Fillet Width

Builder's Forum
1

I am building a Chesapeake 17 LT.  I plan to tack the hull together with epoxy/wood flour smears, pull the wires and then apply the fillets as Laszlo posted a few weeks back.  The manual says the following about fillet width,

"A total fillet width of 1” is plenty; those lusting after an even lighter boat can go with a 3/4”-wide fillet".  

A 3/4" fillet might not quite cover the stitch holes.  Or, is it the exterior unthickened epoxy that seals those holes?  What do you folks use for a fillet width?

Thanks!

Mike

2

   I'll let others with filet-width opinions weigh in more on that. I sort of think that in some areas filets are little more than cosmetic - where they'll be glass-taped over on the inside, and glassed over on the outside and the angle is obtuse, anything that does more than fill in the panel-to-panel joint and gives enough radius for the glass to make the bend probably adds little to the strength of the boat. Where you have 90 degree or acute angles and no glass on neither side, the filet is adding a structural component and thus needs to be bigger.  Not so many of the later joints on a kayak - maybe the bulkheads - but plenty of such joints on other boat  designs.

The real reason I write is to say something about "invisible" stitch holes.  These are accomplished with very little extra time and effort.  Make up an epoxy paste with a mix of cellofill and wood flour that about matches the color of your wood - 50-50 mix is a good approximation for most okume, just go by eye to match. After you pull the stitches use a gloved fingertip to press some paste into every hole on the boat, immediately followed by a good firm swipe with a spatula, leaving as little epoxy surrounging the hole as possible.  That is important to speed up the sanding process.  When hardened, very lightly sand over everything.  Getting a clean (epoxy free or nearly epoxy free) surface around each hole ensures that you'll get uniform coloration (no polka-dot spots) where the epoxy-with-filler paste causes a slightly different color/level of penetration when you do the first full-surface coating with clear epoxy or glass.  This technique prevents several things: no "see thru" holes that let light thru from being filled with clear epoxy, no darker colored holes from the clear epoxy, and no sneaky drip-thrus that can happen during construction. Drip throughs happen when working on one side of a panel (glass or epoxy coating) and epoxy runs through the hole out to the other side.  They a a pain to clean up once hardened, so even if you choose to not pre-fill your holes, watch out and try to clean up drip-thrus while soft during construction. Of course, if all you're worried about is the "10 foot" visual test, or if you're finishing with paint, then filling holes isn't really necessary.

-Bubblehead

3

   I forgot to add. I did my earlier boats with the epoxy tack-welds. Then after watching John do a demo at a boat show I shifted to super glue (easier to spell than cyano-whatever). I'll never go back to epoxy tack-welds, except in the few places where needed to hold some high-stress bent panels.  Super glue tack welding saves soooooo much time and effort that you could order some from CLC today, wait for it to arrive, and then use it - and in several days you'd be in the same place as if you started with epoxy tack welds.  And it allows you to do nicer filets as you don't "bump" over the epoxy tack welds.  I jest, but only just a little.  Remember, the ONLY purpose of the tack welds is to hold things in place between the time you pull the stitches and complete the next steps of construction (filet or whatever). You can go to the hardware store and get some - get the less-runny stuff, maybe advertized as no-drip.  The super thin (often cheapest) stuff is harder to use, super-gel is a little too thick but works fine, and the stuff that CLC sells is (of course) the right stuff for this aplication - moderately thick. And you'll need about an ounce or two for your kayak, so don't get the mini-sized quantities.  But you can always go back and buy more, and of course this stuff is almost impossible to keep for the next boat once opened.  If opened, what you don't use within a week or two always seeems to go to waste.

If you do use epoxy tack welds, minimize them as to amount of glue used and use the minimum # necessary to hold things together.  In many places you can skip over 2-3-4 stiches between tacks.  And clean up all lumps, spatters and drips while still soft.  If this is your first build you are soon to discover that sanding in the nemesis of this construction method, and everything you can do with technique that prevents extra sanding is worth the effort.

4

   Posting yet again.  Maybe not necessary for the kayak, where you're only doing the tack-weld process step a couple of times for the whole boat and almost always on stitched panels, but even then having the spay bottle of insta-set hardener is nice.  On boats where you're contantly putting pieces together (often with tab and slots, or no alignmet/holding system at all - not only with stitches) having the spray hardener is like having an extra set of clamps and a third hand.  Whatever needs holding in place you just squirt with superglue, spritz with hardener, wait 10 seconds, and get on with business!  That's why John uses it to do the simple 90 degree joint/filet example he does during shows.

5

   Bubblehead,

With the CA tack method, do you tack between every stitch, or do you skip 3 or 4 stitches as you suggested with the epoxy tacks?

Mike

6

   I'd tack between every stitch, just because it is so easy - though still probably not necessary.  The CA isn't as strong as the epoxy tacks would be, so it is possible to crack a tack free if you do a lot of wrestling with the boat (twisting it, rolling it over, etc.) after pulling the wires and prior to getting the filets done.  I've only ever popped one or two tacks - I think from flexing the boat when pulling on some stuck stitches without  supporting the (very flexible at the time) hull sides with a second hand or whatever. But the stuck wires were from tacking along the length of lapstrake construction - the glue ran along the seam and touched some wires - probably not a thing for kayak construction.  If it wasnt' obvious, with CA you need to tack where the wood is touching - no air gap - so consider that when stitching, try to get as much of every seam in contact as possible.

7

   Just wondering if anyone has used Tite Bond 3 or similar product to do the tack welding?  Advantages or disadvantages?  Thanks

8

Hi Mike, 

saw the conversation here and thought i could help.

attached below is a boat that i tacked with epoxy, then removed the wires and getting ready for final fillets which i wanted to keep clean and neat and ensure they were not excessive.

for one inch fillets, which is standard, what that means to me is a 1 inch diameter spreading surface (e.g., a one inch wide popsicle stick with a rounded edge).  fwiw, 3/4 inch also works well and have done that too.  as bubblehead mentioned, depending on the angle of the panels....you will get you more or less material in the fillet....  with oblique angles using less material and acute angles, more material.  the key thing is for your glass to be able to easily follow the curve.

the blue tape, fwiw, while a bit of extra work, makes things very neat as it avoids the inevitable epoxy getting outside the lines that is just very challenging to clean up.  so the blue tape in this picture is ~ 1/2 inch on either side of the panels being filleted.  you do the filletting, clean it up, then remove the tape as the final step.

you can see on the piece on the left, that is already done, what a clean effect if gives you.

on anvil's question, i dont consider titebond strong enough for this type of application.  titebond is strongest when you are mating two pieces with mating surface areas and most of the glue is actually squeezed out....which is not really the case with tacking a stitch and glue hull.

anywyay, hope this is helpful.  

h

  

9

My wife has her cast off, Thanksgiving is over and the leaves are almost done needing raking, so I can finally start paying attention to boats again.

Here's the fillet width on my WD12:

As you can see, it's pretty narrow. Here's what the tacks looked like before I applied the fillets and glass tape:

They're also very low profile. The putty is smeared into the crack between the panels. The dark areas on the panels are not putty, just epoxy that has soaked into the wood. The tabs are flat and do not cause bumps when applying the fillets.

The whole point was to minimize the amount of epoxy/woodflour putty to save weight and epoxy (=money). I personally don't use cyanoacrylate glues because that introduces flecks of different chemistry plastic into the joints, whereas smears of epoxy/woodflour are exactly the same material that the rest of the joint is bonded with. I know that other people have had great success with the stuff and I'm not discouraging anyone from using it, but I find it one less thing to worry about when I'm using 100% compatible materials.

For a glass-covered fillet, the vast majority of the structural strength comes from the glass. A thin fillet is just as good as a thick one as long as it keeps the glass from exceeding its minimum bend radius. Better, actually, because it's lighter.

True, it doesn't cover the stitch holes, but it doesn't need to. The glass will cover them and the epoxy from both sides will fill them. In the over 20 years that I've been building S&G boats, I've never had one leak through a stitch hole.

Finally, my WD12 celebrates its 15th birthday in the Spring and the thin fillets are still holding together in spite of lots of loving abuse. Those thin fillets let me keep the boat 2 lbs under the design weight, even though I completely glassed it on the inside, as well as the outside. I've also used this method of filleting on larger and heavier boats, including my 18-ft schooner, and it worked just fine there. It's not just for kayaks.

Laszlo

 

 

10

   Lots of really good info here from experienced builders. I was particularly intrigued by the CA/Accelerant idea for tack welds as I can't reach far enough into my hull to really do neat epoxy tack welds leaning a lot of weight onto the planks. I am going to try the CA route.

I can recommend highly the book and videos that Russel Brown has put out on epoxy basics. That man is a passed master on bright finish epoxy work. Off Center Harbor has a series of videos he did for them. It's paywalled but the site is well worth the $. There is also a basic book he put out that is available in all the usual places. One thing that I learned from him that has transformed cleanup for me is the use of chisel sticks. These are flat flexible sticks, about an inch wide, sharpened at a 20-30 degree angle (like a plane iron) on sandpaper that scoop up the fillet squeeze out. He makes his from some fiberglass sheet or something. I make mine from popsicle sticks. They are amazingly good for their intended use. They make the process of cleaning fillets much easier for me. YMMV.