How To Build D18-Myst
Building a boat is never an easy task,
especially if it is a first time effort. However, it is a
straight forward process and is thoroughly documented in the many
excellent books and magazine articles on boatbuilding available
today. The trick is to simply break the job down into its
component parts and proceed in a natural order. This brief
construction sequence lays out the steps for building Myst
using the epoxy/strip-plank building method described in
"The Gougeon Brothers on Boat Construction: Wood and West
System Materials", published by Gougeon Brothers Inc., Bay
City Michigan. The builder is urged to study this book thoroughly
and refer to it as the primary manual for building this boat.
"Boatbuilding", by Howard I. Chapelle, is recommended as a supplementary text. Its emphasis is more on traditional boats and boat building techniques, but it can be very helpful in learning about the basics of wooden boat construction.
"Boatbuilding Manual", by Robert M. Steward, would also be useful for the beginner.
1. Begin by studying all the drawings carefully to get an overall picture of the boat and how it goes together. The Gougeon Brother’s book and the Construction Specifications text should be refereed to at every step of the process.
Full-size Mylar patterns have been provided for most of the components required to build this boat. Some pieces will have to be scaled or drawn full size, but no lofting is required in the traditional sense.
Where possible, all leading dimensions have been given on the drawings or in the accompanying text. However, an architect’s scale reading 1" = 1'-0" is very useful for accurately taking measurements directly off the drawings where required.
The full-size patterns for the moulds, frames and floors are already drawn to the inside of the planking. No deduction for planking thickness is required.
Drawing #1403 provides scaled construction moulds, drawn to the inside of the planking, for those wishing to build a strip-planked flotation model of the hull first. This is especially recommended for anyone who has never built a boat before.
2. Transfer the station lines from the Mylar patterns to the mould material and set up the construction form as shown in drawing #1403, paying particular attention to which side of the stations the moulds are set up.
Note that there is a transom mould as well as an actual transom. Do not fit the transom at this point, only the mould. Make sure everything is well braced, level and true.
3/4" K3 particle board can be used for the moulds. The strongback may be made of two 20’ long 2x8’s, or four 10 footers joined together. It is not expected that this frame can be made perfectly square and level for setting up the moulds, so the jig should be trued up using a stretched wire Base Line as a guide. See Gougeon Brothers, chapters 14 & 15 for details.
The floors, frames and skeg are shown for clarity only in the construction jig drawing. They are not included in the jig set-up, but are fitted afterwards as described further on in the text.
3. Make up the inner and outer keels taking the measurements from the drawings and patterns. A long batten can be laid along the centreline of the moulds on the construction form to mark the true positions of the stations and the width of the keel at those points. These can then be transferred to the keel planks for lofting, cutting and trimming to shape. A batten bent through all the points is used to define the width and shape of the keel.
Clearly mark the centre line, the station lines, and the frame and floor positions on the top of the inner keel for future reference.
4. Carefully measure and cut the slots for the centreboard case and the skeg. It is probably a good idea to make up the centreboard case and skeg now to make sure of an accurate fit.
5. Glue the inner keel and the inner stem together and fix them in place with temporary holding screws over the moulds and construction form as shown in drawing #1403. Do not fit the transom or any other components at this time.
6. Laminate the risers and clamps in place over the moulds. Temporary holding screws, as well as regular clamps, can be used to hold them together until the glue sets. It is not necessary to glue all the laminations up at once. One layer at a time is preferred. Waxed paper or cellophane packing tape can be used to keep the laminations from sticking to the moulds or any other part of the structure, including the stem.
Note carefully how the laminations fit at the stem in drawing #1402. They are butted, not notched into the stem. Aft, the laminations are simply run out past the transom mould. Once fitted, glued and dried, the laminations can be marked and trimmed flush to the outside face of the transom mould.
The transom can now be made up and glued and fastened to the inner keel. The thwart beam #11 and transom frame #13 are not installed at this time. However, it is a good idea to make them up and pre-fit them to the transom for installation later, after the hull is turned over. Planking bevels can be taken off of the full-size patterns.
Temporarily fasten the clamps and risers to the transom, but do not bond them in place just yet - they will need to be released to allow the hull to be lifted off the moulds. Make sure all temporary holding screws at the stem and transom will be accessible once the hull is planked.
7. Plane and fair the whole structure in preparation for planking, as described in GB chapter 16. Long planking battens can be used as guides for beveling the moulds, inner stem, inner keel, transom, clamps and risers. Cover the moulds, clamps and risers (especially at the joints) with wax paper, cellophane tape or plastic sheeting so the hull can be lifted off later without sticking to any of these components.
8. Begin planking from the sheer clamp up, leaving a slight overlap for fairing the planking flush with the top of the laminated clamps later on. Each strip should be pre-fitted to the moulds, carefully aligned, and drilled for fastenings before gluing up. 1/8" diameter hardwood dowels make excellent edge fastenings and should be set into 1/8" diameter pre-drilled holes about 1 3/4 times the depth of the planking. Four or five strips per side can be pre-fitted at a time before gluing up. The overall fit should be a little on the loose side to allow for glue thickness. It is not necessary to bevel the edges of the strips. A stealer or two may be required to straighten out the run of the planking in places.
The glue for planking should only be thick enough to keep it from running out of the seams. If it is too thick it may cause the strips to bulge apart between the moulds throwing them out of alignment. While not terribly serious, this can be annoying. Wetting out the edges of the planks with unthickened epoxy resin prior to applying the glue is also advisable to assure a good bond between the strips.
Use a pipe cleaner to wet out the dowel holes with glue and drive the dowels flush or set them slightly below the surface of the strip. All dowels should be of equal length and the holes drilled slightly longer to avoid over-driving and splitting the planking. Remove excess glue from off of the planking, both inside and out, with a putty knife before it hardens. Swab off what's left with paper towels dampened in solvent. This will save hours of hard planing and sanding later on. (Methyl-hydrate, available in most hardware stores, is a cheap and effective solvent. "Viva" brand paper towels seem to stand up well to hard usage.)
Fasten, but do not glue, the planking to the clamps and risers. They will need to be released and repositioned later on in the construction process.
Temporary holding screws can be replaced by permanent bronze fastenings where required later on, such as in the inner stem and transom. Steel, round-head wood screws, with washers under them, make good temporary fastenings. They do not tend to break off when being removed. Heat applied with an electric soldering iron will loosen any hard-bonded fastenings. All permanent fastenings should be sealed and bonded in place with epoxy resin.
Please note that it is a good idea to wear a proper respirator with the appropriate filters and to provide good ventilation when working with epoxy and solvents. A powerful fan blowing fresh air across the work area helps eliminate harmful fumes or dust and also helps keep the builder cool on hot days.
9. Do not fair or finish the exterior of the planked up hull at this point. Trace the station lines from around the edges of the moulds onto the inside of the hull with a pencil for future reference in fitting frames and floors, see #12 below. Remove all temporary holding screws and carefully lift the hull off the moulds and construction form, leaving the sheer clamps and risers behind. Set it upright on a padded surface for interior finishing. (Because of the tumblehome in the topsides, it may be necessary to dismantle part of the jig before the hull can be freed.)
It may also be wise to have a few pre-measured cross spalls ready before hand to brace the sheer after the hull is removed from the jig. These will help to prevent the hull from trying to fold back in on itself and distorting before you get a chance to finish off the interior and get the framing firmly in place.
10. Plug all unnecessary screw holes inside the hull with wooden bungs or thickened epoxy to about 1/2 the depth of the planking. Do not plug the screw holes for the sheer clamps and risers. Once the epoxy is cured, fair and smooth the inside of the planking with a blockplane and spokeshave, followed up with 80 grit sandpaper to remove the blade marks. Finish up with 120 or 150 grit paper for a smooth, clean surface. Be sure to preserve the reference lines for the stations, frames and floors.
11. Apply four coats of resin to the interior of the hull. Use a large flat tray and thin foam rollers about 3" to 4" long on a small applicator frame to roll out the resin. Mix only about 6 oz. of resin at a time so as not to rush the job. Smooth out any air bubbles that form on the surface by jamming the roller to keep it from rotating then dragging it back lightly across the wetted surface. This will knock down the bubbles and assure a smooth finish and minimal sanding later on.
After applying the first coat, wait about an hour for the resin to get a bit tacky and then apply a second coat directly over top of the first. Let the resin dry thoroughly before lightly sanding with 80 grit paper. At this point, stop and apply a light epoxy fillet along the edges of the inner stem and inner keel where they meet the planking to fill out the joints and any possible voids that may exist. Build it up in successive layers to keep it from sagging out. Fair and sand when cured, then apply the next two coats of resin over the entire hull - one over the other without sanding in between. Allow the first coat to become tacky before applying the second. Let the resin cure completely before lightly sanding with 80 grit paper and finishing up with 120 or 150 grit. Re-coat any spots that appear thin or oversanded.
12. Make up and fit the frames and thwart webs, and temporarily fasten them in place. Pencil off where the frames and webs lie across the hull and then remove them. Refit the clamps and risers to the hull and mark where the frame and thwart web pencil lines cut across them.
Take the time now to plane the inboard edges of the clamps square to the centreline in preparation for fitting the coamings. Use the upper inside edge of the clamp as a guide. See cross-sections of sheer clamps and coamings in drawing #1402 for details.
Remove these once again and then notch the undersides of the clamps to accept the frame heads. Cut through the risers to accommodate the frames and thwart webs, as shown in the drawings. Provide limber holes through the risers wherever they butt up against the frames, thwart webs, stem and transom. Rebate the aft sections of the risers to take the plywood cover for the aft buoyancy tank.
After final fitting, coating and finishing, permanently glue and fasten all the framing and interior joinery components back into place, including the clamps and risers. All the finished parts of the inside of the hull can now be painted if desired, taking care not to cover areas yet to be glued or coated.
13. Turn the hull back over and begin finishing the exterior by removing all temporary fastenings and plugging the deep screw holes with 1/8" dowels. All exterior holes should then be bored and plugged with wooden bungs set in epoxy glue. Then trim and plane the edges of the planking flush with the inner keel, inner stem and transom. Fair and sand the hull smooth and apply 4 coats of resin as was done on the inside of the hull.
14. An optional layer or two of 6 oz. fibreglass cloth, Dynel, or other fabric can be applied to the hull if desired. This will help toughen the surface a bit, but is not necessary structurally and may result in a little more difficulty making repairs to the hull later on. It will also add some weight, as well as expense - builder’s choice.
To apply sheathing, dry fit the fabric to the bare wood of the hull one side at a time. Staple it lightly in place along the top of the inner keel to keep it from sliding down and apply epoxy resin with a foam roller or squeegee in the usual manner. Wedge shaped darts may need to be cut out of the fabric where it bunches up along the sheer, and is best done during the wetting out period. Be aware also that epoxy takes a long time to set and some sagging of the fabric may occur. Periodic re-rolling may help, but care must be taken not to lift the fabric off the hull and create air pockets.
Once the resin is set, but still a bit tacky, any staples holding the cloth in place can be removed and one or two more coats of resin applied to fill the weave. Excess fabric can be trimmed away later after the resin sets.
Note: Fabric should not overlap the keel, stemface, transom or edge of the planking in any way in order to avoid any possible cracking along these edges in future. Glass the surface of the planking only!
After the resin is well cured, the surface can be sanded smooth in preparation for the second layer of fabric or for painting. Any exposed weave should be re-coated and sanded to ensure a uniform finish.
15. To finish up, seal all end grain thoroughly with epoxy resin and then fit the outer keel and outer stem to cap the planking. Glue on the sacrificial hardwood shoe and skeg, making sure all edges are well rounded and well coated with epoxy. After bonding and fastening the external hardware in place, the hull can be painted and rolled upright to fit the decking, sheer cap, coaming, rubrail, trim and remaining hardware.
Note: the area of the hull between the rub strip and trim strip can be finished bright or painted a contrasting colour to the topsides for effect. An option would be to glue a sheer strake of 1/8" to 1/4" wood veneer onto the planking to give the hull an even more traditional appearance. The area under the veneer should not be sheathed. It should be glued directly to the planking.
16. Finishing the hull is mainly a matter of taste and experience with the different kinds of products available on the market today. It is basically the constructor’s choice, but here are a few suggestions that may be of some help to the first time builder.
* During construction, all parts of the hull and structure to be painted should be given a minimum of three coats of epoxy resin, preferably four, to seal out moisture and stabilize the wood - particularly end grain and faying surfaces. Most of this work can be done on the bench before final installation to make the job a lot easier.
* The interior should be painted with a good quality marine enamel. White or light gray looks good when contrasted with oiled or varnished wood and will help keep the hull and structure cool and stable. The exterior should also be painted, but colour is less critical here and even black paint is quite acceptable, except perhaps in very hot and sunny climates. The transom and sheer strake, on the other hand, can be finished bright for appearance.
*Aluminum oxide powder can be added to the last coat of epoxy resin to act as an undercoat for any surfaces to be painted.
* Varnish finish is not recommended for a craft that is expected to be used hard, oil is better and far easier to maintain, although it must be recoated much more frequently for best results.
* Oil or varnish looks best on bare teak without an epoxy undercoat, but the cedar sheer strake might best be served with spar varnish over clear epoxy resin for durability. However, oil can be used if desired, in which case these areas should then not be coated with epoxy resin or sheathed with fabric.
* Below the waterline, a good hard finish anti-fouling paint can be used for protection.
* Whatever the finish, it is still best to keep the boat on a trailer and stored in an open, breezy shelter away from the elements as much as possible. That way the finish will be preserved and maintenance will be reduced considerably. As with any wooden boat, preserving the finish means preserving the structure. It's nothing to add a coat of paint, oil or varnish regularly, compared to wooding down and refinishing a badly weathered hull.
Copyright 2003