Excerpt from Slider Building Manual
Setting up the strongback
A good place to work is your first priority. It’s almost essential to have a place with a roof, and in the higher latitudes, it’s good to have a space that can be heated– otherwise you won’t get much done in the winter. I built the prototype in a one-car carport. It was a little tight, but there was enough room to assemble the boat on its trailer, which is helpful when you reach that stage. Good lighting is also very helpful, particularly if you’re going to be doing a lot of the work after you get home from your regular job.
You’ll build the hulls one at a time on a simple strongback, which consists of a pair of 16 foot 2X6s, blocked 12 inches apart (for a total width of 15”) and supported by a pair of short sawhorses. Try to find the straightest ones you can, but perfect straightness is not essential, since frames will be set to a string or wire stretched between the ends. The strongback will also serve as a decent mast bench, if you build the sprit-sloop version of Slider
The sawhorses I built were 26 inches high. I’m 6 feet tall, and I still had to stand on a footstool sometimes to work comfortably on the highest part of the bottom. You may want to adjust this height, depending on your stature and flexibility– working on the gunwales involved bending over a lot, for me. At each end of the strongback, nail on a couple of pads of 3/4” ply, as wide as the strongback and maybe 6 to 8 inches long. These will support the stem at the bow end, as well as the string used to center and level the bulkheads and frames, stretched between these pads.
It’s very important to get the strongback level, and then secure the 2X6s to the sawhorses in a way that precludes any wiggling. A strong string (or better yet, a steel wire) will be stretched tightly between the pads– this will give you a perfectly straight and level reference point to get your frames and bulkheads lined up perfectly. I put a shallow sawkerf in the top of each pad so that the wire could not shift, and secured the wire on the fore-and-aft blocking that separates the timbers of the strongback at each end.
The frames and bulkheads are fastened to the strongback by way of intermediary rectangles of cheap 3/4” ply. On your plans, you will see the spacing for these frames, given in inches. It is very important to understand that these measurements are all to the wide side of the frame station. Each frame and bulkhead must be beveled to accept the planking (which curves in or out depending on its position) and it is always the widest edge that falls exactly on the station line. This means that when you set up your stations on the strongback, the ply rectangles to which the bulkheads and frames will eventually be temporaily screwed must face in the direction that allows the wide edge of the frame to fall precisely on the station line. For frames and bulkheads and transom aft of midships, the plywood face to which the frame will be screwed must face aft, so that when the bulkhead is temporarily fastened to the ply rectangle, the bulkhead’s forward edge will fall precisely on the station line, and the aft edge of the bulkhead can be beveled so that the planking fits it perfectly. For stations forward of midships, it’s the opposite– the point to keep in mind is that the widest part of the bulkhead or frame must fall on the station line.
The stations to which the frames and bulkheads will be temporarily fastened can be built of the cheapest 3/4” ply you can find, but they should be fastened to the strongback securely, as they will not be unfastened between building the first hull and the second. This ensure that the beam webs for the crossbeams will be in precisely the same fore-and-aft line. I ripped 2X4s into 2X2 blocks, and fastened two of these blocks to the back face of the ply rectangles, which I made slightly wider than the 12” width of the strongback, so the ply rectangles sat securely on the strongback. Then I screwed the 2X2 blocks to the inside edges of the strongback. I made a V-shaped cutout on the bottom edge of each rectangles, so that they would not touch the wire or string used for centering and leveling the frames and bulkheads. One final thing to keep in mind is that these ply rectangles must be tall enough that you can use two screws to secure the lower edge of the frame to the rectangle, and two screws far enough up the frame to preclude any tendency to wobble. For the #1 frame, nearest the bow, this means that you may have to taper the ply rectangle so that its corner does not stick out past the edge of the bulkhead. This may require a little fiddling after the strongback is set up– it did for me.
The 4th and 5th frames are open frames rather than ply bulkheads, so they will require a temporary crossmembers at the bottom (gunwale) and another temporary crossmember in the middle of the frame, so they can be fastened in the proper place.
Cutting out bulkheads and frames
Because Slider is a catamaran, it’s probably best to cut out all frames and bulkheads at once– this way you’ll know they are exact duplicates. All bulkheads are cut from 1/4” plywood, and then reinforced with soilid timber framing. The two open frames are cut from 3/4” stock– preferably some light strong, straightgrained wood like Douglas fir– and then glued together with a 1/4” plywood gusset at the bottom.
Use of the camber board–
Make a camber board of 1/2” hardboard or Masonite– 4 feet long and 6 inches wide at the ends. Use the dimensions given on sheet #2 and draw the curved side smoothly with a fair batten. This camber board will be used to give a small amount of convex curvature to the topsides, by curving what are called the topside futtocks (or outside edges) of the bulkheads and frames. This modest curvature will make the topsides much stiffer, but will not complicate planking to any noticeable extent. Also apply the camber board to the upper (deck) edge of the bulkheads, but not to the bottoms. These are narrow and do not require stiffening, and a flat bottom will ride on the trailer with less stress. Bear in mind, however, that the measurement given in the plans refer to the straight-across line at the top and sides of each bulkhead or frame. Therefore, when setting the frames up on the strongback, you should measure from that straight-across line down to the string or wire, in order to place the frame or bulkhead the proper distance above the baseline.
I would suggest that you make patterns or templates for each frame and bulkhead before cutting out the actual pieces– this ensure that they are identical– plus it’s better to make any errors on cheap stock, rather than expensive marine ply. I used 1/2” hardboard, which is flat and dimensionally stable, as long as you keep it dry. To mark out a template, strike a midline from top to bottom. Look on the #2 plan sheet to get the top-to-bottom measurement. For example, if cutting out bulkhead #2, the plan shows a height of 29 – 7, which is boatbuilder for 29 inches and 7/8. Mark the vertical line to this height. Using an accurate square, mark out the half-breadths shown on the plans or table of offsets, to get the basic shape of the frame or bulkhead. For the #2 bulkhead the half-breadth is 14 – 1, at the gunwale, so the widest part of the bulkhead will be 28 – 2 wide. Then use the camber board to mark the curvature of the futtocks and deck. It’s best to put the center of the camber board in the center of the edge to be cambered. (The plans, for simplicity’s sake, do not show these edges cambered.)
Once these templates are shaped to your satisfaction, you can start cutting out bulkheads and frames. I used my router a lot in building the prototype. For example, I was able to cut out the bulkheads rapidly by using a straight piloted bit. I clamped the plywood to the templates and ran the bit around the edge– this was quick and ensured perfect duplication. However, you could simply mark the shape by tracing around the template and then cut it out with a jigsaw, or a circular saw set shallow.
I recommend that you make a template even for the open frames at stations 4 and 5. This allows you to get the camber perfect, but it also gives you a good way to glue these frames up in such a way that the shape is perfect. These frames are, in essence, a couple of pieces of 3/4” thick fir, two inches wide at the top and three inches wide at the bottom, joined together at the bottom by a plywood gusset. If you have templates for them, it’s a simple matter to use the template to glue them up accurately, after first covering the template with plastic sheet or wax paper, so the frame will not stick to it.
All bulkheads are framed with 1 1/2” wide clear fir 3/4” thick– or other strong light rot-resistant wood. These are necessary to give adequate stiffness to the 1/4” ply used in the bulkheads. Because these framing members must be cambered on the sides and deck edges. I glued them to the bulkhead with the midpoint of the framing piece even with the midpoint of the ply bulkhead. This left an equal amount of framing piece sticking out past each corner of the ply bulkhead where it curves in. I again used a piloted trimming bit to carve off this excess wood, but it would be almost as easy to plane it off with a good sharp handplane. Or you could mark it and trim it prior to gluing it on, if that seems easier to you. It’s important at this point to take your measurements from the bulkhead rather than the plans, since the bulkheads should be the correct shape, and it is usually best to take measurements for mating parts from the parts to which they must fit.
No fastenings are used to hold the bulkheads and frames together– the epoxy alone will be very strong, due to the large gluing surfaces. The lack of fasteners will prove helpful when cutting notches for the longitudinal stringers– you won’t have to worry about hitting a stainless screw while routing out these, or when beveling the edges. Only temporary fasteners were used in the structural areas of the hulls. It’s my opinion that carefully engineered joints made with epoxy are just as strong as joints that are additionally secured by fasteners. Fasteners increase weight, provide embedded hazards for edged tools, and may provide a pathway for moistrue and rot to penetrate a joint. The only permanent fasteners used on Slider’s hulls were the bolts that secure the crossbeams to the beam webs. Even these are not strictly necessary if you glue the beams to the webs, but I decided to keep the possibility of wider beams available, in case I was ever tempted to give Slider more beam, for carrying more sail. The only other permanent fasteners are in the center deck and duckboards, and the screws used to secure deck and mast hardware.
For temporary fasteners, I used coarse drywall screws– these are cheap and hold well. Do not, however, forget and leave any of these in the structure, as upon any exposure to salt water they will immediately corrode into lumps of rust.
Setting up bulkheads and frames
At this point, an absolutely necessary tool is a plumb bob. I splurged and got a nice one of turned brass, though a lesser plumb bob will serve you just as well.
To set up your first frame (the #1 bulkhead, which separates the bow flotation chamber from the storage space) attach the intermediary rectangle of plywood to the strongback, so that the flat unencumbered face of the ply faces forward. You have already made sure that the strongback is level, or at the very least, that the string or wire baseline is level. Now make sure that the intermediary rectangle of ply is vertical, using a good bubble level. When it is, secure it to the strongback with long heavy screws– I used deck screws.
The frame will be screwed to this temporary plywood rectangle. A couple of quick-release one-handed clamps are very useful for getting each frame set up perfectly before the temporary screws fasten the frame or bulkhead to the intermediate ply.
Each frame will have a vertical line marked on it at top and bottom. If the plumb bob’s string is clamped at the top of the frame so it lies along the mark, and the string also matches the mark at the bottom (deck side) of the frame, then you can be sure the frame is level and square to the strongback. If the tip of the plumb bob is also exactly over the string or wire baseline then the frame is in its correct horizontal position. It then must be moved up or down until it is in the correct vertical position. It is best to measure the distance from the bottom side of the frame to the wire or string, but also, as a double-check, you can measure from the deck edge to the string. Bear in mind, however, that this latter measurement must be taken from the straight-across line at the deck edge, and not from the cambered actual edge of the bulkhead, as this camber will throw off the measurement if included.
I would recommend that all the intermediate rectangles of ply be covered with plastic sheeting or wax paper, so that any epoxy drips will not accidentally glue the ply to the frame or bulkhead. If this happens, you’ll have trouble lifting the hull off the strongback.
Another very important thing to remember is that the solid timber framing of the bulkheads will face either fore or aft, depending on the position of the frame. Bulkheads #1 and #2 will have their framing facing forward, so as not to be visible from the cockpit, and bulkhead #5 will have its solid framing facing aft, for the same reason.
Once all the frames and bulkheads are secured to the strongback, I find it helpful to clamp a temporary stringer across the top of all frames, to keep them from wiggling around independently under the stress of being beveled and notched for stringers.
The last important part of setting up the frames is the inner stem. This should be set up on the forward pad and then carefully fitted to the framing of the first bulkhead. This is a highly important structural member, since it not only provides a landing for the longitudinal stringers at the bow, it also serves to distribute into the rest of the structure any shock loads from running into docks and rocks. Make sure it fits well, and check to be sure it conforms to the overall curvature of Slider’s bottom. This is best done by clamping a batten to all frames, as above, and then allowing the batten to extend forward to the forefoot of the bow. This will not be a perfect curve, because the stem is straight on the bottom, but this will look fine when finished, since there is little curvature to the bow end of the bottom. The main thing here is to be sure the bottom edge of the stem continues the sweep of the hull’s bottom fairly.
Remember when fitting the stem that the #1 bulkhead will be beveled so that the side closer to the bow will be tapered in that direction. Fit the stem to the first bulkhead in such a way that when the bottom is beveled, the stem will still be level with the framing. In practice, this means that when the stem is first fitted, but before the bulkhead is beveled, the stem will appear to attach to the frame a little below the edge of the framing. When this edge is beveled, the stem will appear to fit perfectly and the planking will be able to lie flat and snug across the bulkhead framing and the stem.
There are several way to attach the stem to the #1 bulkhead, but I recommend epoxy, with a standard 1/4” fillet and then glass tape, between stem and bulkhead framing. This is simple and clean, as well as very strong.
At this point, the shape of the hull begins to appear. Once you have fitted the longitudial stringers, you’ve really begun to make progress.
Remember to keep that temporary stringer clamped to the top of the frames and bulkheads to stabilize them while fitting the permanent stringers.
Before proceeding, I recommend that you temporarily clamp the sheer clamp to the lower outside edges of the frames and bulkheads. Then, by sighting carefully along this stringer, you can tell whether or not your sheer line is sweet and consistent. I neglected to do this on one of the prototype’s hulls, with the result that there is an unfortunate bump in the sheerline that annoys me every time I notice it. If you see a problem, it may be that one of your frames or bulkheads is set too high or too low, and this kind of problem is much easier to correct at this stage.
The next job is beveling the frame and bulkhead edges. It’s better to do this before fitting the stringers. You can do this in many ways. The main thing is to check the bevel frequently as you develop it.
One fast way to bevel not just the edges of the frames and bulkheads, but the edges of the stringers, is to rig up a power plane with a long stick extending rigidly out to the side from the shoe of the plane. The stick must be long enough to reach from the edge of one frame to the next. You simply put the planer up to the edge to be beveled, and make sure that the stick rests on the adjacent bulkhead (the one that determines the angle of the bevel) and plane away until you’ve removed enough material. Always be very careful not to cut away any of the widest edge. And remember that a power plane is a very dangerous tool.
It’s almost as fast to use a good sharp block plane to do the bevels. Just lay a stick across the frames that need to be beveled to each other, and keep cutting until the stick lies flat across both bevels. Or you can use a belt sander, but again, be very careful not to cut the bevel too deep. The wide side of the frame should remain intact.
Once all bulkheads, frames, and transom are beveled, check the bevels one last time with a flexible batten, laid from frame to frame. The idea is that you want all the planking to fit flat against these bevels, with no high or low edges to distort the lay of the ply.
If everything looks good, then fit the midstringer first. This is the simplest stringer, and it lends stability to the framework. All stringers are basically 3/4” by 3/4” solid stock, modified with a bevel on the top surface so that when the hull is upright, the stringer will not trap water on its upper surface. The notches must be cut into the frames and bulkheads at the points given on the plans. Keep in mind that just as the frames were beveled, these notches are also beveled, so that the stringer’s outer edge matches the outer edge of the frame perfectly. I made a jig for my router that incorporated a flat piece of ply for the router to slide across. Rails constrained the router to cut a notch the width of my stringers, and 4 foot long extensions allowed me to clamp the jig to the edge of one bulkhead and to an adjacent bulkhead, so that the bottom of the notch was properly beveled. Because the top of the stringer is cut at an angle to avoid trapping water between stringer and planking, a little work with a pull saw or coping saw will be necessary to fit the stringer exactly.
I’m not the world’s best carpenter, so when I was cutting these notches, I was continually grateful that epoxy is a good gap-filling adhesive. The main thing is to be sure the stringer’s outer surface is flush with the frame’s outer surface. If you should over-cut these notches, just shim the stringers up with a chip of wood and use plenty of epoxy.
The only tricky bits for installing these stringers comes when fitting them to the stem and to the transom. The best way to fit the stringer to the transom is with a blind dado– in other words, the end of the stringer should fit into a pocket in the transom that does not show on the aft side. The transom is built of 1/2” ply, and these blind dadoes should be 1/4” deep. An easy way to do this is to laminate the transoms from two pieces of 1/4” ply, cutting the stringer landing from the inner ply before gluing it to the outer ply.
Fit the stringers to the stem by tapering them over their last several inches so that when fastened to the stem, they are exactly 1/8” thick at the forward part of the stem. (By the way, the plans do not show a specific position for the midstringers on the stem– just pull them against the stem where they fall and mark their position.) Cut this taper off the stringers from the inside of the stringers, so that they lie flat against the stem. The stem is 3/4” stock, and with a 1/8” of stringer showing on either side, and planked with 1/4” plywood, the width at the stem ends up one and a half inches, which is the actual thickness of the 2X stock from which the outer stems will be shaped. On the inner stem, between the mid-stringer, chine log, and sheer clamp, glue packing pieces cut from 3/4” by 2” stock and shaped to lie even with the stringers. These greatly increase the gluing surface for the planking at the bow, making the whole assembly much stronger. Once the hull is planked, an outer stem will be shaped and glued to the inner stem, packing pieces and planking. This outer stem is shaped from a solid 1 1/2” X 2” timber to continue the sweep of the hull to an edge, which should be rounded off to a radius of 1/4”. In other words, the bow should not be knife sharp, as this will make it more vulnerable to damage.
The chine log and sheer clamp are notched in and fastened on in a similar manner. One big difference is that both sheer clamp and chine log must be beveled to accept the bottom planking and the decking. One way to do this is to set the stringers in so that the part that needs to be beveled off sits proud of the framework. The angle of the bevel changes slightly over the run of the stringer, so it may be impractical to precut the bevel (however, if you do precut the bevel, a little epoxy slurry may serve to even the surface for planking.) In the case of the chine log, where the bottom joins the topsides, the inner edge of the stringer should be set flush with the bottom of the frame. The outer edge of the stringer will stick up, and can be planed off flush with the bottom. On the sheer clamp, the situation is reversed. In that case, the outer edge of the clamp should be flush with the deck line, and the inner edge will be proud of the deck line and must be planed off.
Once all stringers have been installed and beveled so that the planking will lie smoothly and completely against them, planking can begin.
Begin by scarfing two 4′ X 8′ sheets of 1/4” ply together. I used the Harold“Dynamite” Payson technique, because I wanted to retain the full 16 foot length of the combined sheets, and scarfing by tapering the edges results in a loss of a couple inches of overall length.
In brief, the Payson scarf consists of a couple strips of fiberglass tape epoxied to either side of the butt joint between the two sheets. I did it this way:
I set up the scarf on a piece of Melamine shelving, in order to get the glass and epoxy as smooth as possible. First I put down a sheet of wax paper to preclude sticking the scarf to the shelf. I wet out a piece of 5” wide fiberglass tape, cut from 6 oz. cloth, with epoxy and laid it across the shelf. I basted the edges of the plywood to be joined with a thickened slurry of epoxy and silica to fill in any gaps– and then butted the pieces together on top of the wetted-out tape. I put another 5” tape on top of the joint, then wax paper, then another piece of Melamine shelving, then about a hundred pounds of cast iron barbell weights. (Buckets of water will also work to press the joint down.) Leave overnight and the next morning you’ll have a 16 foot panel. You’ll need two of these per hull.
The planking is offered up to the framed hull, and marked for cutting. Clamp the panel to the framework in a close approximation of its installed position, using an occasional temporary screw to pull in the planking at bow and stern. At the same time you mark the outer edge of each planking panel by drawing around the outside of the framework with a pencil, also mark a line on either side of each stringer, frame, and bulkhead. When the panel is removed for cutting, you’ll have its outer shape and the positions of each structural element marked on it. This is very important, because from the inside of the panel you will drill fastening holes into the areas where you will be fastening the planking to the stringers, before permanent gluing. This will be an enormous convenience when the cut panel is returned to the hull framework to be glued and temporarily screwed to stringers and bulkheads. Without the pre-drilled holes for fasteners, you’d be fastening blind, and might not hit the stringer every time.
Very Important: Mark both topsides planking panels before fastening either one permanently to the hull framework. If you mark, cut, and fasten one side before doing the marking of the other, you’ll have to crawl up inside the hull to mark the second plank, which is much less convenient than just reaching through the open framework to mark it.
The topsides planking should be fastened to the framework with an epoxy slurry thickened with silica or other high-strength filler– thick enough that it doesn’t run off vertical surfaces. The secret to a good epoxy bond is to put glue on both surfaces to be bonded, so put the slurry on the stringers, chine logs, sheer clamps, inner stem packing pieces, and frame and bulkhead edges. Because you marked the position of the stringers and frames on the planking, it will be much easier to get the epoxy on the right areas of the planking.
The planking should be screwed to the stringers as quickly as possible, so that the planking will be stable by the time the epoxy starts to kick off. In hot climates you may need to use a slow hardener to give yourself enough time. For temporary fasteners, I used the smallest drywall screws I could find, and I drilled pilot holes through the pre-drilled holes in the planking, so as not to split the stringers, which are small in cross-section. Work from the center of the planking up and down and out to both ends, always fastening the ply to the midstringer first.
When the epoxy has set for a day or so, remove the temporary fasteners, and true up the edge of the planking where it intersects the bottom of the boat. Just as with the sides, you want the bottom planking to lie fairly against the chine logs and bulkhead bottoms.
Very important: Cut limber holes in bulkhead #2 and frames #3 and #4 before planking the bottom. At this point it’s easy to do with a router or a coping saw. I forgot to do this with my second hull, and it was not easy to get those limber holes cut from the inside of the boat. These limber holes allow you to bail the whole hull at once, rather than having to bail out the individual sections, and they also promote good ventilation– important for preventing rot. Do not cut limber holes in bulkhead #1 or #5, as this would open the flotation chambers forward and aft of these bulkheads. These flotation chamber have ventilation holes at the top of the bulkheads, but these will not allow the chambers to fill, since even with a big hole in the cockpit portion of the hull, the boat can’t float low enough for these vent holes to be below water. In the case of a capsize, these holes will be below water, thus forming an airlock that will keep the hulls floating high.
The final touch before planking the bottom is to strengthen the forefoot at the bow, by gluing long slender wedges of solid 3/4” stock between the inner stem and the chine logs. This has the effect of making the forefoot into one solid piece. These wedges should be about 9” long, starting from the point where the chine logs intersect the inner stem.
Glue and temporarily screw the bottom panel to chine logs and framing.
When the epoxy is well-set (at least overnight) remove the temporary screws. The screw holes will be easiest to fill and fair at this point, with the hull still upside down. Use a low-density filler such as microballons to make up a fairing putty with epoxy, rather than using silica, which will be very difficult to fair, since it’s so hard.
After the holes are filled and faired, the edge between the topsides planking and the bottom must be rounded over to approximately a 1/4” radius, so that this edge can be sealed with fiberglass tape and epoxy. I used strips cut from 6 oz. cloth.
Also, at this time the outer stem can be shaped and glued to the bow, covering the planking, the tips of the stringers, and the packing pieces. I used long drywall screws top and bottom to hold the outer stem on temporarily until the epoxy kicked. The holes these screws leave when removed can be filled before glassing the outer stem to the planking, using two layers of tape, one 11” wide and one 15” wide, so that they can wrap well around the stem and back onto the planking.
Turning the Hull
You’ve reached the point where you can remove the first hull. This must be done before glassing the hulls to a couple inches above the waterline, because the daggerboard case must be constructed and fitted before the hull can be glassed on the bottom.
You”ll have to reach up inside the hulls to unscrew the bulkheads from the plywood rectangles to which they were attached. Try not to disturb the rectangles, since as long as they remain unmoved on the strongback, you can be sure the frames and bulkheads are set at identical stations. This is the time you’ll be really happy you covered the rectangles with wax paper or plastic. If you didn’t do that, this is the time you will be really sad you didn’t.
Once the hull is off the strongback and blocked up level and at a convenient working height, fit the rubrails to the sheer. These must be cut or planed off level with the top of the planking and the sheer clamp, because the deck planking will overlay both rubrail and sheep clamp. Like most of the longitudinal stringers, the rub rails are basically 3/4” by 3/4”.
Look at Drawing #3 to see how the rubrails are tapered into the bows. Round off the aft corners of the rub rails.
A breasthook must be glued into the bow. This is a piece of 3/4” plywood, tapered to fit between the sheer clamps, and with a slot cut out to fit it around the top of the inner stem. The deck planking, when glued onto this structure, will connect the whole thing into a very solid block. The breasthook also provides a strong area onto which the forward mooring cleats can be through-bolted.
The daggerboard case can be fitted to either the port or starboard hull, and this decision should be made on the basis of whether the captain is right-handed or left-handed. I didn’t think this through and just put the case in the first hull to come off the strongback, which happened to be the port hull. But I was lucky. The captain, and that’s usually me, should sit in the same hull as the daggerboard, so he or she can raise or lower the board, depending on the course and circumstances. I’m right-handed, so at first I worried because I had to steer with my weaker left hand when in the port hull. But it turned out that steering doesn’t require as much strength as working the sheets, which I do principally with my right hand. Were I left-handed, I’d want the daggerboard in the starboard hull, so I could work the sheets from that side with my stronger hand.
While the case can be built in either hull, don’t be tempted to move it to the outer side of the hull. A board that is canted outboard is almost impossible to pull up if it gets stuck for some reason (like hitting a sandbank at 6 knots.) With the case on the inner side of the hull, you can stand on the center deck and pull with your feet under you– an impossibility if the case points outboard.
The case is assembled from 1/4” plywood and 3/4” solid stock. Be sure to apply fiberglass cloth to all inner surfaces before final assembly, and then glue the case together while the epoxy in the cloth is still green (within 24 hours) so that the bond will be chemical as well as physical. A few inches of the case will always be submerged when the boat is in the water. It is difficult to get antifouling well up inside the case, but worth the effort it takes if the boat is to be left in salt water for any length of time. The case is fitted into the hull, against and aft of the #4 frame, and is glued to the frame, to the sheer clamp, midstringer, and chine log. The case is reinforced by the side deck, the seat rail, by two 3/4” by 3/4” rails applied to the outside of the case, and by shims between the case and the hull planking. These shims may need to be wider at the aft end in order to have the length of the case fore and aft running parallel to the hull’s centerline. When installing the case, run a string down the centerline, so that you can measure from the centerline and be sure that the case is parallel.