Steel Keelsons in Wooden ships
- April 5, 2015 at 5:11 pm #8442
I recently read ‘Master in Sail & Steam: The notable career of one Maine Shipmaster’, by Charles S. Morgan (Maine Maritime Museum, Bath, 1981), a fascinating little biography of Captain Frank Hewitt Peterson (1876-1958). Among the vessels that he commanded was the five-masted schooner JAMES W. PAUL (1,808 grt). He notes that she had a steel keelson when built (1901), but this fractured well before he took command (1912), and a wooden keelson had been built up around the broken steel beam.
I presume that the idea was to create more space in the hold, and to save both time and money in construction. For much the same reason she had steel knees, but these had been quite common for many years.
It is no real surprise that the rigid beam keelson did not cope with the working of a large wooden vessel, but I wondered how many other vessels this idea was tried on?
Frank ScottApril 12, 2015 at 2:01 pm #8747
W.H. (Bill) Bunting of the MarHst-L forum has pointed me towards R. L. Snow & D.K. Lee and their excellent book ‘A Shipyard in Maine: Percy & Small and the Great Schooners’ (Bath, ME, 1999) p.80. They note that the 3,401 grt six-masted schooner ELEANOR A. PERCY (P & S hull number 7) of 1900 was fitted with a riveted steel plate, 1 inch by 28 inches by 290 feet, which was sandwiched between the third and fourth keelsons and bolted through with 1¼ inch iron every 9 inches. The keelson was sistered on each side, as was standard, and stood perhaps seven feet high.
It is said that when the steel sandwich filler was inspected some years later it was broken, which is no surprise given the degree to which she & all the other great schooners worked in a seaway, and this experiment does not seem to have been repeated.
FrankMay 5, 2015 at 10:44 am #9367
I have had quite a few responses on this topic from another forum, and these are summarised below:
A. An additional factor in the cracking may have been lack of ductility in the steel. Low ductility makes metal more prone to fatigue cracking, and brittle, low ductile, steel remained a problem right through until after the Second World War.
B. There was a suggestion that the builders of the big schooners fully understood the consequences of countless numbers of bending moments over the years. However, they hoped that the steel keelson would delay the day of reckoning, allowing them to pocket a comfortable profit before that happened.
This was countered by another member who noted that full understanding of metal fatigue did not start until the 1920s and 30s and was not part of an engineer’s normal work until computers became ubiquitous enough for finite element analysis to become routine. Much of the early work on metal fatigue was done in response to problems with early aluminium aircraft frames. Moreover, even though scientific understanding of metal fatigue theory dated from the nineteenth century, fatigue failure continued to be a serious problem well into in the twentieth century. It took a long time for designers and engineers to get on top of the problem.
Another factor is that the number of cycles is not the only variable; the percentage of yield stress achieved in each cycle is also important. While a test billet could fail at 100,000 cycles of 90% of yield, the same billet might easily withstand 10 million cycles at 20% of yield. This matters because the frequencies of ocean waves differ dramatically in storm conditions compared to normal (moderate) sailing conditions. Converting cycles and percent yield into calendar time was not possible in 1900, and it is still a challenge today. Oceanographic factors were poorly documented until well after 1945.
Finally, the originator of this point commented that he was referring to the way in which the builder(s) and managing owner(s) understood of what happened to the structure of a big schooner over the course of time, sailing heavily laden with coal one way, regularly taking the ground when working cargo, and sailing ‘light’ for the other leg, and at sea the hull constantly flexing, loosening and depreciating. All of them came to use their steam pumps more and more to keep them afloat. Although the builders and owners would not have said that what they were doing was “converting cycles and percent yield into calendar time,” at a basic level that was what they were doing when they made the decision to build these big schooners. These vessels were not normally built from drawings, much less after any number-crunching. It seems probable that the decision to add the steel to the ELEANOR A. PERCY’s keelson (normally a stack of hard pine about seven feet high, bolstered with sister keelsons) was a matter of, “It might help stiffen her up a bit, and it couldn’t hurt, so let’s give it a try.”
It is a measure of the stress and strain that the ‘great coal schooners’ endured that diagonal iron/steel strapping did not work out well on them, and that before long bolts would shear off, and the strapping would break. By contrast, this system had a very good record with the few wooden square-riggers it was employed on.
With thanks to Paul Adamthwaite; Bill Bedford, W.H. (Bill) Bunting), Rick Spilman, and A. Steven Toby, all of the MarHst-L Forum.
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