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What Happens When Stitch-and-Glue Boats Get Old?
By John C. Harris
November, 2014
"Stitch-and-glue" is a style of boatbuilding in which pre-fabricated plywood parts are assembled with epoxy and fiberglass to create a rigid, durable hull. While the techniques and materials have varied over the last forty years, within recent memory the process involves sealing everything in the boat with waterproof epoxy, inside and out. These boats are pickled in epoxy, so to speak. Reinforcing and sealing a wooden boat within a matrix of epoxy and fiberglass yields remarkable strength and durability.
But just HOW durable? How do wood-epoxy-composite boats hold up after ten or fifteen years of hard usage?
At Chesapeake Light Craft we maintain an enormous fleet of wood-epoxy demo boats and prototypes. I took a stroll through our showroom and warehouse with a camera, documenting the wear and tear. We'll look at how this construction technique holds up out in the real world, and what YOU can do to make your stitch-and-glue boat last for decades. Something to emphasize: CLC's demo fleet is subject to appalling abuse. Most people will never use their stitch-and-glue boats this hard. Which is why our long-term fleet is a perfect testing ground for the ruggedness of wood-epoxy construction.
(click on photos to enlarge)
This Wood Duck 12 Hybrid was built in 2006 and still looks new, despite heavy abuse in our demo fleet.
For detailed case studies, read on! For those with a short attention span, here's the digest version:
1. Keep the wood from getting wet by protecting the integrity of your epoxy and fiberglass "envelope." If water gets behind the epoxy and fiberglass, the wood swells. Like ice cracking concrete, wet wood will crack the protective coating, allow in more water, and initiate a cycle of decline.
2. Keep sunlight off of epoxy. Epoxy is miraculously strong and it's absolutely waterproof, but UV light is epoxy's Kryptonite. It won't last more than a few months in direct sunlight before oxidizing and cracking. (Any epoxy manufacturer claiming otherwise is signalling that they are not to be trusted.) Protected with coats of varnish or paint, epoxy will hold up for decades. Maybe forever. We just don't know! Well-maintained wood-epoxy boats from the dawn of the epoxy age in the 1970's are still like new.
Eastport Pram Hull #1
Age: 15 years
Damage: Extensive moisture and UV damage to transom.
Cause: Not enough epoxy on the transom, combined with over-sanding during the finishing stages.
Fix: Sand down to bare wood, build up coats of epoxy, then sand and re-varnish.
Prognosis: Some discoloration might persist after the repair. Stripping the transom and gluing on a thin veneer before refinishing would hide the damage entirely.
This is the very first Eastport Pram, and it's been used hard and put away wet. With more than a thousand Eastport Prams all over the world, Hull #1, built early in 2000, may one day end up in a museum. Right now it's looking a bit frowzy, and it all goes back to a bit of haste and carelessness when it was built.
Eastport Pram builders are advised to apply two or three coats of epoxy to the transom to protect the wood, followed by coats of varnish to protect the epoxy. A prototype built in hurry, it looks like no more than two thin coats of epoxy were applied to this hull. That probably would have been enough to protect the wood, but the builders were overzealous with the sander while prepping the boat for varnish. In the pattern of the damage, you can even see where the sander really dug in, to smooth the ends of the planks around the perimeter of the transom. In these areas, the epoxy was either ground away entirely, or only the thinnest coating remained. In the noise and haste of a boatshop it's all too easy for epoxy surfaces and bare wood to blend together. This boat got a couple of coats of varnish and for years it survived unending demos and boatshows.
Varnish, however, is NOT a waterproof coating. Varnish is water-soluble, and water will pass through a coating of varnish with shocking ease. And that's what happened here. This boat has spent the last few years living on my back porch, exposed to the weather. Moisture has gotten into the plywood transom and caused enough shrinking and swelling cycles to cause the epoxy to peel off. The bare wood has weathered. Adjacent areas show the telltale dark splotches of moisture trapped beneath epoxy.
Fortunately the damage is shallow. A thorough "wooding" of the transom_removing all remaining epoxy and varnish with a sander_followed by several thick coats of epoxy, careful sanding, and finally at least three coats of varnish, will restore Eastport Pram #1 to showroom standards.
Here are some general notes on refinishing CLC boats.
PocketShip Hull #1
Age: 7 years
Damage: Water incursion has discolored the transom.
Cause: A tiny crack in the aperture for the tiller has allowed water to penetrate between the fiberglass and the plywood.
Fix: The transom will have to be stripped and a fresh face veneer glued on.
Prognosis: A fussy repair, compounded by the boat having an expensive LPU automotive finish, but the boat will look like new.
PocketShip's first tiller was too fat for the opening in the transom. The very first time I sailed the boat, I put the helm hard over and heard a cracking noise. I'd split the plywood at the transom aperture. It took seven years, but since PocketShip lives outdoors 24/7 much of the year, water crept in between the sapele plywood transom and its tough 6-ounce fiberglass sheathing. The trapped moisture caused a nasty discoloration. If no action were taken, the wet area would gradually grow for another few years, ultimately compromising the strength of the transom as the wood becomes saturated.
This winter we'll use a router to remove the outer 6mm or so of the entire 18mm-thick transom, then glue on a fresh veneer. Then the transom will be fiberglassed, and the boat sent off to the body shop for a re-spray.
Had I repaired the tiny crack in the plywood soon after it happened, I'd have been spared the trouble. A strong case for an ounce of prevention...
PocketShip Hull #1
Age: 7 years
Damage: Peeling finish on bowsprit.
Cause: UV degradation of varnish allowed the epoxy coating on the bowsprit to fail, eventually resulting in water incursion.
Fix: Sand bowsprit down to wood, then rebuild the epoxy and varnish.
Prognosis: The bowsprit is solid timber, not plywood, so there's plenty of wood to sand. It will be "as new."
Most of PocketShip's wood work is protected by canvas covers when it lives outside, but not the inboard section of the bowsprit. Nor has the bowsprit ever been refinished. So this is what seven years of persistent sun, rain, heat, and cold can do to a neatly, carefully-finished bit of wood. First the varnish oxidized and wore thin, then the exposed epoxy turned yellow and cracked in the sunlight. Once water could get under the epoxy, it was all over: peeling and staining popped up really fast. Last season there was just a little cloudiness; this season the finish on the bowsprit started to melt quickly. This will be an easy bench project for the winter. And maybe I'll have a canvas sleeve sewn up to protect this bit, too.
Eastport Pram #109
Age: 12 years
Damage: Palm-sized ding in seat has penetrated the epoxy, exposing bare wood.
Cause: Rough handling at boatshows and demos.
Fix: Local patching and filling with epoxy, followed by fresh varnish over the entire seat.
Prognosis: This is recent, and there hasn't been time for much water penetration. So while there may always be a little discoloration, this will clean up well.
This workhorse Eastport Pram was built specifically for boatshow and in-water demo duty in 2002. It gets tossed around, crunched on rocky beaches, and crammed into the back of our van for shows. Stuff happens, and something big obviously got dropped on the seat, cutting right through the varnish and the epoxy and into the wood. This is fairly typical damage for a small boat. If repaired quickly, there'll be no water damage and the repair should blend in. If you look close, the shadow of a similar contusion, repaired at some point in the distant past, is visible just to the left of the fresh ding.
While major sections of the Eastport Pram design are reinforced with fiberglass, the tops of the seats are not. It's possible that a layer of fiberglass on these seats would have prevented this gash. Fiberglassing the seats adds a good bit of time and expense to the kit, but perhaps a boat destined for such abuse might have benefited from the extra trouble.
Eastport Pram #109
Age: 12 years
Damage: Epoxy coating has failed at seat corner, exposing bare wood.
Cause: Over-sanding of the interior epoxy coating at the corner of the stern seat allowed moisture to enter.
Fix: Sand down to wood in surrounding area, build up coats of epoxy, then refinish with varnish.
Prognosis: No water damage, so the repair should blend in.
This is another illustration of how a lack of caution with the sander cut through the heavy epoxy seal coats during the finishing stages of this display boat. Varnish concealed the absence of epoxy, but varnish lets in the water. Eventually the varnish melted away, and now we're looking at bare wood. Little nooks and crannies in wood-epoxy boats require patience on the part of the builder. It's awfully easy to grind off your epoxy coating without even noticing, until a few years of weathering reveals the weak spot. This sort of thing would be repaired at the same time as the ding described above, and the entire interior of the boat would be re-varnished in one shot.
Chester Yawl Hull #1
Age: 11 years
Damage: Water incursion from the underside of the seat has damaged the epoxy coating.
Cause: While stored upside down on our travel trailer, water can pool on the seat overhang. The moisture has found its way through the plywood and lifted the epoxy coating on the top surface.
Fix: Sand down to wood locally, build up epoxy, refinish with varnish.
Prognosis: Minor discoloration is possible, but the fix will probably last for years.
We're careful to seal both sides of every piece of wood we put in a boat, and this Chester Yawl was no exception. But given enough time, water is an amazing solvent and will find its way in through the tiniest pinholes in your epoxy coating. That's what happened here. In this case, the water has managed to penetrate the epoxy AND the 9mm thickness of the seat. Pretty amazing what water can do. This will clean up easily. How would we prevent this in the first place? Make sure every surface of the boat has a thick epoxy coating right from the start, and try to be mindful of pooling water while the boat's on the road.
Chester Yawl Hull #1
Age: 11 years
Damage: Original transom succumbed to UV damage.
Cause: Years and years of road travel caused the varnish on the transom to fail. When the varnish was not freshened, the epoxy failed as a result of UV damage.
Fix: The original transom was badly discolored, so a 3mm sapele veneer was glued over the old transom, which is what you see here.
Prognosis: Looks better than it did when new!
Our demo model Chester Yawl has logged tens of thousands of road miles, upside down atop our big trailer. That's a LOT of rough treatment. Had we kept after the varnish, the original transom would still be like new, but a few seasons of inattention allowed the transom to degrade beyond repair. We glued on a thin sapele outer layer, covering up the damaged surface. Then we coated it with epoxy, and refinished the entire boat. The dark sapele is even prettier than the lighter-colored okoume, so there's a silver lining to this particular tale of neglect.
Skerry
Age: 8 years
Damage: Wear on rails has exposed the end-grain of the plywood.
Cause: Being slid off of roof racks a thousand times.
Fix: Sand, seal with epoxy, and refinish the interior.
Prognosis: With no water staining, this particular patch will blend seamlessly.
This Skerry was built in 2006 specifically for demo duty, and it's been the subject of sometimes frightening abuse. It travels everywhere on roof racks; my estimate is that it's got 100,000 road miles at least. That's a lot of sliding on and off the roof racks, and that has worn through the epoxy coating on the rails of the boat. Of course, water is getting into the exposed end-grain of the plywood, but the area of damage is so large that the moisture evaporates right back out again. So for the moment the damage isn't spreading, but this needs immediate attention to prevent permanent damage to the plywood.
Many builders of small boats use various woodworking schemes to cover the end-grain of the plywood. For example, you might mill a rabbet in the rails so that solid timber conceals the plywood edge. This is a good practice, but it's a considerable escalation in the joinery skills required to build a Skerry. Simply making sure that there's plenty of epoxy on the rails and touching up damage will ensure that the boat last for decades.
Skerry
Age: 8 years
Damage: UV-related discoloration around hull repair.
Cause: The epoxy of the repair and the epoxy on the hull are different ages. Prolonged UV exposure (despite the protection of varnish) has caused the epoxy to fade at different rates.
Fix: Nothing easy. "Wooding" the entire plank to remove all epoxy would restore a consistent coloration once sanded and varnished, but this is a lot of work! A quick fix would be to use a darkly pigmented varnish, like Cetol, throughout the interior. The dark Cetol, while not the most attractive of varnishes, would mostly conceal this patch.
Prognosis: This will always be a visible repair.
Skerry #1, built in 2001 or so, perished in a car accident. The boat in the picture was built in 2006 as a replacement, but a few years later suffered a gruesome parking lot accident that took a bite out of the rail. (Far more damage happens to boats on shore than ever happens on the water.) Staff boatbuilders grafted in a neat patch, and for awhile it blended so neatly that the repair wasn't obvious unless pointed out. To save time, only the damaged area was sanded down to bare wood and recoated with epoxy and varnish. The epoxied repair, years younger than the original hull coating, has aged in the sunlight at a different rate, causing a splotchy look.
This brings up an important point: Even protected by varnish, epoxy will still age and change color with prolonged exposure to sunlight. (This Skerry spends at least three months of the year outdoors, in direct sunlight.) This aging need not be a concern; generally it's a GOOD thing, with an overall "mellowing" effect to the coloration that just looks better with time.
What to do, then, when you need to make a repair to an area that you can't conceal beneath paint? Think of how auto body repair works: If you have damage out in the middle of a body panel, the ENTIRE PANEL is refinished so that the coloration is consistent. And so it is with boat repair. In this case, we really needed to sand down the entire upper hull panel when the repair was made, so that epoxied repair on that panel would age at the same rate as the surrounding surface. Of course, that would have multiplied the number of hours required to effect the repair. This is why auto body repair work is so expensive. Having done yeoman duty for so many years, this faithful Skerry will likely be retired and a new display model built.
Northeaster Dory #1
Age: 6 years
Damage: Deep gouge in topsides panel.
Cause: Hull was dropped while being loaded on CLC's big travel trailer, falling on the end of a crossbar.
Fix: Localized epoxy repair, followed by fresh varnish.
Prognosis: This will always be a visible repair.
This is a similar situation to the Skerry, in that the damage is not easily concealed. In the event, we chose to "patch and fill," and made no attempt to disguise the damage. A strip of okoume veneer might have been grafted over the gouge, but this would have been a long and fussy process, and required the stripping and re-coating of the entire hull panel. This is the downside to any sort of "clear" finish, whether it's a boat or your coffee table. Once damaged, it's very hard to make the damage go away. Were this a painted surface, you'd never know it was there! That's one argument for an all-painted "workboat finish."
Northeaster Dory #1
Age: 6 years
Damage: Varnish decay on thwarts.
Cause: Prolonged exposure to weather has caused the gradual deterioration of the varnish.
Fix: Sand and re-varnish.
Prognosis: With annual upkeep, these varnished thwarts can be kept in as-new condition.
I've included this example for one reason: the thwarts of our demo-model Northeaster Dory are varnished, but NOT epoxy-coated beneath. Furthermore, Northeaster Dory #1 lives outdoors any time our showroom is open, which is six days a week, 52 weeks a year. So this is what happens to varnished wood: the sun beats down, the varnish degrades, moisture intrudes, the wood shrinks and swells, and CLC boatbuilder Bill Cave's job grows ever more secure. It's interesting that the varnish failed on the darker wood first. Either the varnish does not adhere as well to the mahogany as it does to the lighter-colored cypress, or the darker wood gets hotter in the sun and accelerates the decline of the varnish.
Without the epoxy to arrest the shrinking and swelling cycle of the wood, these thwarts require fresh varnish at least once a year.
