VI. Battens, Stringers, and Seat Faces
Building the Core Sound 20
March 24, 2008
NOTE: This article is divided into chapters. Click here for the Table of Contents.
After a long week of filleting, taping, sanding, and fill-coating, the boat is finally ready to receive the keel batten, stringers, and seats which provide structural rigidity to the hull and provide space to sit and store gear. A lot of work is involved at this stage, but here, I'll summarize the main steps in the process.
First, we installed a keel batten running from the forward bulkhead to the transom to stiffen the hull for riding on a trailer. Somehow, we neglected to install this before fiberglassing in the aft bulkhead, so we had to use a saw and chisel to make an opening in the aft bulkhead to pass the keel batten through. It took about an hour of fussing around, but we finally managed to pull it off, so as you can see in the pictures, we now have a nice, stiff keel batten (made from 1" x 4" Douglas Fir) running down the centerline of the boat's interior. We also ran a small epoxy fillet (1/2" radius) along each side of the batten so that it would "blend" smoothly into the hull rather than look like a simple square-edged board. Later, we will round off the top edges of the batten with 1/4" roundover bit on the router, to give it a finely contoured shape and to protect the edges from chipping.
Next, we installed the front mast step. Our boat will carry two masts, but the forward mast is so far forward that it needs a flat base to rest on above the aggressive V-shaped hull. To provide such a flat base, we installed a vertical piece of plywood capped with another, horizontal piece shaped to fit the triangular space where the hull sides converge at the bow. It is very important that the boat be accurately leveled at this point so that these pieces can be installed and leveled properly. The plans specify a 3-degree rake to the masts, so we installed the mast step 3 degrees off of true horizontal as well. This will allow the bottom of the mast to sit squarely on the mast step, and it will also ensure that any water that finds its way down the mast hole will drain aft, where we will install a small PVC drain to lead the water into the cockpit bilge.
Then, we added the hull stiffeners. The Core Sound's hull is only 1/4" thick in the contoured front section, so there are six angled stringers in front of the bulkhead and four parallel stringers behind the front bulkheadall used to strengthen the forward hull. Here, too, we ran a small epoxy fillet (1/4" radius) along each side of the stringers to ensure water will never penetrate between them and the hull, and to give them a smoother, aesthetically-pleasing appearance. Once the epoxy dried, it was impressive and reassuring to feel how much additional stiffness these stringers lend to the hull. Originally, I had reservations about building the forward hull as thin as 1/4", but with the stringers installed, I am confident the hull is more than adequately strong.
Later, we installed the partial bulkheads which reinforce the sides and provide support for the seats. These bulkheads divide each seat internally into two separate, watertight compartments. They also stiffen the side-to-hull joint along the middle of the boat, providing significant structural strength.
Once the partial bulkheads were filleted and fiberglassed in place, we installed long stringers running from the aft to the forward bulkhead to define the top edges of the seat faces. This part of the process takes a lot of tedious measuring with levels and plumb bobs, but it's important to take your time at this stage if you want straight, level seats. In our case, patience paid off. The stringers came out dead level both fore-and-aft and athwartships (side to side).
Next, we cut out carboard templates to determine the size and shape of the seat faces. We could have cut these pieces directly out of plywood, but when you're working with such expensive materials, mistakes are very costly. Our carboard templates allowed us to get the shape exactly right, and then to transfer it to the plywood sheets. The result was an excellent fit. For accuracy's sake, we deliberately left the tops of the seat faces 1/4" taller than needed. After the seat faces were installed, we used a block plane to shave the tops of the seats down to be dead-even with the stringer. This is the easiest and surest way to get a perfect fit.
With the seat faces installed, the interior really begins to take shape. It's exciting to see how much legroom the cockpit will provide and how much cargo room will be available to us inside the seat lockers. Some of the legroom in the forward half of the cockpit will be lost to the centerboard case, but it will still be adequate for comfort. In the aft half of the cockpit, where we'll spend most of our time, the legroom is luxuriously spacious (a little more than 36" from seat to seat!).
Next, we sanded inside the seat lockers. Some folks neglect this part of the process because the compartments will never be seen once the seat tops are in place. But we think it's worth the effort. If you don't sand them thoroughly, reaching around inside the hatches later can be a painful affair as you scrape your skin on all the little jagged bits of grit or fiberglass. Those little jagged bits can also cut or shred some of the things that get stored inside the hatches (plastic bags, lifejackets, etc.). So we made our seat lockers very smooth.
Then, on the starboard side just below the seat stringer against the hull, we cut a 1" diameter hole in each of the forward, middle, and aft bulkheads. Here, we will run 3/4" PVC tubing to accommodate electrical wiring in the future. In the short term, we're planning to use portable, self-contained LED lights (made by AquaSignal) for our nighttime navigation lights, but later we may want to add permanently-mounted onboard electronics (such as a depthfinder and GPS/Chartplotter) so we thought it prudent to install the conduit now. The tubing will permit us to run wiring easily from the bow to the stern, as well as into each of the two seat lockers on the starboard side. Before we install the seat tops, we'll install the PVC and seal around the holes to maintain the watertight integrity of each bulkheaded compartment. We'll also cap the PVC tubing until we need it.
Finally, we gave each of the seat lockers three coats of epoxy to seal and protect the wood from water intrusion (in case moisture ever gets inside the compartments). We were originally planning to paint inside these compartments, but the clear-coated wood is so beautiful, and leaving it clear-coated will make it easy to inspect for wood rot in future years. Instead of paint, we decided to line each compartment with a plastic mesh that is designed to serve as a no-slip surface for tables and workbenches. It's cheap, it's lightweight, it won't absorb water, it will "breathe" (not promote mildew), it will protect the epoxy-coated wood from scuffs and dings, and it should discourage items from sliding around inside the compartments. It will be awhile before we're actually stowing gear inside the seat lockers, but now is the time to install the mesh because it is much easier to cut it to fit the compartments before the seat tops are installed.
© 2008, Wesley Kisting