Passagemaker Plans Build - CPES & Epoxy

After having serious water instrusion issues on my EP after only a few years, I'm seriously thinking about soaking the PM parts with CPES prior to coating with epoxy and assembly.  A previous post on this topic brought to light that the CPES probably won't penetrate past the first ply layer through the glue.  My thought was that at least it'll turn the tropical ply layer into brown plastic and could possibly weep up the exposed cut edges, providing more protection at the laps.

So the first question is do you think this is advisable as a method for long term waterproofing?  This leads to the second question is do I then try to coat the parts with epoxy as per the manual ASAP to get a chemical bond, or do I let the CPES cure, then sand and apply the epoxy coats later?

A third thought is that someone mentioned that penetrating epoxy is just diluted regular unthickened epoxy, so I've been a sucker for buying the 1:1 two part CPES mix, when I have plenty of regular epoxy for the project.


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RE: Passagemaker Plans Build - CPES & Epoxy

Seems the folks at West System are not enthused about the idea of thinning epoxy:


RE: Passagemaker Plans Build - CPES & Epoxy

Thanks for posting that Michael, it was a very interesting read.  While doing some other research on boat building forums, one of the arguments against is that because CPES is thinned epoxy, once the thinner evaporates, you're left with porous epoxy.  While that may be true, I have used CPES on a kid-sized picnic table made out of contruction grade plywood, sealed it with CPES and it has been totally impervious to being left outside over a PNW winter with ground contact.

My thought is that if I'm still doing the epoxy coats as per the manual, and if the CPES doesn't do any actual harm, other than making the boat a little heavier, wouldn't any additional protection be a good idea?  I have actually stock-piled the CPES in anticipation of this build, so it's already paid for.

Keep in mind that I need to get enough seasons out of my PM in order to build the NanoShip 3.0 with my son whenever it becomes available...

RE: Passagemaker Plans Build - CPES & Epoxy

Cap’n, a few questions (to better understand your history with this issue):

1) When did you build your EP? As in, your first kit? First-ever epoxy-over-plywood boat?

2) History of water intrusion mentioned with your EP; when, after beginning to use the completed craft, did you first become aware of this? Where did it first appear & then where did it progress to over time?

3) Ever have any nagging doubts over your assembly techniques? Things maybe you  could have done differently that might have helped overcome what you later found to be happening?

4) Any experience with vacuum-bagging? I ask ‘cause I’d think this’d be how I’d approach trying to ensure getting really deep penetration of CPES into marine ply layers / end grain once parts were 99% shaped to fit.

My first adventure in boatcraft (polyester resin over fiberglass on exterior CDX frames, redwood strips) was a disaster after a few years’ exposure. Way too heavy but it was fun to sail while it lasted....

RE: Passagemaker Plans Build - CPES & Epoxy

 Wow, spclark!  Some seriously penetrating questions (pun intended).  I'll tackle them as listed.

1.  My Ep was built 4 years ago from 1/4" Home Depot oak plywood (I know).  It was my first boat build ever and it was plans-built, although I have a ton of furniture-making experience.  The parts stitched together as well as any CNC kit, which made me feel great.  It was a prototype to make sure I could pull it off as a foray into plans-based boat building as a possible future addiction (check), hence the poor quality of material selection.

2.  The first hint of water intrusion happened after I capsized on Lake Union during Duck Dodge.  Even with the buoyancy tanks built as prescribed by the plans, the dinghy sank until the gunwales were about two inches under water, making self-rescue impossible.  With help, I drug it ashore and then home where there was noticable slosh in the aft buoyancy tank.  With no way of draining the supposedly waterproof volume, I installed a drain/scupper to drain the water.  Black spot/cancer started creeping all over and through the boat from there, delaminating the ply/glass/graphite.

3.  I followed the build manual very closely and the only deviations I took would've had no impact on this issue.  The only thing I would've done/will do differently on my PM, is installing 6" deck plate/inspection ports in the fore and aft buoyancy tanks that can also be used for airing out the tanks.  I will also be adding additional glass and epoxy coats to those tanks prior to enclosing them with the thwarts and I'll even see if I can add additional sealant through the deck plates once the thwarts are permanently installed.

4.  I have the large RoarRocket vacuum bag for doing skateboards and veneer, but nothing 12' long.  I used to own the West System venturi nozzle-based vacuum bag kit that uses a compressor instead of a vacuum pump.  That's a really interesting thought.  I hadn't thought about vacuum bagging, but at this point don't really have the funds for an unexpected expenditure of that size.  But once again, that brings up the issue that CPES probably won't penetrate the glue layer under the top ply layer.  It might help soak into the end grain of the cut edges though, but maybe not anymore than several manually applied coats until it kicks.

Good stuff.  Thanks!

RE: Passagemaker Plans Build - CPES & Epoxy

Let's shave this beast with Occam's Razor.

Observed: Hundreds of EPs and PMDs have been built without running into this problem, even though no CPES was used.

Observed: Eastport Prams are not supposed to get water into their sealed airtanks.

Conclusion: This particular EP had some fabrication issues and ended up not being built the way it was meant to be built.

First corollary: adding CPES to the PMD build will not address the root cause, which is the fabrication issue.

Second corollary: the real solution for the PMD is to concentrate on resolving the fabrication issues and the rest will take care of itself.

Adding CPES into the mix simply complicates everything and introduces lots of new potential failure points. Witness this thread, full of questions and speculations on how and when to apply CPES.

If it was my boat, I'd grab some scrap and practice encapsulation and assembly techniques before starting the build.

Good luck,



RE: Passagemaker Plans Build - CPES & Epoxy

Hey CS, I’ll beat the dead horse a little more…
Is it possible you’re conflating thinned PVA glue to size end grain for joinery with thinning epoxy?
Epoxy doesn’t dry like the glue we use for woodworking. It is 100% solids and cures through chemical reaction - there is nothing to “dry”.
Have you come across info on temperature changes and outgassing of plywood? If the temperature rises after epoxy is applied the expanding air within plywood has to go somewhere and bubbles out through uncured epoxy. That leaves an opening for water infiltration. Thinning epoxy with solvent has the same effect, the solvent has to evaporate through the uncured epoxy in same way. It’s a real thing, don’t ask me how I know. My big takeaway from the West System link is using heat gun on the wood to thin epoxy and draw it in, but heating shortens pot time and the faster kick may reduce the wicking time. I’ve never had any trouble having epoxy wick into end grain/edges. You do have to keep an eye on the process though and add epoxy as the stuff gets pulled into the wood. It’ll continue to wick for 10-15 minutes, more if cure time is slow.
As I said on the recent rudder post, every time I try to outthink John I end up with a longer, heavier, more expensive build. l’ve never had an issue that could not have been solved by being more careful.


RE: Passagemaker Plans Build - CPES & Epoxy

To Laszlo's wisdom, we might add that a cautious boatwright would be sure to install access hatches for any closed, theoretically "airtight" spaces.  Heck, nothin' is ever perfect that way, except that such unventilated spaces are a pretty nearly perfect source of trouble sooner or later.  It's best to be able to open 'em up and let 'em air out.

My Passagemaker's air chamber hatches are always removed as soon as we get home, a check is made for any possible water intrusion, and the hatch left open until the next outing to make sure the space remains ventilated while the boat is stored.

The hatches themselves can be a source of water intrusion, of course, and one needs to be careful to bed the frames down well and make sure the threads or gaskets are free of sand, grit, or other debris.  Also, throughbolts for the rudder gudgeons can give water a way to sneak in.  Even if you were really carefully about bedding those down, all the flexing and strain on 'em can let a little water in.

Hey, water just wants to have fun, and it'll sneak in anywhere it can lookin' for opportunities to see what's on the other side.  <;-)



RE: Passagemaker Plans Build - CPES & Epoxy

Laszlo and Gramps have pretty much nailed it here. Captain says he built his EP from oak plywood from Home Depot and later says it’s a poor quality of materials. Couldn’t agree more! The manual for the EP mentions several types of marine plywood that are suitable for building, e.g. okoume, sapele, meranti, etc., and specifies BS1088. It also clearly states not build it out of anything not sold as marine-grade. The PM manual says the same thing. Using the afore mentioned oak plywood is the best explanation of the failures that followed, the water in the sealed compartment and the subsequent black ick and delaminations. There are a lot of posts on different forums about the compatibility of oak and epoxies with a lot of differing opinions. It may be entirely possible to build a boat from oak plywood and thoroughly seal it for years of use but instead of re-inventing the wheel, as in using inferior materials and CPES, why wouldn’t a person just buy the materials listed by the designer? As Laszlo pointed out there have been hundreds of the things built using the right materials and not having these issues.

And I agree entirely with Gramps about putting an inspection port in the sealed compartments of any boat. I, too, leave the ports open any time I’m not on the water. 

George K

RE: Passagemaker Plans Build - CPES & Epoxy

I didn't post the question to get lambasted for being a crappy builder who built a crappy boat, I asked about using CPES in addition to the procedures in the manual for my next boat which is okoume.

I'm not even saying there's anything wrong with the EP's design, although it was impossible to self-rescue after swamping.

It was built in a shop that stayed at a constant 65°F during the entire build.

I'm the one who has invested in the okoume and I'm the one who's going to put 100+ hours into the build, so I'm just trying to get the most bang for my buck.  The PM manual from 2008 certainly isn't perfect and I'm just exploring an option to possibly augment the build.  Since is defunct, I'm doing that here.  I didn't expect to get a new orifice torn.

If the members here are too small-minded to even consider adding something to a build to make it better, then flame me for asking, then I will go elsewhere.  This makes me really sad.  This has been one of my favorite forums of all time and I believe I've helped a lot of people and provided differing opinions respectfully and constructively.  I was just looking for some help in return.  I know I used the wrong plywood on the EP, but that wasn't my question.  I'm not lamenting my EP, I'm trying to build a much better PM.

RE: Passagemaker Plans Build - CPES & Epoxy


I wasn't lambasting anyone, just trying to say that the CPES was not the fix for the problem with the original boat, was not necessary for the next one and could cause more trouble and mess up your build. I was suggesting more practice with the epoxy encapsulation because, according to you that's what failed on the first boat. It was a suggestion to try and guarantee your success with this boat by addressing the actual root cause instead of expending effort on something unrelated to the original problem.

It was not a personal attack and it's unfortunate you took it that way.




RE: Passagemaker Plans Build - CPES & Epoxy


I didn't mean to give offense with my remarks, and I sincerely apologize if I did.

Sounds like you learned some things from your Eastport Pram build, and I think you are on track to make use of that on Passagemaker Dinghy project.  It's a great boat, by the way; you will have a blast with it.

A good friend of mine, a skilled boatbuilder and designer, was a longtime friend of the late Meade Geougeon, one of those Geougeon brothers of West System, from whence the Epoxyworks publication and the article I referenced above.  I think my friend would advise you to forego the CPES as being, at most, unnecessary for what you have planned for your PMD.



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