length of keel "for tonnage"

[hamilton]

Just wondering if someone can fill me in on what "length of keel for tonnage" is and whether it is simply the full length of the keel or some portion of it....I encountered the term looking over the scantlings for the 1719 Establishment included by Lavery in his Anatomy of the Ship for the 20-gun ship Blandford.....

hamilton

[russ]

In its simplest form, it is the length on deck minus 3/5 of the breadth. If the length on deck were 50 ft and the breadth was 17 ft, then the length of the keel for tonnage would be 39.8 ft. Let us say the depth of the hold was 4 ft. Now, multiply 39.8 x 17 x 4 and you get 2706.4. Divide that by 94 and you get 28 79/94 tons.

 

It is not the actual length of the keel, but what they used in the tonnage calculation. This is called the Builder's Old Measure. It was used through about the mid 1860s in the US and was replaced by the Moorsom system that more accurately calculated internal capacity.

 

Russ

Edited August 7, 2017 by russ

[hamilton]

Thanks Russ - so the obvious follow-up is how can the total length of the keel be determined from the scantlings?....If there is a gun deck length of 106' and a length of keel for tonnage of 87' 9" (as is listed for 20-gun ships of the 1719 Establishment)....Or is there another calculation? Thanks again!

hamilton

[trippwj]

There is no way to determine the actual keel length using keel for tonnage.  The actual rake of the stem would allow one to determine the foremost position, but you would also need the rake of the sternpost.  3/5 max beam is an estimate of the rake at bow and stern, although the accuracy for a given vessel could vary greatly.

 

Ideally, you may be able to find reference to length of keel "to the touch", which is total keel that "touches" the sea floor, including the rising wood.  Alternatively, it could be measured from the plan.

 

 

[hamilton]

Thanks Wayne....hopefully the plans I've ordered from NMM give some indication of this....

hamilton

[russ]

I agree with Wayne. Look at the plan when you get it and see if it is marked on the plan.

 

Russ

[trippwj]

Here is a quick graphic which may help to understand the difference between actual and tunnage keel length.

 

[Windships]

In my research for a book project, I found Douglas MacGregor (I think in Fast Sailing Ships, but also in other of his writings), and John Lyman to be the most reliable sources on this arcane subject. Lyman's work, as I recall (we just moved so everything is tossed here...) is in early volumes of American Neptune October 1945). William Avery Baker has something to say about it as well: William A. Baker, A Maritime History of Bath, Maine and the Kennebec River Region, (Bath, Maine: Marine Research Society of Bath, 1973).  And Marion V. Brewington, contributor, “Tonnage Rules of 1799,” The American Neptune, Notes 1, no. 3 (July 1941). W. Salisbury, “Early Tonnage Measurement in England, IV. Rules Used By Shipwrights and Merchants,” The Mariner's Mirror 53, Number 3 (1967). As the thread indicates, many formulae were tried (and a few established as standards for a time...) to estimate the internal carrying capacity of a hull (that's what tunnage/tonnage means in your period of interest), but the results of applying those formulae are just that, estimates or approximations. For my book, I devote an entire chapter to the subject, but do not claim to be an expert by any means. The few references I list here are by no means exhaustive. There may be articles in our own Nautical Research Journal--a surprisingly oft overlooked source, for a myriad of topics in our field.  Good luck.

[trippwj]

6 hours ago, Windships said:

In my research for a book project, I found Douglas MacGregor (I think in Fast Sailing Ships, but also in other of his writings), and John Lyman to be the most reliable sources on this arcane subject. Lyman's work, as I recall (we just moved so everything is tossed here...) is in early volumes of American Neptune October 1945). William Avery Baker has something to say about it as well: William A. Baker, A Maritime History of Bath, Maine and the Kennebec River Region, (Bath, Maine: Marine Research Society of Bath, 1973).  And Marion V. Brewington, contributor, “Tonnage Rules of 1799,” The American Neptune, Notes 1, no. 3 (July 1941). W. Salisbury, “Early Tonnage Measurement in England, IV. Rules Used By Shipwrights and Merchants,” The Mariner's Mirror 53, Number 3 (1967). As the thread indicates, many formulae were tried (and a few established as standards for a time...) to estimate the internal carrying capacity of a hull (that's what tunnage/tonnage means in your period of interest), but the results of applying those formulae are just that, estimates or approximations. For my book, I devote an entire chapter to the subject, but do not claim to be an expert by any means.

All very good resources, and most available via the interweb or used book sites.  The entire series by Salisbury in MM is worth a look, if only to trace practice back to source documents.

 

In terms of contemporary records, Sutherland (1711) offers a good description.

 

You have me curious, sir - tell us a bit about your book, please.  The brief tease you offer is tantalising!

 

[Windships]

RE my book project, here is an excertped cut and paste from another discussion on the forum--originally related to answering a question about armament of the vessel CHALEUR while in Royal Navy service.

 

 As you can see Charlie, someone  "has tried to reconstruct Chaleur." But not in the way you might have thought. The Admiralty draught for Chaleur was made shortly before she was sold out of service, not before she began her naval career. But I'm getting ahead of myself...

 

How do I know this? I have been a student of this vessel for a very long time, and am reasonably close to submitting my book ms to publishers yet to be identified. The work focuses on her life prior to being acquired by the Royal Navy, and the last five months of her life in naval service. Harold Hahn has already treated her time in service.  At the NRG Conference in San Diego this October [2016], I will be speaking about developing a plausible framing schema for the vessel, based upon clues on the Admiralty draught, and other research into eighteenth-century merchant vessel construction in North America. A plank-on-frame model---made to eventual drawings using this schema, is a worthy challenge for any scratch builder. A bit more complex than the “Admiralty style” of framing.

 

Here, in no particular order, are some of the questions asked and answered in my book, after deep digging in primary source material at The National Archives, Kew, England, other archives and the kindness of other scholars and colleagues:

 

My initial contrarian hypothesis about the origin of Chaleur, and why it was rather strongly dismissed by many of our knowledgeable colleagues. The detective work—my own and that of valued research associates in England, Canada and elsewhere, that proved me correct; and, which resulted in many other interesting findings about this vessel. How and why I selected the vessel which I’m now absolutely confident became Chaleur. Guidance for anyone wishing to do similar research about other vessels of this period in our history.

 

Why Hahn and many others who have since relied on Hahn, were misled by the absence of key information not provided by his UK researcher about Chaleur. When and where was she built, and by whom? Who owned her, and where did she go? How did this vessel in particular become one of six choices for purchase by the Royal Navy? Why any model you (made or) make based on Hahn and Chapelle, and even the Admiralty draught--after all your hard work, will not produce the representation you thought you were creating. Background on the Smithsonian model in this post, and why it is a misrepresentation as well.

 

Why most everything Chapelle wrote, and he and William Avery Baker concluded about Chaleur is not correct. Did Admiral Colvill---who was ordered to purchase "six Marblehead schooners or sloops" really get what he directed others to find and procure? Something about the identities of the two schooners purchased at Boston at the same time as this vessel. Errors about some of the six purchased vessels, even in the Admiralty correspondence. Biographical information about the owner of the vessel when she was first registered; in the context of the brewing conflict between Loyalists and those seeking independence from England.

 

A truly unprecedented in-depth analysis of Chapelle's early writing, thinking, and rationale behind developing and presenting his drawings; and, his admonitions to--and complaints about, we in the model making community.

 

My intent is to include working drawings for model makers. They will enable more accurate representations of the vessel; prior to her purchase, and thereafter during her short career in the Royal Navy. Each rendering will be based heavily on what was thankfully recorded in her last log.

 

Last…why, the fact that a draught of Chaleur survived, has such significance; as compared to those for Halifax, or Sultana, and others from that period.

 

Stay tuned. And I hope to see many of you in San Diego in October. Thanks for the opportunity to comment.

 

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