Peel-ply and pre-stressed composite with stitch and glue

Newbie question.  Bear with my ignorance.

Does it work to put the outer hull fiberglass on the precut plywood pieces flat and peel-ply before the stitch assembly?

Put the inner hull fiberglass on the usual way.  Then fiberglass tape the exterior seams.  Goal would be to reduce sanding.

I thought that this might make the plywood composite too stiff to bend and of course there is the need to get a good bond of the fiberglass tape at the joints to the underlying fiberglass layer.

I thought this approach might work best when the hull pieces are larger, seams and curvature of the hull are minimal.  On something like

WRT getting a good bond at the seams I thought to put some kevlar tape under the peel-ply at the edges of the panel.  Then after curing, sand the edges enough to fuzz the kevlar.  Exposing the kevlar fibers would allow a better bond with the seam tape.  Would probably want more than one layer of seam tape with different thicknesses to get a feathered edge after sanding.

The exterior fiberglass would be prestressed by bending the panels after cure.  Prestressing generally makes structures stiffer, or lighter for the same stiffness.

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RE: Peel-ply and pre-stressed composite with stitch and glue


It's not the flat (or curved, flat) surfaces that are hard to sand.  Especially if you completely fill the weave of the cloth and avoid epoxy drips and runs.  Its the selvage on glass tape, the fillets themselves, and the inner angles and corners that requre most of the work and and provide most of the frustration.  Mostly because it's hard to get at them with random orbital or even finish sanders.

That being said, there is nothing fundamentally unsound about your idea.  I don't believe that the epoxy/glass layer will add much difficulty to bending panels.  You might need to be careful not to wait too long after the epoxy has fully set before installing a panel (I mean weeks, not days) because epoxy will probably get more brittle over time.



RE: Peel-ply and pre-stressed composite with stitch and glue


I just re-read your posting.  Could it be possible that you're overthinking the problem?  It might be more prudent to just carefully follow the CLC manual for your first build.  Innovation is great, but a little real-world experience will help you innovate more successfully.  The techniques described in the manual were developed and tested by professionals and, if followed correctly, will guarantee a successful build.  Anything else is an experiment with all the attendant risks for failure.

As I reviewed your post, a few issues stood out:

1.  Glassing one side of a panel before bending will probably work.  Glassing both sides could make the panels too rigid to bend or cause compression failures on the concave side, or tension failures on the convex side, when bending.

2.  Kevlar is notoriously difficult to work with, and is difficult to both cut and sand---not to mention expensive.  I believe this would add cost and labor with no appreciable benefit.

3.  I don't know which boat you plan to build, but the comment about using two layers of tape of different widths to get a feathered edge is an old technique that is entirely unnecessary with the materials and techniques promoted by CLC.  Again, it adds labor with little, if any, benefit.

CLC boats and kits are superbly engineered for their purpose and the materials used.  Anything can be improved, but the chances of a first-time builder making major construction improvements successfully are, in my opinion, very slim.



RE: Peel-ply and pre-stressed composite with stitch and glue

   I have to agree with Dick. When you get a hull assembled (I built a Skerry) and lay the fiberglass cloth on the outside of the hull it is amazing how smoothing it down with your hands causes it to conform to the shape so well. I think the fiberglassing was the easiest part of the build. It it said and I found it to be true, that with your first build you will tend to use more epoxy than necessary and adding more glass tape, resin and the associated work of sanding and sanding and sanding to hide the woven edges really seems unnecessary. .

RE: Peel-ply and pre-stressed composite with stitch and glue

Dick wrote:

>I don't know which boat you plan to build, but the comment about using two layers of tape of different widths to get a feathered edge is an old technique that is entirely unnecessary with the materials and techniques promoted by CLC.  Again, it adds labor with little, if any, benefit. <

When the outside glass goes on after the stitch and glue step, it spans the joint between the plywood pieces.   If I put the glass on the plywood before stitching it, then I would need to tape the seam.  Using two layers would over engineer the seam to get bonding to either side.

Thanks for your response.  I'm hoping that someone who has actually tried what I propose will tell me that it did not work out the way they expected it would.

Besides the reduction in sanding I like the idea of using the peel ply to get excess resin out of the weave.  That make the fiberglassr stronger and lighter and it is a good alternative to vacume bagging and prepreg

RE: Peel-ply and pre-stressed composite with stitch and glue


Wing15601 and I have both successfully built stitch-and-glue boats.  Perhaps we are not experts, but we are both far more experienced than we were before our first builds.  I suspect that you are unlikely to get a response from someone who has actually tried what you propose.  Anyone who has built a plywood, epoxy, and fiberglass, stitch-and-glue boat has learned that the least-cost (time, materials, and money) path to a superior finish is to use the methods described in the CLC manuals and to exercise care to avoid the epoxy runs and drips that force extra sanding.

My boat's fiberglass exterior is finished with multiple coats of one-part polyurethane over high-build primer.  After buffing it with an automotive buffer and very fine buffing compound, it looked like gel-coat and has survived its first season on the salt water with no signs of deterioration.

Vacuum bagging and prepreg are techniques for production (or very expensive one-off) fiberglass construction.  Because you are seeking alternatives, I assume that you understand that they are not applicable to stitch-and-glue plywood construction.

From my perspective, you would be better off investing in a high-quality random orbital and finish sander with an integrated HEPA dust collection system---and paying close attention to the CLC manual and the Tips for Boatbuilders on this Web site.  The methods and techniques therein described have evolved over 20+ years of continual improvement and represent the experience of and feedback from the thousands of people who have built CLC boats, kayaks, and canoes.

Of course, its your money and your time, so you are certainly free to do anything you want.




RE: Peel-ply and pre-stressed composite with stitch and glue


i have not done exactly what you proposed but did do something similar.  

for the Arctic Hawk, by the noted builders at Superior Kayak, all the side and bottom and deck panels are glassed on their inner surfaces prior to assembly. bulkheads are glassed on both sides prior to assembly.

the focus on the inner surfaces ensures a very nice smooth, light interior on surfaces that are often difficult to handle efficiently once the panels are assembled.   fillets are the primary work done on the inside in this technique.  fillets are kept neat and light by premasking (do some searches to see how to do it).    saves a tremendous amount of work being able to work these pieces when they are flat and easy to get to.....

in Superior Kayak's approach they don't 'preglass the outside of the panels becuase it is very easy to work the external glassing becuase of the shape (relative to an interior curve.)  so preglassing the exterior surface doesn't really save time or improve the quality of the build vs what you can do once the hull is assembled. 

so....i respectfully disagree with some of the folks above that CLC technique is prescriptive and you can't take some alternate approaches.  my personal perspective is that CLC techniques are 'best value' of time and finish....but certainly not the only approach.

with respect to peel-ply and vacume bagging.  these techniques typically go hand-in-hand. the purpose of it is to increase the glass to resin ratio and get a finished interior surface.  peel ply without vacume bagging, is, in my view kind of a waste of time. becuase there is no pressure that will force out the excess resin.   also, in most well finished kayks, peel ply is not used to get the external finisihed surface.....the surface of a female mold with release agent is how you get a an exterior surface. that said, without vacume bagging, another way to improve the resin to glass ratio is to work on flat or external surfaces and tightly pull the cloth and properly squeegee away excess resin.  using a lighter weave (e.g., two layers of 2 oz cloth vs one layer of 6 oz cloth will also help improve the glass to resin ratio if properly applied.

my view on kevlar is not worth the trouble.  not really a material that works well without access to vacume bagging and advanced cutting capabilities.  not really  a good 'by hand' material to work with.

one thing that might be an idea to consider relative to your what is the it to get a superior finish?  is it to have an ultra-light boat.   if there is something special you are trying to achieve you might start with the objective and folks can suggest techniques that are more directed to achieving that.

all the best.






RE: Peel-ply and pre-stressed composite with stitch and glue

just another couple notes....on inside fillet and cloth.  

in addition to masking taping the filet to keep it neat and clean...there are a couple other elements to very slick, nice looking fillets.

use a properly recessed/curved stick (like a spoon) to shape the fillet.  the width of the curve should match up to your masking tape.

then wait for the fillet to get to a 'gum' consistency before removing the masking tape and placing the glass tape on it.  this will prevent you from deforming the fillet by laying glass on the fillete while it is still 'wet'.

when the fibreglass tape is now in place...wait for it to become 'plastic' consistency then cut the edges of the tape off with a razor knife.  the edges of the woven glass tape are thickened/woven differently  to keep the glass tape from unravelling.  this create a ridge that sticks up when epoxy is applied.   it is easy to cut off when plasticy and then you have a nice finished edge of the fillet tape.


RE: Peel-ply and pre-stressed composite with stitch and glue


I really like your suggestions for creating the fillets and removing the selvige from the glass tape.  Learning to make a neat job of the fillets took far too long.  Your technique makes excellent sense.



RE: Peel-ply and pre-stressed composite with stitch and glue

Hi h.  

Interesting info on Superior Kayak application of glass to the inside surface of kayaks before assembly. Thanks.

WRT your comments about peel-ply, look at:  Seems to be useful without vacume bagging.

While I'm a newbie to CLC boats, I've made some +100 sq. foot fiberglass structures, so I have (too much) experience with sanding.

I don't doubt that CLC procedures produces a beautiful boat in an efficient manner and that the manuals are excellent.  

Peel ply is obviously not relevant to a compound curved surface with a lot of seams like a kayak, but I'm curious about the applicability of peel ply to boxy designs with large relatively flat hull components.

What got me thinking about this is , a boat that I'm interested in building. Now that I go back to read that article a fourth time, it seems that the only fiberglass sheathing on this boat is on the bottom, and the joints are 'chine logs'.  And as noted in the blog, everything is prefabricated, epoxied and finish sanded flat on the bench prior to assembly.  The plywood is epoxy sealed without glass so the ply-peel might only serve to make the epoxy coat too thin.  There's a photo of John putting the epoxy/glass on the bottom after assembly but no ply-peel in sight. The bottom is only curved in one axis, so ply peel would lie flat but for the three slight strips running the lenght of the bottom. Since the bottom is a 'wear layer', a thicker layer of epoxy is productive/desirable.

I wonder if the ply-peel might provide a toothier finish for a layer of paint on the sides of the hull and further reduce sanding?



Sliding rigger on short and heavy rowing/sailing boats

I wonder if anyone has fitted a Sliding Rigger to a CLC boat that is too short for a Sliding Seat Rowing Rig?

Here is an explanation of the sliding rigger

I own one of Virus's Turbo II milk bottle rowing shells with a sliding rigger and it is very nice to row on a choppy and windy lake (whitecaps optional!). Most of my rowing is done in racing shells on the river in calmer conditions.  

Now I understand that rowers using fixed seat with fixed oarlocks have beaten sliding seat rowers on endurance races, but sliding seat/rigger rowing cured my back problems, and I hesitate to wager my back with any prolonged fixed seat rowing.




RE: Peel-ply and pre-stressed composite with stitch and glue

Whoops.  Disregard my last post.  I was trying to start a new topic.   

RE: Peel-ply and pre-stressed composite with stitch and glue


By the way, I was not saying that the CLC techniques were prescriptive, only that diverging from them before acquiring any practical experience increases one's chances for failure.  We all stand on the shoulders of those who came before us---that's how we get the chance to climb higher.



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