Simplified lapstrake Building Method

I have been looking at an adaptation of a lapstrake design, see http://www.boatdesign.net/forums/wo...storation/zipper-seam-construction-18316.html. In that project I was trying to eliminate the relatively complex mold required for that method. While doing that I came up with an alternative approach.

In the Simplified lapstrake Building Method the developed planks are cut out of thin ply with a lap allowance added to the bottom chine edge, say 3/8" or 9 mm. A row of staples are placed inside each plank, except the garboard, along the path of the bottom chine, 3/8 from the plank edge. The planks are then pulled together with several elastic straps from gunnel to gunnel on the outside face of the planks. The unglued hull will be a bit floppy so a center station mold will still be required in all probability.

When the planks are pulled together in this way, it acts like the stitches in stitch-and-glue construction: the planks bend and the hull forms to its finished shape as the seams are closed up. I have demonstrated this effect in tests, although not on an entire hull yet. In this case, instead of the plank edges butting along the chines, they will overlap with the lower plank butting against the staples.

At that point the hull can be inverted and epoxy poured into the laps. Stems and other stuff are added in the usual way, but I want to keep it simple at this stage in the discussion to get you opinions on this idea.

 

You are describing the traditional lapstrake building technique. That's more less how the Scandinavians did it.

 

- they used binding to fasten the planks, I understand. I doubt they had staples! They started with keel and stems, then added the stems befre inseerting ribs and other internal structure. Fastening techniques caried at different times, I believe. They worked without a mold, as I wish to do. There are a lot of similarities, but a lot of differences too.

 

The system is basically the same. The planks are cut and then fastened together. The hull takes shape gradually. I don't see pouring glue as a good building technique. You may have dry spots and/or have to leave large gaps for it to flow. Gluing and fastening as you go is way easier, faster and has better quality control on the seams.

 

Study "lap-stich" method used by Chesapeake Light Craft.

 

Reading the start of the thread I notice that you say the planks won´t butt along the chines but overlap. If they don't overlap, the hull is not lapstrake.

 

liki: Similar concept but important differences. No stitches - the pressure of the binding holds the planks together, and the staples avoid cutting rabbets in thin ply. I knew about lapstitch but arrived at my method by a different route.

Gonzo: you don't HAVE to like it!

 

It's not about liking. If you don't cut rabbets at the plank ends, they will look like a ladder. Whatever little work you save, it will be multiplied to make the stem to fit. Esthetically it would be rather odd too, but that is a personal matter. I don't see the savings. Rabbeting planks takes very little time.

 

Good point. It may be better to brush unthickened epoxy into the gap first then top up with the thickened stuff. Iain Oughtred illustrates this in his Clinker Plywood Boatbuilding Manual, but he first cuts a bevel along the edge of the lower plank and applies glue to that. In the lap-stitch method developed by Chesapeake Light Craft the laps are stitched dry and epoxy poured in as I propose. I worry more about glue runs inside than I do about dry spots.

Another good point. I haven’t decided how the planks will meet the stem. I can cut rabbets or gains as Iain Oughtred shows in his book, which is the usual way and not too hard. Or I can taper the lap width to zero approaching the stem but that will require extra reinforcement of the joint; that will be OK if the decks hide it! Another idea is an external 3 - cornered plywood wedge, cut with a feather edge like a scarf; it should be OK under paint but might show through varnish; either way I would test it first - not on a boat. I’m not sure how easy it would be to cut but at least it can be done on the bench. Currently I am trying to figure out if a twisted scarf joint can be arranged between 2 planks but it sounds complicated. Still thinking ...

 

I have repaired some Ian Oughtred's boats in England. I'll post some photos later.

 

This gives you an idea of an Ian Oughtred design.

 

I wonder what it hit; doesn't look like that boat could move fast enough to do all that damage even on a rock. Did not seem to break the half-rib either -is that a typical hole?

Did the glue unzipped at the seam? With that much of a lap width I would have expected to see bits of garboard veneer left behind.

In that design those planks really bend at the bow, it must be difficult to get a close joint in that area. I am considering a canoe (Rushton's Wee Lassie) which will have an easier shape.

The gains/plank rabbets show up nicely in the first image. Nice garboard patch BTW - will the next plank up be difficult, getting the lap to the next plank from the inside? I noticed a pencil line on the patch; I assume it's for the lap but it seems wider than the original.

 

The tide came in and it pounded on a rocky beach for a couple of hours. That boat was built in Devon and Ian had some input. The seams didn't fail at the glue line, the wood fibers broke. It was built with epoxy are copper rivets; belt and suspenders. The next plank was harder. I posted those photos because they show better the construction detail on the rabbet and frame.