Courtesy of David VasquezA 1774 advertisement in the Norfolk edition of the Virginia Gazette showed that at that time mulberry wood was considered the equal of black locust for trunnels, probably for shipbuilding.
Recently, Walt Ansel, the director of the Henry B. duPont Preservation Shipyard at Mystic Seaport Museum in Connecticut, forwarded an email he received from David Vasquez, writing from the Norfolk, Virginia, area with the following inquiry: “My question is pretty simple but esoteric. Am working on researching (among other things) what a certain individual was doing as a business in the 1750s to early 1770s, and to that end was looking at the hundreds of court cases they were involved in at the time, which still hasn’t helped. But then I came upon this ad in the Norfolk edition of the Virginia Gazette from 1774: ‘MULBERRY and LOCUST TRENAILS, may be had by applying to Richard Templeman, & Co. July 12, 1774.’
“When I saw ‘trenails,’ I immediately assumed they were the kind most often used to keep beams in houses together. But upon searching the internet a little, I saw that those were usually made of oak, while mulberry and locust were mainly used for ships and boats, perhaps because they’re more pliable? Can you tell me if that is correct? And if so, can one glean anything, at all, from such an ad? Incidentally, this Richard Templeman operated in Norfolk County, which, of course, does and did have deep maritime connections, and his name is most often seen in the court records as a partner with Scottish merchants of the time. In fact, I was surprised to see his name alone in this ad because he is usually seen on paper as a partner with a Scottish merchant. Furthermore, I do know that he owned partial shares in ships—inventories of his property on his death in the 1780s mentions fractions, such as one-eighth, of shares in various ships. I’m not sure if that’s relevant.”
Walt added, “This was intriguing. Have you ever heard of such a thing? Certainly, black locust has been our go-to for years. Shipbuilders in Essex, Massachusetts, used oak, and I’ve heard of hackmatack used in Nova Scotia for softwood-planked schooners.”
In 2012, I wrote a column devoted to trunnels (WB No. 226). I quote here a segment of that column that deals directly with the question concerning the historic use of mulberry and other woods for trunnels in colonial America:
“In the mid-16th century, William Douglas, reporting on British settlements, proclaimed: ‘In shipbuilding, they ought to use only white oak for timber, plank, and trunnels.’ This statement might surprise anyone who knows that black locust (Robinia pseudoacacia) is the preferred trunnel wood in the United States and has been for a very long time. The contradiction lies in the native range of this tree, which is located in the central and southern Appalachian and Ozark mountains—places deeper into the interior of the continent than had been settled by the middle 1700s.
“By 1808, Boston shipbuilders were using trunnels of white oak but also occasionally of locust from Virginia. By this time, builders in Philadelphia, Pennsylvania, and Louisville, Kentucky, were almost exclusively using trunnels made of black locust, while those in Charleston, South Carolina, and Savannah, Georgia, preferred trunnels of the heart of longleaf pine, when the side planks were of the same species, and of live oak, locust, or red mulberry (which is as good as locust) when the sides are of oak, according to an anonymous report from that year on North American trees.
“It should be noted here that black locust, red mulberry (Morus rubra), Osage orange (Maclura pomifera), and Pacific yew (Taxus brevifolia) are listed as the most decay-resistant woods in North America by The Wood Handbook. Each could be used as trunnel wood in the right situation.”
The right choice of wood for trunnels depends on two major factors: availability and appropriate matching with planking wood. As Walt notes in his remarks when forwarding David’s original question, hackmatack (also known as tamarack or larch) was often used with pine or spruce planking in the Canadian Maritimes.
A species not often mentioned today as a possible trunnel wood is Osage orange. But Samuel J. Record in his 1934 book, Identification of the Timber of Temperate North America (John Wiley and Sons, New York), said this about Osage orange: “The principal uses of the timber are for fence posts, insulator pins, treenails, and wheel stocks.”
Matching Woods
In my 2012 column on trunnels, I didn’t address the issue of matching wood properties between trunnel and plank or frame. The most critical features are relative wood densities, as measured by specific gravity, and side-crushing strength, as measured by compression parallel to grain. If the trunnel is much denser than the timber, splitting, or at least deformation, can occur. If the trunnel is much less dense than the timber, it will provide little fastening strength and may loosen with time.
The simplest solution is to use the same wood for trunnel and plank or frame, as recommended by William Douglas above. This works well if the wood has high decay resistance, as in the case of white oak, live oak, or longleaf pine. But where planking is not decay-resistant, a more durable trunnel is preferable since the exposed end-grain provides an ideal entry point for decay fungi, hence the widespread use in the past of highly decay-resistant woods such as black locust, red mulberry, and Osage orange.
In the table above, I have provided values for some trunnel and planking woods based on specific gravity and a Janka side hardness test, a measure, named after its creator, Gabriel Janka, for the force required to push an 11.28mm steel ball half of its diameter into a piece of wood. I had wanted to use compression perpendicular to the grain values, but was unable to get this measure for some of the woods, so have used side hardness as a rough proxy. For white-oak or red-oak planking, black locust is a reasonable density match but because of its higher hardness, the trunnel diameter needs to closely match the bore hole size. Red mulberry is a closer match with white and red oaks, while black locust is a good hardness match with live oak.
In Norway, common juniper (Juniperus communis) is often used as a trunnel wood when planking with Scots pine (Pinus sylvestris). Both woods have similar densities. Juniperus communis also grows in North America and could be used as trunnel wood with red pine (Pinus resinosa), which has properties nearly identical to Scots pine. Tamarack has properties similar to juniper and, as noted by Walt, has been used in Canadian shipbuilding, although it is somewhat less decay-resistant than juniper. U.S. West Coast builders could use Pacific yew as a reasonable substitute for black locust.
Ship vs. House
As noted in the email from David Vasquez, trunnels are used in timber-frame building construction as well as in shipbuilding. Timber-frame builders favor octagonal-shaped trunnels in which the corners of a square peg are eased. Driving the slightly oversized trunnel crushes the edges and ensures a tight fit. By contrast, boatbuilding trunnels are usually turned round and are wedged at one or both ends. The cylindrical shape mirrors the bore hole, ensuring a fit without crevices that could invite water or air seepage and the accompanying decay fungi. Some older boats, especially in Norway, were fastened with eight-sided trunnels, which were fashioned from split logs to avoid the grain runout that might result from sawn blanks. But since the 1930s, trunnel-cutters have been used to produce cylindrical trunnels in Norway. I should point out, here, that Norwegians distinguish through-trunnels from blind, or stopped, trunnels, which they call coaks (dopps in Norwegian).*
Currently, the use of trunnels glued with modern adhesives has gained favor, especially for joining framing sections that will later require further shaping. This avoids potential chance encounters between shaping tools and bolts or screws. This kind of joinery also avoids possible metal corrosion problems down the road.
And now, for a bit of controversy, I offer several opinions on the origins of the word trunnel. The prevailing view traces trunnel from “treenail,” although a few suggest it derives from “through-nail.” But recently some historic sleuths have proposed that trunnel derives from the Old English word “trenag,” which purportedly means peg. Support for this interpretation can be found in the Norwegian word for trunnel, which is trenagle.* The Oxford English Dictionary lists neither trenag nor trenagle, siding instead with the treenail-to-trunnel theory. I hold no opinion on the subject, but would be interested in hearing if any WoodenBoat readers can provide support for any of these theories.
Dr. Richard Jagels is an emeritus professor of forest biology at the University of Maine, Orono. Please send correspondence to Dr. Jagels by mail to the care of WoodenBoat, or via email to Senior Editor Tom Jackson, tom@woodenboat.com.
*Kristiansen, Asmund, Carvel Technique in Norwegian Boat Building, 2003, Hardanger FartØyvernsenter, Norway. 34 pp.