Introduction: How to Construct Ribs for an 18 Foot Grand Banks Dory
I'm building a traditional 18 foot Grand Banks dory. The dory will be discussed in a future Instructable but thought it might be interesting to focus on how I constructed the ribs which are the heart and soul of the dory, or more properly, the skeleton of the dory which supports the entire rest of the boat.
I have used a combination of traditional and modern techniques and a lot of help from friends and family that I refer to as the "planking crew."
The dory is being built with plans from http://www.doryplan.com/
In summary, the rib construction involved learning the traditional building method from The Dory Book, harvesting white oak logs with a major branch sticking out at nearly the correct angle, milling the logs into 1 inch thick boards, drying boards in solar kiln, planing boards from 1 inch down to 3/4 inch (20 mm) thick, using a plywood form to mark and rough cut the rib shape from the oak board, use the same plywood form and a router to create the final rib shape, and join 2 halves with a finger joint for installation. Each of these tasks will be discussed in detail in the following Steps.
A word on nautical terminology. There is a lot of it and I'm just learning it. Jack left port (i.e., left = port) is my starting point. And there are multiple words for the same thing. Ribs = frame = brace = knees and sometimes are combined like knee brace. I'll use "ribs" throughout.
The primary purpose of the dory is to carry picnic supplies and picnic princesses (i.e., persons not rowing) to islands off the coast of Maine. There are a lot of picnic princesses in our family, hence, why I am building an 18 foot boat.
Step 1: Traditional Building Method From the Dory Book by John Gardner
The Mystic Seaport kindly gave permission to use pages from the following:
The Dory Book, by John Gardner - This book is the most comprehensive book on dories ever published. More than a decade in the making, it is at once a history of the dory, a practical handbook on how to build a dory, and a compendium of dory designs with full construction details. 8 ½" x 11", 275 pages, 153 illustrations, 23 plan sets, index, paperback binding. Purchase from Mystic Seaport at http://www.mysticseaport.org.
I highly recommend The Dory Book to anyone interested in dorys. The Mystic Seaport is also a very cool, working, maritime museum. The museum is currently renovating a former whaling ship. You can almost smell the tang of the salty air.
A traditional method for constructing a rib or any other boat part is to find wood in the shape that is needed instead of either bending the wood or constructing from multiple pieces. The Plans called for three pieces. Using my method, it only requires two pieces. This reduced any weaknesses at the wood joints due to my substandard carpentry skills. Substandard to sh***y is how a Scottish friend would express it. In addition, the three pieces of wood creates a pocket to trap water with a potential for rotting. Water is only good on the outside of a boat. Not so good on the inside.
I literally took pages from The Dory Book, made a crude drawing to explain what heck I was doing and to look for suppliers. Refer to the 3 pages shown below. The idea is to obtain a white oak log with a branch sticking out at the correct angle to create a "hockey stick" and then join a pair of the blades of the hockey sticks together to create a complete rib. Refer to page 68.
In a Reny's store in Topsham, Maine, an old dory is part of the store displays and has ribs constructed as described in The Dory Book. I had to move the pillows to obtain the photo of ribs.
White oak was chosen because it was locally available, incredibly strong, and well suited for boat building because the cells of white oak are filled with tyloses, which restricts the movement of water. In contrast, red oak lacks the tyloses and water could move through red oak like a straw. The Plans called for mostly pine. Since white oak is roughly twice as strong as pine, I generally used boards with half the thickness of the pine boards, called for in the Plans, to have the same strength but reduce the weight of the boat.
Step 2: Harvesting Logs
First a word on safety, white oak is wicked heavy. I harvested wood from felled tree tops. The top of any tree, laid on it's side, on the ground, has all sorts of forces just waiting to be released when cut with a chain saw. Those forces could kill you and, unless you need killing, be darn careful. Consider using a professional logger to harvest this material; they have the equipment and experience to handle logs. (I attempted to find a logger but had no luck.)
Look very closely at the first photo and you'll see a chain hanging from the base of a log. I was cutting the base of the log when the entire top of the tree shifted downward, the cut collapsed, and pinched the chain. Luckily, I was able to extract the bar of the chain saw and had a second chain which I used to carefully cut out the trapped chain. It could have been the end of that day of harvesting.
I harvested the logs in a fire wood cutting area in our local state forest following the harvesting of timber. The tree tops remain following timbering. For $3, you are welcome to cut as much "fire wood" as you can haul out in a day. Instead of fire wood, I harvested wood for the ribs.
I harvested this wood in the same county that we live to avoid transporting any ash borers, which are the bain of ash trees.
Since the trees were growing in a thick forest, they grew relatively vertically and, hence, the limbs grew a more shallow angle to the trunk of the tree. I'd recommend finding trees near the edge of a woods, where the limbs would grow more horizontally and have a steeper angle relative to the trunk. This point will come into play during routing of the rib shape.
I made a small triangle template with the correct angle to determine whether the particular tree was worth harvesting. Refer to second photo. I also made cuts parallel with the tree trunk to remove excess wood. Green or undried white oak weighs 44 pounds per cubic foot and I needed to reduce the weight of each piece as much as possible in order to:
A. transport them to the truck and
B. wrestle them into the truck.
The estimated weight of the pieces ranged from 100 to over 200 pounds and at my physical limit to move. I tied each piece to a 2-wheeled dolly and rolled them to the truck over highly uneven ground. Plenty of exercise was obtained. A small tractor or back hoe with a winch would have made this process a lot easier. There was a lot of wood that was inaccessible due to the terrain.
I used Sithl chain saw with a 24 inch bar to do the cutting.
Step 3: Milling Logs
The oak logs need to be sliced or milled into 1 inch thick boards for drying and cutting out the rib shapes.
A local gentleman with a Wood-Mizer portable saw mill does custom milling. The Wood-Mizer products are manufactured in Indiana and are cool tools. http://www.woodmizer.com/us/home.aspx The oak pieces were irregularly shaped. The Wood Mizer is a very large band saw that could handle both the irregular shapes and large width of the pieces.
I was impressed with how easily the Wood-Mizer cut through the wood, especially after doing my work with the chain saw.
Step 4: Drying Boards in Solar Kiln
I built a solar kiln to dry wood for this build. A complete description of the solar kiln can be found at:
The graph shows moisture percentage versus time. The target range was 6 to 8% moisture; the moisture content used in furniture building. The oak was partially air dried, therefore, had a starting moisture content of up to 11.5%. Freshly cut wood can have moisture contents up to 25 to 30%.
In order to reduce the amount of cracking or checking at the the ends of the boards, the ends were varnished to plug up the wood pores in order to reduce the amount of the drying taking place at the ends. For subsequent boards, I purchased material specifically designed for this purpose called Anchor Seal, a wax-like material.
A concrete block was placed on wood to reduce the amount of warping while drying.
Step 5: Planing the Boards
I used a Grizzly 20 inch wood planer to plane the 1 inch thick wood down to 20 mm (3/4 inch) thick. A wide planer was needed because some pieces were up to 18 inches wide.
I hired a electrician to wire up of the planer since it is 220 volts and I am afraid of big electricity. The electrician also diagnosed a problem with the control panel switches. Thank goodness for professional help.
My work shop is smallish. In order to create the most working space, I installed a wheeled dolly under the planer to move it into a working position and then return to a more out-of-the-way position. A dolly was needed because planer weighs approximately 1,000 pounds.
During initial set up, we installed a Hoosier dust collector. It was not needed because the shaving would not shoot out of the planer. We did collect the shavings in a wheel barrow for future uses.
Step 6: Rough Cutting With Plywood Forms
I created a plywood form of the necessary dimensions and used the form to mark the shape on the oak boards.
3/4 inch plywood double-sided with birch was used for the forms. 2 smooth sides allowed the form to be used on either side, which ever was best for the particular piece of oak. I checked and rechecked the measurements prior to cutting forms. If there was a mistake, it was going to be the same, consistent mistake on each piece.
I slightly increased the width of the form to create a wider and stronger rib.
I also increased the length of each arm of the rib to provide some working length. It turned out that the additional length was needed and provided flexibility on where the center joint was placed to avoid knots or other imperfections.
The beveled corner creates the drain along the inside corner of the dory.
I used a jig saw to rough cut the rib shape. The issue is how close to make the cut. The blade is not perfectly perpendicular to the face of the oak. Cutting too close would remove structural material but leaving more material would have left more wood to cut with the router. I left approximately 1/8 to 1/4 inch of wood outside the marked form.
Step 7: Projectiles in the Workshop.........are Not a Happy Thing.
Another dangerous part of this project was routing the rib shape.
I had several projectiles shoot off the router table and hit the workshop walls. Very disconcerting.
Since the oak trees grew in a relatively thick forest, the branches grew more vertically and at a shallow angle relative to the trunk of the tree. The ribs require a steeper angle, hence, the wood grain runs across the rib. Refer to the photo below. The router bit would catch on the grain and send it flying. To resolve the projectile issue, you could find a tree near the edge of a woods where that the branches would grow more horizontally, at a steeper angle relative to the trunk, which should allow the grain to follow the shape of the rib or follow suggestions below.
1. Use smaller diameter router bit. I originally used a 1 inch diameter flush trim router bit and then switched to a 1/2 inch diameter bit. The smaller diameter bit was easier for me to control.
2. Use jig saw to trim close to line. As I became more experienced with jig saw, I cut closer to the line which left less wood to be trimmed off with the router.
3. Back cutting. Staff at a local woodworking tool shop suggested back cutting (i.e., cutting against the direction that the router would naturally follow due to the spin of the bit). In difficult areas, back cutting seemed to allow greater control.
4. Hand routing versus using a router table. Guiding the router by hand seemed to offer more control than using a router table.
The woodworking experts out there may have better, safer suggestions. Thankfully, there were a number of extra boards. The fails became really nice fire wood. The wood scraps have kept us warm this winter.
Step 8: Routing the Final Rib Shape
After rough cutting the rib with a jig saw, the plywood form was reattached to the oak with double-sided tape.
The double-sided tape provided a secure connection and also created a small gap between the oak and the plywood.
I used a Whiteside 1/2 inch flush trim router bit to trim the oak board down to the shape of the plywood form. The router is adjusted up or down until the bearing of the router bit rides along the plywood form.
Step 9: Filling Holes With Epoxy Resin
There are natural and man-made imperfections in the oak like knot holes and router cuts. I used epoxy resin to fill the holes. I created a temporary dam with painters tape and filled the cavity using a syringe to make sure the resin was injected into all the cavities. After the resin hardens and tape is removed, it is possible to file or sand off any rough edges.
I purchased Entropy Super Sap 100 Epoxy Resin purchased from Jamestown Distributors. Staff at Jamestown Distributors are very knowledgable. Entropy epoxy resin contains "bio-solids" and I assumed that there was less need for respiratory protection since there are less petrochemicals. I used the resin in a well-ventilated area. More info on the resin from http://www.entropyresins.com/
I recommend purchasing the pump dispensers for mixing the resin and hardener. I initially used industrial syringes for measuring and dispensing but the pumps are much easier to use and less messy. Syringes or pumps are also available from Jamestown Distributors.
Step 10: Join 2 Rib Halves With a Finger Joint
I used a Porter Cable Model 890 2.5 horsepower (HP) router and CMT finger joint router bit to cut the finger joint. The finger joint was used to join the 2 halves of the rib together. The white oak is pretty tough wood and I would recommend at least a 2.5 HP router. A smaller router might bog down with cutting the joints. I spent a lot of time adjusting the router bit up and down in order for the 2 sides to match closely; within a millimeterish. There is a wonderful quote on a boat building email forum that said "Fit till you're proud, nail it home, and go sailing." This is proud for me.
I clamped 2 rib pieces to a cross support on the dory bottom. The Plans called for a rib at each cross support. The ribs pieces were moved back and forth until they closely matched the width of the dory bottom at that position. The dory is wide in the middle and narrows to each end.
Using a Veritas right-angle drawing tool, I drew a match line across both rib pieces. The match line was used to determine where cut the rib pieces to the proper length at the finger joint. The match line was placed generally near the center of the dory but was moved either port or starboard to move the cut away from knots or other imperfections.
The rib pieces were unclamped, the match line was continued down the side of the rib piece with the Veritas right-angle drawing tool. I added 4 mm of wood toward the center of the dory to account for the wood removed by the finger joint bit. A circular saw was used to cut along the final line and the router was used to cut the joint.
Since the dory bottom is gently curved, the outside-edge of the vertical components of the rib pieces had to be trimmed to match the curve. Trimming the rib pieces allows the planks to fit flush against the rib. I used a Swanson T-bevel sliding square tool to determine the needed angle of the cut and the angle was transferred to a circular saw. The circular saw was used to trim the rib pieces.
After trimming the rib pieces and routing the joint, I clamped and dry fit the matching rib pieces back to the cross support boards to check the fit and make any corrections as needed.
I drilled a hole to both create a pilot hole and counter sink the screw. A silicon bronze screw was used to attach the rib to the cross support board. McFeelys supplied both the drill bit and screws. McFeeleys carries a screw for marine construction because the shank of the screw is as wide as the threads. The shank fits tightly against the wood and reduces any leakage along the screw. Silicon bronze was recommended for marine construction. I prefer the square drive screws available from McFeelys than the Philips head screws available elsewhere. I found that the pilot hole needed to be slightly longer than the screw or I would occasionally shear the screw off in the pilot hole. For sheared screws, I would remove the broken part, redrill the pilot hole at a slightly different angle, and attempt to use the same counter sunk hole. The Plans called for #8 screws but I increased size to #10 to provide stronger screws and reduce the shearing problem.
Step 11: Gluing and Screwing the Ribs to the Cross Support
After drilling the pilot holes, the rib pieces were unclamped and coated with the epoxy resin. The resin was used both to create a protective coating and glue the finger joints together and glue the rib pieces to the cross support and bottom.
After coating the joint and bottom of the rib, the rib was reclamped and screwed in place.
Once screwed in place, the reminder of the ribs was coated with resin to completely cover each rib. The resin allows the beauty of the wood grain to shine through.
This process was repeated at all five cross support boards. The cover photo shows the complete rib construction with a batten joining ribs.
There you go, simple as that. Hope to be sailing in the dory one day soon with you, my dear picnic princesses.