Construction of new catboat "Mystic"


The boat is all done and in the water! She sails wonderfully, and is a lot of fun:



Below is the chronology of its construction:


To start, here are the lines plans. They were done using the software 'DelftShip', and were based on the original catboat design I did about 15 years ago. The lines were modified to give a little more depth amidships, more curvature to the garboard line and cross-section in the floors, and is one foot longer with a slightly higher transom edge to clear the waterline.



The hull will be framed in White Ash, with a laminated keel and sawn frames. The planking will be 6mm marine plywood, using epoxy-glued lapstrake construction. The mast will be made of vertical-grain Sitka Spruce, with an unstayed gaff rig.


Construction began not with the full size, but with a 1":1' scale model to check the fairness of lines and general layout. Here are some photos of the model:




Then, since the workshop still had another project being finished, the tiller carving seemed like a nice way to get it going. That began with a clay mockup of the eagle head and ropework, which was then carved into the full-sized Cherry tiller:




Now, ready to start real construction, work began with the frames. The full size lines plans were drawn up and transferred onto card stock, one frame per sheet. The card stock makes it much sturdier and easier to handle in the workshop than a vellum drawing. The frames are cut from 3/4" thick white ash. The wood was layed out to minimize cross grain, with the joints half-lapped and epoxied together. Once the epoxy was set, the frame outline was traced onto the wood blank using the card stock patterns, and band-sawn out:




Once the frames were all sawn out, it was time to make the keel. It was glued up out of three laminations of White Ash - the center lamination 3/4" thick, and the outer two 5/8" thick. The center lamination had a gap left in it to make the centerboard slot. The edges of the outer laminations were coated with a layer of fiberglass cloth and epoxy to give it better wear resistance to the movements of the centerboard, since once built it is very hard to get back in and repaint!


In the back of the first photo you can see where the keel gets taller. This is the portion back by the transom, where it is the deepest. That portion of the keel had to be pieced up, with the joints in the laminations staggered for strength, as shown in the second photo.


Once the keel was done, the stem was also laminated up. Since the stem wraps around the forefoot to be joined to the keel, the laminations were rotated from each other so that there would be no cross-grain all the way through the curve and the joint. The joint with the keel was half-lapped, with a White Oak knee across the inner surface for strength. The whole thing was through-bolted, with the upper bolt being a silicon bronze eyebolt which will be used to pull the boat out of the water back onto the trailer.



The leading edge of the stem was tapered to give a finer entrance into the water, and also for appearance above the waterline:



Here is the centerboard trunk - each end projects down through the inner keel to help locate the trunk. It will later get blocks on either side to give places to fasten it to the keel, and also to hold several of the middle frames which would have gone all the way across.


Now, it will really start to look more like a boat! The next step is to set up the frames as they will be planked. This is just a mock-up stage, to check for fairness of the frames and to position stringers, deck beams, and seat supports. Each frame had to be extended down to a common plane so they would stand in the correct position while upside down. This was done with 1x3 pine boards, with 1x2 cross-pieces to stiffen them and provide a place to attach them together. These pieces are just temporary.


Here are the first few frames set up:



All of the frames are now set up, and were checked for fairness - came out right first time!



Here the outer ribs are being bent on. They are 5/16" thick white ash, soaked in water overnight to make them pliable enough to bend. Once dry, they are epoxied on. The ribs add some strength and tie everything together.



Once the ribs were epoxied on, it was time to notch the frames to fit around the inner keel. To do that, cutoff pieces of the outer and inner keel were used as templates to get the notches placed correctly:


The final step on the notching is to cut back the ribs to allow a place for any water that gets in the boat to drain down to the lowest point:



Since all the frames are done, it is now possible to finish off the work on the stem. Two things need to be done to it. The first is to add a bolster piece just inside where the planking will meet the stem. These pieces add additional support to the ends of the planks. They are rough-sawn from 3/4"ash, epoxied in place, then the final bevelling is done with chisels and planes:




Once the bevel of the bolster pieces is done, the stem itself is notched to receive the ends of the planks. This notch has a 90 degree angle at its bottom, and the notch is angled to match the bevel on the bolster pieces.




Now on to a fun part (and one that really adds to the look of the boat), fitting the transom. The transom is a bit tricky, since it sits at an angle different than all the frames do, and the edges have to have a rolling bevel to exactly match the edges of the planks. The transom is made out of 5/4" Mahogany, glued up out of narrower boards. It is attached to the keel with an oak knee, using lag bolts into the keel and carriage bolts through the transom. First, the blank for the transom is fitted up with the knee to get the bottom edge of the transom done:




Next, the shape of the transom is transferred from the plans, and the outline sawn out. The bevel is done using a drawknife and planes, using a batten to get the angle to the frames correct:



After this, the seat supports and deck beams can be added. At the ends of the hull the deck beams go full width, a half-inch below the deck line to allow for the thickness of the deck planks. In the rest of the hull, the deck beams only go 7 1/2" from the sides of the hull, to frame in the side decks and coaming. These beams are half-lapped into vertical supports. Three of them also join into the seat supports, and there are two full-width seat supports at the stern (the seats will run down both sides of the cockpit and wrap around at the stern). Also, it is time to fit lengthwise stringers down the inside edges of the frames, to add stiffness to the hull. All of these pieces are much easier to fit now, before the planking is on since you can reach all around to measure and fasten.




So, all the frames are done, as well as the stem and transom. The next step is to fit the centerboard case into the center of the middle frames. The four middle frames have their centers cut out to the width of the case, and screwblocks are added to attach the frames to the centerboard case as well as to attach the case to the top of the inner keel:



Here is a shot of the centerboard trunk installed on the keel (this was taken later, after painting was done). Note the attachment of the frames to the centerboard trunk.



Last to go in on the framework is a few vertical supports for the foredeck (on a catboat, there is a tremendous load on the foredeck to support the mast and all the force of the sail, since there are no side-stays on this type of rig). After this, the framework is turned right side up to make it easier to fit the mast step and the king-plank for the foredeck, as well as the stringer to connect the inner edges of all the side deck beams.  There are also some additional supports under the rear deck to handle the loads that will be put on the mainsheet traveller which will run across the rear deck surface.


The last of the hull pieces to be built indoors is the coaming, which will run down either side of the cockpit, with tight radius bends around the aft end of the cockpit and a single large radius bend at the front end of the cockpit. These bends are laminated out of thinner material, soaked to make them pliable and then bent over forms. The forms have a slightly tighter bend and go slightly past the desired angle, since even laminated pieces will spring back slightly when released from the forms. After bending (forward coaming on a semi-circle form, stern forms on a quarter-circle form), the pieces are left to dry thouroly and then the two halves of each are epoxied together. The sections of the coamings down the sides of the cockpit are made from single pieces rather than laminating, since they have very little bend to them.





Once the wood was bent on and let dry, the two layers were epoxied together. This required clamps. Lots of clamps. LOTS OF CLAMPS!!! Just about all the small clamps I had - nearly a hundred of the things! Needed so many since the epoxy made the thin laminations bow just a bit apart, and I wanted a tight joiint along the edges.



Then, all the pieces will be sanded, primed, and painted, ready to be set up out in the garage in the spring for final planking.


Painting.... Lots of painting....!




And some varnishing on the transom and centerboard trunk cover (the upper edge of the transom is still straight in this photo - it will be cut to the curve of the deck after planking and the deck are on. The lettering on the transom parallels what the curve of the deck line will be:



Once all the painting was done, the framework was set up once more and thin battens used to mark where the plank edges would be. The battens were adjusted till a fair curve was found for each plank, with even plank widths all the way up the hull. One tricky place is where the first plank (the garboard) meets the stem, due to the extreme bends here - care was needed to give it a good appearance while keeping the shape easy to form from the planking.



Winter is dragging on, so I got the mast, gaff, and boom made up while waiting for warmer weather. Those will be made out of vertical-grain Sitka Spruce, which is lightweight, very strong, and can take bending loads well. The sail has been ordered from Gambell and Hunter Sailmakers in Maine, and will hopefully be here by then as well (I can carve and build, but my sewing is NOT up to making a sail!). The mast is laminated up from two layers of 2" thick Sitka, while the boom and gaff could be gotten out of one thickness. The blanks for both the mast and the boom had to be made of two lengths spliced together to get the 14' long pieces needed. A handheld power planer was bolted to a pair of guides, and the Sitka pieces put between a pair of 8:1 aspect ratio wedges. The planer was then run down the wedges to plane the ends of the 8' long boards to a smooth, straight wedge shape that could be epoxied to another identical piece to make up the 14' long boards. Those long boards were then glued up to make the thickness needed for the mast.



Once the blanks were made up, the centerlines of the spars were laid out, and the widths marked. The spars are not straight-sided, but are tapered. The mast is 3" thick at the base, and tapers to the top. The gaff and boom are 2" thick at their widest points, which are a few feet from their forward ends, and taper down at both ends a bit. The blanks were tapered while still square, then the rounding process starts. This is done by first planing off the corners of the square blanks to make an eight-sided cross-section. Then, the corners are knocked off of that to make a 16-sided cross-section. These spars are small enough that the 16-sided shape could be hand-planed and sanded round from that point. The result is a spar that looks like it was done on a lathe, but it is all done with hand planes and sanders - actually it goes pretty quickly.


A spar gauge used to mark the sides so that it could be then planed down to an 8-sided piece:



First corner planed off:



Second corner...



Third... (notice the LARGE pile of sawdust accumulating)



And fourth corner planed off. Now, the mast blank is a tapered eight-sided length. After that all that needed to be done was to plane off the eight corners and round it off. This was done by eye, and the result sanded smooth. The same process was done for the boom and gaff (spars that hold the top and bottom of the sail). All were varnished.



Then, it was time to make the boom and gaff jaws, which guide the ends of those spars on the mast. A thick piece of white oak was marked for the shapes, and run through a bandsaw to cut out the pieces:



The jaws were sanded smooth, varnished, and bolted to the boom and gaff. For final varnishing, they spars were hung from a work support and a final thinned varnish coat applied:



The toggle in-between the gaff jaws provide a surface to spread the load of the gaff against the mast as it swings around in the wind. The mast where the boom will rest will be covered in leather to prevent chafing, as will the inside of the gaff jaws.




Last to be made are the centerboard and rudder. The centerboard is cut from a 1/2" thick board, tapered where it hangs down from the hull, and then a recess is cut to hold lead weight to let it sink. I used 50-cal roundball lead shot that I had from my flintlocks (another project entirely!), hammered to a flatter shape, laid into the recess and epoxied in place. Then, a thin layer of fiberglass cloth and epoxy resin covered the board to stiffen it. A similar process was done with the rudder, except without the lead weights.


After all that, finally ready to set up out in the garage to plank it in the spring!

Here goes outside finally - set up out in the garage, on some indoor/outdoor carpet to save both my feet and any tools that may get dropped:



First planks on (finally!)



The planks are cut from 4x8 sheets of 6mm (just under 1/4") thick marine plywood. This marine plywood is made up of 5 equal-thickness layers of Okume wood, with no voids, and glued with a waterproof glue so it will not delaminate even if it does get wet. Since the planks are more than 14' long, they must be glued up from two lengths of the plywood. The same scarfing jig as was used on the mast is used again, but with a lower-angle wedge. Two layers of the plywood (rough cut to the approximate shape of the plank, with some extra for final fitting) are stacked in the jig and cut together. Then they are glued up with wax paper and clamps. When dry, the plank can be fitted and trimmed down to its final shape:


At the ends of the planks, gains are cut to make the ends of the planks all lie in a flat plane with each other. This serves a couple of purposes: first, it prevents any gaps under the planks, and also it looks much better! The gains are cut with a rabbet plane, set up with a side fence so the gains are 3/4" wide, and also a depth stop set to half the thickness of the planks. The gains are cut full depth at the ends, and taper out to nothing about 1 1/2' back from the ends.



Planking continues, averaging one pair per day (cant go much faster, since the epoxy needs to cure). The planks are overlapped with each other by 3/4", and the laps are layered with thickened epoxy before the plank is clamped on. At the ends, the planks are screwed into the stem and transom. The planks will also be screwed into the frames later on. The locations of the screws into the frames are marked but not drilled yet - the screws will be put in after the hull is turned right side up and the inside painted. Leaving the screws out for now allows the frames to be moved out of the way a group at a time to paint the inside (more on this later).



Really starting to look like a boat now...


The next photo shows a closeup of the plank laps. The inside corner of the joint has a fillet (pronounced 'fill-it', not like the steak) of thickened epoxy added to seal up the endgrain and also to strengthen the joint. This will be done on both the inside and outside of the hull on every lap (sounds tedious, but it goes on very quickly). The epoxy is thickened with a colloidal silica powder - looks like talcum powder, but is made up of tiny glass beads with little spikes on them. It makes the epoxy more of a paste without effecting its adhesive properties.




Here is a sequence showing how a plank is marked and fitted. First, the previous plank must be beveled so that the next one will lay flat against it. To do this, a short straight piece is used as a guide, and the edge beveled until the straitedge lays flat from the mark where the new plank will end and the end of the overlap on the old plank (this is where all those marks made earlier come into play)...


Next a roughly cut plank is clamped in place, and a pencil line traced on the inside where the new plank overlaps the previous one. The positions of the frames are also marked to make it easier to see where the frames are, since that will be measured from next...


Then, the plank is turned over, showing the traced pencil line. The width of the overlap, in this case 3/4", is set on a pair of dividers and that distance marked periodically down the plank....


Then, the distance from the edge of the previous plank to the edge of the new one is measured...


And marked on the new plank. This is done at every frame...


Then, a line is drawn with a flexible batten through those sets of marks. This shows the outline of the new plank...


Which is then sawn out and the edges planed smooth with a hand plane. The plank is now ready to attach.


Planking contiues on.... Getting close now, 9 of ten planks per side are on....



And the last one goes on!


A view from underneath - a sample of things to come (stand on your head to look at this one to get a better idea of the finished boat!)


More pictures to come as the boat progresses.... stay tuned! .... Next step is to do the rest of the fillets on the outside, and then the outside will be sanded and painted. Then the fun part - turning it over finally and doing the interior.


To go to the second page of this project, CLICK HERE