Installing Hull Planks

Next up to light some fire under my feet is none other than the third member of the previously mentioned Car, Boat and General Design Club. At church, between services, near the offering box, where we regularly have our scheduled meetings, Bob Herrold asked me what my time schedule was for the boat to hit water. I said that I was optimistic for a spring of 2025, which gives me two years from today.

That seemed unacceptable to Bob as he had a disappointed expression on his face. He said that it must be a pretty complicated boat! True, but with other life complications. I need to work as hard as Bob does in his volunteer work at the hospital.

Consider it a challenge taken, and I am determined to shift into a higher gear. The cross frames are mounted, and the keel and structural beams are connected to the transom. The chine is now complete, and all surface parts have been faired.

The time has arrived to put the hull planks on the bottom of the boat.

Below is shown how the tongue and groove planks machined on my router tables from 1/2″ Marine Grade Plywood fit together.

The large washers for the screws are needed to hold the front planks to the keel frame. The extra length will be cut away later in the fun stage of final shaping.

The most difficult parts are the border planks which must be shaped to fit to the keel or the chine. When they don’t line up side by side, I sometimes use a guide block as shown below to pull out a depressed area. Getting a great fit to the chine is a challenge also, and when it is close, sawing through the joint is a good way of reducing the high spots.

When dry assembly is done, the hull planks are numbered, removed, glued with epoxy, clamped, and screwed to the frame members.

The epoxy takes a few hours to set up, but I generally wait over night to make sure it is hard. Then all of the screws are taken out, because any metal left in a potentially wet environment will corrode and the wood around it will eventually rot.

The surface created is already pretty well shaped, due to the benefit of the tongue and groove method of joining pieces. Sometimes, as shown above, an alignment block helps to flatten a poorly cooperating board.

After this layer is glued on, a thorough sanding will be done to “fair” it smooth without high or low areas, only regular curves. Then, the half inch bottom plywood will be covered by a second layer of 1/4″ plywood, making a strong and stiff 3/4″ bottom surface.

Boat building is a long, demanding process, so dividing it into smaller steps helps to see progress. This step of seeing the structure begin to take shape is a strong, motivating milestone.

Another encouragement comes from other boat builders. We are few and far between, so we don’t tend to have much routine contact. However, in the history of building both my boats so far, curious people from 140 countries of the world have checked in. Thanks to recent readers from Belgium and Ecuador. I hope your boats are coming along spendidly.

Stiffening the Chine

The pretty curve of the chine previously shown was made from a two piece assembly of 1″ x 1″ cherry, which was the maximum thickness to make the bend comfortably. After the outside shape was established, I added 1/2″ laminations to the inside of the curve.

I have about 20 small spring clamps, and 20 more larger ones for a task just like this. I love my wood screw clamps, my pipe clamps and some miscellaneous hand squeeze clamps, but more often than not, I reach for these useful spring clamps.

Once the curve was established, the 1/2″ layers easily fit to the curve and began adding great strength. As shown below, two laminations started from the front and at each cross frame, another layer was added until five were in place. Since this assembly was edge to edge long grain, I used Titebond III, but from here on, most of the connections will need to be structural strong. That will take Epoxy.

This becomes the chine line, and the future spray flat.

Encouragement continues to drift in: We recently went to a graduation open house for Keegan New, whose family lives on a small farm of mixed metaphors. On one hand is the car barn which reflects their family’s love for old cars, and fixing them up. Grandpa New got it started with his restored Dodge Charger and interest in the classics. Among the grandchildren, there is a restored old VW van, a Dodge Dart, and a couple other Mopar cars in progress.

The other barn is more along the lines of a typical 4H family, and Keegan took Jan and I there, with particular pride in some sheep he was raising to show at the fair.

This sheep is named “Jan,” and Keegan mentioned she should compete successfully, with the well developed hind quarters.

The next two sheep appear some what embarrassed when the person they are named after: “Doc” and “Lehman” actually shows up to say hello.

I think Andy Warhol said that everyone gets fifteen minutes of fame. This coming September at the Cass County Fair, I look forward to getting a generous lifetime dose.

Final Fairing

When the cross frames have been mounted on the strong back, the longitudinal center support beams are installed, and the transom is firmly connected to them to resist 3D forces, we are ready to move on. The next step is preparing the wood edges that contact the shell so when I add the hull planks over them, they will lay in the most fair curves.

Below I am getting some help from Owen, Jane and Will, my grandchildren.

Fairing means making a curve regular so that no noticeable dips or bulges are present. I start with the tape measure to try to get both sides of the boat symmetrical. But sooner or later, it becomes an exercise in hand and eye work. Long straight edges are helpful near the back of the hull, as there is a 6-8 feet flat zone on both sides of the keel.

However, as the runners go forward, they need to follow the curve of the hull, and a straight grained bendable stick helps find the high spots to work down. Ultimately, the eye gives the final inspection and Jane and Owen appear to be satisfied.

The further we go toward the front, the more critical and difficult the fairing becomes, to see how the planks will lay on the compound curves. Below, Jeff Margush, my main partner in design crime, is working multiple test sticks close together, to sleuth out how this difficult front end can get fair and fine.

Someone should have told me how difficult it is to design and build a vertical bow shape. Much chair time for thinking and some couch time for dreaming is required . . .

The Chine Line / Scarf Joint

The line where the bottom of the boat meets the side is called the chine. For slow moving, displacement boats, that area is rounded for the most efficient travel. But, for speed boats like the one I am building, the motor is strong enough to push the boat up onto a plane.

Edges created by a sharp chine on the sides and cutoff at the transom, lets the water separate cleanly from the boat, reducing the wetted surface. This loss of frictional resistance allows planing boats to reach amazing speeds.

When the chine line is defined, it is partly visible when the boat is at rest, and more fully shown at planing speed. It becomes an important part of the visual profile.

That edge must be strong also, because the corners are where the boat may contact a dock or an object in the water. For my boat, I am using one inch thick Cherry wood to make the chine log, as it is sometimes called.

The trouble is that the boat is 20′ long and my longest cherry is 12′ long. This requires joining two pieces using a scarf joint. Below are shown cutoffs from free hand cutting the roughly one foot angled ends.

The ends are not a perfectly consistent angle, so they are sanded, using a backer support to keep them from bending.

Then, the sides were matched together and assembled with two screws to prevent sliding under glue and clamp pressure.

Below is one 22 foot chine log clamped together.

Now they are ready for glue clean up and assembly onto the boat.

The chine log dimensions were picked specifically so it could be bent on a comfortable, easy curve from front to back. This is intentionally done without steam bending which is cumbersome and can give irregular results.

When the scarf joint is well done, and the grain of the both pieces are selected for longitudinal grain, without knots, the log will bend very consistently. As it is temporarily clamped in place, it helps to show where to adjust the cross frames on the way to creating a fair and beautiful curve.

Wooden Boat Transom

The transom leads the pack of all of the engineering challenges presented in boat building. In my case, it will need to be strong enough to hold the weight of a 500 plus pound outboard motor, with all of the rotational forces of acceleration and turning. Last, but not least, the transom will need to stay intact in the bounce of choppy water, and the serious bumps from road pot holes and railroad crossings.

The keel stem and long boards are looking strong enough to bear up to normal water pressure forces and the forward pressure from the motor. Next, in order to model where the transom would go, I cut a pattern out of cardboard to visually evaluate the best place. The tip approximates the mounting angle for an outboard motor.

I picked a location inside the first cross frame and screwed a slat at the recommended 13 degree angle to act as a guide for the router. Then, I routed a 3/16″ deep groove, 3/4″ wide for the end blocks on both sides. Much greater strength is gained with a cross grain stop.

Here are the stop blocks in place, and a temporary view through the sub floor transom and fuel tank space.

The transom was laminated from four pieces of 1/2″ marine plywood with epoxy. One more 1/2″ ply will be added to make a strong motor mount plate.

Once the transom blank was adjusted to fit the keel, and inside the runners, it was epoxied in place, against the cross stops.

Below, the keel has been cut shorter, and the first frame partly cut out to reveal the motor mount area. The scrap pieces are temporarily used on the transom help to spread pressure evenly as the fifth and last lamination is epoxied in place.

The rest of the stern will be built out when the boat is turned over, adding more transom support structure, but that’s for another day.

Intuitive Wooden Boat Engineering

Boat strength is an imperative topic in the creation of a boat, designed to safely carry people. If you want the full story in mathematical detail, Dave Gerr wrote a book called The Elements of Boat Strength for Builders, Designers, and Owners. You could call him “Noah Thing or Two.”

He lays out multiple graphs of plank and frame dimensions for all sizes of boats. This gave me comfort on the first boat when I planned the shell thickness of 1/2″ on the side and 3/4″ on the bottom. When I covered it inside and out with fiberglass fabric embedded in epoxy, I figured it was all good. So far it has survived lots of railroad crossings which will show up the weakest link.

Since I started with the 1/2″ Marine plywood, CNC cut cross frames, I needed to first strengthen them.

The Alaska Yellow Cedar left over from the first boat served admirably to stiffen the edges and provide general frame strength. The deck will be reinforced after turning it over.

Next, the frames needed to be connected, and the keel was the first place to start. The fair curve of the line was more critical than strength at first, so I used a single piece of Cherry that was planed down just thin enough to make the bend without needing to do any steaming. Ah the beauty of the line, however weakly drawn!

Then I added thicker wood under the long keel in proportion to what strength might be needed at each area. The boat is upside down right now, so the upper left corner of the boat is going to be the lower front of the hull when it is done.

The triangle corner brace is a three piece lamination of marine plywood. Of all corners of the boat to take a hit, on a rock, the sand, a log or a dock, this is the likely place where the most damage would be done.

Across the top of the single board that created the keel line, I laminated a second board to give it more stiffness. The back 8 feet are straight, for consistent planing.

Internally, the long boards were added to tie it all together, define the space for the fuel tank, and to pass the force of the future motor to the boat as a whole.

This is a wider boat than the first one I built, and it seemed like it could use a second long runner, to help stiffen the shell. I sawed and chiseled out some notches on the frames and runners to retain the best strength on both parts.

Someday it will sit for long periods of time on a trailer. The outer runner is about where the trailer bed rail will hold it, which can deform the hull if it is not strong enough.

A finely curved laminated stringer at the chine line (where the bottom meets the side) will be the remaining connector before the hull planks go on . . .

The Best Laid (Boat) Plans . . .

The new speed boat is coming together sweetly:

It will be 20′ long by 7’6″ weighing about 2100 pounds, and capable of carrying 8-10 people. This will be powered by an outboard motor of 150-200 Horse Power to push the boat to perhaps 45 MPH. At 450 pounds, the outboard delivers a much better power to weight ratio, and sitting right there on the transom, makes for easier maintenance. An old Mercury 200 Tower of Power like the one below would be the perfect attitude, but then, there goes the ease of maintenance.

The new wooden speedboat will follow a similar construction plan as the first, built of wooden cross-frames and stringers. This time, however, I plan to use a more local variety of wood, starting with the lumber left on my racks from a decade plus of projects. This will include some White Oak, Alaska Yellow Cedar, some Mahogany. These are from long and straight boards, with no knots, and rot resistant.

But my 10-12′ American Cherry lumber is also great to work with, and can be sized appropriately for the strength and function needed. Building a hull stiffened by fiberglass cloth, embedded in epoxy to keep the water out, is a far more important factor than the wood type.

The design concept has firmed up as well, taking inspiration from boats like the Frauscher below.

Some examples of work from my design program are shown below. This is not exactly the boat I am building, but it shows what fun a fairly simple program can create.

The boat shown below is also not the exact model I used for the frames. It does however, show a more vertical bow line, and forward leaning transom above the waterline.

The first serious step towards production was making a series of PDFs of the bulkheads from my boat design. Below is cross frame number 6, third from the front. My old computer with the free boat design program is 25 years old, and with my lack of tech savvy, I hoped that it could still be used.

One day I came to the moment of truth. Was this to be only a design hobby or am I actually going to build a boat? I called Tyler at Cutting Edge CNC in Millersburg, Indiana to ask if he could use the PDF’s. He said that it was quite possible and he would give it a try. In few days later, he said bring the wood!

For the last boat, (frames shown on right), I used large patterns and assembled all of the frames from Alaska Cedar and Marine Plywood parts.

This time I am trying a different approach, having the frames cut from 4 x 8 sheets of Hydrotek plywood. Then I will reinforce them later.

At Johnson’s Workbench in Charlotte, Michigan, I bought the 6 sheets of plywood, and dropped them off to Cutting Edge. Another couple of weeks, and voila’ the possibility of a boat became real!

After I received the cross frames, I went back to my computer design program to review the actual model’s side view lines. This was for the final information about how to position the bulkheads vertically, especially the front 3 or 4.

With apparent careless habits from new computers, I did not press save one time, and experienced the unfortunate disaster of the old days of computing. The current design concept was not shown above. . . because it is gone.

None of my efforts, or advice from experts to recover the design worked, and there I lost many hours of irreplaceable work. There is a lot about building boats that is like life.

Till next time . . .

Boat Building Wood 1

The design of a new wooden boat requires thinking about the choices of wood. Trying to keep the water out of the floating space takes a combination of strength, stability, toughness and endurance. Western Red Cedar, Alaska Yellow Cedar, Sitka Spruce, cypress, teak, ash, white oak, and mahogany are some of the most highly prized woods for the beautiful traditional wooden boats of the last century. 

Some physical properties that matter most for the wood in a boat are: strength, density, hardness, stiffness, bending properties, moisture resistance, and dimensional stability. From a practical standpoint, some of those factors may be overridden by cost, being able to source them close by, and working ability. With all of that in mind, here is one of my personal favorites:

Alaska Yellow Cedar – It is not cheap, in 2023 around $10-15 / board foot rough. But everything else about yellow cedar is amazing. Mine came in generous 4/4 thickness 1″ x 6″ x 16 feet long with no knots. The prime vertical grain boards are straight, lay flat, are very stable and weather resistant. It is very light weight, and has an exceptional strength to weight ratio which is great for boats or airplanes. The distinctive aroma advertises its unique personality, which is like your Grandma’s cedar chest, spiced up a bit. 

But it really shines when you actually pull it off the rack and put it to work.

Alaska Yellow Cedar cross frames and stringers.

The tight consistent grain cuts so consistently and smoothly, that it makes hand tools seem like a good idea. A bonus is that it over a few years working with Alaska Yellow, it has never once given me a splinter. I love this wood.

Perhaps you can imagine how sorry I am, that the original stash I bought in 2013 to start the first boat is coming to the end.   But, there are other wonderful wood choices . . stay tuned.