Laying Heron’s Keel: Making Trunnels

Posted By on September 20, 2009

The first course of Heron's keel is laid in place.

The first course of Heron’s keel is laid in place.

We began laying Heron‘s keel on June 27, 2009. Her keel is five thicknesses of white oak planking held together with locust trunnels. Yes, we made the trunnels. Okay, Chris made most of ’em, but I made several dozen at least while I was home on a short vacation from my job out on the Isles of Shoals, and had the blisters to prove it. Which isn’t bad for a couple hours’ work.

Chris splitting locust with a mallet and froe.

Chris splitting locust with a mallet and fro.

Much of the weekend involved pounding trunnels. Trunnels, or “tree-nails,” are wooden pegs used in place of nails. When properly tarred, they will last longer and be stronger than metal fasteners. Our trunnels are made of yellow locust wood obtained from an acquaintance’s woodlot. We have filled several five-gallon buckets with finished trunnels, and will probably go through a couple more before this project is done.

Shaping the trunnel blanks with a hatchet.

Shaping the trunnel blanks with a hatchet.

There are several steps involved: Rough blanks are split out of a small slab with a froe (also spelled frow). The blanks are further cut into shape with a hatchet, then the ends pointed slightly with a block-knife. The finished blank is then pounded through a sharpened metal jig. Each one takes a couple of minutes to make.

Sarah uses a block-knife to shape the ends of the trunnels.

Sarah uses a block-knife to shape the ends of the trunnels.

As you can see by the photographs, a lot of the tools are very simple. We make many of our own tools, either because authentic equipment is unavailable or prohibitively expensive, and also because there is an additional satisfaction in making the tools as well as the project itself. Chris has worked as a blacksmith for years, so we have a forge set up on the property. He made the froe and the block-knife. The mallet/club was roughly shaped from a piece of firewood.

Trunnels are pounded through a sharpened metal jig.

Trunnels are pounded through a sharpened metal jig.

Once the trunnel blanks are split out with the fro, they are split again the other way to produce a blank about 1″ square and 8″ long. We then cut the corners off the bottom of the blank using a block-knife, a single-edged blade with a hook at one end attached to an eye on the face of the wooden block. It operates kinda like one of the old-fashioned “guillotine” paper cutters. The purpose of this trimming is to make the blanks fit better into our jig.

Chris starts the second course of timbers for the keel.

Chris starts the second course of timbers for the keel.

The jig we use is essentially a piece of sharpened metal pipe. The blank is placed in the hole at the top and pounded through with a mallet. The splinters fall off to the side and the finished trunnel falls through the bottom into a bucket when the next one is started.

For construction, the keel timbers are cut with overlapping edges at the joints and clamped in place. Each edge is tarred together, both the joint and the surface of the timber itself. A hole is drilled through the timbers, and the trunnel dipped in tar and hammered through with a mallet. Heron’s keel is made of three courses of white oak.

As of this writing (September 20, 2009), the keel has been complete for a while and most of the frames are stood. (I’m running a little late in posting about it.) More photos & an update on the continued progress will be out in the next couple weeks!


About the author

I'm a museum professional with an MA in Museum Studies and Atlantic History. A lot of my research has been in colonial and maritime history, as well as material culture of the 16th - 19th centuries. I've held a lot of weird jobs covering everything from beekeeper to tall ship deckhand. I currently live with my partner on the Canadian border in Vermont.


7 Responses to “Laying Heron’s Keel: Making Trunnels”

  1. Lloyd - Nicholas says:

    Hi guys – looks great – Can’t wait to see it in the water.

  2. Sarah says:

    Thanks! We can’t wait, either. đŸ™‚

  3. We are very interested in the trunnels. I am going to be building a wooden snipe sailboat. I am wondering if i could use trunnels instead of metal fasteners. What advice could you give me? Best wishes for your project, sincerely, John Gatewood

  4. Sarah says:

    Hello! Ekk says he thinks the scantlings may be of too small a dimension for trunnels to work. (He says he might be wrong on that, but doesn’t want to recommend them just in case.) Trunnel construction usually means massive.

  5. JIM DEREYNIER says:

    Would trunnels work on Alaskan Yellow cedar deck where frames are either doug fir or spruce ( Sitka?). I am drilling out iron nails ( actually use a core tool-3/8″ OD, Have been epoxying 3/8 dowels in but am concerned that movement will break to epoxy- This is a 33ft Atkin schooner- built 1957

  6. Sarah says:

    Hi; Ekk says – with the disclaimer that he is no expert – that he would use something with more resilience than epoxy for the trunnels, but trunnels should work okay. What you might want to do is ask around on an Atkins builder forum to see if anyone else has tried it with that design. ~Sarah

  7. […] and shaping trunnels, copying the equipment as seen at Essex Shipbuilding Museum. We wrote a blog post about the whole trunnel process a few years […]

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