Fiberglass before assembly - CLC Heresy?

Hello all,

We're well into our NE dory build, which is going overall well.  

I recently came across the Russell Brown series on Offcenterharbor and it raised some questions about the CLC method I wanted to ask the more knowledgeable souls of this message board.  

Namely: why wait until the boat is assembled (stitched and tack welded) prior to fiberglassing?  Why not fiberglass the panels while they're flat on the workbench (while fiberglassing is comparatively easy), THEN assemble/stitch, fillet and maybe apply fiberglass tape to the seam/fillet for added strength.  Seems it might be a bit easier?  Maybe it would be way heavier, or weaker?  Penny for your thoughts...


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RE: Fiberglass before assembly - CLC Heresy?

Hi JFTee, 

reasonable question....and i have some experience and thoughts i would be happy to share.

so first, no heresy here.  there is a lot of variation in build approaches that can be taken.  CLC, to keep their manuals simple, has a baseline approach that works well for those who don't want to get into the minutae of all the variations that can come into play and the materials engineering/complexity/time tradeoffs that need to be evaluated as you deviate from the baseline.  

so it's not heresy to suggest different approaches.

from my perspective, the short answer to your question is yes, in many builds there are opportunities to glass a piece before stitching it together and it may make it easier at times (albeit maybe a bit slower) to get really smooth surfaces if you can sand the pieces while it is lying flat.  for example, on the Arctic Hawk kayak, the recommended construction is glassing the inside of of the hulls is that you glass all hull pieces prior to stitching them together which leads to a very smooth inside construction with subsequent fillets and tape.  however, on the outside of the hull, you don't do that and the outside hull is draped with a single piece of glass. as adding a tape line on the outside to get the requisite strength would add time and weight and require a lot more sanding.

so for example, in many builds, bulkheads and other parts are routinely glassed (if the need glass) prior to assembly.

the principle that you are balancing, is 1) do you need the glass to span the joint for strength, 2) based on the shape is it easy to span with one piece or not and 3) what other factors like concave or convex shapes are involved, or multiple layers of glass that need to be applied  that make it relatively straight-forward to do in one piece vs breaking it up into multiple pieces.  

if you had a particular part of construction you wanted to ask the community about, it may be easier to give a suggestion.  but i would just say that all kinds of variation from the baseline, if well reasoned and thought out, are possible.




RE: Fiberglass before assembly - CLC Heresy?

What Howard said +:

If you're building "tortured plywood" style, it may be impossible to bend the wood to the required shape if it has a layer (or layers) of glass on it, especially if the epoxy has had a chance to mostly cure. For example, closing the bow of the WD12 requires a nearly 90 degree twist in just 6 feet of length. It's barely possibly with bare wood, it'd probably be impossible with a piece of glassed wood, even 4 ounce glass, and definitely impossible with fully-cured glass/epoxy.

Also keep in mind that glass cloth adds a lot of tensile strength to the panel and that maximum tensile strength is achieved with long continous strands of glass. So a single piece of glass on the whole surface will have better tensile strength for less weight than a patchwork of individual pieces.

Finally, as an example of a CLC boat that had its parts glassed and then assembled, there's the Outrigger Junior. If you examine the line drawings you see gently curved flat panels, flat bulkheads and a gently curved flat deck, just the kind of design that is friendly to pre-glassing.

So it's definitely not heresy, but if you pick the wrong boat that'll be its own punishment.



RE: Fiberglass before assembly - CLC Heresy?

Thank you Laszlo, and Howard for your thoughts.  Both make a lot of sense.  

I've really enjoyed building the boat we're working on and have been expanding my interest for the next build - I've looked at the Viola 14 sailing canoe (a Storer boat) although at this point, it's looking like the Outrigger Junior will be my next build.  I suppose for the OJ, in particular, I wondered about glassing the interior surfaces prior to assembling the boat, since the working area is very small once the hulls are stitched up.  The OJ has no real manual, so it brought to mind these questions about the order of construction.  

I'd be curious to see if you thought the OJ could be glassed on the interior prior to assmbly.  It doesn't seem to have any crazy 90 degree twists, although I could be wrong.  It also may be that the strength needed for a Proa, which can be expected to "fly a hull" may require the continuous fiberglass and I'd hate to go for a sail only for my boat to shatter in half.  


RE: Fiberglass before assembly - CLC Heresy?

I guess I wasn't clear enough, the OJ prototype was glassed inside and out before the panels were stitched together. The CLC crew also used peel-ply to eliminate drips and to assure uniform saturation. So you'd be building it the same way as CLC.



RE: Fiberglass before assembly - CLC Heresy?

   Over the winter, prior to assembly, I've been putting one or two coats of epoxy onto some of the larger pieces of my Autumn Leaves kit.  From the above, is it rational to conclude that a piece that needs to be curved into shape, such as the 3 hull sides, per side, should not have their clear coats of epoxy applied to them, prior to being bent into place, stem to stem?  This would be before any fibreglass is applied to the surface. I realize one or two coats of epoxy is going to make a piece of plywood stiffer than without the epoxy; I'm just worried that, from the epoxy coats, they would be rendered TOO stiff for the amount of bending required so as to form the gently curved side hull. Thanks

RE: Fiberglass before assembly - CLC Heresy?


I think this has been covered, but I'll add a bit.

Building a MC 16 gave me the inspiration and confidence to build Russell Brown's 18 ft PT Skiff. Thanks John!

The PTS has a lot of frames and longitudinals that would have been a lot more difficult to work around to fiberglass after assembly. The MC didn't.  So with a particular boat, or even a particular area in a boat, you just need to balance how much labor you will save against any negatives such as undesireable stiffness, or added weight (minimal). The PTS wouldn't notice the little additional weight. I don't think there is any loss of strength with the discontinuous fiberglass at the fillets, with the more than adequate overlap. And it wasn't hard to keep smooth... there was never any selvage to deal with as all strips were cut out of cloth...even though I didn't always use peel ply.

Regarding the stiffness of a pre-glassed panel, Russell directed that some ot the strakes not be pre-glassed in the bow  (or that it even needed glass at all on the inside of these, although I 'glassed them later).

So you just need to consider whether to pre-glass based on the situation.

I learned a lot building the Mill Creek, and even more building the PTS. Talk about saving weight, if I were to build another MC, I think I'd glue the deck down with sheet rock screws later removed as the PT boats are done. The bronze nails look good but must weigh nearly a pound.


RE: Fiberglass before assembly - CLC Heresy?

   Uh, that was my post.

RE: Fiberglass before assembly - CLC Heresy?

   Laszlo - how do you know so much about the OJ prototype (how they used peel ply etc)?  Are there resources online that I've missed?  There's scant little about the boat that I've found. 

Also, when one is layering or overlapping fiberglass cloth, as is supposed to be done over the keel and deck-side joint with the OJ, which process is generally followed?... 

Laying fiberglass cloth, wetting it out, partially allowing it to cure and then laying on the next sheet of fiberglass and fill-coating when all the fiberglass is on the boat?


Laying fiberglass, fill-coating and essentially finishing one panel/area, then sanding or fairing the area that's going to be overlapped and laying the next sheet of cloth down on the adjacent panel?

RE: Fiberglass before assembly - CLC Heresy?

Cuz I'm a nosy old fart who lives 20 minutes away from CLC and they're too polite to kick me out when I walk into the shop :-)

A bit more seriously, there's also been stuff posted by CLC on this forum, as well as presentations at the open houses and boat shows. But never underestimate the power of living close enough to snoop around in person. I've even got some pictures of the interior of the prototype, showing the internal construction, taken by sticking a camera through an access port and shooting blind and hoping for the best.

This, if you've ever wondered what it looked like inside. I've also had the opportunity to sail with John Harris aboard the prototype and I got to hear all about the design and build.

About lay-ups, I've always done the first - complete the lay-up and do the fill coat later. You don't really need to sand the edges before adding the overlapping piece unless it has a ridge, like the selvedge on glass tape. Sanding to feather after the layup is complete is fine for bright finishes and for paint you don't even do that. Instead, you put on fairing compound and sand during the fairing process.



RE: Fiberglass before assembly - CLC Heresy?

   Hey Laszlo,

Thanks for all the info.  What would I need to do to get a hold of your other OJ pictures? Trying to do all the recon I can before I drop $8k on a hobby. 


RE: Fiberglass before assembly - CLC Heresy?

You'd need to wait until I dug them out and post-processed them. I'll look, but I'm really busy right now and a lot of them didn't work out in terms of lighting, focus, etc,. so there may not be many more usable ones.



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