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Boatbuilding Methods: Plywood

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We are starting at the point where the frames have been cut outand assembled. (For a description of how frames areassembled, see Frame Kits in the "About our Plans and Kits"directory.)

Building forms may vary in type but the principles are

Boatbuilding Methods: Plywood Page 1


basically the same. The assembled frames are mountedon two longitudinal stringers that have been leveled bothlengthwise and athwartship. Each of the frames is spacedthe distance specified in the plans and centered. Theframes are left loose until adjustments for minordescrepencies are made. Then the frames are attached tothe form using wood blocking or metal angles. Usually theframes for inboards are fastened permanently as the setup members serve as motor stringers. The frames forother types of boats are most often only temporarilyfastened. Refer to the plans for specific instructions. Ofcourse, some small plywood boats use much simplerbuilding forms, and in the case of Stitch-N-Glue boats,none at all. NEXT

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The breasthook is a triangluar shaped piece of plywood that isattached to the stem to provide a place for the sheers to attach.The breasthook is glued and fastened to the stem before thestem is attached to the frame.

Here a plumb-bob is being used align the stem. Theplans have given a distance from the set-up level to thetop of the breasthook. Sufficient blocking is added to raisethe breasthook to the proper position and the stem andbreasthook assembly are firmly anchored in position.



Since the keel in the after section of a planing hull, inprofile is a straight line, it is best to align the transom bybringing it up to the proper height using a straight-edge onthe keel to assure that this line is true. If a transom kneeis called for, it can be used to determine the angle of thetransom. After alignment the transom is anchored inposition and braced to the form as necessary to assure itwill not move during construction. NEXT




The chine is clamped in position while it is sprung aroundthe frames to determine the correct angles for the framenotches. It is imperative that the chine mate firmly in thenotches and does not merely bear on one corner of theframe.

The builder is shown using a scrap of plywood as a jig todetermine the set-back of the chine from the forwardedge of the stem. The stem will eventually be "faired" orbeveled so the line formed by the chine will extend to thecenterline of the stem. If the design utilizes a chineblocking member, as this one does, it may be necessaryto adjust the chine blocking to compensate for the



thickness of lumber you are using. Without chineblocking, the position (up or down) of the chine on thestem is determined by allowing the chine to take a smooth(fair) bend around the framework. Although the exactheight can vary, the opposite chine should be at the sameheight. NEXT




Fitting the chine at the stem is accomplished as shown.Be sure to leave the chine long. Allow it to extend beyondthe transom as subsequent fitting may require it to bemoved forward.



The stem should be braced to prevent movement wheninstalling the chine. Chine (and sheer) lumber should becarefully selected for straight grain. Often the screw in theforward frame is left out when springing the chine intoposition. This eliminates the tendency of the chine tobreak at this point. The screw will be driven in when theplanking is applied. The chine and all subsequentlongitudinal members will be both fastened and glued inposition. NEXT




The notches for the sheer (or sheer clamps) must beangled as was done for the chine. In some cases thesheer is built up from two laminations. It is imperative thatthe sheer members be set in vertically from midshipforward. Attemping to twist and bend them to fit theplanking contour will frequently cause them to break.Later in the fairing process the sheer will be beveled sothat the planking will mate on a flat surface.



The sheer has been angled to butt properly to the stemand is now glued and fastened to the breasthook. Again,leave the sheer long until it is properly fitted to the stem.NEXT




FAIRING: It will be necessary to "fair" the variouslongitudinals. One method is to file a notch conforming tothe frame contour at each frame along the chine, sheer,and keel. The angle of intermediate notches can bedetermined by using a straight edge across members andgradually adjusting the notch until the straight edge restson flat surfaces.

FAIRING: These longitudinal members are then



planed to match the angle of the notches. Be sure thatthe resultant surface is "fair", without humps or dips.NEXT




FAIRING: A line is drawn from the frame closest tothe stem, or the next aft frame, to the center of the chineat the stem. The portion above this line must faired toprovide a flat surface for the bottom planking to mate to.The side planking will be fastened to the portion belowthis line. In most instances, the chine will follow the angleof the side frames so that fairing the chine for the sideplanking is unnecessary.

FAIRING: Any minor discrepencies must be faired



out of the frames. In planing boats, it is imperative that thelongitudinal lines in the aft section be straight lines. Use astraight edge to determine fairness. Curved lines on aplaning boat can cause "porpoising", or to ride bow down.Although this effect does not occur on displacementboats, lines should be fair for esthetic reasons and unfairlines will have some effect on performance. NEXT




FAIRING: To insure that the longitudinal lines aresmooth, even, fair curves, stand back occasionally andsight along the area being faired. Dips and humps mustbe removed. If necessary another thin piece of wood canbe glued into low spots and the area re-faired.



FAIRING: A short length of plywood is used to checkthe fairing in the forward portion of the boat. Considerablematerial may have to be removed along the stem toprovide a solid landing for the bottom planking. Note thatsheet planking will naturally bend to form a convexsurface. NEXT




FAIRING: A short length of plywood is also used tocheck the fairing for the side planking.

PLANKING "PATTERN": Fitting the plankingis easiest done by leaning the panel against the side ofthe boat and roughly marking to shape. Don't leave anymore material overhanging than necessary as scraps maybe utilized in other parts of the boat. Note: We arefrequently asked, "Where are the planking patterns?" In frameconstruction, minor differences in frame spacing would make



patterns useless. The boat itself is the pattern.

NEXT




All mating surfaces are coated with glue. A paint rollerworks well for this purpose. Follow the gluemanufacturer's instructions and fasten panels in placebefore the glue sets as a good bond is imperative.

Usually several locating screws are used to position thepanel while fitting and drilling for screws. The planking isfastened to the longitudinals, stem and transom only; notto the frames. After fitting and drilling, the panel isremoved and all mating surfaces are coated with glue.



The panel is then screwed in place. NOTE: The plywoodpanels shown in many of these photos are full length; it is morecommon to use standard 8' panels and join them with scarfjoints or butt blocks. NEXT




After the first side panel is installed the excess along thestem is sawn off and planed smooth so that the secondside will lap the first side. Here the builder is trimming thesecond side which will then be faired to match the firstside.

BUTT BLOCK: Side and bottom planking usuallyrequire a junction to make the panels long enough.Although scarf joints can be used, the more common



method is to use a butt block. Butt blocks are usually thesame thickness of the planking being used. The joint isalways made between the frames (not on the frames) inas flat an area as possible. Note that separate butt blocksare fitted between the battens. The planking is temporarilyheld in place, holes drilled into the butt blocks, the firstplanking section removed, and the butt blocks glued andfastened to the planking. The next planking section isinstalled after the first in glued and fastened in place,gluing and fastening to longitudinals and butt block. NEXT




In designs that have frames notched for the battens, it iseasiest to wait until after the application of the sideplanking before installing the battens. These membersare notched into the frames the thickness of the lumberbeing used. After installing, check that the bottom linesare true. It may be necessary to fair or kerf the forwardends of the battens to conform to the shape of the bottomplanking.

The bottom planking is clamped or located with several



screws along the centerline of the keel. The forward endof the planking is roughly marked to shape and a linescribed along the chine. As much excess material aspossible is cut away in the forward section to make iteasier to force the planking into position. NEXT




TRANSITION JOINT: In the forward sectionthere is usually a point where it is no longer practical tolap the bottom planking over the edge of the sideplanking. At a point we call the "transition joint", thebottom planking changes from lapping to butting to theside planking. At the stem, the side and bottom plankingwill be in-line. The photo below illustrates the appearanceof the joint after the planking has been installed. NEXT




TRANSITION JOINT: These four photosillustrate the transition joint.A Depicts the transition joint after the side planking hasbeen applied. Note that forward of the cleft, the sideplanking is fitted to the line on the chine. Aft of thisposition, the planking is left projecting above the chine.B Shows this same area after the projecting plywoodplanking has been faired, flush to the chine.C Illustrates the appearance of the joint after the bottomplanking has been applied. Observe that the portionforward of the bottom planking butts to the side planking.Aft of this area, an abrupt transition is made and thebottom planking laps the side planking.D Shows the finished joint, as viewed from the side. Thetransition point is clearly illustrated, the area forwardbeing butt joined, the portion aft, lap joined.



TRANSITION JOINT: One method of markingthe line on the bottom panel, forward of the transition joint,is to coat the sharp edge of the side panel with chalk orcrayon. The bottom panel is bumped on this edge totransfer the line to the underside of the bottom plankingfor subsequent cutting. NEXT




TRANSITION JOINT: It will be necessary tocarefully hand-fit that portion of the bottom planking alongthe chine that will butt join to the side planking. NOTE: Tofacilitate bending, toweling has been placed on the area ofmost stress, boiling water poured on, and allowed to setseveral hours or over night.

In all cases, after fitting one panel, the contour should bemarked to the panel for the other side. It is, of course,advisable to first check on the opposite side in case thereare any variations. NEXT




The bottom panel is liberally coated with glue andfastened into position. Note again the transition joint. Thelapped portion, aft of this point, is left oversize andtrimmed after the panel is fastened in place.

The two bottom panels will butt join along the keel untilthe curve of the stem becomes too severe. From thispoint forward the second half will lap the first panel. It is,therefore, necessary to fair the first panel as was doneforward of the chine transition. NEXT




After righting the hull, it should be levelled and chockedsecurely in position. At this point of construction the hullcould twist. It is imperative that the hull be held in position,and re-levelled if moved.

The planking extending above the sheer should now beremoved. Depending on the type of boat, side decking,cabin, seats, etc. are installed. Next




When intermediate deck beams are used, they shouldbe blocked between the sheer clamps as shown. Thebattens are notched into the frames and deck beams andend against the sheer with a fitted bevel. If you do notwish to see the batten ends notched into the dash beam,the can be glued and fastened to blocking on the forwardside of the dash beam. The strongback (center batten)can be partially notched into the breasthook and taperedto make a smooth flowing curve to the stem.

he floorboards are usually fitted soon after the hull has



Tbeen righted to provide a flat work area for the builder.Here, the buider is using a stick to transfer the outline ofthe hull side to the floorboard panel. Floorboards areunsually in serveal sections, with a removable centersection for bilge inspection. NEXT




Be fore applying the decking, it is often advisable to paintor otherwise seal the forward area where later access willbe difficult.

The sheet plywood decking is normally put on in twoparts, with the junction over the strongback. The sheeredge is left oversize for fitting after the deck is glued andfastened in place. NEXT




Butt joints are made along the side deck as required.Note that the foredeck extends along the side deck as long asthe panel will allow. Joints near the deck beam will tend tocrack after rough usage.

It is good practice to install much of the interior fittings,including through-deck chainplates (sailboats), steeringand wiring, before the decking is installed. Many areasare not readily accessible after decking. NEXT




Centerboard and daggerboard trunks are fiberglassed onthe inside before assembly. This protects the inside of thetrunk from abrasion when the board is raised or loweredand also seals it against water damage. The photosabove illustrate the normal procedure.A Each half is assembled.B Fiberglass cloth is fitted, then applied.C The cloth is trimmed and any burrs sanded away.The final step is to glue the two halves together. Wewould recommend using thickened epoxy and using along dowel to form the resin that squeezes out on theinside into a small fillet. If a sailboat is going to leak, it willleak around the board. If the hull is fiberglassed on theoutside, we would recommend tucking cloth, as far aspractical, into the trunk to protect the exposed edge ofplywood.



The hulls shown in the preceeding photos have all beenplaning powerboats. The procedures are much the samefor plywood rowboats or sailboats, but because sailboatstend to have more "rocker" in the bottom, they may lookdifferent on the building form. Frames may not all mountdirecting on the building form. Some may have temporarybraces across the frame that will rest on the building form.This will also apply to some powerboats. Other designsmay use much abbreviated forms or in some cases, noneat all. In all cases, the plans override any differences inthe procedures shown.

Return to Plywood MethodsProceed to Multiple diagonal planking

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