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Thread: Fixing unfair steam bent keel

  1. #1
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    Default Fixing unfair steam bent keel

    I'm building the Herreshoff Dinghy which has a sprung keel. It's 1 3/8 inches thick white oak, which I steamed and bent over the molds.

    Unfortunately, the curve aft of station 7 is pretty tight and my bending didn't produce a fair curve as you can see in the picture below.

    20181108_160416.jpg
    *Note - I left the keel long for now, it will get cut so that it only extends about 2 inches beyond station 8.


    What's my best course of action to fair it out? Is it salvageable?



  2. #2
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    Default Re: Fixing unfair steam bent keel

    It looks like there was a knot very close to that hard spot in the curve. About the only way I could have seen making that stick work would have been to define the intended curve with a piece of wood between the moulds so it could have been clamped continuously along the curve (and clamp that high spot down).
    It would have to be steamed for this to work.

  3. #3
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    Default Re: Fixing unfair steam bent keel

    Spring a batten next to it and draw a pencil line. Maybe it is not as far out as it appears and can be faired.

  4. #4
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    Default Re: Fixing unfair steam bent keel

    Since steaming dries the wood, I'd soak it in water for a day or two, then resteam it and bend it with some extra support as nedL suggests.

    /Mats
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  5. #5
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    Default Re: Fixing unfair steam bent keel

    Or, you just build to the keel you have. The option would be to redo the keel.

  6. #6
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    Default Re: Fixing unfair steam bent keel

    I would steam another one. This early in the game, you want to get the best start possible.

  7. #7
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    Default Re: Fixing unfair steam bent keel

    I had the crazy grain around a knot near the end of an outer gunwale give me an unfair curve. I am redoing it, not because it is non-functional but because it offends the eye. I plan on cutting the kinked part off and using the wood for the inwale, which is shorter.

    Looks like you have a lot of deadwood/skeg to add to that spot, so you may be able to just plane off the biggest hump and cut the rabbet fair. Draw a fairer curve on the keel with a batten to check if you are getting too close to the edge to do this. Don't worry if your bottom curvature in that spot isn't exactly as drawn on the plans, it is probably not a dealbreaker but you might have to redo a mold as well. In traditional Newfoundland boatbuilding the lines were slightly adjusted to the materials available, especially at the stem where naturally curved wood was used.

    If you are choosing to redo it, using a former mentioned above sounds like a good idea, but it also might help to leave the end a couple of feet longer. Steam or not, it is much easier to bend curvature into the middle of a piece than at the bitter end.

  8. #8
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    Default Re: Fixing unfair steam bent keel

    Quote Originally Posted by Schooner36 View Post
    I would steam another one. This early in the game, you want to get the best start possible.
    Good advice here. Also, you might consider making a solid form under the workpiece where it goes into the sharper bend. This will allow the piece to be clamped onto the form to avoid putting all the stress on one portion of the keel.
    Last edited by Jim Ledger; 11-09-2018 at 09:54 AM.

  9. #9
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    Default Re: Fixing unfair steam bent keel

    That is a very easy piece of oak to remove and throw away.
    Much easier than most of them that have boats attached.

  10. #10
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    Default Re: Fixing unfair steam bent keel

    Quote Originally Posted by Schooner36 View Post
    I would steam another one. This early in the game, you want to get the best start possible.
    +1
    If you have much grain runout or any knots, the board won't bend well. The area near the knot bent more because it is weaker than the rest of the board.
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    Default Re: Fixing unfair steam bent keel

    I should clarify a couple things. There is no knot or grain runout at the hard point in the curve. I believe the hard point was caused because I used a form above the molds (i.e. on the bottom of the keel) and the ends of the form (which was of doug fir) crushed from all the pressure. So I don't believe it's an inherent structural weakness in the wood itself, but rather my own mistake.

    Does that change anything to those who suggested redo'ing over some kind of fix?
    Last edited by ptscho; 11-09-2018 at 12:36 PM.

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    Default Re: Fixing unfair steam bent keel

    BOI - Yes, there is a lot of skeg to run along this section. Just planing the rabbet fair seems like an ideal solution to me in terms of not wasting material, as long as I would be left with enough to fasten the garboard. I'll have to check just how much would need removal with some battens.

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    Default Re: Fixing unfair steam bent keel

    Quote Originally Posted by ptscho View Post
    I should clarify a couple things. There is no knot or grain runout at the hard point in the curve. I believe the hard point was caused because I used a form above the molds (i.e. on the bottom of the keel) and the ends of the form (which was of doug fir) crushed from all the pressure. So I don't believe it's an inherent structural weakness in the wood itself, but rather my own mistake.

    Does that change anything to those who suggested redo'ing over some kind of fix?
    No, by using a form under the keel annd ensuring that it is wet enough and steamed for long enough it should bend rounds without problem. As you have left extra length on, bend the extra bit around a slightly tighter radius curve than the keeper part.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Fixing unfair steam bent keel

    Quote Originally Posted by ptscho View Post
    I'm building the Herreshoff Dinghy which has a sprung keel. It's 1 3/8 inches thick white oak, which I steamed and bent over the molds.


    20181108_160416.jpg
    Quote Originally Posted by ptscho View Post
    BOI - Yes, there is a lot of skeg to run along this section. Just planing the rabbet fair seems like an ideal solution to me in terms of not wasting material, as long as I would be left with enough to fasten the garboard. I'll have to check just how much would need removal with some battens.
    There is a fair bit of deadrise there, so by skew nailing you will have plenty to aim at.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Fixing unfair steam bent keel

    Quote Originally Posted by ptscho View Post
    I should clarify a couple things. There is no knot or grain runout at the hard point in the curve. I believe the hard point was caused because I used a form above the molds (i.e. on the bottom of the keel) and the ends of the form (which was of doug fir) crushed from all the pressure. So I don't believe it's an inherent structural weakness in the wood itself, but rather my own mistake.

    Does that change anything to those who suggested redo'ing over some kind of fix?
    It looks like the growth rings loop around the knuckle as if there was a knot in the log next to the plank. Maybe it is just saw marks, but in your picture it does look like the grain is running around something. If you can plane it to a fair curve with enough left to nail, it should be fine. The planks and frames probably provide plenty of strength.

    whatknot.JPG
    Last edited by MN Dave; 11-09-2018 at 09:16 PM.
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    Default Re: Fixing unfair steam bent keel

    ^...Correcto.

  17. #17
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    Default Re: Fixing unfair steam bent keel

    Thanks for taking the time to draw that out MN Dave - that is super useful to see.

  18. #18
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    Default Re: Fixing unfair steam bent keel

    Follow up in case anyone's interested - after reading all the feedback and checking how off it is with some battens I've decided to redo it. I hate scrapping the wood, but it would bug me knowing it's not right.

    Thank you all for the feedback, much appreciated. I'll post a picture of the new one when it's done (though that probably won't be until the weather warms up again in the spring).

  19. #19
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    Thumbs up Re: Fixing unfair steam bent keel

    Good move. Keep us posted on the build.
    -Dave

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    Default Re: Fixing unfair steam bent keel

    It almost seems a few strokes with a good plane would eliminate that hard spot without weakening the material all that much. Might be worth a try before you scrap it. On second look, maybe not...

  21. #21
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    Default Re: Fixing unfair steam bent keel

    Got a warm day and attempted round 2 with no success. Much straighter grain, steamed about 15 minutes longer, over a sturdier jig, but it failed in tension and split.

    In the interest of saving wood, money, and time - any opinions on laminating this curve and attaching it to the rest of the keel? (either scarfing it in, or lapping the laminates into notches in the keel as I'm gluing). Total keel length is just over 10 feet, and this section would be the aftmost 14-18 inches.

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    Default Re: Fixing unfair steam bent keel

    That's where I'd go next.
    Is your oak green or kiln dried? I'm surprised it failed again.
    -Dave

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    Default Re: Fixing unfair steam bent keel

    Hmmm,.... sorry to hear that. You really shouldn’t be having this kind of trouble as you really aren’t asking much of it (not much of a bend).
    I see no problem with your ‘plan B’, that should work just fine ( either way you proposed it).

  24. #24
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    Default Re: Fixing unfair steam bent keel

    It will probably be less work to build up the underside, fair it in, then correct the rabbet.

    I'm having a hard time understanding what's going on there, but perhaps you can build up the underside as suggested by adding a transom knee that extends past the unfairness. Glue it in place with epoxy then fair the rabbet, even if that means cutting it into the knee. Then it won't look like a repair.

  25. #25
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    Default Re: Fixing unfair steam bent keel

    You could build a jig with the correct shape then steam the section between the frames again and clamp it to the jig to get the right shape. Building the jig would be the hardest part. I would steam it inside a plastic tube that can be slid onto the end of the piece and slid off when you are ready to clamp it up. Note only steam the spot you need to bend. Two hours work and you are done.

  26. #26
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    Default Re: Fixing unfair steam bent keel

    How big is your steam box and what are you using for a steam generator? In your picture it looks like there is no bend in the wood between stations 6 & 7 all the bend is just forward of station 7. Are you etting the wood hot enough in your steam box. The steam box should be as close to 212 F as possible and not below 200F. It is the heat that softens the lignin in the wood its release allows the wood fibers to slide and bend. The steam is merely the carrier of the heat. Here is a link to a pretty good explanation of steam bending. www.leevalley.com/en/html/05F1501ie.pdf
    That keel is a relatively shallow bend. I have gotten up too 3" radius bend out of red oak using boiling water and a pvc tube with out any problems. I think you might be losing too much heat from your steam box.

  27. #27
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    Default Re: Fixing unfair steam bent keel

    I might consider applying a galvanized steel tension strap just as it comes out of the steam box.
    (Some "duct strapping" or "sheer strapping" wrapped around the butt end and clamped, with the ford end maybe pinned and clamped at a place well ford and between stations)

  28. #28
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    Default Re: Fixing unfair steam bent keel

    I am not familar with your oak, we do not use it downunder.
    But this techinque may work as it is used when one does not have a steam box.
    Take the timber to the band saw and cut horizontally at least 1 or 2 even cuts horizontal to the keelson.
    Note I think it is a Keelson not a keel. But I might be wrong - not for the first time!
    Cut to 100 to 200 mm forward of the last frame. Use the thin blade of a bandsaw.
    And then gently bend it to shape on the molds. Check the shape looks okay (ship shape with design) with a batten.
    Once you are happy with the fit, remove, use a wedge to open the cut up a little and a syringe to inject glue into the cut, then fasten the keel into the molds before the glue hardens.
    Iain Oughtred refers to this techinque in 4-41 of his book Clinker Plywood Boatbuilding Manual.
    You could reverse the keelson so that the hard spot wood grain is on flat part of the boat......what is the other end like with respect to grain?

  29. #29
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    Default Re: Fixing unfair steam bent keel

    Take a look here (you can see how simple this fixture is)

    http://www.leevalley.com/us/wood/pag...73&cat=1,45866

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    Default Re: Fixing unfair steam bent keel

    Quote Originally Posted by Todd D View Post
    You could build a jig with the correct shape then steam the section between the frames again and clamp it to the jig to get the right shape.
    That's actually what I did from 2 2x6's. Here's a picture:
    20181209_170136.jpg
    It's cut for a slight overbend, by about a 1/2 inch on each end. The notches are so that my pipe clamps would get purchase easily.

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    Default Re: Fixing unfair steam bent keel

    Quote Originally Posted by Woxbox View Post
    Is your oak green or kiln dried? I'm surprised it failed again.
    It's air dried, though I couldn't tell you the moisture content.

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    Default Re: Fixing unfair steam bent keel

    Quote Originally Posted by bruce johnstone View Post
    How big is your steam box and what are you using for a steam generator? ... Are you etting the wood hot enough in your steam box. The steam box should be as close to 212 F as possible and not below 200F.
    Steam box is white pine. Interior dim of 4x8 inches.

    Steam generator is a 1/4 barrel keg (5-6 gallons) with automotive radiator hose. I use a 100k BTU propane burner.

    The keel stock is 1 3/8 inch thick and I steamed for 90 minutes.

    I drilled some small holes along the box for venting. I also continuously checked the temperature through these holes using a probe thermometer and the box registered at 210-212 the whole time.

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    Default Re: Fixing unfair steam bent keel

    I'd be tempted to rip that plank in half, same width, half thickness, and laminate it in place.
    Looking at the first pic, the plank didn't seem to spring properly between the forms to the left (between 7&6?). Thats a straight line all the way to that hard spot.
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  34. #34
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    Default Re: Fixing unfair steam bent keel

    Quote Originally Posted by ptscho View Post
    Steam box is white pine. Interior dim of 4x8 inches.

    Steam generator is a 1/4 barrel keg (5-6 gallons) with automotive radiator hose. I use a 100k BTU propane burner.

    The keel stock is 1 3/8 inch thick and I steamed for 90 minutes.

    I drilled some small holes along the box for venting. I also continuously checked the temperature through these holes using a probe thermometer and the box registered at 210-212 the whole time.

    Man, that should have worked. How long was the wood out of the box before you got it clamped down? That's the only missing piece of information here, and if the piece didn't have time to cool then it just plain should have taken the bend. But anyhow, since you've gone to the trouble to make that form, might as well use it for a lamination.
    -Dave

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