Hatching a Plan

I'm enjoying a welcome relief from the sanding monkey mode as progress continues forward along the hull lengths.  This episode will require beginning with an image of an assembled part to understand the discussion to follow:

Above is a hatch that will provide ventilation through the forward bunk and a hatch mount.  The mount has radiused corners to match and accomodate the inside and outside hatch radiuses.  Box joinery provides a suitably strong connection between the mount's straight and curved sections.  The hatch mounting holes have been drilled out oversized and filled with epoxy to prevent water intrusion through the screw holes and to provide better holding power for the screws.  This mounting surface was later nicely flattened by working against sandpaper attached to the table saw surface.  

Above are all the parts for two hatch mounts shown with the box joint cutting jig.  A side piece is shown clamped to a jig that guides the work over the router bit within the red circle.  I enjoy an incremental fence with templates for easily creating box and other jointery.  The fence only moves in 1/32 inch increments so precise alinements with the templates are no problem when repositioning the work for the next cut.

In the foreground are three stages of producing a corner piece.  First is the blank followed by box joint cuts and finally the inside radius is cut.

The corner piece inside radius is roughed out on a band saw then mounted in a special jig to finish the inside radius.  The router bit is surrounded by a collar 1/8" larger in radius than the router bit.  The jig's base has a radius 1/8" larger than the desired finished part's radius.  The jig's radius rides against the collar to control the bit's cutting path.  

The bit is shown in the elevated position to make the final cuts.  The bit's cutting edge is not long enough to span the material's cut face and a lighter cut is easier on the set up.  For these reasons the initial cuts are made at half the material's height as shown on the corner piece.    The bit will tear out material if allowed to exit the work in the same direction as the bit rotation.  The cuts are only made partway past the center position to prevent tear out, then the part is flipped over to cut what was previously the upper uncut half.  The work's edge near the bit shows the upper burnt looking finished radius and the lower uncut section.  The next cut, on the end opposite the bit, will machine the part's upper radius face to the pencil line on the part's top and flush with the finished radius below.  

This fixture wedges the side pieces against stops that define the dimensions and keeps the assembly square as the epoxy cures.

When you build something, you know where all the warts are.  After cutting the first inside radius I did a trial fit of a corner piece with two side pieces against the hatch.  I judged it was necessary to increase the inside radius.  This unnecessary change reduced the corner sealing area width.  May I not suffer leaks as a result.

Plywood will sheath the deck.  The plywood must conform to the bulkhead curves and the shear sweep.  The installed hatch mount will stand proud of the deck about 1/4 inch.  In the image above the mount is lowered to clamp flush with stringers running between bulkheads.  This is to hold all the various pieces in the installed positions while not touching the fishing line stretched between the high points of the fore and aft bulkheads.  This set up is to determine the gentle curve just fore and aft of the mount.  These curves must be duplicated on the lumber held to the mount by the fore and aft yellow tipped spring clamps.  The deck sheathing will then have an attachment surface adjacent to the mount.

A spring clamp is removed and the lumber moved up until it just touches the fishing line.  Marks are made at the fishing line and at the positions against the stringer.  These three points determine the curve.

With sheet material the three points determining a curve can be laid out with protruding nails marking the points.  A batten pressed against the nails can be used to draw the curve.  The lumber was cut to length and left no room for nails.  An alternative method was devised as shown above.  Spacers are glued to the batton ends at a distance matching the work piece's length.  The spacers rest against a straight edge and a clamp bends the batten at the fishing line mark to create a curve.  The batten is aligned with the lumber stringer marks and the c clamp is tightened until the top edge of the lumber is just visible to draw the correct curve.  The curve radius can be adjusted over a range determined by the c clamp tension and the spacer thickness.

 The plans call for three, 3/4" by 1-1/4", stringers to run from this compartment and two additional compartments forward to the bow.  The hatch installed in this compartment requires an additional stringer, this should result in a stiffer deck.

Inside, under the hatch, will be retractable screens to provide shade or to exclude small creatures while allowing air flow.

Decked Out

Completing the sanding on the aft two compartments has led to exciting developments in this area.  Above the mahogany aft deck stringers are fitted and resting on the deck beams.

The aft decks are fitted and attached to the stringers by screws.  Much work remains before the decks are epoxied in place.  The interior surfaces will receive two epoxy coats as well as paint before installation.  The light stringers create a deck that is too springy for my taste.  I'm considering an additional deck beam to better support the longer stringer span.  This led to an attempt to enter a hull and take some under deck measurements.  I placed a piece of lumber under the skeg so my weight would not over tax the hull rotation arrangement suspending the hull from the ceiling.  I climbed onto to a chair and placed one foot into the hull.  This quickly proved to be a less than wise idea as the hull started to rotate with my foot pressure.  A stupid accident story was averted.  Any additional deck beams will have to wait until the hulls are resting on cradles.  

Above is a view through two compartments forward of the dark aft bunk compartment.  These two compartments have the bulkheads tabbed to the hull panels with fiberglassed fillets.  Epoxy fillets are also applied on top of the stringers and along the sides of the butt blocks and backing pads.  The fillets on stringer tops will prevent condensation and debris from collecting in the lower hull panel end grain.  The butt block and backing pad fillets are just to give the hull a more finished appearance.  The above image shows the finished fillets and fiberglassed areas after three days of sanding.  Three days of sanding are ahead to bring the second hull to this state of completion.

Much of my time is spent sanding so I'm doing what I can to make it easier on myself.  I've made two radiused sanding tools to shape raw fillets and a small sanding block for flattening areas.  A piece of neoprene foam conforms to many shapes when wrapped in sand paper.  I've stock piled sandpaper cut to fit the various tools.  Initially the sandpaper was attached with hot glue, but this was not satisfactory and it took a while to change the sandpaper.  Staples are now used to attach the sandpaper.  A groove is cut under the areas where the staples are applied.  This arrangement keeps the staples below the sandpaper surface and prevents the staples from scaring the work.

Possibly my readers find all this talk of sanding tiring, I find it makes my fingers sore.  I've taken to wrapping my finger tips in tape so the bones don't start poking through.  Above is a fiberglassed fillet in the finishing process.  The area below my hand has been finished, the fiberglass edge is blended to the adjacent material while the surfaces are flattened and abraded for the painting to come.  A newly fiberglassed edge is lumpy with sharp skin tearing points that must be removed.  Great pressure and fine control are possible using the sanding block's smallest face to knock down the fiberglass edge.  The block is held at a slight angle to taper the fiberglass edge and blend it in.  Above my hand is an edge beginning in the tapering process.

With a few days of sanding I will have over half of the boat's compartments "finished".  The compartments ahead will be come more involved with designing and fitting two hatches in each hull.  It is likely only be a break from sanding rather than an end to sanding.