Glued plywood lapstrake- scarf in situ?

[MushCreek]

Somewhere I read about scarfing plywood planks in situ, in other words, right on the molds as you're building the hull. This as opposed to scarfing together panels, and then cutting out the planks. I was playing around shaping the garboard out of scrap materials, and I'm going to use it as a pattern now that it's shaped. Right now, it's clamped to the molds, and I'll glue some splice blocks onto the three separate pieces before removing it so it holds its shape. To be sure that I don't run out of marine plywood, I'm going to lay out the planks as separate pieces to get as many out of a sheet of plywood as possible. I'm afraid that if I scarf together whole sheets, I may not have enough due to the curvature of the various pieces, not to mention trying to handle a 4' x 20' piece of plywood.

Anyone here heard of scarfing in place? Possible? Probable? Class Five Cluster Cluck?

[Andrew2]

I found it easier to scarf off, on the bench. I would shape the (in my case) two parts of the strake on the mounds,including the scarf, then lay a ply batten on them to pencil a line for alignment on the bench, with distance marks to control the overlap. Scarfing whole sheets always sounded a bit wasteful to my stingy mind. If painting the hull, the batten can be screwed across the joint then the strake clamped to the bench before removing the battern and gluing the joint.
My hull was only 15ft and the ply sheets 10x4ft.
My concern would be the scarf following an even curve, if done on the moulds.

[Rich Jones]

I've built five glued lap boats. The last two I scarfed the planks right on the molds.
Worked out fine.

[MushCreek]

The boat I'm building is a Peregrine 18. The hull is pretty slender, so the bends in the planks are very gentle except the twist at the bow. I wouldn't put scarf joints in areas of extreme bending or twisting anyhow. It sounds feasible; I guess I'll do the garboards that way, and then see how I feel about it.

[rgthom]

I have only built 1 boat, but working alone and 2 scarfs per plank the only way I could manage was to scarf in place. It worked fine. I clamped over each scarf with a length of the same thickness ply, it came out fair.

[AJZimm]

I've built two glued-lap boats by scarfing the planks in place on the boat, both about 18 feet long. I primarily did it that way because my shop is too small to have a separate layout space to scarf together full size sheets or even full length planks.

Fairness of curve is not an issue, providing you define the plank lines beforehand with full size battens temporarily attached to the moulds, and use scrap ply patterns for each piece of plank. Doing it that way you can lay the pattern ply over the battens and trace the outline on the back, then transfer it directly to the plank ply.

I did find that towards the ends, where the planks are more curved, there is a tendency to get some edge set from the full thickness ply compared to the thinner pattern ply, so cutting the ends a little wider and trimming on the boat seems to do the trick.

[SBrookman]

Did all mine, 2 per plank, for this 20'er in place. The backing plates needed to be more robust at the turn of the bilge. Lots of holes to fill but that's what epoxy is for.
scarf.jpg

[jpatrick]

I've built two glued lap boats and scarfed all the planks on the bench. For the second boat, I too wanted to minimize the amount of ply to purchase. This was simply a challenge I set for myself, more than anything else. I use an adjustable pattern to determine each plank's shape. John Brooks explains this pattern in his book. Mine is adapted from his. As long as one has sufficient room in the shop, there is no downside to scarfing on the bench.

Plank scarfing - 4.jpg

The photo depicts the new plank on the left with the adjustable jig on the right. The plank sections have been located in place and are awaiting epoxy and clamping. I tend to do this operation as the last one of the day. The epoxy sets overnight and I hang the planks the next morning. Two mirror image planks are glued at the same time.

Jeff

[rgthom]

My hull was built right side up. I can see how upside down would be a lot easier when doing full length planks scarfed on the bench.

[timo4352]

Did mine on the boat.
Packing tape to keep stuff from sticking, and drywall screws 'til the epoxy sets...
The clamping pads (scrap plywood) were re-used over and over...