Laminating Stems

Discussion in 'Wooden Boat Building and Restoration' started by ancient kayaker, Feb 23, 2011.

  1. ancient kayaker
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    ancient kayaker aka Terry Haines

    On my current project I did not laminate the stems, they were each fabricated from 3 pieces of wood. Now I have a bit more experience with laminating I wish I had done them that way, I think they would have been tougher and maybe nicer looking.

    I found cutting the rolling bevels for the planks a harrowing experience. It was not difficult, once I gave up using a spokeshave and figured out an easy way to cut them with a chisel. But the stems for a lightweight boat are rather delicate, especially if they are rather long, as they are for this boat, and I broke one.

    I have an idea for the next time, as follows:-

    Cut strips for laminating.
    Screw them (still straight) to the edge of a plank, using plastic or brass screws.
    Mark and cut the rolling bevel (the bevel angles can be worked out during lofting).
    Remove them from plank: soak, steam or whatever. *
    Then bend them over a suitable jig.
    When dry, glue up, using screws or dowels in the screw holes at one end to line them up.

    * For this boat only the part round the sharp turn of the stem needs steaming. This can be done simply without building a steamer box by resting the strips on a saucepan of boiling water and covering them with an oversized lid. For the rest of the bend a one hour warm water soak is sufficient - based on my trial.


    It should simplify cutting the bevels and minimize breakages. Did I come up with this yet another idea that has been used for countless years by boatbuilders, or is there a fatal flaw? If it works it is a useful trick.

    Any other neat ideas for stems?
     
  2. michael pierzga
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    michael pierzga Senior Member

    Sounds good. Dont know if it fits into your design , but if your building an epoxy boat with a gentle sweep stem ... a false stem...two part...is a easy way to simplify cutting the rolling bevel into the stem and it generates a razor thin plank stem cap joint on a bright finished boat. The stem will probably have to be steamed, then laminated as you describe to avoid springback . Laminate the cap and stem over the mould at the same time, with a sheet of plastic between the cap and stem . Separate , cut the bevel on stem then cap and trim flush For a gentle bend on a small boat , try a hot air gun to relieve the wood strips as they are bent over a mould. .

    I like false stems...if its a fine stem profile, sooner or later it will get whacked and dinged then have to be capped for repair.
     
  3. gonzo
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    gonzo Senior Member

    I am not sure how you glue a stem to the edge of the plank. The stem determines what the edge of the plank will be. Either way, it is a complicated system. Look at what was developed through the centuries of boatbuilding. It is usually the most economic in time and materials.
     
  4. ancient kayaker
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    ancient kayaker aka Terry Haines

    I tend to minimize epoxy: the stem I am looking at presently has a very sharp curve (4" rad) but elsewhere it curves gently. The saucepan idea is good for steaming the middle of a long strip - I found it on the Wooden Boat Forum - but the hot air gun sounds neat. Good idea to bend the false (outer) stem at the same time ...

    You must have the lofting data to pre-determine the bevel, of course, and it’s not really complicated. The added step - attaching the strips temporarily to a plank for shaping - eliminates other steps. Screws would be better than glue - plastic or brass screws do not damage the cutting tool - but I use glue to joint planks together for ripping strips, it reduces waste and is safer when getting near the end of a plank.

    I study traditional boatbuilding methods and they give me many of my ideas. What might traditional boat builders have done over the centuries with modern materials? Methods are always limited by available materials, these days we a limited by shortages of good quality, straight grain lumber and naturally shaped crooks - the local park will not allow me to harvest fallen trees; it’s annoying to see all those spars and stems just rotting there.
     
  5. gonzo
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    gonzo Senior Member

    For laminating small stems, I use a jug of water, a bristle brush and a propane torch. Keep the wood wet while you heat it and you can bend it to really sharp curves.
     
  6. michael pierzga
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    michael pierzga Senior Member

    Good on you....I hate " gap Filling" "Rubber Gloved" " Half Tub wasted " epoxy !!!!!! Cutting the stem rabbit is a challenge...but half the reason you are messing around with boats is the challenge of using tools, your skills and thinking correctly.

    Go for it !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

    Hopefully your next boat will be one hundred percent epoxy free.

    Epoxy free craft are beautiful things that smell good, look good, last good and make you feel good.

    Oh and a propane torch works well...but I prefer a hot gun......no black skid marks. Black plastic, wet towels and bright sunshine also works well for small stuff and patience. . .
     
  7. ancient kayaker
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    ancient kayaker aka Terry Haines

    It is epoxy-free so far, but I'm not religious about it, it will get epoxy where needed. I'm not much on patience though ...
     
  8. PAR
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    PAR Yacht Designer/Builder

    Use a vertical laminate, rather then a horizontal laminate and a dory style stem cap, which commonly is called a false stem. This doesn't change the need for a rolling bevel along the rabbit or inner stem if a two piece arrangement, but can serve to cover the planking end grain, mechanically locks the hood ends in a two piece assembly, offers a replaceable, protective outer element to the structure, so it can be R&R'd when necessary, also doesn't need to be bent or steamed and simplifies the mill or hand work necessary.

    If you're not going to use wood butcher's friend, then your piece fitting ability, will have to go up into the water tight joint arena. If you do elect to use wood butcher's friend, then you can hack the stem out of whatever with a hatchet and glob enough goo on it, to make a perfectly water tight and seamless (under paint) stem.
     
  9. ancient kayaker
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    ancient kayaker aka Terry Haines

    I am using a false stem as you describe. For the laminated version the stem and false stem would be bent at the same time.


    I like “wood butcher's friend” (WBF) - such a poetic term! However, I plan to make the stem and planks fit properly and will use Titebond III between them. I will use WBF to attach the false stem.

    Some canoe and kayak builders dispense with the stem altogether, and use a poured epoxy stem molded in place instead - ugh! I admit I was tempted to do that when I started boatbuilding but as my skills improved my stomach became more sensitive ...




    For those interested in such things the math is as follows although the graphical method is easier:

    Depth of bevel D is related to the angles S and P at which the planking meets the stem in the profile and plan views as follows:
    D = w.cot(P)sin(S) - where w is the width of the bevel on each side

    For a plumb stem where S = 90 deg this basic equation simplifies to:
    D = w.cot(P)

    In my case the plank lines are parallel in both the profile and plan views so:
    A = w.cot(P) where A is a constant

    That simplifies the basic equation for me to:
    D = A.sin(S)
     

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  10. PAR
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    PAR Yacht Designer/Builder

    Your friends are correct, in that their poured stems are more efficient, effective, water tight, stronger, faster and more durable. Personally, I wouldn't pour the stem, which is novice like, but I would make a healthy fillet behind the planking, that was temporary held in position with whatever. The only place I'd have a piece of stem like material is where the bow eye would live. On the boat sizes you build Terry, this wouldn't be much more then a 6" or 7" long piece of 4/4's stock, tapered substantially at each end to avoid stress risers and WBF'd in place.
     
  11. ancient kayaker
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    ancient kayaker aka Terry Haines

    - but also heavier. I would worry about ability of the resin to absorb the shock of a head-on impact if the thickness were excessive, but a nicely-profiled fillet with glass tape undeneath should be every bit as effective at the stem as it is along the seams of a S&G hull. The resin stem is OK decently hidden under the deck of a kayak but for a canoe where it can be seen and where lightness - for me at least - is of the essence, I would still prefer wood for lightness, toughness and esthetics. A lot of those kayaks rely on glassing for much of their strength, with a double layer over the outside of the stem, but you know how I feel about that stuff ...

    That is about what I used for my solo ply canoes, which had fairly straight stems. For those I glued a half of the stem to each sheer plank while it was flat and beveled it before gluing them together; very easy and simple to do if you're working without a building mold as I tend to do.

    The one I am working on now has a long curvy beast of a stem like the illustration above.
     
  12. PAR
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    PAR Yacht Designer/Builder

    I would suggest a well made fillet and biax'd seam is lighter then a wooden stem of the same strength and stiffness. I'd agree a big hunk of poured in fillet would be heavy and unsightly, but if you arrange a fillet with taped edges, then fabric, then possably filling the weave with a wood colored skim coat, again also taped to define and limit the edges. The net result is a perfect edged stem or seam reinforcement, with pleasing looks, light weight, absolute water tightness and elongation to match or exceed the panel strengths surrounding it. These techniques are especially helpful on long curved seams like the one you're tangling with. As with everything in WBF land, it's all in the prep and technique. I generally use the blue painter's tape unless I'd being anal about the looks of the fillet, then I switch to the fine line (PVC I think) tape, which is much smoother then the crape paper of the blue stuff. With a bit of practice you can make the seam look like it has a molded piece of wood colored plastic down the seam, with machined edges.
     
  13. ancient kayaker
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    ancient kayaker aka Terry Haines

    Sounds like a good plan and certainly an efficient solution for the hassles of working with this style of stem.

    I have to admit I am rather enjoying the challenges of stem carving. This not like me at all: I am generally all about getting the job dones as quickly and efficiently as possible. Perhaps I carry the craftsman gene after all ... unless I have become anal in which case a change of diet is indicated!

    ps I hope you are feeling better.
     
    Last edited: Feb 24, 2011
  14. PAR
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    PAR Yacht Designer/Builder

    Technically, I'm allowed to use the laptop to log on and talk to folks, but the desk is still off limits. I was warned about her . . .

    If you watched the filleted seam process, as I just described in person, you'd probably drop your chisels and start taping up your boat. I usually don't bother with the tape trick, knowing I'm going to paint, so fairing putty is coming next. I don't like the look of fillets on natural finishes, but this has changed over the years, where I can now accept this look. I guess it's like square headlights, which took me a while to learn to like too.
     

  15. ThomD
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    ThomD Senior Member

    The stems of a lot of canoes and kayaks are highly overbuilt. One place where it makes sense, is where there is a lot of hollow in the design, whether that makes sense is another mater. But the added stem lams allow the hollow to be carved in. Otherwise a filleted stem is far more efficient. The fillet can often be microscopic. I made a pair of 16' cat hull where all I did was wipe each side of the ply with a bit of filleting blend about a cigarettes worth, and press them together. Of course the outer stem was glass taped. Been around for 15 years and has proven amply strong.
     
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