Wooden Boat People
By McKenzieDriftBoat.com
Keelson, or not to Keelson...
Okay. As I delve deeper and deeper into this world of boat building I continue to see that designs, and building/engineering practices are ever changing. I make this observation to preface my question; My plans call for a keelson to be used (a 1x6 beam running the length of the boat, centered on the bottom of the frames, essentially sandwiched between the frames and bottom panel of the boat, inlaid in to the frames). Noe framed boat that I have seen of modern builds call for a keelson aside from some of the sturdier white water drifters (or dories). What are the thoughts here? I am building on a strong back, and do not have panel specs, so my thoughts are that this piece will aid in keeping flex down in this process, not to mention on the water. With that said I don't want to add any steps to this build that are not required. Not because I don't enjoy it, but if it is not necessary to do why add the time and the weight. Thoughts?
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Replies to This Discussion
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Permalink Reply by Riverman on
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I have the plans you do, plus another set of plans without a keelson.
Probably, many will say a keelson is not needed at all, but it does add lots of support front-to-back and side-to-side on the bottom frame of a boat. It even adds extra support to the plywood bottom. A 1x6 doesn't weigh that much either.
I like the plans you are using... the strongback gets the boat up off the floor.
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Jordan: As a general rule of thumb it is usually best to follow the plans- but deviate if it makes sense. You are building on a strongback. The boat is a flatbottomed DB with some rocker fore and aft. The bottom is probably 1/2" and the sides 3/8". I assume the boat is being built"upside down" and the frames are attached to the strongback with cross braces at or near the shear line. This is the way I build canoes and glued lapstrake boats. The canoe uses a keelson because the bottom is made of 2 pieces attached to the keelson at a slight angle- to guve a slight "V" bottom to aid in tracking. Since the bottom is 2 sections they have to be attached to the keelson with epoxy and silicon bronze nails. The current build(peapod) has a flat bottom and no keelson.- also built on a strongback over 10 shaped moulds with a very slight rocker. It will have a keel added after the hull is complete.
Take this as one man's 2 cents worth. The bottom does not need a keelson because the hulls "stifness" is provided by the frames and sides attached to it. As I see it the only reason to have the kelson is to hold the frames in proper "register-spacing and plumb" while the sides are attached to the frames. The keelson just keeps them from wobbling all over the place whille attaching the sides. If it were me I would eliminate the keelson and avoid having to notch the bottoms of the frames(weakness)- but you could temorarily attach a length of 1x4 or 6" to the "inside" of the frames with drywall screws to keep things properly spaced
The boys might give more advice- Good Luck
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Permalink Reply by Jordan Davis on
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Yes. The stability offered by the keelson while attaching sides was something that was at the forefront of my mind. But using it only as a brace during building also makes sense. This boat has LARGE beam, much larger than any other drifter I have seen built. Could the keelson afford the boat something in that aspect as far as having longer lower cross members?
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Jordan: If the bottom of the frame is "longer- greater beam" to my thinking , putting a notch in it will not make it stronger- just a point of weakness. My DB is ( I think 54" at the bottom and 72" at the locks- but it is S&G) its out on the Columbia River so cant't really measure it up.
Good Luck
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Not that the notch would, but marrying the keelson to the frame via epoxy (or other adhesives used in our hobby) might create strength. Thanks so much for the input. This is exactly why I posted. I knew the critique would get the mental juices flowing.
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