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No it's not a typo, that's "battern" not batten. It's a cross between batten and pattern. It's the method I use to make very accurate patterns or odd shaped spaces on curved surfaces.

The sketch shows a very simple V bottom building jig. Well how do you make the plywood panels fit the bottom with out templates or patterns?

The joggle stick is the answer. I have a dozen or so different joggles, each a different thickness and shape. The shape doesn't matter, it just needs a point and a distinctive set of notches.

The battern is a piece (or more) of thin plywood, lightly tacked to the station molds. It fits between the edges of the panel you're trying to describe. For those that are interested this is a "spling" method. These pieces of plywood just need to bend fair and contact the molds.

Lay the joggle on the battern with the point at the end of the panel and trace the body of the joggle directly on the battern. Move down a few inches and do it again. You'll trace the joggle dozens of times, which will define the perimeter of the space you want to make.

Remove the battern and place it directly on top of the plywood you'll use for the planking. Line up the joggle with the tracings you have on the battern and make a mark at the point of the joggle. This will be on the plywood you want to cut. Mark the point of each joggle tracing on the battern, then remove the battern.

You now have a bunch of marks that define the perimeter of the panel you need to cut. Spring a batten through the marks (use nails or ducks to hold the batten) and cut. When you test fit it, you'll find a near perfect match. No ruler is necessary, you don't need to do any math or reading, no compass or tracing blocks and you can reuse the battern you made the marks on, by erasing the marks with denatured alcohol (if pencil) or sand them off.

This trick works on developed and flat surfaces. So, if you need a bulkhead in an odd space, brace up a board that's smaller then the space you need and drag out a joggle stick.

Anyone that's tried to fit carvel or lapstrake planking will appreciate this trick, but it works on all sorts of stuff, where you need a pattern or have to spile a shape.

I have seen many variations of this theme but this is by far the best so far!
Usually they involve attaching the sticks to your "battern", this one requires only on stick.

Thanks for sharing Paul.

Btw, I have contemplated with the idea of cutting my sheet stock into "planks" before scarphing and the making the scarphed blank slightly curved instead of scarphing the whole sheets. Did you ever try that? Any ideas pro/con?

It's very common to cant the rough plank blanks, before spiling. It's necessary in certain places on the boat, or you'll never accommodate the twist. So, yes, rough cut well over size plank stock and cant the next piece at the scarf (or Payson butt joint) so it approximates the curve, twist, etc. Scarfs are nice, but unless the plank will be brightly finished, I see no reason for the bother of a scar when a Payson butt joint will do. The way to determine how much to cant each plywood segment is to lay the plank pattern or battern on the planking stock and cock it to match the spile or battern marks.

I hate sanding epoxy, even more so if there is glass in it  >  That is why I decided not to glass the hull except for the deck.

On the other hand, working with wood, plywood included, is a joy to me so I prefer working with the scarfs.
I will build a jig to plane the scarfs so it will be easy to plane the scarfs.

If you do the butt joints my way and press them under a prepared piece of wood, you'll have nearly perfectly fair, very little sanding needed joints. With just a little practice (a couple of board joints) you'll learn how to do it very cleanly, with little mess.

Yes, sanding epoxy and fabrics ranks up their with a good case of hemorrhoids, but an often necessary requirement. Since your build is a glued lap, you'll be playing with epoxy plenty. For what it's worth, it's very difficult to sheath a lapstrake hull. Most don't, but some will 'glass just the flat portions of the planks, particularly the garboards and the first few broad strakes. This can help to some degree, but the edges and especially the exposed end grain of the planks are the most vulnerable areas in lapped planking.

This is a real world application of this "joggling" technique. A nice curvy hull shape and you need to fit a bulkhead, piece of furniture, cabinet, etc. against it.

Place a piece of plywood (or stiff cardboard) inside the area, then "pickup" your "tick" marks. The joggle stick is sometimes called a tick stick, because it leaves a bunch of tick marks when used.

You can see I've placed and traced the joggle stick so the point hits the hull sides about every 6". I closed this spacing down at the sharper turns to help define them better.

With the now marked up piece of plywood, you can transfer these marks to a piece of wood that is big enough to fit the space. Spring a batten between the marks and cut to the line.

Looking at this you see I turned over the joggle stick a couple of times to make the point fit the space better. It looks confusing as a drawing, but in real life it's about as easy a method as you can ask.