Epoxy, fiberglass, filet vs. screw, glue, paint construction method

I have built a Sassafras 16 and Kahalo SUP.  Both craft are completly sealed with epoxy and use epoxy fillets and fiberglass in essential areas for strength and durability. My newest project is a Joel White Shellback Sailing Dinghy kit from the wooden boat store. The instructions for this kit call for glueing the beveled edges of the planks together with thickened epoxy and fastening with bronze screws. Outside of that it does not specify any fiberglass or epoxy on any other parts of the boat. I plan to paint everything except for the thwarts, so there will be minimal varnishing and bright wood.


Now on to my questions. I found the unasembled kit on CLC's classifieds section. It was purchased in 2015 and the construction manual book was first published in 1993 and my version is the third printing from 2000. I'm wondering if the thinking (and accesability) around epoxy and fiberglass has changed since the instructions were written. Should I alter the construction method to include, if not fiberglass on the bottom plank (the boat includes an outer keel and quarter round brass rubstrips on bow and stern), then at least coating the entire boat in epoxy? I know there are a buch of shellback dinghys out there, especially in Brooklyn Maine, where there is a racing fleet. Do any of you users have experience with this boat or method of simply painting plywood? I would love to skip fiberglass and epoxy, and move straight to paint, but that is a different methodolgy from the CLC kits I have constructed and I don't want to regret it down the line.  Thanks for any advice. 

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RE: Epoxy, fiberglass, filet vs. screw, glue, paint construction method

   Sound like your boat is unfinished wood that doesn't need any epoxy or glass on any of the major surfaces for strength.  Even so, my vote is that everything will last much longer AND be much easier to paint AND use less paint AND is much easier to get a nice smooth paint job with less sanding if you give is a single coat of thinned (or unthinned) epoxy, then sand everything smooth, then proceed with your paint or varnish job.  Gives you a nice hard, smooth, near waterproof surface even before you start with whatever finish you are using.  I've done the "epoxy pre-coat" thing on many wood projects, nautical and otherwise, and I think it extends the life of the project and the time between any need for refreshing the paint/varnish finish by a lot.

RE: Epoxy, fiberglass, filet vs. screw, glue, paint construction method

It's plywood-on-frame vs stitch-and-glue with a handful of WEST (Wood Epoxy Saturation Technique) System thrown in.

Your kit is based on the plywood-on-frame building approach which developed from various plank-on-frame techniques which used mechanical fasteners (trunnels, screws, nails, etc.) to hold the planking onto the frame. As time passed, waterproof glue was added to the process and the mechanical fasteners became backups in case the glue failed. Even though the plywood plies are held together by glue, many people are uncomfortable with the idea of "only" glue holding something together. They may have a point, though, since at the plywood mills specialized equipment is used to assemble the sheets using glue formulations, heat, pressure and quality control that is impossible to match in a home garage/shop. As a result, many boat designs moved from solid planking to plywood but kept the fasteners even though they added glue. That's your kit's heritage.

The epoxy as glue is probably for several reason - it's more available and less demanding to apply than resorcinol-type glues and it has gap-filling properties. The resorcinol glues are similar to what the plywood mills use but can be mixed at home. However, they still need a lot of clamping pressure and are particular about their cure temperatures. Moder waterproof carpenters' glues, such as Titebond III, are very much easier (and safer) to use than resorcinols (or epoxy, for that matter) but they, too, require tight joinery and a fair amount of clamping pressure. First time home boatbuilders may not have the skills or tools to make high tolerance joints, so using thickened epoxy as glue is a good choice. It not only tolerates gaps, it actually works better with them.

So your kit is basically a traditional, painted plank-on-frame boat that has been updated to use plywood and a better glue. That's why you don't see any fiberglass or epoxy encapsulation.

I built something like that (a sabot dinghy) back in college and I have to completely agree with Bubblehead that coating the entire boat with epoxy will not only give you a better and longer-lasting paint job, it will make the boat last longer. My sabot only made it a couple of years before it rotted beyond the point of being worthwhile to repair, whereas my Brand X S&G dinghy is 14 years old and going strong.

Plywood-on-frame boats tend to start rotting at the inside chines where water gets into the joint and endgrain. The next most popular place is on the exterior chines. The sides and bottom ususally start later, unless something penetrates the paint. It also makes a big difference if you're sailing in salt or fresh water. Fresh water is hell on wood while salt water kills the rot organisms. Remember too that okoume has pretty poor rot resistance. That's why it's so important to seal it away from water.

With all this in mind, I would absolutely second Bubblehead;s recommendation to coat the entire boat in epoxy. If it was my boat I would also apply a layer of 6 oz glass to the bottom and run it 2 inches up the sides. This would protect the external bottom from abrasion and the outside of the chines from water intrusion. Inside, I'd paint on several coats of epoxy over the chines and chine joints and saturate the endgrain with epoxy before gluing. It's vital to keep the water, especially fresh water, out of there. Also, store the boat with the bottom up if you have to store it outside.

Finally, if you're really feeling ambitious and it's not too late, it's possible to do an S&G build of a plywood on frame boat. I did that with a Bolger Single-Handed Schooner some years back. It was designed as a plywood-on-frame boat. I replaced the chines with taped seams and glassed the boat inside and out. It ended up lighter and stronger.

Have fun with your build,






RE: Epoxy, fiberglass, filet vs. screw, glue, paint construction method

  Bubblehead. Thank you for the advice about coating everything with penetrating epoxy. That is not a difficult step and I will do that on both the exterior and interior. 


Laszlo, Thanks for your very thoughtful response as well. I really appreciate the lesson on the different construction methods. It all makes perfect sense. WIth your perspective in mind I'll be able to make informed decisions at each step of the way. I think I will use fasteners to make glueing the planks together easier (instead of difficult/awkward clamping). I will lay down fillets on the exterior to clean up the joints and will probably add a layer of 6 oz fiberglass as you suggested. I'm not sure I'll fillet and fiberglass tape the interior joints, but I will definetly apply at least one layer of epoxy to the entire boat. This boat will not be a yacht tender and will not be stored in the water. I will trailer to launch and I have indoor storage options. It will only be used for fresh water, and even if I took the boat out once every weekend (a pipedream) during the season, that would only be max 20 times per year. So I'll balance its limited future use with the additional construction steps and additional material purchases. 

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