Not for nuthin'…. But….. once you’ve got plywood scarfs joining panels on a Chamberlain Marblehead gunning dory — or any stitch-and-glue / fillet-and-tape hull — the next move that makes the boat is a clean epoxy fillet. Today’s tip: get the radius right, mix to the right thickness, and tool a smooth cove that glass tape will love.
Why it matters: a fillet is a cove of thickened epoxy bridging an inside corner. WEST SYSTEM calls it out as both a bond-area booster and a structural brace — and every joint that’ll get fiberglass cloth needs one so the cloth isn’t bridging a sharp corner. Too thin and it sags or starves; too skinny a radius on a loaded seam and you’re asking the plywood to do work the fillet should share.
Materials
- Marine epoxy resin + hardener (WEST SYSTEM 105 system or equivalent)
- Filler for thickening: colloidal silica, microfibers, and/or WEST 405 Filleting Blend
- Fiberglass tape (for structural seams / anywhere cloth will cover the joint)
- Plywood joint already dry-fit and clamped (bulkhead-to-plank, chine, etc.)
Tools
- WEST SYSTEM 804 reusable mixing sticks (rounded end ≈ 3/8″ radius) — or tongue depressors / craft sticks with the end sanded round to your radius
- 808 plastic squeegee (cut or bent) for larger radii
- Disposable brush, mixing pots, gloves, putty knife
- Zip-top bag or cake-decorating bag for piping long beads (optional)
- 80-grit sandpaper for post-cure fairing
Steps
- Dry-fit and prep. Joint faces clean, dry, and abraded if you’re bonding to cured epoxy. Have clamps, sticks, and tape cut before you mix — thickened epoxy doesn’t wait around for you to dig through a drawer.
- Wet out (two-step bond). Brush neat (unthickened) epoxy onto both mating faces. WEST’s preferred two-step bonding wets porous wood so the joint doesn’t go resin-starved when you load it with filler. You can proceed while it’s still wet, or any time before that coat reaches final cure.
- Thicken to mayonnaise / peanut butter. Mix resin + hardener thoroughly first, then blend in filler until you hit WEST’s filleting consistencies: mayonnaise (clings vertically; peaks fall over) or peanut butter (clings; peaks stand). For a vertical cove that holds its shape, peanut butter is the safe call. No strict scoop recipe — judge by eye; add filler gradually.
- Apply the bead. Load the joint with enough thickened mix for the cove you want. For long runs, snip a corner off a heavy zip bag and pipe it like cake frosting. You’re aiming for a continuous bead that’ll fill the corner when you tool it — not a skimpy ribbon.
- Tool the cove. Draw a rounded filleting tool along the joint, dragging excess ahead of the stick. WEST’s 804 rounded end leaves about a 3/8″ (≈10 mm) radius cove with a clean margin on each side. For larger fillets, use an 808 squeegee cut or bent to the radius you need. Refill voids with the scraped excess; scrape the outside ridge clean with the stick’s square/bevel end or a putty knife.
- Radius reality check. A 3/8″ stick cove is the everyday shop fillet. For a structural fillet without glass, boatbuilding practice (and WEST testing cited in builder notes) points toward a radius on the order of 3–4 × panel thickness — e.g. on ¼″ ply that’s roughly ¾″–1″. With glass tape over the fillet, you can work smaller and let the tape carry load — which is how most stitch-and-glue / fillet-and-tape dories are built.
- Tape while wet (or after cure). WEST: fiberglass cloth or tape may go over the fillet before it cures, or after a full cure and sanding. Wet the fillet and landing zone with neat epoxy, lay the tape, and stipple until it’s uniformly transparent without floating the weave in a puddle.
- Cure, then fair. After full cure, sand the fillet smooth with 80-grit, wipe clean, and seal with a couple coats of neat resin/hardener before paint or varnish.
MOAM’s shop note: Don’t tool a fillet with a mix that’s still “ketchup.” It’ll sag into a flat puddle at the bottom of the joint and leave you sanding forever. And don’t skip the neat wet-out on plywood — end grain and plies drink epoxy; a peanut-butter-only pass on dry wood is how you get a pretty cove that pops off when the boat works. On the Marblehead dory chines and bulkheads, I cut a couple of spare sticks to the radius I want and keep them in the glue kit so I’m not reshaping tools with sticky gloves.
MOAM Out.











