Help with Keel/stem timber assembly and offsets

Discussion in 'Wooden Boat Building and Restoration' started by longfellow, Oct 30, 2009.

  1. longfellow
    Joined: Apr 2009
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    Location: upstate NY

    longfellow Junior Member

    My keel joins the stem forward of station one, just before station zero. The halfbreadth of the keel at Sta 1 is 2 inches. The stem's halfbreadth is 1 1/4 inches. The dilemma is; what is done about this differnce in widths where the keel joins the stem? There is an abrupt change in width here with the four inch wide keel butting into a stem at 2 1/2 inches wide. The rabbet halfbreadth on the keel at Sta 1 is 1 1/4, as it also is on the stem. On the keel though, the bearding line runs out to the full 2 inch halfbreadth while at the stem, naturally, the bearding just goes out to the stem width which is the 1 1/4 dimension. There doesn't seem to be any issue with leaving everything alone (except perhaps there being a place for water to collect in this corner). But I would also still have plenty of nailing surface in the rabbet of the keel if I faired the keel's width to blend in smoothly with the more narrow stem but it will not look fair having to narrow up so quickly and will likely also leave some unsupported end grain (or grain runout, if you will) on the garboard. What is typically done here. I am positive that the entire stem all the way to the front end of the keel is supposed to be 2 1/2 inches.
    Thanks,
    Ed
     
  2. Gilbert
    Joined: Aug 2004
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    Gilbert Senior Member

    Tapering the keel piece to two and a half inches at its forward end as you are suggesting sounds like the best thing to do. Depending on the station spacing, the slope of the planking, etc. there could still be a pocket for water to stand but it should be much smaller if so. It is pretty standard to use pitch or cement to fill recesses caused by frames, floor timbers, and such meeting centerline timbers to prevent water standing there.
     
  3. gonzo
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    gonzo Senior Member

    I am not sure what you mean by rabbet halfbreadth. The rabbet is cut so the plank lays easily in it. As you use a batten, it will fair itself.
     
  4. longfellow
    Joined: Apr 2009
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    longfellow Junior Member

    Gonzo,

    Rabbet Halfbreadth - The distance from the longitudinal centerline of the hull to the rabbet when viewing either body sections or the hull's plan view. It is right on the table of offsets and is necessary to fair the rabbet, to develop body sections and such. Ed
     
  5. gonzo
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    gonzo Senior Member

    As long as the rabbet line, the one you see as a seam from outside is fair, the rest resolves itself
     
  6. favoredhand
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    favoredhand New Member

    What If

    What If at the section your're describing is covered with a bulk head or interior faming. How much will this effect the overall? Typical on chine hull construction to fade the keel into the stem.
     
  7. longfellow
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    longfellow Junior Member

    I am not worried about appearance; only structural integrity. The halfbreadth of the keel at its extreeme end is wider than the stem which is my only 'curiosity.' This happens between station one and station zero. By the way this is a bent frame hull if that helps you advise.
    Thanks.
    Ed
     
  8. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    It's not unusual to have the keel batten (the batten is assumed) taper to nearly that of the stem's sided dimension. Often the keel batten is slightly wider at the intersection of the stem.

    What I'm hearing is you have a 4" keel batten landing under a 2.5" stem. The usually approach is to fair from the point the batten is narrower then the entry angle permits. In other words, the planking is attempting to land on the stem's rabbit and the garboard seam is also coming up to meet the stem too. All the while the boat is tapering down to the "entry". This wedge shaped area is eventually going to get smaller then the keel batten is wide, so it's also tapered to match. Yes, this does open up some end grain, but it also offers a little more area to support the garboard.

    If you had a picture or two, I could attempt to describe it better, as it's simpler then it sounds when I re-read what I've written.

    As fair as structural integrity, if the "meat" at the base of the stem or the end of the keel batten isn't sufficient, then a "gripe" is usually installed, which looks like an upside down knee. The nature of all the pieces converging into this area tends to make it quite stiff, unless it's a racer and they've whittled weight out of every location to "ease her burden". It's not uncommon to see a fairly rapid taper on the keel batten.
     
  9. longfellow
    Joined: Apr 2009
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    longfellow Junior Member

    More detail

    Here is the issue in question. You can't see the rabbet line drawn on the stem siding that I will be cutting, however at the joint which butts into the keel the rabbet is about 3/8 inch in from the front face. Again, the rabbet halfbreadth at this location is the same as the halfbreadth on the stem, just forward (In other words, it fairs down to the stem siding which is all goodness. But the step down in width will still exist of course as the middle line will be out here unless I fair the keel's width to meet the stem.
    Thanks, Ed
     

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    Last edited: Nov 6, 2009

  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Yep, that's right you fair the keel to meet the stem, though if you happen to have a deeper rabbit on the keel, it's no big deal and a fairly common occurrence. If you lay a batten across to get an idea of how the garboard will land on the stem, you should see how much of a triangle will be made. If the planking will stand proud, you have to taper of course, but if the planking will land in the rabbit, then no taper is necessary. Don't forget to use a stopwater on that joint.
     
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