (talk) 20:00, 12 February 2012 (UTC)

Definition of Ton
From the text: Thus, Builder's Old Measurement estimates the cargo-carrying capacity of a ship in "tons", a measurement that has nothing to do with weight. Umm, ton is a measurement that today has a great deal to do with weight. Should the text be changed to read had nothing to do with weight? Or, maybe change the spelling of the unit of measurement referenced by the article to tun. — Preceding unsigned comment added by 67.238.100.58 (talk) 22:07, 4 October 2012 (UTC)


 * "Tun" is archaic. "Ton" is also used to measure size in measures such as BOM, gross and net register tons, and gross tonnage.  None have anything to do with weight.  Kablammo (talk) 23:28, 4 October 2012 (UTC)

That's insane. From the Wikipedia article on the word ton (first sentence, actually): ''The ton is a unit of measure. It has a long history and has acquired a number of meanings and uses over the years. It is used principally as a unit of weight, and as a unit of volume. It can also be used as a measure of energy, for truck classification, or as a colloquial term.'' My searches on the inter-web reveal definitions that rely on the word weight as well. So, then, how does ton have nothing to do with weight? — Preceding unsigned comment added by 67.238.100.58 (talk) 14:55, 5 October 2012 (UTC)


 * Let me be more specific. I said above, "ton is also used to measure size", in Builder's Old Measurement, Gross register tonnage, net register tonnage, and gross tonnage, none of which measure weight.  displacement and deadweight tonnage (neither of which I mentioned above) do measure "weight", in metric or standard tons.  This article is concerned only with BOM, not any of the others. And BOM does not measure weight; it measures tons burden (or burthen), and when used with BOM, "tons" does not mean weight. Kablammo (talk) 17:01, 5 October 2012 (UTC)

Are there other (extra) abbreviations for Builder's Old Measurement?
Is it o.m. and OM? Is there a formula for converting Builder's Old Measurement to the Moorsom System (n.m. or NM)? At least that's what I think the Moorsom systems abbreviations are? Broichmore (talk) 12:54, 26 March 2018 (UTC)


 * Burthen did not actually measure depth, but instead expressed it as a fraction of breadth. This led to narrow but deep vessels, which reduced both measured tonnage and seaworthiness.The Design and Construction of Ships pp. 197-99. In contrast, Moorsom used actual depth. So no conversion is possible.  Kablammo (talk) 15:39, 26 March 2018 (UTC)
 * Thanks, thats clear. I think that info should be included in the article. Also can we add o.m. and OM to Builder's Old Measurement (BOM or bm) list of abbreviations? Broichmore (talk) 19:45, 28 March 2018 (UTC)
 * Hi Broich. No objection to adding the abbreviations, as they both appear to have been in common usage.  Our article now treats burthen as simply BOM, but burthen itself changed over time.  I hope to have a couple of sources soon which should help trace that development. I'd be happy to assist in updating this article (or another) to do that, but my schedule is pretty indeterminate right now.  Kablammo (talk) 13:07, 29 March 2018 (UTC)

Edward III's tax
At what "today" is the current value of Edward III's tax estimated and by what means on which historical currency site? Errantios (talk)
 * The inflation template used is the UK inflation template, but the use of "today" and similar indeterminate terms appears to be disfavoured: Template:Inflation. Kablammo (talk) 11:49, 17 January 2023 (UTC)
 * Thank you - have clarified. Errantios (talk) 12:52, 17 January 2023 (UTC)