rounding the edges

I'm a first time boatbuilder and am working on a wood duck 12.  I'm about to put the deck and hull together for the last time and will then need to round the edges.  The manual says for instance to round one edge to 3/8" radius.  How do you gauge this and prevent from getting into the second, darker layer of plywood?

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RE: rounding the edges


If you round even to a 1/4" radius, you're going to go through the top layer (veneer, really) of plywood.  That's why you see many people paint the sides and continue up over the top, to cover the nails AND to hide that sanded edge.

As to gauging the curve, my hull was rounded about the radius of a dime and I was able to glass over the edges without too much difficulty.  But my deck I rounded over to about the size of a nickle, and it was much easier to pull my scraper across the deck and down onto the sides (without having the glass come back up off the wood)... so the larger the radius the easier the glassing, in my experience.

Good luck,


RE: rounding the edges

I am also a first time kayak buikder. My question is how best to sand the ends of the copper wire on the hull? Do you use a grinder, saw, sand paper, etc????

Also, has anyone tried to put the deck onto the hull w/o the use of nails, screws, copper wire? Why not just epoxy?

RE: rounding the edges

Larry's absolutely right. Fiberglass has a minimum bend radius. It varies with the thickness of the glass, but 5/8" (about the size of a nickle) is a good general one to use. It works fine for 6 oz. glass and lighter. Heavier glass needs a larger radius, lighter glass can work with a tighter one.

When you try to wrap glass around a turn that's too tight for its weight, it will spring back and pull away, leaving bubbles. If you force it to stay, say with a wrapping, you get rid of the bubbles, but weaken the layup. This is because the glass fibers no longer flow smoothly. Instead they bend and fold, which forms a stress concentrator. So always respect the minimum bend radius.

As far as the plywood layers, my feeling is that it's an attribute of the materials. Plywood is layered, if you build with it it's natural and normal to see the layers. Besides, the edges have a lovely aesthetic of their own. Straight ones look like inlay when sanded and varnished, while angled ones look like agate (especially on sapele). I wouldn't worry about it, especially since it doesn't affect the handling or strength of the boat.


The deck and hull are bent to such a degree that they won't line up without something holding them together. You have to have some fasteners to make sure that all the edges line up for the epoxying step.

If you don't like the fasteners, you can use temporary ones - tape, straps, etc. For my WD12, I used the recommended copper wire as the initial fasteners. Then I put low flat smears of epoxy between the wires. Once they cure, I cut the wires and pulled them out, then did the real fillets over the smears (or tacks or welds, as other folks call them - not that they're anything at all like welds). This eliminates the question of sanding or grinding copper. Click on the picture below to see a larger image which shows the wires & smears at my WD build pages.


RE: rounding the edges

Quickstart --

Laszlo describes one approach with the wires.  I left mine in, and used flush wirecutters to trim then, and then a small, finely-toothed file (the sort modelers use on metal) to file the ends flush, working carefully to avoid scarring the wood.  That sounds tricky, but actually it's quite easy, albeit rather repetative.

Before it is cured, epoxy is a pretty good lubricant! If you tried to attach the deck without some sort of fastners to hold it in place, the deck would slide all over the place and you would have a miserable time, learning all sorts of new vocabulary.  Also, unless you used a LOT of clamps to hold the deck firmly to the sheer clamps along its entire length, the deck probably would cure with a lot of waviness along the sheer and you would be VERY unhappy with the results. 

Again, Laszlo offers a bunch of good suggestions about fastners.  I used silicon-bronze screws so I could dry-fit the deck first.  To finish the boat, I painted the hull and carried the paint up on to the deck far enough to hide the screws, so I didn't have an aesthetic problem there ... but frankly, even the screws wouldn't be terribly noticeable if you varnished the entire boat. 

If you are a first-time builder, my recommendation is to follow the book and avoid making additional problems for yourself. And remember, this is a boat that's going to see a lot of use; it's not a piece of fine furniture.

RE: rounding the edges/attaching deck

The epoxy is strong enough to hold the deck once dry.  The trick is getting it firmly held down to the shear and getting it to stay in one place while doing so.  You will at least need some temporary fasteners.  I have used a stapler and nylon webbing for the job.  I stapled thru the webbing (and a plastic sheet to avoid gluing it to the deck) and after the deck was dry, used the nylon webbing to peel up the staples.  You will be left with a string of punctures, but no nail or screw heads.

RE: rounding the edges

For what it's worth, I just used tubular nylon webbing to put my decks on when I originally built my NorthBay.  I did "prebend" the deck for a couple days (dry) beforehand, which helps a lot as well. 


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