Article on Marine Plywood Standards
Starting on Skerry Hull,
Cutting and assembly of lots of pieces.
I finally received my plywood and started my Skerry. Someday soon I will have a boat. It is a bit intimidating really. The method of boat building is called stitch and glue and is supposed to be very forgiving. The pieces get stitched with wire and glued with thickened epoxy.
The Skerry is 15 feet long and plywood is only 8 feet so it has to be joined. The joint is called a scarf
Cutting scarf joints in panel to make the pieces long enough is surprisingly simple.
I made a router jig but it turned out that cutting by hand using a block plane is faster and more accurate. I suppose it is hard to make a perfect joint but I'm hoping that at least one side will look good enough to keep natural colour. The worse side will go to the outside of the boat and be painted.
Gluing the scarfs is a bit scary at first. I taped both sides of the joint then used wax paper instead of plastic wrap. It behaves better and doesn't stick to itself like plastic wrap does. I tried to make at least one of the 2 sides match perfectly. I'm hoping to fill and paint one side and keep the interior bright. I carefully un-clamped while still a bit soft and cut off the epoxy that had squeezed out.
Checking the instructions. Check twice cut once!
Transferring the measurements to the boards, here is what will be the bottom of the Skerry boat.
I snapped a chalk line for the middle and made my marks on tape. It is easy to change when a mistake is made. I used a long thin board to join the points. I'm quite accurate mostly but at one point the point was about 1/8 inch off. I'm hoping this will disappear under the fillet later.
Cutting along the lines I drew. I bought a couple dozen saw blades and change them as soon as the cut starts to get messy. I found that a coarse metal blade works better than a wood blade. it's quite slow but does not leave a burr. It is hard to make a perfectly smooth line though and I'm hoping little jumps will sand out.
NOTE: because the joints get a bead of thickened epoxy (fillet) the edges are not visible in the inside of the boat at all.
After setting up the 16 feet side blanks and transferring the points by measuring and using a flexible stick to join the points between measurements I was ready to cut the sides of the Skerry. I checked twice and still expect to find something wrong. Murphy's law is alive and well in my home!!
Although the process is not difficult in itself, it is awkward to manipulate the big floppy pieces of wood.
I cut 2 panels together for each side. That way if there is anything a bit off at least I will have a symmetrical boat.
I now have all the pieces of the Skerry sail boat cut out except for the mast step and the reinforcement on the bottom of the front seat. I will wait till I have an exact diameter for the mast. I'm substituting a round mast for the square one in the design. For no other reason than I like round better.
The rabbets have been cut in and that went very easily. The router cut the plywood smoothly and easily. The short tapering rabbets which blend the panels front and back however were much harder to cut. The little plane kept getting caught up in the plywood cross grain. I finally used a sharp scraper and this worked better. A bit of sanding finished the rabbet.
This is the first hint this might end up looking like a boat after all.
After much fiddling and making of small holes for the copper wire, I have started assembling the boat. The base and first panels did not fit perfectly. The base was about a half inch too big.
I did some "adjusting" with my block plane and now things will be coaxed together without too much fuss. I'm depending on the filling putty to hide any imperfection where the end of the base and the front meet. I've only roughly tied the base to the first panel. I'm thinking I'll adjust everything when the third panels have been added.
I added the 3 frames and they went in without too much trouble. They are only tied to the base at this point. Second panel was more docile than the first and attached itself to the first without much argument ... yet.
Boat certainly is big. Fills my living room quite completely.
The bulkhead are wire stitched, and third Panel is in place.
What a day! 2 steps forward, one step back. I finally managed to get the bulkheads wired in proper position. Not easy because the panels have to be coaxed and curved into position and it's hard to do. My wires kept breaking and wood got a bit scraped on the outside.
Not really a problem because it will be painted but nerve wracking. I have a few gaps here and there and I will have to rely on the filling capacity of the epoxy paste more than I had hoped. The Skerry hull is quite symmetrical and well formed and I think that is quite important. It actually looks like a boat now. What a treat! After suffering all day I took a break cleaned up the area and took a look. Then I went to bed happy!
The Hull is being glued, my Skerry looks like a big canoe!
Detail of hull, it's called stitch and glue because you literally stitch the plywood together and sew yourself up a boat!.
After finishing wiring the third panel, I turned the hull over on workhorses and checked the alignment of everything.
In all projects there is a dark and gloomy period where nothing seems right. All I could see were the scrapes, gaps and bits that didn't quite fit right. HOWEVER the hull shape seems to be true. It measures nice and symmetrical still and stems seem perpendicular. There is a ray of hope surely.
I started gluing between the wire ties. I was lucky and did not get any drips to the inside. It looks like a boat now and my family actually believes me. Everyone who has actually seen the boat have commented on how nice the lines are!
I removed most of the wires, put a bit of filler epoxy in the wire holes and started pouring epoxy in the channels made by the panels.
Epoxy is a wicked material that flows mercilessly and can get through 1/16th of an inch! So I taped the inside seams with masking tape. This made my job easier.
The outside ridges are supposed to be nicely filled with epoxy using a syringe. That part I had no problem with, but, once in place epoxy very slowly creeps downhill and starts dripping at the bow and stern. I expect I will have to fine tune my hull! (read sand a whole lot.)
After turning the Skerry over, I filled the inside stems with a thickened mixture of epoxy. While everything was still wet I put on a fiberglass strip and painted it with epoxy. Except for the annoying little threads of fiberglass things went very well.
The epoxy did it's best to flow to the bottom of the boat but I was merciless in sopping it up.
Tacked the 3 bulkheads with thickened epoxy.
Epoxy in bow and stern add strength and rigidity. Erased any pencil marks
Masking tape between bottom and second panel make it easier to trim the glass cloth after it's been wet. Winston supervises.
I got up early to work on hull. Sanded all the touch-ups I did last night. Vacuumed and dusted the hull. Erased a few lines I had left.
I think I'm ready to epoxy the inside of the boat.
I measured and rough cut the fiberglass cloth so it would be all ready. I then made a thickened epoxy mixture and smoothed out the bottom - first panel seam with a smooth fillet. The seam was pretty rough I'm afraid it might show up.
After trimming the epoxy cloth to size I made sure everything was ready for resin.
Resin is nasty stuff. It crawls down any incline and is determined to make runs and puddles! Wicked I say.
Managed to get the resin spread out with minimal runs. I have a couple of puddles though.
I let things harden up then trimmed the extra cloth and removed the tape. The Skerry now needs to set longer before I can put my first over all coat of epoxy resin on the inside.
Inside bottom and first panel of my future Skerry have a coat of fiberglass cloth and resin.
As I go along I measure to make sure everything sets up square and untwisted.
The SKERRY HULL construction continues here
Read about other parts of the boat being constructed
This web site reflects my personal ideas and doesn't represent anyone else's point of view.