Covering the Bottom with Ply

Fig 1. - Clamping down a sheet to mark the shape

Marking and Cutting...

Now that the frames and sides are trimmed its time to apply the bottom plywood.  There will be two layers of 1/2" ply installed for strength.  The first layer will be glued and screwed to the frames and the second layer will be glued and screwed to the first.  The first step is to cut a half sheet and line up with the closest frame toward the stem (or front) that will cover from side to side.  From there its pretty simple, just a matter of clamping down the ply and marking the cut where the outside of the side ply intersects the bottom (Fig 1).
Once marked, cut to the line and set aside.  We opted to do all of the cutting at once since there was going to be a lot of glue mixing and screwing down once we started.  We suited up in coverall suits to protect our clothes and skin.


Installing...




Fig 2 - Squeezing bead with Ziploc pastry bag.

Installation was messy, awkward but simple. The epoxy was mixed to a peanut butter consistency using fumed silica and milled fiber for strength.  We used a short cup to fold a quart Ziploc bag in and dumped the mixture, forming a pastry bag to squeeze along the frame edges (Fig 2). 



Fig 3 - Brushing the drainage holes to seal the wood.
Also note the bead of epoxy spread along the frames,
ready to receive the plywood.



We also took the time to saturate the limbered drainage holes in the frames which would be tough to get to once the plywood gets installed (Fig 3).  The plywood was screwed down, one after the other and now we are ready for the next layer of ply.




Fig 4 - Glue spread waiting for next sheet

Next layer of ply was marked and cut the same.  We were sure to stagger the joints so there wasn't a weak spot formed.  Each sheet took between 12oz and 36oz. of epoxy mixture.  This was mixed to mayonnaise consistency with a notched trowel.  The awkward part was just trying to hover over the glue long enough to get the panel lined up before dropping into place.  Fig 4 also shows the previous sheet edge to the right and the pencil mark on the left that was used to line up the sheets as we went along for cutting; as well as, a stopping point for the glue.  We didn't attempt to glue all of this at once.



Filling out the Tyvek suit to its breaking point...

Extending the side angle through the bottom ply...

Just as the title states the bottom ply must be cleaned up by following the side angle.  Not much to say here, no real tricks.  I used a power plane and belt sander to do this.  The following pictures show how this should look when finished. The stuff on top is curls from the power planer. Next up, the keel...







Prepping To Cover the Boat's Bottom

Fig 1.  Marking board that is the same width as the frame and is notched
to clear
the protruding chine and plywood edge.  The darker board is there to help hold it in alignment.

Now that the sides are finished, it's time to prepare those sides for the bottom ply sheathing.  Because the chine and plywood edges are 90 degree edges. We have to trim those edges at an angle to match the boat sides so that the bottom plywood will lie flat.  We also need for the plywood sides to assume a nice, close fit to the bottom and not have humps and bumps that keep them from lying tightly on the frame bottoms.  Just as the frames created a nice fair curve for the plywood sides, we need for those same frames to create a nice fair curve on the bottom.  How to accomplish this?...


Figure 2. Frame bottom transferred to outside surface of side.

To prepare, we need to mark the outside plywood surface with the frame's bottom edge, basically extending that edge through the plywood.  This was accomplished as seen in Figure 1.  Once finished we will end up with a series of marks that look like the ones shown in Figure 2.  One thing to note is that the bottom of this boat is a continuous curve from front to back.  This creates rocker.  In a boat's design it provides maneuverability.  You can spot this gradual arc by the horizontal frame pencil line in comparison to the edge of the plywood. See how the left side is closer to the edge of the ply than the right edge of the line?  And obviously the bottom is sloping from left to right.  That bottom ply will contact that left edge of the frame.  When the boat is flipped upright, we will fill in that gap with epoxy creating a structural joint, as well as, using screws to hold the bottom to the frames.


Now that we have all of the lines drawn we will place one screw at the end of the line closest to the plywood edge. (in figure 2 taht would have been at the left edge of the pencil line).  Again, this represents the edge of the frame closest to the bottom and the one that the bottom ply will come into contact with when screwed and glued down tight.



Fig 3. Screws driven along pencil line temporarily to rest the batten on to drawn a fair curve.

Figure 3 shows this.  This particular screw is located in the middle of the line as it represents the Station 12 frame, the middle and flattest part of the boat's bottom.  What this picture also shows is the spline or batten strip resting on top, not attached.  We prepared this by ripping a 1/4" thick strip out of some scrap 3/4" pine, 12' long.  When bent along the tops of the screws, the spline gives us a nice fair curve that gets us much closer to what the finished boat's bottom will be.  We will used thickened epoxy along this joint which is gap filling but the closer the better.

Figure 4. Line marked along top edge.

Now that we have a line to follow its is time to chose a way to cut down the edge protruding above the frame level to that line.  It's a good bit of material to remove and we wanted to get it as cut as quickly and accurately as possible.  We eliminated a power planer since the amount of waste to be removed varies and might be hard to keep level. We eliminated the jig saw because it was such a gentle curve and decided on the circular saw.  It can handle gentle curves easily and has a foot that can be adjusted at an appropriate angle to handle most of the cut.  Things get steeper near the stem so we will have to use the planer to level down to the frame.  We used a bevel gauge to establish the angle and transfer that to the circular saw foot.  Unplug the saw first.  We used a clamp to keep the guard back while we transferred the angle to the saw.  See figures 5 & 6.


Fig. 5  Getting the angle using the bevel gauge



Fig 6  Transferring to the saw to set the angle.

 Now its a matter of carefully cutting along the line and getting used to the flavor of marine plywood with a hint of epoxy.  By the way, wait till the epoxy is fully cured. Green epoxy will gum up your tools and is still unhealthy to breath when not fully cured.  Here (final few pictures below) is the result with some minor hand planing to finish off.  Note that it is fairly level now and ready to provide a fair surface for glue and screws.  This wide edge will provide a nice glue surface for the bottom ply.





Plywood Sheathing the Sides

Applying epoxy to the stem
 for the 3/4" filler strip

 A few last minute details....

Here we (my father and I ) begin sheathing the sides.  The only wildcard is the question of just how flexible the 1/2" marine ply is?  It hasn't kept me awake at night, sweating profusely and asking for divine intervention; however, we have wondered if  a nasty shock is in store for me when we was ready to push the plywood in two directions, having wished we had opted for one of the more flexible plywoods. 
There was a few last minute preperations to make...
We had originally intended to inlay the chines into the stem. Basically, cut a notch for them to fit into.  When we laid then up to the stem we realized that if we did this we would leave very little of the stem for fasteners. This may have even created a weak point.  Instead we fastened them to the outside of the stem.  We then cut filler strips, epoxied them in place and screwed them in position.  The result is, we now have one, uninterrupted plane to land the plywood on and was ready to clamp, mark, cut, glue and fasten.


Epoxy fillet and filler piece added.

We also had to deepen the 1" x 3" chine notch as it created an unfair bulge at Station #20 or the one right ahead of the transom.  It wasn't a big deal.  We just backed out the screws and used a Bosch flush cut saw to accurately deepen the notch about 1/2".  We did the same to the other side, then adjusted the edge of the frame that gets sheathed to match the now deeper chine.  Not bad, just a few minutes with a planer.


Clamp, mark, cut, glue and fasten...

Marking bottom edge of ply using the chine

So, as the title states, this is basically the sequence of steps in sheathing the hull.
Picking  the "A" face of the AB ply (not easy so far, they look the same) we prepared ourselves by positioning C-clamps close by and lifted the ply into position.
 
Step 1 - Clamp:
Starting at the stem, we clamped the ply at the upper and lower chine, starting from the back, and then clamped the upper edge of the ply leaving the hard twist at the bottom of the stem.  ***I'm building this hull upside down so we are using relative terminology to help everyone stay oriented.*** At the bottom of the stem, we used a bar clamp, screwing and pushing the ply in position till tight.  So far, so good.  No cracking noises.

Step 2 - Mark:
This part needs little explanation and you actually see me doing this in the photo to the left.  We used the outside edges of the chines to mark the shape of the plywood panel cut which meant some crawling around the strongback to make sure we have marked all edges.  We also went ahead and marked the chines at the plywood edges so that we had some idea of when we were close to proper position when it came time to fasten the cut panel. We also used this edge mark as a center mark for the butt blocks that will fasten panel to panel.

Step 3 - Cut:

Saw cutting on table. Depth set just below plywood.

Follow the line.  We used a circular saw since it was faster, the curves were gradual and we could set it to just cut through the ply and my panel could stay on the cut table without a lot of drama (falling pieces, saws binding, bleeding shins and contortionist positions trying to hold an 8' long cut together). Believe me, if you are going to cut much ply, take the time and a few bucks and make a proper table to cut on. It may even save a finger.

Step 4 - Glue:

We have covered the basics before.  We guess the real take away is to make the glue a little thicker than you may think.  We used a notched bondo squeegee to apply the glue.  We used some sheet metal notchers to make the teeth but you can do it with a razor knife.  It needs to be spread fast and we followed the squeegee with the plate held under it catching as much as we could that dripped off.  We generally mixed around 12 oz. per plywood panel.  We used a 5oz. dixie cup as a scoop and used about 1 1/2 cups of silica and 1/2 a cup (dixie) of milled fiber; came out somewhere between the consistancy of mayo and peanut butter.  Move briskly if its warm or buy slow hardener.

Step 5 - Fasten:

A repeat of step one with the potential of getting really nasty with epoxy so wear your protection.  We covered the chines and frame edges with the goo so its everywhere to touch but went well having the lines to go back to.  We did lightly clamp the pieces and adjust with a block and mallet before cranking down.  We used a combination of 2" and 1-1/2" 316 SS Screws.  No problems there and kept abot a 6" or so spacing pattern.  It seems extremely solid.




Two sheets glued in. Note the butt block at the edge of the plywood.
6" wide and two rows of 1" screws to hold it. Work from the top and bottom
toward the middle to pull it together slowly. Helper is admiring his work. Little does he know
that he has epoxy in his hair while putting on his glasses.




 





Another view.

 

 



Opposite Side Done

Transom, Chine and Inwale... the build resumes Late July

TRANSOM AND STEM...



Transom mounted to strongback.

Now that we are flush with material (for the forseeable future anyway) I am pushing forward with finalizing the frames.  I left off in the assembly with the transom.  That would be the back of the boat that you typically see adorned with the ship's name.  This particular one is made from two layers of 1/2" ply, laminated together with epoxy glue and screws.  This will also be covered in a layer of mahogany lumber and finished clear with a thin white band of paint along the sides and bottom to represent the edges of the hull planking. That comes later. This paint border is a design feature that works for this classic take on what is already a classic, and thanks Brad for the "yacht styling" tip.

Stem and Frames #2 & #4

The other end or bow (pronounced as in "to take a bow") needs a vertical post for the plywood to join.  This is referred to as a stem.  Like the transom, it attaches to the strongback to hold it in the proper position relative to the other frames and at the proper angle. You can see it to the right. At the same time I attached the last two frames that form the short fordeck.  They are different in that they have a solid, arched deck beam.  You can see it in the same photo titled "Stem and Frames #2 & #4, hanging at the bottom (remember we are building upside down).

INWALE & CHINES... 

Now that all frames are in place we need to attach them together along the boat's length.  The chine and inwale serve a structural purpose and provide a fair curve along the hull to scribe the plywood sheets along.  As a structural element they provide reinforcement along the plywood joints where bottom meets sides, and sides meet deck. For the side to bottom joint I will use a 1" x 3" member referred to as the chine and for the structural member along the deck and hull side joint called the inwale, a 1" x 2".


Jig mounted to table with a chine clamped in place.

For material I am using the same clear southern yellow pine that the frames were constructed from.  So, my wife and I were back in the shop working both ends of the planer and tablesaw.  God Bless her... she wears the battle scars as proof that we just spent some quality time together. 
The maximum length of my stock is 12' so I need to join the 12' strips into longer pieces so that when they are bent to the pre-notched frames, the resulting curve will be smooth and continuous.  If I tried to just join them at a frame, the result would be a hard bend or kink... not good.  So, how is this accomplished you ask?  Well, this is done using what is referred to as a scarf joint.  That is basically a very long, shallow angle milled or cut, on each end of the board matching each other and provides a lot of glue area to join the boards.  The first step is to cut the joint.  Some plane these stacked in a pile, others saw.  I used a router with a jig constructed on the table saw that gave me 8" of joint on a 3/4" thick board.  Why 8"? Use the rule of thumb that you want 8x (or more) of the thickness of the board being joined.



Bottom view of router base

Marking the angle to joint to

I cut a piece of ply that attaches to the router in place of the plastic base via the same screws used by the original base.  I also slid the router perpendicular to the jig and marked the stopping points for the router bit.  I used some scrap pieces of hardwood to create stops so that the bit wouldn't bite into the jig at the ends of travel.  also, I screwed down a piece of 3/4" x 3/4" scrap along the inside edge of the jig to stand the chine off so that I could cleanly pass the router bit across the chine.  The only thing that I found was that when I got near the feather edge of the cut, the router bit would grab that piece hanging onto it and tear it off.  I decided that instead of nibbling off in multiple passes, I would just marke the angle and take it to the jointer to hog out almost all of the wood and just use the router to clean and true up the joint.  Like so...



Now that this is done I have a stack of scarfed pieces ready for glue...

Folks, we can't stress this enough but when you truly have a wood joint that is going to see alot of tension (and bending these chines in two different directions at once qualifies) you need to use the strongest glue possible.  If this joint may also see moisture (the bilge of a boat), you need a waterproof glue.  Not water resistant, waterproof. You don't want this joint coming apart down the road.  Use epoxy.  We will use in excess of 20 gallons on this project and its is time to put on the respirator, gloves, glasses and whatever else is needed to keep it out of your lungs, eyes and skin and get with it.  We use a combination of fillers to add

thickness to the consistancy and strength.  For this purpose I use fumed silica (respirator) and milled fibers.  The epoxy is Raka brand which I like and is a 2 to 1 ratio resin (2 parts resin to 1 part hardener). Observe all safety precautions, ventilate the area well and work quickly if you are using a medium hardener and, it's 90 degrees out like I did.  To extend this "kick over" point, immediately pour your mix into a flat paper plate to spread out the surface area.  Epoxy sets faster if contained in a cup.  I laid down a layer of plastic film over my work bench and started gluing. I used pocket hole screws with a backer piece of polyethelene cutting board with two screws across the scarf to serve as a clamp until the following day.  They came out easily and the HDPE backer just fell off.  In the "Transom View" you can see the finished pieces laying across the frames, approximately 28' or so long. 





Transom View... Chines and Inwales laid across frames ready to be fastened into notches

Now, all that remains is to get these on the boat.  Notice that there are notches in the corner of the frames. There are also notches in the transom at the upper corners and notches where the arc of the transom begins.  The purpose of these is to recieve the chines and inwales.  Since these will lie at an angle to the vertical plumbed frames, I will skip the gluing now and install with #12 - 316 stainless 2" screws...2 per joint.  When the boat is flipped, we will create an epoxy glue fillet at these joints and along the chines and inwales from one end to the other for added strength. We started in the middle and worked our way toward each end.  They bent in just fine. Here is the final result... 

Ready for Plywood

 

In this view you can see the compound curves and get a sense of the shape of the hull.
In the foreground you see a 4' x 8' cut table for ply.  Set the saw depth slightly deeper than the ply and cut through. It will only make a harmless kerf on the top surface of the 2" x 4" frame.  Everything sits in place, no dropping parts on your shins and cord.  It's about 32" tall.