Sunday, February 22, 2015

Birdsmouth mast glued up

I have had the parts for the mast cut out and ready to go for about six months (see <this post>), and this weekend seemed like the right time to assemble them.

I decided to construct a jig to facilitate holding the staves in position while getting them clamped up.  I gathered a couple sawhorses and several other stands and spaced them out along the length of the mast.  I then measured the mast rough diameter at each station and cut out matching profiles from some 1/4" plywood.

I then attached some short pieces of 3/4 plywood recycled from the building jig to each support so that I would have something to attach the profiles to.  Setting up a laser level made it fairly easy to align the supports.  On each one I had drawn a horizontal line and a vertical line, and layed out and cut my semicircles from the intersection of the two.  Having the lines left over on the supports was key to easy alignment.

Here's a shot showing the vertical alignment.

And here you can see the horizontal alignment.  I held the profiles in place with clamps until satisfied with the alignment, then drove a couple screws through to fix them in position.

This setup ensured the jig was straight in both directions, and aligning the center points automatically took into account the taper in the mast, which is not constant along the length.  Here's an overall view with the mast dry-fit in place.

With the jig set up, I next ensured I had the plugs for the ends of the mast ready to go.  The top end is plugged by a simple octagonal stick about 3/4" thick.  The plug at the base of the mast is also octagonal, but protrudes from the end with a square section that will fit into the mast step.  

I cut away the top of the plug so there would not be an abrupt transition from solid to hollow. An abrupt transition can cause failure at that point if the mast is under bending stress.  That won't be the case here, as this is a short plug about 1 foot long, and the mast is supported well above that height at the cabin roof, but I had seen it done elsewhere and thought I may as well do it.

With all the pieces ready, I lined up all the mast staves and clamped them together.  I thought it would be easier to apply the epoxy this way rather than handling each stave individually, and it worked out well.

I first wet them out with unthickened epoxy using a short 1" section of roller.  I did the V side and the back side, then the V side again.  The idea is to let the wood absorb what it can, so that it doesn't suck the epoxy out of the joint during glue-up, leaving a weak spot.

Once the staves and plugs were wet out, I mixed and spread thickened epoxy on the V side. I made a little custom spreading stick by sanding it to a point and filing notcches in the edge.

The notches leave some epoxy behind, so that there is an appropriate amount distributed along the joint.

Holding the stick at an angle allows it to fit the sides of the V.

No photos of the epoxy spreading, as things were just slightly frantic at this stage - I wanted to be sure the epoxy didn't start to cure before I could get it all clamped up.  I was glad to have my wife's help mixing up epoxy.

Once all the staves were spread with epoxy it was back into the jig with them, which made the alignment and fitting together of the joints a snap.

I used hose clamps to pull the staves together, and then applied zip ties to hold them in place, then moved the clamp down and repeated.  I had a number of hose clamps, so a left them in place periodically, rather than unscrewing them all the way to move them past the next support cradle.

The next day I removed the clamps and saw that things were looking pretty good.

I got out my block plane and planed down the projecting corners to make the mast 8-sided.

And then planed the corners to make it 16-sided

And then then 32-sided.  The mast is now a bit smaller than the support jig cutouts and tends to slide.  I moved the end support and raised it up to provide an end-stop.

And then planed the ridges again to be about 64-sided.  It's a bit hard to be sure where you have planed and where you have not at this point.

Lots of neat curls resulted.  Too bad I can't think of a use for these.

Next I'll switch to sandpaper to remove the remaining ridges, then round off the top and apply some finish.  Not sure yet whether I want to put a couple coats epoxy and then varnish, or maybe go with white paint instead.

Sunday, February 15, 2015

Rudder hardware alignment

The block of laminated plywood shown below, which I call the rudder head, attaches to the transom of the boat and connects the tiller (steering handle) with the rudder.  I've previously detailed the construction of this part and that post is < here >

I have had the hardware (pintles and gudgeons) that attach this to the boat on hand for some time, and recently went ahead and took the time to get them installed.

Because the rudder head is somewhat thicker than the cast bronze hardware, I needed to carve out recesses.  I marked out the outlines and started trimming away with a chisel.

After some work and repeated fittings the bottom part is in place. That wasn't so bad.  

I debated for a while about just where to put the top fitting.  I wanted the separation between the two fittings to be as large as possible.  On the bottom one I had to avoid the recess where the rudder fits.  On the top one I had to make sure the mounting screws would not hit the haul line tubes which run inside. Once the location was decided, I carved away wood so the top fitting would fit.

I then mounted the corresponding parts to a piece of board and checked the fit.  I found that the rudder head did not slip smoothly onto the transom fittings, a sign of an alignment problem.

I thought for some time about how to check the alignment of parts.  Just eyeing things up didn't seem to be sufficient.  Since each half of the fitting has a part with a hole (the gudgeon), and one with a rod (the pintle). I hit upon the idea of putting a close-fitting rod through the gudgeon hole and checking the alignment with the pintle.  I went through my scrap supplies and found that I had an old aluminum arrow shaft that was the perfect size.  Putting this through the gudgeons showed up the alignment problem.

Now that I had a way to check my alignment accuracy I could take steps to get things lined up. Starting with the pintle that mounts on the transom, I put it on a surface plate (very flat surface), and used a taper gauge to check the height of the pin at each end.  I found that the pin was parallel to the surface plate and didn't need any work, so that was good.

Putting the arrow shaft through the gudgeon and doing a similar measurement, I found the rod was not parallel to the surface.  So I put the part in the vice and started filing off the high side.

Without too much effort I got the parts to align well.

With these parts aligned, I knew that if I could do a similar alignment on the rudder head half that my problem would be solved. 

Here's the setup for checking the alignment on the rudder head. 

In this case, adjustment was not so easy, as I had to carve away plywood to get things to line up, but eventually I got it pretty close. 

Mounting the transom half to a test board things now slid together pretty well.  

My next step was to figure out where on the transom to put the parts.  I drew a center line for left/right alignment, and then clamped the parts on and adjusted for vertical height.

I needed to make sure the tiller handle had clearance in the transom opening, and wanted to have my rudder uphaul/downhaul lines clear the edge.

Once I finalized the position I marked the heights of the parts, then removed the rudder head.  I again used the arrow to make sure the fittings were aligned, and drilled bolt holes.  I decided to install fiberglass patches on the inside of the transom to toughen up this surface and keep the nuts from digging in.

When I drilled the holes, I had a little chip-out, so I filled that (the white in the photo below) before applying the fiberglass patches. 

After the epoxy cured, I used a  scraper to taper down the edges, and then applied some fairing compound to blend them in. 

When that cures a little sanding should have this ready for paint.  It's nice to have these parts ready now to install.

Saturday, February 7, 2015

Seat back tops laminated and installed

Before doing any more painting I next wanted to create and install the tops on the seat backs. This is the last structural part of the boat to be built, so getting this done is a great milestone.

I've been thinking over time how I wanted to handle this part.  Some builders don't have any trim installed in this area, and some builders have fairly wide tops installed, the better to sit on. Because I don't yet know whether I'll want to perch up there much, and don't know where the favored location will be if I do, I decided to just install a medium wide top, as I can always modify that later if I want to.

I decided on a top that is about 3/4" thick and 2" wide.  I laminated this up from four 1/2" strips of pine, which take the bend fairly easily.

I put clear packing tape on the tops of the seats, so that I could laminate the tops in place. It was another glue-up that took most of my clamps.  I used C-clamps to clamp sticks to the seatback on the inner part of the curve, then pulled in the ends with the handscrew clamps.  I used lightweight bar clamps down to the bottom of the seat back to pull the top down to the curve, some small bar clamps with sticks to align the top of the lamination, and some small bar clamps and c-clamps to hold the laminations together.  Quite a conglomeration.

After the epoxy cured I had two tops that were curved just right to fit the seat backs.

I knocked off most of the squeeze out with a scraper, and then a quick trip through the planer had them looking nice.

The next step was to determine the edge profile.  I cut off a bit of the extra length and layed out three different radii on the edges.  My largest roundover bit is 1/2" radius, so I used that on the inner top.  I didn't want the outer edge to be completely rounded over, so used a smaller bit on the bottom edge of that.

The only tricky part to fit was the return at the front of the cockpit.  This has a compound bevel where it meets the cabin side, and it's easy to get too short as you sneak up on the right fit. 

But I got this side just about perfect.  As for the one on the other side, well, that's what thickened epoxy is for...

I primed the bare wood with unthickened epoxy, and then used silica-thickened epoxy to glue down the parts. After the epoxy cured and the clamps were cleared away I was pleased with the way things were looking.

And a little sanding dresses it up even further.

When I clamped these for gluing, I tried to let them hang over to the inside just a bit, so that I could bring them back flush with spokeshave, sandpaper and scraper.  This shot is from before I did that.

After bringing the insides flush and cleaning up a bit of squeeze out on the underside I sanded them all over and then finished up with a fillet of epoxy.  Here at the cabin junction:

And all along underneath the edge.

I climbed in the boat and tried them out and found this bit of wood provides a really nice arm rest with no sharp edges, and sitting up on top for a bit to stretch my legs if wanted should be very doable, too.  All in all a nice looking and functional addition to the seat backs that finishes things off nicely.

Sunday, February 1, 2015

Upside up again - fairing and finishing

With the centerboard slot gasket installed I completed turning the hull right-side up again.  I grabbed a couple of the stands that were under the building jig and screwed parts of the jig side panels to them to make a stand to raise the hull off the floor, and it sits nicely on the skegs. I expect to put similar cross members on the boat trailer for support there.

I had noticed while installing the centerboard slot gaskets that the uphaul line for the centerboard was not going to line up as I expected with the hole in the front of the centerboard case, being an inch or so too low.  Not sure how I messed that up.

I decided to fix that by routing the line out of the back edge of the board vs. the top.  That position comes around higher when the board is raised.  I bored the new hole.

And filed a rope channel.  On what is the front face of this photo you can see the old hole filled in with epoxy.  This should put the rope close to the right height when the board is raised.

With the hull upright I proceeded to trim and round over the top of the rubrail.  Always satisfying to make curly shavings with the plane.

Here's a view from the bow of the result after routing off the corner and doing some sanding.

And then I worked some more at fairing the deck/cabin joint.  This was necessary because of the fiberglass tape that I applied on the exterior to strengthen that joint.  I iterated a couple times on this and then decided it was good enough.

I also finished up the fillet and fairing of the top of the mast trunk.

And then I could move on to paint.  I had done the cuddy interior and the floor while the boat was upside down, so now I continued with the seats and seat backs on the inside, and the deck, cabin and roof.

I was second guessing my choice of color for the deck and cabin roof until I layed out the sail for a color comparison.  The sail and the roof/deck are in the same color family and should look good together.

Here's what things look like after two coats of paint. 

And here's a view towards the bow.  It's fun to see the finish going on.

I've got at least one more coat of paint to apply, and will need to be a little more careful at the line where the two colors meet to get that looking good.

Next up I'll be laminating the top trim for the seat backs.  That will add about 3/4" more height to the seat backs, and I'll be able to put a generous round over on the edge for back comfort.  I'm planning to have the top 2 inches wide to make a comfortable arm support.  Stay tuned for that.