Transition joint or full length butt joint

[unseen wombat]

So I was re-reading Devlin's book on stitch and glue, and I finally think I understand how the "transition joint" near the bow can actually work and be made fair. Still it seems to me that a butt joint the full length of the boat would be easier to make. I don't remember seeing anything about transition joints in Payson's instant catboat book.

My question is for those of you who have already built a stitch and glue boat, did you build it with the transition joint or the full-length butt joint? And how did it work out for you? If anyone's done it both ways, which is easier?

[duluthboats]

The easy thing to do would be not to build a boat at all. ;-) A butt joint when reinforced properly can be as strong as a scarf. But the butt may create a hard spot or cause some other problem with some designs. A scarf will give you a joint that is very similar to the joined material in strength and give. Best to follow the plans. Play with some scrap you will find that scarf’s are easy.
Gary :D

[unseen wombat]

Oh... No, you didn't understand. I'm not talking about joining panels end to end. I meant what this guy is explaining on his April 4th, 2009 post here: http://cstiernberg.googlepages.com/scrapbook, where you notch the bow end of the side panels so that it transitions from being a lap joint aft, to a butt joint forward. It sounded like black magic to me at first, but I see that you just have to round over the bottom panel forward of the joint, and the side panel aft, (or vice versa, depending on how you lap it). But I still think just making a butt joint between the sides and bottom sounds easier, but maybe I'm overlooking something as I've never built a boat before.

I'm totally in favor of scarf joints for joining boards end to end. I can see how they're superior to butt blocks, and I don't think they'd be any harder to make than butt joints with a simple router jig.

[PAR]

On tapes stem builds, the type of joint at the seam is basically irrelevant. In fact, you don't want well fitting joints (sloppy is good), nor anything sticking up within the joint (like the corner of a lap), just bring the two pieces together (some use stitches), so their alignment is correct, then pile on the goo.

Joint strength comes from the fillet and tape on the inside and the rounded over filler and tape on the outside. You could cut the wood with the claw end of a hammer and it will still work fine, though you'd need a lot more filler.

The important thing is panel alignment. Use you eyes and sight down the panels, double check measurements, etc., then apply the stick-um.

[unseen wombat]

haha, I'll have to try that sometime. I thought it didn't make a difference, but Devlin seemed to make a big deal about it in his book. Glen L Witt mentioned it in his book too, but he also said that you can do the butt joint, thought it's more difficult.

[rwatson]

How can you have a full length butt joint when for most of the hull the panels are almost at right angles to each other ?

[PAR]

What everyone seems to be missing, is what happens as you approach the forward sections of a taped seam V bottom boat, along the chine. The angle becomes more obtuse and difficult to "seat" against it's neighboring panel.

Many use a transition joint, which is a backed out joint on each panel, that is filled with thickened goo and tape, rather then the near 90 degree butt joint and fillets used further aft in the boat.

This is a fine and strong way to do things, but isn't the only way and possibly unnecessary from a structural point of view.

The bottom line is panel orientation. If the panels are held where they're supposed to be, until the goo cures, it doesn't matter what kind of raw wood joints are used, just so long as the reinforced thickened epoxy is there.

[rwatson]

What everyone seems to be missing, is what happens as you approach the forward sections of a taped seam V bottom boat, along the chine. The angle becomes more obtuse and difficult to "seat" against it's neighboring panel.

This is a fine and strong way to do things, but isn't the only way and possibly unnecessary from a structural point of view.


Well, I thought it was obvious. Its not that the stern section is harder to 'seat ', because it doesnt 'seat'. It just lays against the underneath panel. 'Seating' isnt required until the angle gets too obtuse. Devlin explains it in easy to follow language, and I dont understand what the point being made is in the initial post.

Of course its not a structural necessity, but in most cases, by gum, the 'overbite' look is plumb ugly if you dont transition near the bow.

[PAR]

Agree with the amount of confusion on this topic. When bending in these panels, this sort of thing comes naturally to most. Typical taped seam instructions cover the issue fairly well too.

As to the original question of how many use the transition joint, well I suspect most do on initial builds, but then develop their own methods, once an understanding of the process needs is acquired.

[unseen wombat]

Sorry if it was a stupid question. It just seemed hard to understand at first. It seems to me that it should be possible to set one edge of a panel next to the other edge and not have to cut any notches at all. And the only reason there's an overbite in Devlin's example is that it was a v bottom with pretty vertical sides, and he was lapping the side panel over the bottom one aft, and then at the stem, he had to cut it to turn it into a butt joint. But if he would have just used a butt joint aft, I think the problem could have been avoided. (Not to second guess a master or anything, I just don't understand why he couldn't have done it that way).

[PAR]

Again there are a number of ways around this. I usually roll over the inside edges considerably, leaving little more then a veneer or two in contact at the joint. This is filled with the fillet and forms a plastic longitudinal stringer, the length of the chine. When I radius the outside corner, I'm cutting mostly thickened epoxy, knowing the end grain is still embalmed in cured goo. This is my way. I also rarely use "stitches", preferring to align things over temporary molds, braces, etc. and just lightly tack the edge if necessary to keep it in place. This usually permits me to run the fillet the full length of the chine in one shot, instead of piece mealing it until the stitches are removed.

Pictured are three plywood seam sections. The top an obtuse joint, much like what you'd find in the forward sections of a single chine build.

The very left image is the plywood aligned, pinned, stitched or other wise held in position. Note I radius the inner edges to offer room for the fillet. The middle column shows the inside of the joint completed, fillet and two layers of 'glass tape. The right hand column shows the exterior of the joint filled and taped.

The middle row is how I do the majority of near right angle joints. This saves epoxy as I don't have to back fill the outside of the joint. It just requires you cut the bottom panel a little long and then grind it back when ready to tape the outside of the joint.

The lower row shows the more conventional way of doing this joint, with filling required on the outside of the joint as well as the inside.

[unseen wombat]

Thanks PAR, that's very helpful. I didn't think about rounding the inside edges like that.

[rwatson]

.....But if he would have just used a butt joint aft, I think the problem could have been avoided. (Not to second guess a master or anything, I just don't understand why he couldn't have done it that way).

Until you have done a small sample, you will probably not see why a butt joint aft is the harder way to do it.

Par gave an excellent hint when he said "It just requires you cut the bottom panel a little long and then grind it back when ready to tape the outside of the joint."

You see, the nuisance of having to fit two edges close together is done away with for most of the chine, until you get to the very obtuse angles near the bow.

If you tried to 'butt joint' all the way along the hull, you are making so much MORE work for yourself. Just let it 'hang' past the bottom panel until the inside has been 'glued', and then plane it flush.