- Cleanup puzzle joints.
- Fill screw clamp holes from puzzle bonding with a syringe of thickened epoxy.
- Sand panels and edges.
- Put three coats of epoxy on edges. I found it was easier to get this done before surface coating.
- Sheath the inside with 300gm/sqm satin weave glass.
- Trim excess glass at edges of the panel at mid cure.
- Hot coat a second fill coat on the glass before full cure.
- Once cured, sand any remaining fiberglass overhang missed by trimming flush with panel edge.
- Scrub amine blush off with 3M Scotch Brite and water. Mop amine off the surface with a sponge. I use a small bucket of water and I change the water as soon as I see any cloudiness from the collected wax. Dry the panel with a clean towel before it starts to dry. You want to get any remaining amine off while it is in solution and has not dried back onto the surface.
- Hand sand panel with an 80 grit flat board to flatten the coat and knock of high spots where epoxy might have pooled.
- Sand panel to a dull even color eliminating all shiny spots. This used a random orbital sander with 80-100 grit.
- Bevel off interior corners of edges where they will be bonded together to form chines. This allow the wired panels to sit against each other much easier than with sharp corners. I used a laminate trimmer with a V bit.
- Vacuum, vacuum, vacuum and wipe, wipe, wipe the panels clean.
- Recoat the panel with epoxy, scrub and sand four more times. I switch down to 120 grit on these coats.
- Stack the panels in symmetrical pairs. Measure and mark the locations of holes for wire stitching. These are placed 1/2 inch from the edges at increments of 5 - 7 inches apart. I want them evenly spaced so that the panels while tighten uniformly. The hole locations need to avoid the bulkhead placement points where you won't be able to manipulate a wire. The two panels to be stitched together must be marked at the same places along the chine.
- Once the layout is correct. Drill holes through both panels at the same time. This is done with a 9/64ths bit.
- Glue the stringers along the main hull panel shear. There will be a separate post on this.
Task time: 95 hours
Total project time: 597 hours
I'm interested to hear you laminate the insides of the hull panels before stitching them together - I was thinking of doing the same.
ReplyDeleteBut do you really need all that sanding? I was planning to put them in a vacuum bag and do the whole thing in one step (hopefully), with all the stringers in place...
Or am I missing something?
I am using Russell Brown's build methods. It would be very difficult to do as good of a job on the interior of a stitched boat as on a flat table.
ReplyDeleteYou need at least three coats of epoxy to be waterproof. The ama has ballast tanks that will need six coats (more on that later).
You need to sand each coat back to dull gray for maximum adhesion. I believe that using peel ply would be equivalent, as it would remove amine blush and provide a rough bonding surface. It can be difficult to get large pieces of peel ply to lay perfectly flat without bagging. Russell told me that he thought the peel ply-ed surface ought to be sanded where stringers and bulkheads would be bonded.
You can probably get one coat or a little more with a vacuum bag session. I had thought of doing this. So you would need three or more vacuum bagging sessions. This takes a lot of time and a ton of consumable materials. I have tried this. It does provide a very nice finish and removes excess epoxy. Sanding also removes excess.
If you are rolling out coats of epoxy, you are also going to want to sand because it is hard to get a really flat coat especially on the second hot fill coat.
This is discussed in Russell's epoxy book, PT Watercraft build manuals, Chesapeake Light Craft literature and "The Gougeon Brothers on Boat Construction". This is also taught at the WoodenBoat school and the Northwest School of Wooden Boats. Jim Brown's literature says that every surface, bonded or not, needs three coats.
I have seen some plywood boats that are falling apart after 20 or 30 years. Newick's boats built in the 70's and Russell's boats look really good.
I am looking for alternatives that would reduce sanding and provide a more uniform "manufactured-type" process.
If water makes it to the wood, you are screwed because it might not show up for a while and it would be very difficult to get it out.
Understood.
ReplyDeleteThe tests I have done with vacuum bagging use a fridge pump and a simple polythene sheet bag, taped at the edges.
I get excellent results and there are no materials wasted - I can reuse the polythene many times.
I use no breather / bleeder and get a good vacuum and an excellent surface finish.
So far I have only done one coat at a time, but I suppose I could roll out the first coat, let it cure for a while, then roll out a hot coat, and put the piece in the bag... Or maybe all three coats? Would that work?
Alex,
ReplyDeleteIt is a good idea to try. I'm wondering if hot coating will give you the same flat surface. Any imperfections in the first coat will transfer through. If you are using peel ply, you could try bagging three times with full cure and possibly save sanding. I would try a few experiments. You might contact Gougeon tech support and see what they think.
Alex,
ReplyDeleteIt is a good idea to try. I'm wondering if hot coating will give you the same flat surface. Any imperfections in the first coat will transfer through. If you are using peel ply, you could try bagging three times with full cure and possibly save sanding. I would try a few experiments. You might contact Gougeon tech support and see what they think.