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Thread: Trunnel Fastening

  1. #1
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    Default Trunnel Fastening

    I just got a call from, Ward Vance the owner of the 59' Sewanhaka Schooner "Charmian" that is under restoration in Dana Point CA. The question was as to what kind of wood should be used for the trunnel fastening of the new white oak futtocks that are needed in some areas. Ward asked if white oak should also be used for fastening. This brought to mind, the thousands of trunnels I once made for the construction of the mine sweeps that were built by Hubbard's South Coast Co. in Newport Beach CA. The Navy specs. called for trunnels made of black locust and that is what we made them of. The old shipwright I was working with told me that locust is stronger than most woods in resisting shear loading, stronger than white oak. It also is highly resitant to rot. The wood is so stong in this respect that it can be filed directly across the end grain with a farriers rasp without the slightest tearing. It is also highly resistant to splitting all trunnel fastenings were either open wedged or fox wedged. So, it looks like "Charmian" will have her sawn frames fastened with locust.
    Jay

  2. #2
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    Default Re: Trunnel Fastening

    As I started to read your post I thought you were going to ask what wood to use and my first reaction was to tell you to use black locust. afaik it's the traditional choice.

    Doug

  3. #3
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    Default Re: Trunnel Fastening

    Interesting to hear that somebody has some considerable hands-on experience with trunnels. I've used them here and there over the years, usually replacements in repairs, but I've never seriously hung any plank using them. They fascinate me, though. More so these days with the cost of bronze fastenings in the larger sizes or similarly sized copper rivets. The issue for plank, of course, is shear strength. Seems that locust has stood the test of time there.

    I am wondering, though, whether the use of modern adhesives might eliminate the need for wedging, which is tedious. My thought is that gluing them in place with epoxy might be a lot more efficient, and maybe even provide better holding power, than wedging. Of course, you'd have to run a groove or two down the sides to allow excess googe to squeeze out when it was driven, but it seems it would be a lot quicker than cutting the slots, making the wedges and all that. You would have to drill the whole trunnel out to remove one, but I've never found a loose wedged one yet, either. They seem to swell in really tight if they were properly dried and the hole properly sized to begin with.

    Any thoughts on this, Jay?

  4. #4
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    Default Re: Trunnel Fastening

    I would expect that the glue would fail, cross grain situation which glued joints don't like. A proper trunnel is like a rivet, the joint can expand or contract as needed.
    Another issue is repair, if the glue does happen to hold, it would be necessary to drill to a larger size to remove the trunnel, where drilling a smaller hole down the center to weaken it enables a trennel to be removed with a drift punch, without changing the original size.
    TALLY HO
    Ken

  5. #5
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    Default Re: Trunnel Fastening

    When we built Friendship (http://www.salemweb.com/frndship/) they (NMHS) were sticklers for "authentic" details. They wanted locust plugs over countersunk screws to simulate trunnels.
    We had to cut hackmattack knees and then notch them to slip over galvanized steel knees. If you ever have the opportunity to visit the ship in Salem, make friends with a "friend of Friendship"(or whatever they're calling themselves now" and ask to go into the lower holds so you can lift up the sole and see the "authentic" 3/4" thick galvanized steel floors If you get a chance, pry off a ceiling board in the lower forward hold. I wrote my name on every single one and some choice poetry on many

    Doug

  6. #6
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    Default Re: Trunnel Fastening

    I use thin epoxy with trennels for two reasons: Seal the end grain of the plank; and provide a little lube to get the trennel in. I don't think a well fitted trennel needs a blind wedge to stay in. Nor does it need the glue to stay in. Figure about 1" diameter trennel for every 100' waterline. So a half inch trennel is pretty big and even with the contraction of a normal haul - not any three years on the hard - will not loosen the fastening the way it will with screws.

    One trick I use is to have the trennel grooved lengthwise partly so excess epoxy will run out and mainly to relieve the air pressure of driving the trennel in. It should be that tight.

    G'luck

  7. #7
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    Default Re: Trunnel Fastening

    What Ian said except I wouldn't use the epoxy on the trunnel. I have a couple of plates in storage for cutting the grooves in the trunnel by making the dowel and driving it through the die....we used black locust but I also used bois d'arc when it was available...(preferable)
    Wakan Tanka Kici Un
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  8. #8
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    Default Re: Trunnel Fastening

    We turned our trunnels for the sweeps out on a small metal lathe that had a lever action tail stock with a Morse Tapered spur driver in the head stock. The screw feed automatically cut them in one pass. They were jig split, for the wedges, on a band saw. Those trunnels were 1/2"X 6" We used them for hanging planking. Trunnels are really only practical for fastening heavy planking or futtocks. On a lighter boat, using trunnels would be a study in futility. Here, bronze screws are really the most practical fastener to use. Copper rivets though cheaper from a material point of view are vastly more labor intensive and are a second choice as they can loosen up if a boat is always hauled in the winter.
    Jay
    Last edited by Jay Greer; 10-06-2007 at 08:30 PM.

  9. #9
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    Default Re: Trunnel Fastening

    I've read that 1" per 100' figure before ,interesting ,but wouldn't the trunnel be better referenced from the frame dimension .My frame stock ( for sawn frames) is 1 3/4" sided ...Jay what size trunnel would you spec for that ?
    '' You ain't gonna learn what you don't want to know. ''
    Grateful Dead

  10. #10
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    Default Re: Trunnel Fastening

    Quote Originally Posted by PeterSibley View Post
    I've read that 1" per 100' figure before ,interesting ,but wouldn't the trunnel be better referenced from the frame dimension .My frame stock ( for sawn frames) is 1 3/4" sided ...Jay what size trunnel would you spec for that ?
    Peter,
    In my humble opinion, your frames are too light for trunnel fastening.
    3/8" is the smallest practical diameter for a timber joining trunnel and that would still be large enough to weaken your frames. I feel that bolts or rivets would be a better way to go if you are joining futtocks, especially if your designer specified same. Again for planking, then screws or rivets would be a better choice.
    Jay

  11. #11
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    Default Re: Trunnel Fastening

    Agreed Jay .It had crossed my mind with the price of copper and bronze lately .I have recently acquired a reasonable pile of 5/16" copper rod from a recycler, most of it is becoming futtock to futtock bolts .What remains will become plank spikes ....a common practice in Oz .The balance will have to be bought new .
    '' You ain't gonna learn what you don't want to know. ''
    Grateful Dead

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