Planking the Guideboat

The hull bottom is now sheathed in 4.8mm Okoume plywood.  It provides a nice continuous covering which distributes stresses evenly.  It didn't bend exactly the in the manner I hoped for, but I'll go back with some fairing putty to improve that.  I learned that the best way to created a tight junction with the plank keel when bonding the ply in place was to use #4 x1/2" flat head wood screws as temporary fasteners.  I tried using staples but they didn't have enough holding power.  I also tried using clamps, but couldn't get the proper leverage/clamp placement at the keel.

Sheathing the bottom in three sections; nice to have plenty of clamps.  The keel joint is temporarily fastened with small flathead screws.  I had no problem removing them after the epoxy set.  In the center section, the screws were spaced every 12 inches; at the ends, the spacing was every 3 inches.

Significant curvature in the hull ends.  Need to do some fairing of the sheathing and put an external cap on the hull end ply junction.

With the hull bottom sheathed, I now need to finalize how to plank the topsides.  I am thinking to use 5mm thick solid planks, carvel style, narrow widths, with one or two staggered scarf joints per plank.  But that could change.  I have some planking material on hand, but not enough to finish anything; need to find enough stock lumber to finish it before I get committed.

Garboard sheathing

Using a router with guides, a notched "shelf" has been cut along the edges of the keel to accept the edge of the anticipated garboard.  This will provide backing and bonding surface during assembly.

Creating a rosin paper pattern for the garboard stem ends.  The garboard will be sheathed in three sections (ends and a center piece) of 4.8mm plywood connected by butt blocks.

A simple basin, plastic over 2x4s, has been created to soak the plywood for several hours prior to clamping it in place on the hull frame. A few small objects keep the wood off the bottom of the basin and bricks keep it from floating.

When wet, the plywood is flexible enough to clamp in place without using excessive force.  It will be allowed to dry for a few days (while I work at the clinic) before the clamps are removed, and it is checked and trimmed further.

What I am discovering is that the plywood is not bending according to the designed developable parallel projection.  Instead, the plywood is bending according to an alternate projection which induces lower stresses.  By finding some of the ruling lines (where a straight rule will lie flush with the surface), it appears that the alternate projection is a conic projection with the focus below the keel and about two feet back from the stem. I have not encountered this before.  Perhaps this is part of the concept of "tortured plywood" as described in the Gougeon text.  Long, slender plywood forms will seek to relieve stress when possible by adopting an alternate shape.

This is occurring only near the bow ends where maximum curvature is expected.  When a sheet of thin, flat, flexible, sheet of clear plastic is wrapped around the bow section, it follows the designed developable shape perfectly and lays snugly against the frames as designed.  The more rigid (but slightly distorted) plywood relieves internal stresses and takes on a flatter profile; resisting conformation to the designed shape.  So I am forced into iterations of fitting the ply and reshaping the frames and bow profile taper to accept the altered plywood shape, a time-consuming and exacting process with an inferior result.  Lesson learned: when a lower stress conformation is available, the plywood will adopt it.  But how to anticipate such an occurrence?

The best way to examine this occurrence will be to bend ply around a surface where only the edges are defined and then see what type of curvatures are present at the frame intersections; a future project.

 Future project completed:  I constructed a replica of the forward frames and used stiff cardboard to simulate the sheathing.  The cardboard (like the flexible plastic) exactly conformed to the original frame shapes.  This convinces me that the plywood, by being reduced to only four laminations, may not have a balanced strain pattern when stressed and, thus, not react/bend in a predictable pattern.  If I build a similar hull in the future, I think solid planking, 1.5" to 2" wide and 5.5mm to 6mm thick will work well.

   

A Viking Ship Museum, plus fairing the hull of my new boat

While overseas recently, we visited the Viking Ship Museum and workshop at Roskilde, Denmark.  What a neat place!  They have a museum containing the remains of five Viking ships from about a thousand years ago which were carefully excavated and preserved.  A display illustrating Viking history during the ascendant period is also included.  They also have a workshop in which new Viking vessels are being constructed using the same materials, tools and techniques as the originals.  Rides in these authentic vessels are offered out on the bay using both sail and oars.  Lastly, is the book store providing reference materials, and souvenirs.

Ancient Viking vessel preserved in the climate-controlled museum.

New Viking ship being constructed on site.

Plenty of enthusiastic boaters ready to go out on the bay in their Viking ship.

Reproduction of a Viking warship.  The merchant ships are wider, deeper, with less rowing stations.

This authentic Viking hull, about 100 feet long, is getting some needed maintenance.

Roskilde is a short train ride from Copenhagen's main train terminal; a nice excursion from the central city.  You can walk from the Roskilde train terminal to the museum:  Walk through the pedestrian shopping area (on your right as you arrive) toward the tall cathedral steeple, then walk down the hill, through a park to the museum on the bay.

Back to my own efforts at home:

Fairing started at the ends of the hull.  Because I had used a parallel projections to create the hull, all ruling lines are parallel.  For the garboard the x/y/z projection is 12/4.8/1.6 (12" spacing of frames) which I could mark in pencil on consecutive frames and then use an angle grinder (needed aggressive abrasive cutting) to remove excess material, stopping to check my work by laying a straight edge at the angle of the ruling lines.  With the closely spaced frames, stringers and stem profiles as guides, this fairing was not too difficult.

Fairing of the bow area; a batten has been laid in place to demonstrate the direction of one of the ruling lines.  If the projection in this area is conic instead of parallel, the ruling lines can still be plotted (using the intersections at the keel and frames), but may be more time consuming.

Next to do was fairing of the frames and stringers.  This is fine work, more appropriately done with a plane in most areas.  Because the dimensional changes at this point are minor, I could start making patterns for the future hull sheathing.  The garboard pattern is widest of the projected chine areas and curves downward toward the hull ends; thus, plywood will likely be the best material to use.  I have several sheets of 6mm (5 ply) occume plywood on hand.  It is slightly too stiff for the stem curvature, but I have discovered that I can run it through my planer and make it into 4.8mm, 4 ply, which will take the curvature.  You couldn't do that with non-marine ply because of its inferior inner plys, but for marine plywood the inner plys are also high quality.

I am still looking at options for planking material for the other chines and need to make some decisions before proceeding further. 

Defining the shape

While notches for the stringers were pre-cut in the frames and stems, many of those cuts need to be modified.  The notches were "square-cut" as if the stringers simply passed through at right angles, but, except at amidships, the stringers curve inward and upward as they approach the stems.  So the notches need be be beveled to accept the stringers in a fair curve; a total of 120 notches.  It slows down the process, but provides good exercise as it needs to be done carefully by hand.

It has been said that using developable techniques to design boats tends to result in boxy-looking, uninteresting shapes.  But by using multiple chines, and the inherent accuracy and fairness of the resulting curves, I think that the result can be quite harmonious.

Two longitudinals added so far; two more to go.  I will also add a second strip at the sheer, the inwale.  Beginning to look boat-like, but much work lies ahead.

The inwale and a third stringer have been added.  I have an epoxy allergy (rash), so before mixing a batch, I put every clamp near by, set out the spatula, the applicator, pre-mark every matching location, clear out unneeded objects, put on gloves, etc.  With many small joints to bond, I pre-coat matching surfaces and give the epoxy time to soak in before assembly.  After assembly comes cleanup of any excess squeezing out of the joints.  Thin coats of small quantities cause little exothermic reaction, so the resin takes many hours to harden.  If I warmed my shop up beyond 66 degrees F., of course, the setting would be quicker.

The overall length at this point is 179.5".  The curved length of the sheer is 187.04"  The half angle of the bow is 21.8 degrees.  I used an algebraic equation and projections to provide all the offsets for the hull shape.  I integrated that formula (calculus) to find the curved length of the sheer at each frame & stem location.  I differentiated (again calculus) that formula to find the slope at selected points.  Then I used the inverse tangent function (trigonometry) to find the angle in degrees to set my chop saw.

People say, "Math isn't important; I never use it."  Of course, you don't use things that you have little knowledge of.  I have little use for knitting; perhaps it is because I know nothing about it.  The math I just mentioned is not difficult if you are accustomed to doing such things.

Next to-do is fairing the hull.  Not real fun to do; it is careful work in which the progress is not dramatically evident.  But, it is the foundation for what comes next: making patterns for the sheathing.  Will the shape be nice and linear or have a banana or "S" shape?  I still have not made a final decision on sheathing.  Each alternative has its advantages and limitations.

We are readying for a month-long trip overseas; there may not be much progress in the near future.

Creating the Skeleton of a Boat Hull

My guide boat design is symmetrical at both ends.  It makes for simplicity in building and results in needing only one oarlock location.  Calculating the location of each frame along the sheer curve is best done by measuring from the midpoint toward both ends.  (For reference, the equation used is listed in my blog post of Feb. 11, 2015, Sail Design)

X-dimension at keel:  5.75    17.75    29.75    41.75    53.75    65.75    71.75    83.75    89.75  
Sheer dimension:       5.78    17.85    29.91    42.19    54.67    67.43    73.92    86.99    93.52  (inches)

Most of the frames are set in place on the keel in this photo.  This was just practice to see if everything fit as planned.  The keel sits on paint buckets and most frames are held in place with bungee cords.

If you look closely you can see some wood wedges under the paint buckets.  The keel has been checked for straightness and twist and two battens, marked for sheer lengths, have been clamped in place.  The frames have been mated to the keel with epoxy.  This entire setup is somewhat self-aligning.  I used a square to check that the frames are vertical; no adjustment was required.  If this simple set up didn't do the job, I would have been forced to create an entire strongback to force alignment.

These are the two stems mated with the end frames using epoxy.  The next step will be to bond these stems and the final two frames in place on the keel.  With ten frames already in place, and clamped sheer battens marked for the proper lengths, it shouldn't be difficult to get these bonded in the proper positions.  Then, three more battens/stringers will be added to each side.  At that point it should look rather boat-like.  Two future steps where I anticipate difficulty (time consuming) are fairing the hull and fitting the garboards. 

The hull is starting to come together.  You never have too many clamps for boat building.

It looks much like a wide canoe, but the 44" beam will allow the use of oars.  The 18 degree deadrise creates a narrow waterline width while allowing a low seating position.

The stem pieces came together perfectly using the calculated half-angle of 21.8 degrees and the half length for the curved sheer stringer of 93.52".

Starting to cut wood.

You may not believe it, but I am making progress on the new boat.  It has been slow, because the boat is just my spare time project.  It is ski season; it is tax season; and there is snow to be shoveled as well as the usual life's tasks.  The frames will be built up from sections of solid wood, lapped and bonded; like putting together a jig saw puzzle.  I am not one to show every little detail, because I doubt that my methods are any better than most who are interested in building boats.  So, I'll start taking pictures when I have real completed frames and keel to show.

If I were going to build more than one boat, I would probably use particle board molds to define the shape and then install laminated ribs after planking was completed.

When you build a boat of your own design, there is no simple checking of plans to see what to do next.  Each step is being done for the first time.  So progress is a sequence of asking yourself, "How am I going to build that?  What material? In what dimensions?  What technique?  How will that affect subsequent steps?"  The challenge and risk keeps the build interesting.

A good day for working in the shop; new snow and a high of 17 degrees F.  We are having a snowy winter; in Colorado you never complain about moisture in any form; it is always needed.

Step 1:  Using the listed dimensions on the previous entry, plot out all the points to define the seven different exterior frame shapes and the two stems.  I use rosin paper because it is has the size and rigidity desired (although I recently became aware of a new product "Ram Board" which is even smoother and slightly more rigid).  Decide the desired thickness of frame members, and draw the interior shape of the frames and stems.  Calculate the board feet of lumber needed and buy it.  (1 3/4" by 1/2" cross section looked about right for frames; I used 1 1/2" by 3 1/2" for the stems.)

Step 2:  Find and buy the keel plank.  This needs to be a nice clear and straight piece, at least 7 1/4" wide and 12' long (or you can scarf it).  Layout a center line and transverse lines for the frames every 12" except for the middle of the board where the spacing should be 11 1/2".  All frames (1/2" thick) will be positioned on the tapered side of the transverse lines.  Thus, the actual spacing between frames will be 11 1/2" except in the center it would be 12" if we didn't make this 1/2" reduction.  You can rough cut the taper at both ends of this keel plank, but leave a little extra for the final fitting.

Step 3:  Using the full-size rosin paper drawings, trace each frame component onto your wood.  Then shape each frame component.  I use a table saw for straight cuts, a band saw for curves and a router for laps (joints are half thickness lapped, although gussets would work also).

The 1/2" thick frame member is surrounded by 1/2" thick plywood to provide support for the router base when trimming the half-thickness lapped ends.

Step 4:  Lay out the rosin paper drawings of a flat surface.  Cover them with painters' plastic (very thin and transparent) to prevent resin adhesion.  Mix a bonding consistency epoxy; coat the lapped joint pieces; and place them in the desired pattern.  Repeat this twice because you will need fourteen frames and two stems total.

The stem pieces are doweled and bonded together. The half-angle of the plumb bow is 21.8 degrees which I pre-cut.  The curved portion will have a changing angle, transitioning to an 18.4 degree deadrise which I will trim as a part of fairing.

Step 5:  After the epoxy sets, clean up the resin runs and blebs on the frames.  Time to add some detail to the frames and stems.  I will use a batten/stringer at sheer and each of the three chines and need to mark and cut notches to receive each of these longitudinal members.

Step 6:  Before assembling all these pieces, a method is required to precisely position all the frames-stems-keel.  I could build a strongback with supports to hold each frame in vertical, lateral, and fore & aft alignment; however, there is a simpler method.  Because this hull form was designed mathematically, the sheer is a mathematical curve described by an equation.  Because I use forms of this equation frequently in my boat designs, many years ago I used the calculus learned as part of my engineering training to integrate the equation.  The result is a usable but more complex equation which, by entering X-Y-Z values, can be used to calculate the length of that curve to all frame locations.