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Thread: Transom rods

  1. #1
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    Default Transom rods

    Hello !

    I know I've seen a drawing somewhere showing the glue up / lamination af a transom with some sort of "rod/pin" going through each board of lamination

    What is the official term for these rods/method and does anyone have a sample drawing

    Thanks

    SteveO

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    Default Re: Transom rods

    Drift pins, maybe? That's what they call them in keels/deadwood, I think. I imagine they might help keep things in alignment during the glue-up, but with modern glues I doubt they're necessary.

    I glued up my transom flat, on a sheet of plywood covered with plastic so the glue wouldn't stick. Worked fine for me. I didn't use splines, either--when I looked into it, there didn't seem to be a consensus that splines were superior, and they would certainly have been more trouble.

    So, simple edge-gluing for me. And my boat still floats!

    Tom
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  3. #3
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    Default Re: Transom rods

    Quote Originally Posted by WI-Tom View Post
    Drift pins, maybe? That's what they call them in keels/deadwood, I think. I imagine they might help keep things in alignment during the glue-up, but with modern glues I doubt they're necessary.

    I glued up my transom flat, on a sheet of plywood covered with plastic so the glue wouldn't stick. Worked fine for me. I didn't use splines, either--when I looked into it, there didn't seem to be a consensus that splines were superior, and they would certainly have been more trouble.

    So, simple edge-gluing for me. And my boat still floats!

    Tom
    Thanks !!

    I'm doing a 2" x 36" x 77" Mahogany transom in 2 - 1" overlapping layers

    And what would be the Glue/epoxy/caulk adhesive of choice ?

    SteveO
    Last edited by SteveO24; 09-07-2022 at 01:47 PM.

  4. #4
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    Default Re: Transom rods

    Quote Originally Posted by SteveO24 View Post
    Thanks !!

    I'm doing a 2" x 36" x 77" Mahogany transom in 2 - 1" overlapping layers
    If you run the layers at 90 degrees to each other, you will not need any drifts.
    It really is quite difficult to build an ugly wooden boat.

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  5. #5
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    Default Re: Transom rods

    It’s the knees that are more important than the thickness or reinforcement of the transom .

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    Default Re: Transom rods

    WOW! 77" wide transom...must be a biggish boat!

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    Default Re: Transom rods

    Quote Originally Posted by Peerie Maa View Post
    If you run the layers at 90 degrees to each other, you will not need any drifts.
    What happens when the moisture content of these 1” boards changes?
    Is the glue strong enough to restrain the boards’ expansion?

    The plywoods we know work because the individual plies are thin enough that the glues can keep things stuck.

  8. #8
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    Default Re: Transom rods

    Quote Originally Posted by JimConlin View Post
    What happens when the moisture content of these 1” boards changes?
    Is the glue strong enough to restrain the boards’ expansion?
    .
    The planks will split, it has to

  9. #9
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    Default Re: Transom rods

    Quote Originally Posted by JimConlin View Post
    What happens when the moisture content of these 1” boards changes?
    Is the glue strong enough to restrain the boards’ expansion?

    The plywoods we know work because the individual plies are thin enough that the glues can keep things stuck.
    Are drifts going to do a better job?
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Transom rods

    Quote Originally Posted by Peerie Maa View Post
    Are drifts going to do a better job?
    The drifts will at least maintain alignment.

  11. #11
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    Default Re: Transom rods

    Quote Originally Posted by JimConlin View Post
    The drifts will at least maintain alignment.
    So, you are assuming total failure of the glue?

    OK
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Transom rods

    Epoxy and 3/8" galvanized pins in my transom....
    I am not comfortable hanging my outboard on glued joints only.


  13. #13

    Default Re: Transom rods

    Quote Originally Posted by timo4352 View Post
    Epoxy and 3/8" galvanized pins in my transom....
    I am not comfortable hanging my outboard on glued joints only.


  14. #14
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    Default Re: Transom rods

    Quote Originally Posted by timo4352 View Post
    Epoxy and 3/8" galvanized pins in my transom....
    I am not comfortable hanging my outboard on glued joints only.

    Oak.
    nope
    wheres de knees?
    the OB will “hang” jusfine

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    Default Re: Transom rods

    Quote Originally Posted by peter radclyffe View Post
    Too cryptic for me. Got a comment or explanation? If I'm wrong, I don't mind learning why.

    Off Center Harbor seems to agree that drift pins are used in keels:

    https://www.offcenterharbor.com/vide...t-pins-screws/

    Tom
    Last edited by WI-Tom; 09-08-2022 at 02:36 PM.
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    Default Re: Transom rods

    Quote Originally Posted by Peerie Maa View Post
    So, you are assuming total failure of the glue?

    OK
    If the moisture content of the material changes much, a boards’ cross-grain movement will be connected to the long grain of the other layer by a film of glue. For all species I know of, the cross-grain movement is much greater than the long-grain movement. For the glue to remain intact, its bond needs to be strong enough to completely restrain the expansion/contraction. The force needed to do this is proportional to the thickness. THick pieces impose greater force on the glue than thin ones.

    You can get away with cross-grain glueing if the materials are thin or if moisture content doesn’t change much.

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    Default Re: Transom rods

    Have a read of this SteveO , it may help to answer your question and give some insight as well http://forum.woodenboat.com/showthre...rifts-Threaded

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    Default Re: Transom rods

    Quote Originally Posted by SteveO24 View Post
    Thanks !!

    I'm doing a 2" x 36" x 77" Mahogany transom in 2 - 1" overlapping layers

    And what would be the Glue/epoxy/caulk adhesive of choice ?

    SteveO
    Quote Originally Posted by JimConlin View Post
    If the moisture content of the material changes much, a boards’ cross-grain movement will be connected to the long grain of the other layer by a film of glue. For all species I know of, the cross-grain movement is much greater than the long-grain movement. For the glue to remain intact, its bond needs to be strong enough to completely restrain the expansion/contraction. The force needed to do this is proportional to the thickness. THick pieces impose greater force on the glue than thin ones.

    You can get away with cross-grain glueing if the materials are thin or if moisture content doesn’t change much.
    Jim. Are you suggesting total glue failure when the outer layer swells in compression, and how will drifts help? How much swell, and what forces will build up compared to the strength of the glue?
    I don't see solid mahogany transoms swelling enough to damage the planking nailed around their edges.
    It really is quite difficult to build an ugly wooden boat.

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  19. #19
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    Default Re: Transom rods

    Mea culpa!
    I grossly misunderstood post #3 to indicate that the two layers were perpendicular to one another.
    All of my thought on this was based on that mistake.

    We regret the error.

  20. #20
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    Default Re: Transom rods

    Quote Originally Posted by JimConlin View Post
    Mea culpa!
    I grossly misunderstood post #3 to indicate that the two layers were perpendicular to one another.
    All of my thought on this was based on that mistake.

    We regret the error.
    That was my suggestion in post #4.
    If Steve0 is planning parallel but staggered, an easy way will be to router recesses across the staves large enough to take a drift. Then when epoxying the stack together, the drifts can be laid in the epoxy filled groves during the glue up.
    If the joints land in the middle of each opposing stave, drifts may not be needed, as the staves will come and go together.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Transom rods

    Given that solid timber has the propensity to expand and contract with it's moisture content, the incorporation of solid metal bars that are bonded to the wood by glue, is a mistake. The bars/drifts should be left unglued so that the surrounding wood is left free to expand and contract. In this capacity, the bars/drifts continue to serve as alignment aids.

    Jeff

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    Default Re: Transom rods

    Quote Originally Posted by jpatrick View Post
    Given that solid timber has the propensity to expand and contract with it's moisture content, the incorporation of solid metal bars that are bonded to the wood by glue, is a mistake. The bars/drifts should be left unglued so that the surrounding wood is left free to expand and contract. In this capacity, the bars/drifts continue to serve as alignment aids.

    Jeff
    This^^^

  23. #23
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    Default Re: Transom rods

    Quote Originally Posted by jpatrick View Post
    Given that solid timber has the propensity to expand and contract with it's moisture content, the incorporation of solid metal bars that are bonded to the wood by glue, is a mistake. The bars/drifts should be left unglued so that the surrounding wood is left free to expand and contract. In this capacity, the bars/drifts continue to serve as alignment aids.

    Jeff
    Having expanded and been pushed along the drifts, when they dry and shrink, gaps will open or the paint/varnish will crack and allow water in to the joint. Yes?
    Drifts were always driven into a tight hole, typically 1/16th undersize, so that they really gripped the wood.
    It really is quite difficult to build an ugly wooden boat.

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  24. #24
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    Default Re: Transom rods

    Quote Originally Posted by Peerie Maa View Post
    Having expanded and been pushed along the drifts, when they dry and shrink, gaps will open or the paint/varnish will crack and allow water in to the joint. Yes?
    Drifts were always driven into a tight hole, typically 1/16th undersize, so that they really gripped the wood.

    Then drill the holes larger so that the boards can shrink unburdened. I never said my take here was traditional.

    We still know very little about the proposed build. It may be a trailered boat. The OP seems to have abandoned ship.

    Jeff

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    Default Re: Transom rods

    I'm going to suggest that anyone advocating driving a 36" long 3/8" drift through a 5/16 hole into 1" planks on edge has not done that yet...

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    Default Re: Transom rods

    Quote Originally Posted by SteveO24 View Post
    Thanks !!

    I'm doing a 2" x 36" x 77" Mahogany transom in 2 - 1" overlapping layers

    And what would be the Glue/epoxy/caulk adhesive of choice ?

    SteveO
    Steve, reading through the responses to your questions I think I’d be as confused as heck by now if I were you.

    It would help in providing advice (and opinions) to know what you are building and how you plan to finish it....?? Are you planning to glass over the finished hull and transom? Or just to varnish or paint it? Is the boat going to be left in the water or trailered??? Is it a sail boat, row boat or speed boat with a heavy outboard hung from the transom???
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  27. #27
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    Default Re: Transom rods

    Quote Originally Posted by Canoeyawl View Post
    I'm going to suggest that anyone advocating driving a 36" long 3/8" drift through a 5/16 hole into 1" planks on edge has not done that yet...
    Just so, it is almost impossible to find 5/16th 3' long augers these days.
    However, that does not change the historical facts of wooden boat building.
    It really is quite difficult to build an ugly wooden boat.

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  28. #28
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    Default Re: Transom rods

    3/8" is about the right size for a 1" thick plank. If it was 2" planks I would use 1/2".

    You can drill the planks individually before assembly, say a nominal 12" plank, no problem, or you can weld up a 3' drill bit, it is done all the time I have a stack of them although they are slowly going missing, borrowed, as life goes on. There will be a problem putting a 1/16" larger drift than the hole, you will not be able to do it unless perhaps you are building with Balsa wood.
    A 1/64" smaller hole will be a struggle that may prove fruitless. With a drift buckled, bent and impossible to retrieve, you could resort to tradition, whose I'm not sure, of cutting off the drift and staring over.
    (If I were going to build with drifts through 3ft of timber (which I have done it numerous times for keel bolts from 1/2" to 1" diameter) I would drill exactly the same size hole and say a little prayer that you do not bend the drift while driving it)

  29. #29
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    Default Re: Transom rods

    In post #3, the OP said he was going to do the transom in 2 each, 1" thick layers. He will end up with a 2" thick transom.

    Jeff

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    Default Re: Transom rods

    Quote Originally Posted by jpatrick View Post
    In post #3, the OP said he was going to do the transom in 2 each, 1" thick layers. He will end up with a 2" thick transom.

    Jeff
    I noticed that, but I wouldn't put drifts on a glue line. A 2" x 36" plank is going to move a lot. I would expect it to grow and shrink 1/4" or more, it will be impossible to restrain that. Better to build it so it can move, or resaw that into thinner planks and laminate it with epoxy effectively making plywood.

  31. #31
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    Default Re: Transom rods

    Quote Originally Posted by Canoeyawl View Post
    here will be a problem putting a 1/16" larger drift than the hole, you will not be able to do it unless perhaps you are building with Balsa wood.
    A 1/64" smaller hole will be a struggle that may prove fruitless. With a drift buckled, bent and impossible to retrieve, you could resort to tradition, whose I'm not sure, of cutting off the drift and staring over.
    (If I were going to build with drifts through 3ft of timber (which I have done it numerous times for keel bolts from 1/2" to 1" diameter) I would drill exactly the same size hole and say a little prayer that you do not bend the drift while driving it)
    You appear to doubt whether you can drive a drift into a tight hole.

    Scan_20220910 (2).jpg
    From Ted Frosts book from Tree to Sea, the build of a steam drifter in 1917.
    On a visit to the Brest Maritime Museum, I learned that their shipwrights could drive copper bolts through the deadwoods of a ship of the line. They did use a couple of tricks. They bored the hole with a step in dia halfway through'and made the bolts with a matching reduction in diameter, so in effect they were only driving the bolt into half of the depth. They also put an iron tube over the bolt and drove it down with a drift in the tube to stop it from bending.

    Mind you, I did make this suggestion earlier, which seems more sensible than drifting two 1'' panels together and then gluing them up to make 2''.
    Quote Originally Posted by Peerie Maa View Post
    If Steve0 is planning parallel but staggered, an easy way will be to router recesses across the staves large enough to take a drift. Then when epoxying the stack together, the drifts can be laid in the epoxy filled groves during the glue up.
    Last edited by Peerie Maa; 09-10-2022 at 01:24 PM.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Transom rods

    Realistically, what would be the point of full lenght drifts in a transom? The boards are fastened to a fashion piece and a central knee/sternpost, they're not going anywhere. The drifts have only one purpose, keeping the edge of the boards aligned by limiting any cupping, and for that purpose all that is needed are short drifts, a few inches into each board. If the planks are thick enough one can use trunnels or pinned floating tenons instead of metal drifts.

    For a two layers glued construction the drifts are superfluous, regardless of how the layers are oriented to each other. The glue area between the two layers is so large that the shear forces on the glue are less then the wood strenght, the boards will split before the glue fails.

    It can be advantageous to use locator pins during glue up, but for that a pair of dowels or biscuits is enough.

  33. #33
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    Default Re: Transom rods

    ^ Just so.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Transom rods

    Quote Originally Posted by Rumars View Post
    Realistically, what would be the point of full lenght drifts in a transom? The boards are fastened to a fashion piece and a central knee/sternpost, they're not going anywhere. The drifts have only one purpose, keeping the edge of the boards aligned by limiting any cupping, and for that purpose all that is needed are short drifts, a few inches into each board. If the planks are thick enough one can use trunnels or pinned floating tenons instead of metal drifts.

    For a two layers glued construction the drifts are superfluous, regardless of how the layers are oriented to each other. The glue area between the two layers is so large that the shear forces on the glue are less then the wood strenght, the boards will split before the glue fails.

    It can be advantageous to use locator pins during glue up, but for that a pair of dowels or biscuits is enough.


    How do you know that the boards are fastened to a fashion piece and a central knee/sternpost?

    Other than it being a 2" x 36" x 77" Mahogany transom in 2 - 1" overlapping layers, have I somehow missed something in the OP’s only two posts on this forum (according to his post count) that says what he’s building and how?
    Larks

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  35. #35
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    Default Re: Transom rods

    You haven't missed anything, I dont have more info than you. I know of only two ways of attaching a wooden transom, as described or with epoxy fillets and glass. Someone asking about drifts is unlikely to be building S&G, and you can't just screw or nail the transom to the plank ends without some form of corner reinforcement. A boat needing a 2inch transom will also have at least some way of connecting the transom to the keel.

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