Duckworks Magazine - Building a D4 Dinghy

Building a D4 Dinghy

By Pat Johnson - Pensacola, Florida - USA

LOA - 7’9”
Beam – 4’1”
Draft - 6” board up and 24” with it down
Weight – 75lbs

Click images to enlarge

I’d like to share my experience in learning how to use epoxy. Several years ago I decided I wanted to master some of the basics regarding Epoxy and fiberglass. I had touched on the basics off and on again through the years while repairing small cracks and holes but had never actually used the process for construction. While preparing for the actual “hands on” part of the education I read various articles and books and in the end decided that rather than build a box in the learning process, I might just as well build a small boat.

I am not a master carpenter but I have owned several houses over the years and have a fair level of knowledge regarding basic power tools and general household maintenance. Luckily for me, my expertise at covering up my mistakes at home maintenance turned out to be one of the primary skills needed for building stitch & glue (and screw & glue) boats. Unless you are building “Bolger Bricks” (a brick shaped dinghy with no difficult cuts or bends), you will likely have some pieces of wood that do not fit together as precisely as you planned and you’ll need to cover the gaps and round the corners. By the way I have built a Bolger Brick and liked many of its characteristics, so I’m not knocking that design.

I used West Systems epoxy and filler on my first boat but have experimented with several varieties since that time. I use Epoxy because the resin is absorbed by wood and virtually ends the chances of wood rot due to water. That characteristic allows me to use the cheapest plywood available in my boat building projects. There are many other epoxies out there but West Systems is probably the most readily accessible to the average Joe (or in my case, the average Pat). The West Systems fast hardener’s quick cure properties were also a big draw since my skills don’t include a lot of patience.

There are three things you MUST know before attempting any of the following at home.

A Belt and Palm sander are your best friends
Plain white vinegar will clean epoxy off your hands if you clean them before the epoxy begins to harden (Yeah, I know you’re supposed to wear gloves)
Never mix more epoxy than you can use in five minutes (ten minutes in the cooler months). It’s easier to mix more than to spread a smoldering glob of semi hardened epoxy.

There are a lot of boat-building websites. While many of the boats will stir your imagination regarding beauty and performance, remind yourself that simplicity is the key to an enjoyable “first time” boat-building project. After a good deal of searching I decided on a dinghy called the “D4”. I decided to buy the plans for $35 to ensure I got it right. In retrospect, I might have done just as well with the free plans that were offered, but it pays to be cautious when doing something new. I also decided to build the sailing version since the cost was nearly the same and I would have a more versatile boat at completion. I reviewed a bunch of online tutorials on construction techniques from various websites. A Bolger Brick (very simple) would have been a much better first time boat (much simpler with few curves).

I decided to build the sailing version since the cost was nearly the same and I would have a more versatile boat at completion.

Armed with the plans, the epoxy materials and a couple sheets of plywood, I began. The first thing to do was to draw the shapes on the plywood so that the individual pieces could be cut out. The plans were a little difficult to piece together for this process and it took a little while to get it done. Subsequent boat plans were much easier having had the initial learning experience under my belt. I used a circular (skill) saw to do most of the cutting and it was done within an hour or so. Next the assembly steps were begun. I attached the two sides to the forward/vertical side of the center seat by drilling holes in the side and the corresponding vertical piece and stitched them together using 8 inch long electrical ties (this is the stitching part of the “Stitch & Glue” process). It is amazing how well the electrical ties allowed the two pieces to be cinched together. They held together well enough to be freestanding and with a fairly strong joint. Attaching the bow and stern was accomplished using the same technique and the plywood had already begun to look like a boat 20 minutes after the initial stitch. The next steps were to insert the remaining vertical pieces and then flip it over to attach the bottom. Before flipping the boat back upright I used duct tape along the bottom edges to keep the epoxy from running out of the crack. I had put all the electrical tie ends on the outside of the boat where they could be more easily cut off after I finished the inside of the boat.

After flipping the boat to an upright position the long awaited epoxy process started. Filling the seams with a mayonnaise/peanut butter consistency mixture of epoxy and filler and then shaping it to a “fillet” was done first. I did the filleting in small secitions to ensure it didn’t harden while I went to the next step. While the epoxy fillets were wet & still curing I placed 3-inch fiberglass tape over the fillet and painted it on with a mixture of West Systems epoxy & hardener. After the final filleting and taping were done on the inside, I took the opportunity to epoxy all of the interior plywood using a small 3-inch wide roller. I left the boat to dry till the next day even though the fillets were cured to a hard state within about 3 hours. The epoxy leaves a glossy varnish-like finish on the wood. It is not quite as smooth as varnish and requires further preparation before painting or varnishing but I will get to that later.

The next day the epoxy had fully cured and I flipped the boat upside down so I could work on the bottom. First removed the duct tape and cut off all the electrical ties that were sticking out. I used wire snipers to cut them as flush as possible to the wood. After cutting all the ties off I used a palm sander to ensure the remaining portion of the electrical tie was flush of below the surface of the plywood and a belt sander to round off the sharp edges of the plywood joints. Then I finished sanding the joints with a palm sander. From beginning to end of the boat building project, I never used anything but 50 or 60 grit (coarse) sandpaper. A quick wipe with acetone removes the wax produced by the epoxy curing (it will gum up your sandpaper if not removed). The epoxy will cover the insignificant scratches easily so fine sanding is not needed. Sanding the epoxy that has already cured with coarse sandpaper leaves a surface suited for painting or varnishing. Once the bottom was shaped smooth, I used the same epoxy/filler mixture to cover the relatively small gaps on the bottom of the boat and again fiberglass taped the joint with 3-inch tape. I then covered the entire area of the exposed plywood bottom with pure epoxy using the 3-inch disposable roller.

From beginning to end of the boat building project, I never used anything but 50 or 60 grit (course) sandpaper.

I let the boat dry over night to ensure the epoxy had time to cure completely. Once again I flipped the boat over. At this point the boat weighs nearly 50 pounds so it’s still easy to flip and yet is already very stiff and has no noticeable flex. At this point I began considering what hardware I would mount and where. It’s very difficult to mount hardware after the area is enclosed with a seat top and back. I epoxy glued a backing plate of 1x4” to the lower portion of the bow and installed an eyebolt towards the bottom and through bolted a towing ring to it. By the way, always use stainless steel or bronze for any metal hardware. I used stainless steel. I also installed the lower gudgeon for the rudder with a backing plate of 1x4” wood. The bow and stern seat tops would seal access to these areas so these pieces of hardware need to be installed prior to gluing on the seats. I also installed a mast step at this point. I used 2” PVC end cap as a mast step and built up a little support for the bottom in the deepest point of the bow. Then I PVC glued a piece of 2” PVC into the mast step with the top extending several inches above the bow seat top’s level.

After installing the stern and mid seat tops, I drilled a hole in the bow seat to go around the PVC mast step. I then installed the seat top. Once the seat tops had all cured, I cut the mast step PVC off about a half-inch above the bow seat. I filled the gap between the PVC and the bow seat with epoxy and carefully wiped all the excess off the PVC. When this was dry I applied a bead of silicone caulk around the bow seat hole and I then PVC glued a PVC coupling onto the protruding half inch piece of PVC pushing it down onto the bead of silicone to ensure a watertight seat around the mast step.

The next step was to epoxy glue a rub rail along the top edge of the boat sides to add some protection and to give me something to mount the oarlocks to. This was pretty easy with the aid of a bunch of clamps every 6 to 8 inches to hold the 1x2” strip of wood to the curve of the boat side. Once this had fully cured I was able to install the oarlocks. I was careful about the placement of the oarlocks to ensure they were far enough aft to allow a good rowing stroke. I fabricated the rudder and attached the pintles then installed the upper gudgeon on the hull. I then fabricated the dagger board. At that point everything was complete with the exception of a mast and sail.

I had looked at lots of rigs for dinghies and had selected a sprit rigged sail. I like the simplicity of a freestanding mast. The low aspect of the sprit rig and the corresponding short mast size made sense for a small boat. The ease of storing the shorter mast and the fact that the shorter sail plan would cause less heel were big pluses for a small boat. The ease of stepping the mast and the ease of furling the sail when not in use were two other big advantages. Having a free standing mast meant stepping the mast would take about two seconds to slide the mast into the PVC mast step. Doing anything in a small boat in windy conditions can is a dangerous job so any opportunities to simplify the design should be used. Being able to roll the sail around the mast and tie it off in less than a minute was a safety-plus as well as being convenient. Also with a freestanding mast that rotates in any direction, in an emergency you could simply let go of the mainsheet and allow the sail to weathercock away from the wind in a gust. While the sprit rig sail won’t perform as well to wind as a triangular sail plan, it will beat the pants off anything going off the wind. The sprit acts like a spinnaker pole and holds the sail out like a barn door. The other reason I selected the sprit rig was that I could easily make the sail myself.

A sprit rigged sail can be made from a flat piece of material. I made my prototype from a 99 cent 6’X8’ tarp. I used one of the existing sides and grommets for lacing the sail to the mast. I also used the existing bottom edge and grommet for attaching the mainsheet. I did have to cut and hem the top and trailing edges of the tarp and install a single grommet in the top peak so that I could attach a sprit to it. Sewing a blue 99-cent poly-tarp can be done on any sewing machine. In fact I have heard of people using double-sided carpet tape instead of sewing the tarp. I used round molding obtained from Home Depot for the mast and sprit. I was concerned about their strength but after a couple years of sailing in all kinds of weather I can assure you they will do the job. I drilled a hole in the top of the mast and rounded the edges so I could use a short line attached to the top of the sail to run through the top of the mast and back to a cleat on the lower part of the mast. I also drilled and rounded a hole in the end of the sprit to attach the sail peak to. A rounded hole in the bottom end of the sprit was used to attach the line that raises & lowers the sprit. The 99 cent polytarp sail has lasted for 4 seasons although it’s beginning to show signs of wearing out. That’s 25 cents a year for sail material so you better work that into your boat building budget (ha! Ha!). I now use polytarp for all my small boat sails. If one will last 4 seasons I can’t justify the cost of buying Dacron. I could make 40 polytarp sails for the same price as one made from Dacron.

The D-4 sailing dinghy performs remarkably well in heavy weather. Although I have to be a little cautious with breaking seas, I regularly sail the D-4 in 15-20knot winds but have been caught in squalls with 40+ knot winds. I do take a plastic cup and a sponge to bail with. Generally all I get is spray and an occasional wave slap that spills into the cockpit. Even if the cockpit were filled the boat would float with the gunnels above water due to the three watertight compartments contained within the 2 seats and bow area of the boat. I have not tried to mount a motor on the D-4 but she sails & rows easily. I figured the epoxy worked so well on the boat that I might as well make the oars as well. An 8’ 2”x2” and a piece of scrap plywood made one of the prettiest $3.00 oars you’ll ever see. I made the oars approximately 7’ 5” long so I could really get a stroke each time I row and still be able to stow them inside the boat. Consequently I can easily row much faster than the plastic dinghies sold in the local “monopolistic” boat supply store. The oarlocks should be placed just aft of where your knees reach when seated in the rowing position. The handles should nearly touch when the oars are positioned straight abeam. Finally, the longer the oar is the better for ease of rowing.

Go build a boat. It’s a fun way to learn to use epoxy and fiberglass. It has proven to be a way to have fun boating without having to take out a second mortgage. In fact, it can be a fun way to produce a little extra money. Regardless, I really don’t care what it is as long as there’s some fun it somewhere. Most of us “Good Old Boaters” are somewhat budget minded when it comes to our boating experience and this is something every “Good Old Boater” should know about. I spent approximately $250 for epoxy, wood, hardware and sails when building the D-4. I have built some simpler boats for half that amount.

Go build a boat. It has proven to be a way to have fun boating without having to take out a second mortgage.

The only drawback to using West Systems is the expense. West Systems is NOT cheap at nearly $110 a gallon for epoxy and hardener. However, if you can find a boatyard that buys it by the 55 gallon drum you may be able to get a deal on having them refill your 1 gallon can. Locally, I have a yard that sells it to me at nearly ½ what it costs at the West Marine/Boat US stores. I initially used West Systems 406 Colodical Sylica filler for my fillets but have since found the generic equivalent Cabosil to be much cheaper. A good source for cheap chip brushes is www.harborfreight.com Cabolsil filler and fiberglass tape can be bought reasonably at www.fiberglasssupply.com.

About the author…. Pat Johnson builds boats as a hobby and has built about 20 odd boats to date. All of the boats are less than 16ft and about half are power and the others are sail or row boats. Pat enjoys helping others get started building boats and offers to show people how it’s done if asked. Pat lives in Pensacola Florida and often sails in Pensacola Bay and surrounding rivers and lakes. Pat’s most common advise to people thinking about building a boat is to start small and start now!