Ship Modeling FAQ, Question: Trunnels --- Revised: December 15, 2004

What are "Trunnels", and how do I use them?

"Trunnels" are wooden pins (literally "Tree-nails") or dowels that are used to hold wooden parts of a ship together. Trunnels were used instead of metal nails both because they were cheaper, and because metal exposed to salt water promoted rotting of the wood (especially if dissimilar metals might come in contact, such as iron spikes and copper cladding).

Dockyard Model, circa 1730 British model of a Spanish ship, showing large trunnels.

In spite of their appearance on some old models (see right), trunnels were commonly 1 - 1.5 inches in diameter. This table shows the diameter and drill size needed for each diameter at various common scales.

Scale: 1:48 (1/4" = 1') 1:64 (3/16" = 1') 1:96 (1/8" = 1')
Trunnel
Diameter Scale
Size drill Scale
Size drill Scale
Size drill
1" .02083 #76 .015625 #78 .01087 #82
1.5" .03125 #68 .0234 #73 .0163 #78

Scale:	1:48 (1/4" = 1')	1:64 (3/16" = 1')	1:96 (1/8" = 1')
Trunnel Diameter	Scale Size	drill	Scale Size	drill	Scale Size	drill
1"	.02083	#76	.015625	#78	.01087	#82
1.5"	.03125	#68	.0234	#73	.0163	#78

Although it's a good idea to pin any parts of a model together (glue has been known to fail), the place where you're most likely to see them used is for attaching planks. Furthermore, planking needs to have hull and deck planking considered separately.

Hull planking was typically trunneled using one or two trunnels per frame (see below for details).
Deck planking, although originally trunneled, was one of the first places where iron spikes were used for fastening. The reason was simple -- trunnels showed as end-grain and wore much less than the edge-grain of the planks themselves; with all the traffic across a deck, trunnels rapidly "grew" into a forest of "stumps" that impeded movement of men and equipment.
The heads of spikes were sunk below the surface of the deck; the resulting hole was filled with a wood plug whose grain ran parallel with that of the deck - these wore at the same rate as the deck planks (and they were much less prominent in appearance than trunnels would have been).
Hint: While some modelers do use trunnels for decks, others find that a small piece of metal tubing (e.g., a hypodermic needle cut off square) can be used to emboss a small circle, in the planking, that represents the plug...just don't sharpen the end too much, or you'll end up cutting plugs out of the deck planks!

Trunnels are typically made by pulling strips of wood through successively smaller holes in a "Drawplate". (Vanda-La Industries used to make a device for making them from toothpicks using power tools, but that product has been discontinued.) The best wood for making trunnels is bamboo (readily available from barbecue skewers) - it's tough and splits easily.

Making a Drawplate

People have used drill gauges as drawplates, but these tend to wear out fairly quickly (bamboo is also abrasive). If you have access to a drill press, a drawplate is relatively easy to make.

Start with a piece of steel about a half-inch wide and 1/8 inch thick ("hanger-bars" for file folders are designed to be snapped off to the length of the file drawer; the waste piece works fine to make your own drawplate).

Start out by laying out a center-line, and drilling a series of 1/16" holes ("dimples") halfway through the steel bar (1, 2). It's well to have more dimples than you need - as the drawplate wears, you can re-drill each hole to the next size larger, and add a new "smallest" hole to the end of the line.

At one end, using your largest hole drill (e.g., #60), drill into the first of your prior dimples until the drill comes out the other side (3, 4). Repeat with the next size smaller drill (e.g., #61) at the next dimple. Continue to your smallest drill (e.g., #80).

Note: if your drill chuck is too loose (or worn) to hold these tiny drills, wrap a few turns of copper wire around the shank to "bulk" up the diameter so the chuck can grab them.

Where each drill broke through, you're likely to have a burr (4). Using a file or sandpaper on a block, smooth these off. Do not ream out the hole! You want the hole to meet the flat surface with a 90 degree sharp edge (5) (this is where the trunnels are shaved to size; any taper to the hole will compress the wood rather than shaving off the surface! It will also speed wear!)

Making Trunnels

Start by splitting the bamboo into pieces that will fit into the largest hole in the drawplate. Sharpen one end so it readily goes into the hole.

Feeding the stock from the "non-dimpled" side into the first hole; pull it through, shaving off the outside surface.

Repeat with the next sized smaller hole. continue until the desired size is reached. It's a good idea to pull the trunnel through the next hole (one size smaller than the drill you're using) as well - moistened with glue, the trunnel is likely to swell slightly.

Using Trunnels

First of all, if the trunnel is not perfectly round (because you split the stock too thin), that doesn't matter - at these sizes, any gap between the trunnel and the plank will be filled with the glue, and the hole is round!

Some people prefer to trunnel each plank as it's applied, drilling each hole and applying a peg before moving on to the next peg. Others add the trunnels after a group of planks have been mounted. The latter approach has much to commend it (provided you remember to mark the lines of fastenings as you go) - drilling a series of holes and then going back to apply a mass of trunnels is significantly faster than doing them one-at-a-time.

Again, some people prefer to carefully clip off each trunnel flush to the planking before moving on to the next; others just snap them off and proceed to the next, coming back later to cut/sand/file/scrape the surface smooth.

The "nailing" patterns vary with period and plank width - a plank 6" wide might have one fastening at each beam/frame (alternating from side to side: , ` , ` , ` )
a 9" plank might have alternate between one and two: : . : ' : ),
while a 12" plank might have two: : : : : : ).
{John O. Kopf (with a lot of input from the Ship Modeling List!)}

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