Building the Lower Hulls
Finally it was time to start the boat. The back bone (keel) was lofted on the strongback according to the plans and then once I was satisfied with the full
sized plan I transferred the lofted lines to 1/4" hardboard.
These were cut to fit the
lofting lines and then those patterns were used to mark and cut the 19mm Meranti
plywood. After marking the plywood I rough cut with
the jigsaw and then using
the template as a pattern I flush trimmed to size using a pattern bit in the
router. The end result was a PERFECT fit to the lofting. Each piece was screwed
down to the strongback to hold it in position and then the keel flange, butt
blocks, doublers and bulkhead guides were attached. The entire form was sealed
with two coats of epoxy and then it was flipped over to attached all of the
parts to that side as well. Once the first one was done, I did it all over again
to make the second backbone. In hindsight the only thing I would have done
differently is to minimize the number of fasteners (ring nails) that I used to
attach the keel flange (more on that below).
The bulkheads rest on the keel flange and the bulkheads and the backbone are notched in order to lock everything together. Then an epoxy fillet bonds it all together and increases the strength. After that the keel flange is beveled so that the plywood panels that make up the hull will lay across the flange fairly. What I experienced is that the bottom of the bulkheads, where they rest on the flange were only as wide as the flange. So the bevel was pretty much a 45 degree angle from one corner of the flange to the other side at the backbone. I triple checked my lofting of the bulkhead shapes and did not find an error, but maybe I made one. Regardless, it seems to me that is would be better for the bulkhead to be slightly wider that the keel flange, maybe 2 cm on each side, so that you would only take off a portion of the keel flange rather than half of it.
As it was, when I attached the keel flange I nailed it every foot or so and used a drift to counter sink the nails heads, as per the plans, to what I thought was a depth that would allow me to bevel the keel flange. Had the bulkheads been wider than the flange I would have been in good shape but as it was EVERY SINGLE NAIL was in the way. Damn. My first thought was to use a hollow drill screw extractor to remove all of the nails but since the first step was to grind off the nail heads anyway I just ended up using the angle grinder to grind each nail down low enough that they wouldn't be in the way of the hand plane as I beveled the keel flange to the correct angle.
If I was doing it over, ***pay attention here new builders*** I would make sure that the bottoms of the bulkheads were wider that the keel flange dimension when I lofted them and I would use screws to temporarily hold the keel flange in place until the epoxy bonding it was cured and then remove them. The nails turn out to be over kill since this entire area is bonded together with the hull panels by a large fillet. So take heed and learn from my mistakes here!
After both keels were made and sealed, they were sanded in preparation of future
bonding of the bulkheads and hull panels and then the first one was raised into
position. I built an overhead frame of 4X4 timbers that bolted to the strongback,
and eventually to
each other, on which I used handy billys to raise the keel
backbone. Actually it was the boom vang and mainsheet from my
Catalina 25 that I used. It was pretty handy in that the
cam cleats allowed me to hold in place as I adjusted things to my satisfaction.
The only problem was that I was pretty close to the weight limit on mechanical
advantage. When it comes time to flip the lower hull into the cradles I will use
the 3 ton chain hoists to lift the hull from the strongback, we'll turn it in
the slings and then lower it into the cradles. Moving the cradles off of the
strongback will be a lesson in leverage and patience... stay tuned for that
segment!
Once the backbone was raised and positioned on the strongback
it was fastened in place by screwing blocks to the strongback and the stems to
the blocks. Each bulkhead was put in place after attaching the supporting legs
and these were in turn, attached to blocks that were screwed to the strongback.
Careful attention was used here to insure that everything was correctly
positioned and
that the measurements were correct. The end result was that the
bulkheads are plumb and square to the midline and to the station lines.
Once I was satisfied with the bulkhead placements I started
bonding in the stringers. I cut up some small blocks from scrap wood that was
left over from milling the stringers that I then wrapped with plastic food wrap.
The plastic wrap prevents the epoxy from bonding the block to the bulkhead when
the stringers are glued. These blocks were through bolted to the
bulkheads at
each stringer notch. This, in hindsight was way too much un-necessary work. All I
needed to do was screw them in place with drywall screws... quick and easy to put
in and remove. The resultant holes are the same and will need to be filled
regardless. However the blocks are very helpful for clamping the stringers in
place while the epoxy cures. The epoxy mixture I used for this bonding was microfibers and
fumed silica (Cab-O-Sil) at about a 70:30 mixture. Drips and excess
squeeze out was scraped up and reused as much as possible. Any additional excess
epoxy was cleaned up with alcohol wipes. Once the epoxy was cured the blocks
were removed and the area was sanded as needed. Part of the fun of attaching the
stringers was cutting the bevel and fastening the stringers to the stems. I
accomplished this by firmly clamping the ends, which had been left long, in
position and then used a handsaw to cut the proper bevel at the correct length.
You need to remember the account for the thickness of the plywood in determining
the finished length! These ends were then attached with silicon bronze screws
and epoxy.
One other thing I did was to add in an additional stringer.
The plans call for the placement of three stringers per side and then
clamping
blocks for the outer stinger at the overlap for the upper hull panels. This
leaves a large area above the highest stringer unsupported, and I think that
contributes to the "wobble" that occurs when the hull is turned. What appears to
happen is that the hull panels try to run straight between the bulkheads instead
of holding the nice fair curve. So instead of mounting clamping
blocks, I notched the bulkheads at those same locations, as specified on plan
sheet 1, and mounted a 4th stringer. My hope was that this extra support
will hold the sides in place. As it turned out... it worked great! I am
suggesting that everyone consider this addition as it provides several benefits
and the only drawback is a little extra weight.
The plans call for making patterns for the hull sides out of
1/4 hardboard since it is lighter and easier to position and cut to fit. However
on the day that we did this I had lots of help so two people held the plywood in
place while a third marked it, then it was trimmed and fitted and then mounted
with just enough screws to hold it in place. Once all of the panels were cut and
fitted, the stringer locations were marked on the inside and the butt
blocks that fit between the stringers where the panels join were cut and beveled
to fit. The plans call for a long block on the exterior to be through bolted to
the butt blocks with a sheet of plastic underneath to prevent the exterior board
from bonding to the hull. The problem is the bolts themselves get bonded in
place and are
a pain to remove. I eventually went to using just sheet rock
screws to accomplish the same thing. The end result is a nice fair hull between
panels All of the panels were then
removed and coated with two coats of epoxy on the inside surface and then sanded along the stringer
locations. The panels were then permanently bonded in place epoxy and silicon
bronze screws (1x 8). The epoxy was applied to the stringers and edges of the
bulkheads and then epoxy filler was made, again with Cab-O-Sil and microfibers,
which was applied to the stringer surfaces and the bulkhead edges. Once the
screws were tightened the excess filler was scraped up and reused on the next
panel. Then the excess was cleaned up with the Alcohol wipes... No sanding
needed!
Another aspect of adding the fourth stringer is that you no longer need to join the 5th and 6th panels together before attaching them to the hulls. Without the additional stringer there is a large unsupported area where the final panel fits on the aft section, so the plans have you bonding the final section to the panel before it. I did that on the first hull but I won't on the second hull. You will need some clamps to convince it to take the curves but it really isn't too bad.
Once the hulls are sheathed it was on to the fillet between the keel and the hulls. I made this with a structural mix of epoxy and Cab-O-Sil. It took a few applications before I was satisfied with the fairness of this fillet and sanding this mixture is harder than sanding a microbubble or wood flour mix but I wanted it to be very strong. I also elected to add in a thin strip of Purple heart along the edge of the keel in order to cover the plywood end grain. This was bonded in place with the normal Cab-O-Sil / microfiber mix and I removed all of the fasteners and filled the resulting holes with epoxy. I expect this strip to take abuse of groundings in combination with a sacrificial strip of Purple heart outside of the fiberglass. I do not plan to use stainless strips on the bottom of the keel as too many folks have had problems with anchor rodes catching and removing them. I am considering a sacrificial strip of white oak. If I go that route I will add it on with polyurethane caulk and it will get painted with the primer and bottom paint.
After lots of sanding and fairing the hull it was time for the fiberglass. The plans come with a reproduction of an article on applying fiberglass. If you haven't done this before, read that article several times until you feel you have the overall plan down and then practice on a smaller scrap sample to make sure you understand how it all works. For the keel and skeg I am using 18 oz 45/45 bias glass in one layer rather then cutting several sections of the 6 oz woven cloth on a bias and building up the layers. It is more difficult to apply the heavier cloth and it tends to bubble more so a grooved fiberglass roller is essential to work the air out but the payoff is in less prep and application time. I'm not sure that I would recommend it for a novice though, it is still easier to work with smaller sections and the lighter cloth is much easier to wet out.
I applied from the bow stem back to the start of the skeg cut out in one section and did the remain section on a second day. I coated the hull with un-thickened epoxy in the area that I intended to glass and let it cure to the tacky stage. I then positioned the glass and wet it out, using squeegees to work the epoxy up and through the glass until it was completely wet out, working the air out as I went. After completing the wet out, the cloth was rolled and squeegeed to remove excess resin. Once the cloth epoxy was cured to tacky I troweled on a thin mix of microbubbles to fill the weave and trimmed of excess cloth. I quick faired this after it was cured and this is one area that the bias cloth is really nice. Since it isn't woven, the fabric is held together with stitching and these stitches are just proud of the glass surface, so sanding down to the stitching gives a nice easy way to fair without sanding into the glass itself. Once the keel section was done I applied 10 oz cloth on the sides in the same manner.
The comes the hull fairing. Since the lower hulls are the underwater sections I plan to spend a lot of time here getting the fairing as close to perfect as reasonable since a fair underwater profile can really enhance your sailing speed. First I made a few longboard of various lengths that would take self-adhesive sand paper. My plan was to use the notched edge trowel technique of applying the fairing compound, sanding with a long board, filling in the remaining notches and then longboarding the hull smooth. The reality is that if you have the hull mostly faired before you out the glass on there is very little that needs additional fairing. You do need to fill the weave of the fiberglass cloth so here is what worked for me: While the epoxy is still green apply the fairing compound with a smooth edged trowel. Hold the trowel at an acute angle to the surface and press firmly to press the mixture into the weave and coat the entire hull. Once the mixture is cured, sand it with a longboard, sanding the entire surface. Repeat that process a second time and after it cures I marked the hull all over with a pencil. The pencil lines act like a sanding indicator so I could be sure to get the entire hull sanded smooth. At this point it becomes spot fairing. Check and fill (or sand) defects with your hands and eyes. A nice trick is to use a sheet of paper under your hand as you run it over the hull... you will feel abnormalities easier this way. Keep at it until you are satisfied with the hull surface.
Once the hull was faired I applied a coat of un-thickened epoxy to seal it and then sanded the surface in preparation for a planned application of epoxy primer. This will be re-applied just prior to launch and will be followed up with several coats of an ablative antifouling paint.
Now I needed to build the cradles and turn the hull. The cradles support the hulls at stations 3 and 8. I used the bulkheads for the second hull to mark some hardboard that I used to make templates. Using measurements from the actual hull I drew in the keel and then cut it out with a jigsaw. After positioning it on the hull I was able to fine tune the fit by marking the template and then trimming it to the final fit. Two of these shapes were made for each cradle and they were joined with some scrap 2x4 stock. A base and two sides were screwed and glued to finish the process. Then I added some carpet scraps to the inside of the cradle where the hull rests.
Both hulls were turned over using 2 ton chain hoists that I hung from the overhead frames. A sling was passed around the hull, the support legs were unscrewed from the strongback the hull was slowly raised. Once it was high enough we turned it in the slings. We discovered with the first one that it is very easy to turn it this way and it only took two of us to turn the second hull. The completed cradles were positioned and the hulls lowered into place.