Montana Riverboats Dory Building
- Scaled drawings and step-by-step building instructions for All Three Boats
- How to copy another driftboat hull
- How to design and build your own hull from scratch
- How build a stitch and glue boat from someone else's framed-boat blueprints
Stitch and glue wood fiberglass construction--and/or honeycomb coreThese plans include drawings, tool and material lists and written instructions for stitch-and-glue plywood-fiberglass construction. Stitch-and-Glue construction is well suited to the beginning boat builder. At approximately 275lbs. for a finished 15' boat, plywood-fiberglass boats weigh less than most aluminum or molded fiberglass boats.
A fiberglass skin is an essential component of the ribless boat since the glass fabric and epoxy resin give the boat structural strength as well as a tough and durable finish. Epoxy resin is used for all the gluing in the boat as well as for fiberglassing. Polyester resin, which is used in the construction of "all-fiberglass" boats, is not suitable for wood- fiberglass construction because polyester resin does not adhere well to wood. These instructions were originally written assuming the use of Gougeon Brother's excellent WEST SYSTEM epoxy products. But many recent builders report equally excellent results (and attractive prices) using Raka products. Read through the entire text of these instructions before beginning any work.
How long will it take?I once built five boats in 30 days flat (with one employee). But I can't build a single boat any faster due to gluing/fiberglass hardening times. A friend of mine--an MSU art teacher--built a boat from my plans that was perfect. It was prettier than any I ever built myself. It took him 6 months, working by himself, working intermittant evenings and weekends. Many builders finish faster than that. Few, if any, do a better job.
Montana RiverboatsSandy Pittendrigh
118 Erik Bozeman, Mt. 59715
sandy at www.montana-riverboats.com
Specifications: Honky Dory
center line length---------15'
height at the oarlocks---24
finished weight----------230-300 lbs. depending...
capacity-----------------four persons, 1100 lbs.
height at the oarlocks-----24"
Plywood Fiberglass---------Approximately 220-290 lbs.
capacity-------------------three persons, 1000 lbs.
Specifications: Buffalo Boatcenter line length---10'
height at the oarlocks---24"
finished weight----------150-220 lbs.
capacity-----------------3 persons, 825 lbs.
ChineThe curved line formed by the junction of the side and the bottom of the boat.
Stem A thirty inch piece of hardwood, triangular in its cross-section, that joins the two side panels at the front of the boat.
Transom The wedge-shaped piece of plywood that joins the two side panels at the stern end of the boat.
Strongback The temporary form on which the hull of the boat is built. The strongback consists of several trapezoid-shaped stations that conform to the shape of the boat. These trapezoidal stations are made from chipboard scraps or 1"x6" pine boards.
Cord A length of 1"x6" pine board that forms one side of a trapezoidal strongback station. Each trapezoidal strongback station consists of four cords the "top" cord, the bottom cord, and two matching side cords.
Gunwale The "top" edge of the side of the boat.
Beam The distance across the gunwales at the widest part of the boat.
Kick The hardening process of resin and hardener. As resin begins to harden, it is said to "kick."
Woodworking toolsYou will need a hand saw, and either a portable power circular saw (skillsaw) or a power saber saw. A table saw is handy, but not absolutely necessary. You will also need a minimum of eight C-clamps for installing wooden gunwales. These c-clamps must have a minimum throat depth of two inches and a minimum opening of three inches. The more C-clamps you have, the better. Most rental shops rent C-clamps. I use up to 24 C-clamps per side. Other necessary tools include a power drill and assorted bits (including a phillips head screw driver bit), an orbital sander, flat wood rasp, paint scraper, bevel square, spirit level, hacksaw, a smooth faced hammer, and a sharp block plane. A sharp block plane is a key tool. Keeping it sharp is essential. Buy a carborundum water stone or a fine India oil stone and hone the blade frequently. A small abrasive wheel in an electric drill can be used to re-grind a plane blade if repeated honing has rounded off the cutting edge of the blade. You will also need several sheets of 50, 80 and 100 grit silicon carbide floor surfacing paper, and a few sheets of 180 grit aluminum oxide paper. Rental shops that rent floor surfacing equipment also sell silicon carbide floor surfacing paper.
Table SawsIf you want to build a boat it helps to have a table saw. The table saw isn't a requirement, but it does make it easier to do good work, especially when making gunwales and seat parts.
For those who don't have a table saw and who don't want to buy one, you can make one, with a piece of chipboard and an old skillsaw:
...bolt the skillsaw to one side of the chipboard. Hold the trigger down semi-permanently with a nylon strap-tie (you turn the saw on and off by plugging it in to a live receptacle). Then plunge the blade through the chipboard, turn the chipboard over, put it on saw horses and then use clamps and a straight edge to make an adjustable guide parallel to the blade.
It takes a little longer (than a real table saw) to set up each new cut, but it does cut with a staight even line--does just what you need for cutting gunwales out of 1x10 stock or for what ever else. Do be careful. Powertools are dangerous.
Honky Dory Materials
Plywood, Wood and Hardware materials (Plywood-Fiberglass Construction)2 sheets 4'x8'x1/4" AA fir, marine plywood or 5mm marine mahogany
3 sheets 4'x8'x3/8" AA fir, for the bottom and various seat parts. If you use 3/8" plywood you will need to add extra glass. Some builders prefer 1/2" plywood. You may want to use polyethylene honeycomb core for the bottom, instead of plywood. Read the Plascore Bottoms page before deciding.
4 1"x2"x16' oak, ash, or fir boards for gunwales
1"x6"x16' #2 pine boards for the strongback
2 sheets 3/8" CDX plywood for strongback corner gussets
1 lbs 5/8" drywall screws 1 lbs 1-1/4" drywall screws
1 box 3" flat head 1/4", course thread bolts
1 box 1/4" "nylock" nuts
1 box 1/4" flat washers
1 box 1-3/4" ring shanked panel nails
50' 1"x4" mahogany, oak, fir, or ash for seat frames and other interior parts
WEST SYSTEM Materials
Gougeon Brothers Inc. Box 908 WEST SYSTEM Technical Manual
100 Patterson Ave. Bay City, Michigan
5 gallons #105 resin
1 gallon #205 hardener
1 pair mini pumps
1 gallon acetone
1 bag #403 microfibers
1 bag #406 colodial silica
1 bag #407 micro balloons
1 roll 6" fiberglass tape
13 YD. 50" ten ounce fabric
20 YD. 60" ten ounce fabric
ToolsTools for applying WEST SYSTEM resin include a 1.5" or 2" bristle brush with a wooden handle, 1.5" to 6" putty or drywall knives, and foam paint rollers of various sizes. Clean your tools regularly with acetone. (Caution acetone is flammable). Keep the brush and the smaller putty knives in a can filled half-way with solvent, and keep a lid on the solvent can to keep the solvent from evaporating. Hardened epoxy can be burned off putty knives with a propane torch. Use a wide, flat container such as a roller pan with a plastic liner or a plastic dishpan for mixing epoxy. A wide container dissipates the heat created by the reaction of the #105 resin with the #205 hardener. Heat can build up in a small container creating a chain reaction that will harden the resin in a matter of seconds. Overheated resin that is setting up fast does not penetrate or adhere well to wood. Whenever a chain reaction does occur immediately discard the overheated resin and start again. Use rubber gloves at all times when handling epoxy resin. Epoxy resin is a skin irritant, and some people develop allergic skin reactions to it. You may also want to wear a good respirator with activated charcoal elements designed for organic vapors. Always wear a dust mask of some kind when grinding or sanding epoxy-fiberglass. Cheap, disposable vinyl or latex rubber gloves are handy, but I prefer heavier, chemical resistant gloves that can be washed in solvent after each use and reused indefinitely. Chemical resistant gloves can be purchased at most janitorial supply houses. Black rubber mason's gloves are almost as good.
Gluing, Filleting, and Fiberglassing Procedures
Follow the manufacturer's instructions for using WEST SYSTEM products, but also read the following supplementary information.For every gluing, filleting, or fiberglassing process, you will use WEST SYSTEM #105 resin mixed with #205 fast hardener. The ratio is 5 parts resin to 1 part hardener. WEST SYSTEM mini pump dispensers automatically measure the resin and hardener in the right proportion. One squirt of resin mixes with one squirt of hardener. The mixture of resin and hardener will be referred to as "resin" for the duration of these instructions. #105 resin is never used without its corresponding component of hardener, so it is now understood that the term "resin" will mean the proper mixture of resin and hardener.
Priming the PumpsUnscrew the caps from the #105 resin and the #205 hardener and replace them with the corresponding mini-pumps. Hold a Dixie- cup or other small container under the hardener pump and push down repeatedly on the pump. Let the plunger rise up slowly by its own spring-loaded power. Once the pump stops spitting air and is completely primed the hardener collected in the Dixie cup can be returned to the hardener can. Repeat this process for the resin pump, using a fresh Dixie cup.
GluingAlways wet out both sides of any joints to be glued with resin as a first step. Usually one wet coat is enough, but for porous woods and end-grain, you may need a second coat. The wet-out surfaces should look wet. After wetting out the surfaces, mix a second batch of resin and thicken it with #403 microfibers until it is the consistency of sour cream or yogurt. Apply the thickened mixture to one side of the joint to be glued. Clamp the joint until the glue is hard. Hardening times vary considerably with temperature and humidity changes. Immediately clean up any squeeze-outs.
Filleting and PuttyingFilleting is the rounding out of inside corners to reinforce the joint, and to produce a smoothly rounded corner prior to fiberglassing. Use a mixture of 60% #407 micro balloons, thirty percent #403 microfibers and ten percent #406 colodial silica for all puttying and filleting operations. (This mixture works well for me, but don't be afraid to do a little experimenting. Epoxy resin is strong, versatile stuff, and you can get satisfactory results from a variety of thickeners.) Wet out the area to be filled. Mix another batch of resin and thicken (with micro balloons, micro fibers and colodial silica) until the mixture is the consistency of thick peanut butter. Use a physician's tongue depressor (or cut a rounded tool from plywood) to apply and smooth the filleting. Apply the mix thickly in the area to be filled. Then smooth repeatedly with the depressor to form a smooth rounded shape. Press down hard on the filleting tool to squeeze out the excess putty as you form the fillet. Immediately clean up squeeze-outs with a putty knife. For puttying to fill up dings, use the same mix as for filleting.
FIBERGLASSFiberglass is a generalized term that refers to a wide assortment of woven fabrics that are layered and bonded together with various plastic resins. The best resin, in fact the only resin suitable for wood- fiberglass construction is epoxy resin because epoxy is the only resin that adheres well to wood. Fiberglass fabric is a woven laminate material that is made from glass fibers. In its raw form, fiberglass fabric is very soft and flexible, and looks a little like white canvas. When fiberglass fabric comes in contact with resin, the fabric turns transparent and loses its white color. Fiberglass fabric is easy to work with, and can be used for every fiberglassing step in the construction of this boat. Other laminate materials that work well with epoxy include Kevlar, graphite fibers, and polypropylene fabric. If you are familiar with these other laminate materials, feel free to use them in place of the standard fiberglass fabric specified in these instructions.
Working with resin and fiberglass fabricIn order to cover any piece of wood with a layer of fiberglass, start by rough-cutting the fiberglass fabric to the size needed, one to one and a half inches large on all sides. Wet out the wood surface with resin. To apply, pour the resin directly onto the wood surface and spread it with a four or six inch drywall trowel, or pour the resin into a roller tray and spread the resin over the wood with a foam roller. Lower the fabric onto the wet-out wood surface, and pull on the edges to get any wrinkles out of the fabric. A helper is particularly handy when lowering dry fiberglass fabric down onto a wet surface. Two or more workers can lower the fabric into place with a minimum of wrinkles. Use a plastic squeegee or a 6" metal trowel to smooth the fabric. Use the trowel to stretch and tension the fabric, stroking the trowel from the "center" out toward the edges. Once the wrinkles are gone, apply more resin and smooth evenly until the fabric becomes transparent and disappears. But be careful! It is important not to use too much resin. Too much resin will float the fabric on thick puddles of resin. This weakens the finished fiberglass laminate. Use just enough resin to make the fabric transparent.
Trowel any excess resin off the fabric to leave the rough, pebbled texture of the fabric showing on the surface. Avoid slick, glassy puddles of resin on the surface of the fabric. Some glassy spots are inevitable, just try to keep them to a minimum. On the other hand, don't use so little resin that cloudy- white areas remain in the fabric. Use just enough resin turn the fabric transparent, but not enough to float the fabric over thick, glassy puddles. Once the first wet-out coat has saturated into the fabric, you can quit for the day and then proceed with subsequent finish coats at a later date. Or you can wait two or three hours for the resin to become tack free, but not necessarily fully cured, and proceed immediately with one or more finish coats of additional resin.
If you let the first wet-out coat harden completely, you must sand off any hard lumps of resin before finish coating. If you choose to go ahead and finish coat as soon as the first wet-out coat becomes tack free, sanding is not necessary. Use one to three finish coats as needed to obscure the texture of the fabric and to produce as glossy and as smooth a finish as you choose. Spread finish coats with a four or six inch drywall trowel, and then immediately brush out the lines left by the edges of the trowel with a bristle brush. To smooth out trowel marks that have already begun to set up, it may become necessary to dampen the brush with acetone or WEST SYSTEM solvent.
Paint Vs. VarnishThe last step in the boat building process is to cover the boat with an ultra-violet shield--in other words to paint the boat. Ordinary oil-based porch and deck paint is the cheapest alternative. Linear polyurethanes are the most durable and the most expensive. Any pigmented paint is a better ultra-violet shield than a clear finish. When a paint finish is planned, all layout lines, pencil marks, dings, and scratches can be left in place during the construction process with no effect on the finished appearance of the boat. If you want a clear, natural wood or stained finish, you will have to plan for it from the beginning. Your first choices will relate to the materials used in the gluing and filleting operations described below. Filleting is the filling of inside corners with a thickened resin mixture to reinforce, and to round out inside corners before fiberglassing. All gluing and filleting operations involve the use of various thickening agents in addition to the resin that holds everything together. Many of these thickening agents are white or red in color, and they don't look very good under a clear finish. If you are planning a clear finish, use a mixture of fine sawdust, # 406 colloidal silica, and #403 microfibers as thickening agents for all gluing and filleting operations. If you want to stain any parts of the boat, use an alcohol based stain, such as Watco Five Minute stain, rather than oil based stains. Epoxy will not adhere to wood that has been stained with an oil based stain! Do the staining right away, before any assembly process or contact with resin. If you are planning a stain finish, pre-stain the sawdust you plan to use for any filleting or puttying before you mix it with resin.
Part Three Building the Plywood-Fiberglass Boat
a. Strongback is fancy way of saying "temporary plywood or chipboard ribs"
b. Note that the boat hull is built (on the strongback ) upside-down
2 ) Cut and layout the plywood side panels
3 ) Pre-fiberglass the side panels (pre fiberglass the inside surfaces only)
4 ) Mount the sides on the strongback
5 ) Fasten the stem and the transom to the sides
6 ) Make, pre-fiberglass, and install the bottom (pre-fiberglass the inside surface only)
7 ) Fiberglass the outside of the boat
8 ) Rollover the boat
9 ) Install the gunwales and the temporary, cross gunwale braces
10 ) Pull out the strongback stations and fillet the "inside chine corners" of the boat
11 ) Apply a second layer of ten ounce fabric to the inside bottom
12 ) Make and install the interior parts
13 ) Paint the boat