Beam Me Up
February 13, 2018 3:55 AM   Subscribe

I'm trying to solve another carpentry problem. I want to run a beam across a small room which will act as the end support to the floating ceiling and a bit of wall. So it would be great if it could be a nice continuous beam across the room. However, the room is the front cabin of my boat and the geometry of this room is such that I'm pretty sure I won't be able to actually get the beam in place. What are my options?

The room is the front pointy bit, so everything curves out and up. Aftwards there is a door, and a bathroom. There is also a hatch above. I'm pretty sure I'm not getting this thing in whole. So I'm thinking of a joint.
Can I joint a beam in place and have it have any reasonable strength?
It actually won't need to take massive weight, and there are a few other support points along the way, but really the stronger the better.

The beam is part of the battening structure, so it will be totally hidden when we're done.
posted by Just this guy, y'know to Home & Garden (6 answers total)
There are all sorts of splice / scarf joints in woodworking. If the beam can be a composite of multiple pieces, then there can be significant overlap between them to provide rigidity and strength.
posted by nickggully at 4:28 AM on February 13 [2 favorites]

You could Google "sistering a joist" - this is essentially what you are doing. Well, what you could be doing/ one way of getting a long piece of wood into a short space. You take two short pieces and overlap them so that 25% of the total length is overlapped (this is being generous), glue-and-screw them together and, there - looks ok, right? No? OK, two pieces of wood, butted and then two more pieces (or one) sandwiching them, again, to approx 25% of the total length, screw and glue the whole contraption. If looks are an issue, do the one side and then fill in where the sister isn't, (the remaining 7/8th of each joist.)
posted by From Bklyn at 4:51 AM on February 13 [2 favorites]

Well first get a stick or piece of cardboard the same length and try, it's amazing what can be twisted in place. Otherwise a long scarf and the right epoxy should be stronger, finding the right clamps to fit might take hunting around.
posted by sammyo at 5:12 AM on February 13

I find scarfing really hard to do well, so if it were me, I'd probably route a channel in the back (hidden) side of each piece and use slow curing epoxy to hold a wood or aluminum bar in the channel holding both pieces together. This will give you time to adjust and properly clamp the piece in place before it cures and from the outside the result will look like a simple butt joint.
posted by Poldo at 6:08 AM on February 13 [1 favorite]

FWIW, sistering as described by From Bklyn, is/was a standard technique in building v-bottom boats, especially boats with plywood planking. See the example here.

In this drawing, the frame (aka "rib", or in the drawing "futtock") is made up of three straight pieces, tinted yellow. The joints are strengthened with "gussets" as the overlapping parts are called. In this case, the gussets are wider than the frames in order to give more material working to keep the frames at the correct angle.

This is called "sawn frame construction."

Expanding on sammyo's suggestion, I would fit a piece of cardboard or Masonite into place first and use that as a template to make the final parts.
posted by SemiSalt at 7:23 AM on February 13 [2 favorites]

Thanks all.
I ended up doing a glued and screwed half lap scarf joint and then sistered it above and below.

I needed the above and below bits in that location anyway to build up to the point where it will meet the ceiling and the ply framing of the hatch above it, so it made sense to use them as sistered joists anyway.

It'll also have a reasonably decent bit of ply on top, so that will add even more strength.
It's not going to win any woodworking awards, but it works.
posted by Just this guy, y'know at 3:27 AM on February 27

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