Joining Plywood Sawtooth Stepped Joints

Like the stepped joint that I discussed in my previous post, the sawtooth stepped joint is not something that the amateur builder will make from scratch. It may be that this joining method will be a feature of a kit that the amateur builder buys from a kit supplier, so he may do the final assembly of this joint without cutting the shape into the plywood.

This is a modification of the stepped scarph joint. The only difference is that instead of  the straight-line plan shape of the joint, it has a sawtooth plan shape as can be seen in the photo below. The form  in the photo is a true sawtooth shape, with straight lines between the changes in direction of the cutting tool. A variation is for the steps to have a wavy form composed of a series of curves instead of the sawtooth form.

This bulkhead in the photo is from a kit for the Dix 470 catamaran, cut by Exocetus Catamarans in UK.

These joints were developed primarily to get around the alignment problems of the straight variety of stepped scarph. The components that are being joined can easily slide relative to each other, parallel to the steps. The toothed or wavy form of the joint allows the two components to interlock accurately. As long as there is pressure to push the joint together when is is clamped then it will engage accurately.

There is a side benefit to this type of joint that is particularly beneficial to larger boats, with large loads in the structure. The form of the joint does a better job of distributing the loads between the two boards that are being joined. There is a much reduced chance of the joint initiating a crack along the line of one of the surface joints. Nevertheless, joints should be positioned away from the corners of openings and other stress-raisers in the bulkhead or whatever component is being made.

To see our range of designs, go to http://dixdesign.com/ .

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Headoard Kitchen Work

The custom made headboard was collected from the makers last Saturday.  I needed to finish making the bed base and once that was done I could fix the headboard in place.

The bed base lifts up to access a storage space.  Once I have the mattress  (Next Thursday) I can weight it and the base then I can get some gas struts made to the require lifting force to assist with and hold the base up when required.

I have been preparing the kitchen for the breakfast bar, while doing this it became apparent the island unit was pretty mobile at the end section.  This, in a stationary house is no problem but on a boat which moves about could be a problem especially as the weight of the worktops would act as a massive lever if the boat were to thing anything head on, or indeed if while being transported the lorry had to break suddenly.

A solution was needed.  Screwing through the end unit base would not be strong enough the load needed to be transferred through the vertical walls.  

I knew one day I would have a use for the really long screws that came with the engine crate.  

The head is 17mm AF to give it scale

I made a bracket to transfer the load through the vertical panel and some filler blocks to bear down onto once the screws were done up.

Glued and screwed

Stop blocks and 3 screws into the floor

The island end is now nice an rigid now. I will make a nice cover the the metal bracket to hide it in due course. 

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Photos Videos Update

I owe the blog a few photos and gonna chuck in a couple of videos as well.

The new HD battery cables showing 400amp fuse and 500amp shunt

The shunt is there to monitor the battery current both in and out and the information is displayed on the gage 4 down.  Think of it as a fuel tank gage for the domestic batteries.

I finished of the exhaust installation today.  

Exhaust manifold to water separator

Water separator to outside 

Engine start and run

Generator start and run

The reason for the lumpy start is due to me not turning on the cooling water feed quickly enough.

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Chines Part II

After completing the shears, I went back to the chines. Since I had ripped my original 3/4" thick material into two layers, the total thickness was only about 5/8". So I decided to make a mahogany sandwich and add in a 1/8" layer in the middle. So I cut an 8 board to the width of the chine (1 3/4") and then resawed into 1/8" thick pieces on the tablesaw. Since the rough chine length is about 12, I used 8 length towards the front of the boat, put a 45 degree mitre on the end and mated it to another piece long enough to complete the whole length. The middle layer was thin enough to bend to whatever shape needed. The pieces were all epoxied together on the frames using just about every clamp I could find in my shop. The grand total was 90 clamps for each chine lamination. Since I did not have 180 clamps, I could only do one at a time.

After completing the lamination on both chines, the epoxy squeeze out was planed off with a hand plane. I found this easiest to do in my shop with the chine in a vice and moved it along in the vice as I progressed. Then the chines were fit to the boat, epoxied and screwed into place. After all the consternation about the fit to the stem, the chine ended up looking too straight in the forward area and without enough twist so it did not angle nicely toward the shear. I ended up making a long tapered section piece about 3/8" thick at the bottom and 1/8" at the top and laminated it onto the chine from stem to about 8" forward of the frame. Using the small belt sander, it was blended into the chine.

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Sneak Preview Of Current Project

This is what Im up to at the moment.  Seats and storage boxes for the rear deck.

More next time.

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Fiberglassing

Once the boat looked all nice and shiny with perfect wood grain showing through the epoxy finish, it was time to mess it up...big time. So I fiberglass taped and epoxied the joints. I started with the keel joint and used 6" wide tape.

This tape was taped into place with some blue tape to hold it straight and overlapped the transom about an inch. The boat was already prepped for another coat of epoxy, so the fiberglass tape was epoxied and the whole boat got another coat of epoxy. After watching the Glen-L video on how to epoxy a boat, I followed their best practices of taping all joints before using the fiberglass cloth to cover all surfaces. The chine joints were taped and then the transom to bottom and sides were taped. Foam rollers were used to saturate the tape with epoxy. I found a 3" roller worked the best as quite a bit of rolling pressure is needed.

After trying some different epoxy filler to fair in the tape edges and finding sanding difficult, I went and bought some West Systems 407 fairing filler. Since the bottom will be painted, I got over the need to keep the wood pretty and figured I may as well use the right stuff for the application at hand. This filler is supposed to be mohoghany color, but it reminds me of chocolate milk. I slapped it in the areas needed to smooth out the tape transitions and sqeegeed it into a somewhat smooth surface. After curing, sanding with an orbital sander and 80 grit paper worked well and edges could be feathered and surfaces smoothed quite readily. At some point in this process, my wife came down and said "What the Hell?". I quickly explained "It all gets painted later". So it all looked like hell, but was smoother. I kept with just clear epoxy on the sides so I can keep the natural finish, but unthickened epoxy runs and sags like crazy (after you leave the room - just to be sneaky) so its a bit of work to scrape and sand them out.

Then I fiberglassed the transom as suggested in the video to get some practice and confidence. The cloth was cut and taped in place to overlap the bottom by 1-2" and trimmed to fit over the sides a like amount. Corners were smoothed into shape without cutting. Epoxy was rollered in and it all went smoothly. After cure, the edges were sanded down to feather in.

I then laid out the bottom fiberglass cloth on the bottom and trimmed to fit about an inch inside the chine line. My friend Ted said he kept all the cloth overlaps on the bottom of his boat and it simplified the feathering process, so I did mine the same way. I precut the cloth for the sides by splitting lengthwise some 38" wide cloth and rolled it up on shop vac pipes. My daughters boyfriend, Brett was here for an Easter weekend visit, and since he has fiberglassed a boat before, he was drafted into service. We mixed epoxy, rolled it on the bottom and smoothed out any wrinkles and bumps. Brett mixed more epoxy batches, I rolled, and it progressed quickly. We then pre-coated a side and rolled out and positioned the cloth to overlap the bottom 2-3" and trimmed the ends as needed. We rolled on some more epoxy and worked it into the cloth and then did the final side. My daughter Katy joined in and we had three rollers going. It took about 1 1/2 hours to complete the job. After curing for a few hours, the fiberglass hanging over the edges was trimmed with a utility knife. It felt good to have this major step behind me. Thanks Brett!

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Keel Assembly

At some point during the blazing summer, the main keel timber twisted so much that if you looked aft down the timber, the left edge was about an inch off the cradle. I was in a sorry state of affairs for a couple of days after coming back from vacation and noticing this, but then just planed down the top surface of the timber so it was level again and proceeded with life as normal. This was the first in what I imagine will be a long line of oy vey occurrences in which I will need to remember that this is a boat, not a rocket ship.

After epoxying some of the deadwood and a fore knee to the main timber, I started looking around for ballast and floor bolts. I got really excited when I found a company selling galvanized timber bolts for cheap in Virginia and ordered a bunch from them. As an afterthought, I called back five minutes later and asked if the threads were cut or rolled. This is kind of a big deal because rolled threads would mean that Id have to drill a hole larger than the shaft of the bolt to get the thing through which means I would have little springs of water gurgling up through the keel into the hull. The very nice man who answered said that indeed they were rolled and cancelled my order for me. I ended up getting the bolts custom made by a company in Houston called Madden Bolt, and they did a fantastic job.

Here some of the keel chunks are glued together and I have the keel laid on its side to plane it down. I dont think Id drilled for the ballast and floor bolts yet. Note the curved thing in the foreground with all the clamps-- thats the deck beam mold.

Here the keel has been painted with copper naphthenate as a preservative, the ballast and floor bolts have been driven in, and some rebar is being zip-tied/wired to the ballast bolts to support the scrap metal that will be suspended in the concrete ballast.

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