Tree Nails

[BenMP]

I have been reading "Wooden Boat Designs", by Christian Nielsen, and he talks about using tree nails (basically a dowel/peg that is either flared on one side and wedged on the other, or wedged on both ends). At first I thought that it was an availability issue but they were used along side of metal fasteners.

I was wondering since corrosion seems to be a major reason for refastening a wooden boat if using tree nails would lead to greater longevity?

Any thoughts/experience?

[PAR]

A trunnel (what you're calling a tree nail) is an option which has good and bad attributes, much like everything else. Trunnels aren't as strong as metal fasteners, they can rot, they can swell up and split the planking, they're more easily sheared, etc. With the advent of metal fasteners, trunnels took the path of the Dodo for the most part, mostly because of the advantages of metal over the disadvantages of trunnel fastening. This is evolution at it's best. With modern adhesives, the metal fastener is experiencing a similar fate, though at a much slower rate then the trunnel did, mostly because metal fasteners still have uses aboard ship. In the evolution of yacht design the trunnel was kicked to the curb, about as fast as hemp rigging was in favor of mild steel wire rope rigging. In fact, attempts at other forms of fastening where in place for about 100 years, before the mass produced wood screw came to be, such as edge nailing strip planks, all in an effort to eliminate the need for trunnels.

This isn't to say trunnels are dead, but it is to say most see the advantage of other fastening systems. About 1% of all new wooden builds will have trunnels, which is an indication of it's rank as a fastener system. As a very young man I mentioned trunnels to an old timer I admired. His comment was if I wanted rotten frames in several years, then use trunnels, other wise use metal. I questioned this and he said that a trunnel will swell up and shrink, just like the planking and on those occasions that a perfect seal wasn't made, moisture would commute down the hole into the frame where it would remain, rotting the frame out internally. He also mentioned they can wick moisture into the center of a frame as well, because the frames were generally of lower moisture content then the planking and trunnels, so they suck moisture through the trunnels. How much of this you want to believe or not is up to you, but much of it makes good sense to me.

[Fanie]

Hi Ben,

What ever nails you put in there you have to take out again or have fire and brimstone descent on thee



*cough*... *cough*... just a private joke

[Boston]

I made mention of tree nails a long time ago on here somewhere. I build a lot of goofy artwork type stuff and use a number of different all wood fastenings. The primary advantage of all wood fasteners is that as the piece ( boat in this case I guess ) flexes a metal fastener will chew at the wood until it invariably comes loose given enough time, an all wood joint on the other hand flexes evenly and has the potential to last generations. Just take a look at all the old ships being preserved in just about every major city's harbors. Might also take a look at the cost of keeping those old beauties floating.

I've made bazillions of tree nails, when I'm just doing a piece for someones house I use the same type of wood the piece is made from. But back in the day out in my grand dads shop they were typically white oak and they were always bedded in whiting. Whiting is an evil leaded putty like crap you never want to have to play with. a proper tree nail is fluted and has a slight bugle to it about 1/3 of the depth of the plank or piece your attaching. I don't do a lot of Proper tree nails. I tend to just use dowels these days. The idea is that as the planks swell they "lock" onto the nail. when the frame swells it "locks" onto the fluting

my take is like Pars, I think its a solution for a bygone era. I considered there use at one time but after tortuous deliberations I decided planking is a disposable item on a wooden boat in which ease of maintenance is a key component. Your going to end up doing a lot of swearing trying to drill out even a poorly set tree nail VS unscrewing a descent Philips head screw with that other little marvel of the modern world, the cordless screwdriver.

yah there are benefits but ya there are even more draw backs

[hoytedow]

The Trojan Horse was built with trunnels so it could get past the metal detecter at the gate.

[PAR]

. . . yea, but she complained of splinters anyway . . .

[hoytedow]

[Petros]

I use lot of wood dowels on the skin-on-frame kayaks I have built. I tried using metal fasteners but they were not faster to install, they are not as strong in the very small members used on a kayak, and they cost more. So the dowel fastener was actually better, and the kayak is a flexible design so they do not wear the holes larger as the frame flexes.

they do still have useful applications, but as Par points out, for most uses they are just obsolete. If you in a remote location with lots of wood and no nails or screws, than trunnels, lashings and wood dowels are the best way to build a boat....or a Trojan Horse.

[redreuben]

I think they are useful in decorative work, so much nicer than filler over a screw head and coating with epoxy before inserting takes care of the swelling issue and they are much kinder to planer blades ! my .02c
RR

[Boston]

I agree 1000% Reuben
there's a lot you can do with a treenail that you just cant even come close to with a metal fastener

there is something fascinating to a lot of people about a work done with no metal fasteners

[redreuben]

Diverging somewhat but another method of no fastener construction is double headed (formwork) nails, whereby the lower head holds the piece in place while the adhesive sets and the upper head is then used to remove the nail leaving a fastener free piece. But you are still left with holes to fill albeit smaller than a screw.

http://www.answers.com/topic/double-...il-form-nail-1

Also ideal for strip planking.
RR

[Boston]

I've used my share of form nails but only on "forms"
temporary stuff for concrete

I guess I never considered them for glue joints

I prefer to puzzle piece my stuff together and then "lock" it together with wood pins/tree nails/dowels something like that
to each his own

cheers
B

[redreuben]

Bostan,
yes sure for fancy stuff, but for the mundane stuff like edge framing, stringers to ply sheet, laminations etc form nails are cheaper than 50 G cramps !

[PAR]

I'll disagree in that trunnels are effective and in any regard better then metal fasteners, let alone structural adhesive. Dan puzzle joints in marine applications usually means, you've managed to design a joint that will trap moisture within it, instead of the common practice of designing the joint off drain off any accumulated moisture naturally. An example is a simple scarf, which if drawn up by a professional, will always face away from the flow of water, as to prevent water being driven into the joint. Or a simple butt joint on a deadwood assembly where a stopwater (yes it's similar , but not the same as a trunnel) is located to swell at the presence of water and prevent moisture from getting past the rabbet line, keeping the interior of a boat dry.

Trunnels are cute, quaint and effective if you're not especially heavily loaded. Place them in shear and you'll quickly see why they were abandoned 150 years ago, much like tissue paper instead of your hand or a corn cob. Cyclic loading on a trunnel will pull it apart. A metal fastener can be sized to be so much stronger then the surrounding wood, that cyclic loads can only damage the wood, not the fastener.

[BenMP]

PAR,
I'm curious about the cyclic loading, couldn't you make trunnels bigger that wouldn't come apart but that also wouldn't damage the surrounding wood like a metal fastener might?