Starting again: Another guide boat

What if I shorten my guide boat design to 14' to make it easier to transport?  What if I widen the plank keel slightly to make it more stable?  Should I increase the freeboard?  Can we reduce the weight?  Wouldn't it be neat to use all dimensional lumber with no plywood?  Perhaps I can finish it clear.  I want to use a new and stiffer material, "Ramboard", for making patterns; it should be more accurate.  So many reasons to build another boat; none of which have to do with actually using the boat.

For me, designing and building a boat is the equivalent of an artist starting a new painting. What artist only paints a few paintings?  Each painting expresses a separate vision.  Creativity proves we have control over at least part of our lives.  And with the demanding dimensions required in a boat, there is the mental challenge.  And so it begins.

The bow profile built from two scraps of 2x4 Douglas fir.  I built two of these, and they will require further modification for the changing bevel along the lower edge.  I have also roughed out the plank keel, the edge of which will also need to be modified to accept the garboard plank.

This shows a double stack, 12 frames. Two more frames need to be built; both will be bonded to the bow profiles.  Then I can start putting things together.  Of course, these frames will require further modification; notches for the stringers and sheer and further finishing.  They are half-lapped and bonded with epoxy.  Built from lumber left over from other projects; you can notice the varying grain.

The bow profiles have been bonded to the first frames.  Next, these assemblies will be bonded to the keel as the sheer is installed.  The chine and sheer curve lengths and stations have been calculated and, when installed, will force other frames into alignment; thus, eliminating the need for a strongback.

Frames trial-mounted on keel for an initial view.  The frames need to have notches cut for the sheer and two stringers before final assembly.  It is snowing outside with below zero temperatures; a great time for a project like this.

Making progress.  All the frames are in place and the sheer is in place, as well as two strakes.  Note that no strongback was required.  The measurement along the sheer for each frame has been calculated; thus, each frame can only be positioned at one exact place.

This hull will be one foot shorter that the completed hull nearby but with a wider plank keel.  Why am I building two boats so similar?  I have some new planking stock to try out; I have new pattern-making material (Ramboard) to try; and I think the shorter length may be easier to transport.  I have also planed the plank keel down to a thickness of 0.4 inches to reduce weight. 

I used an angle grinder (40 grit) to bevel the stems when fairing the overall hull frame.  All ruling lines are calculated and parallel, which made it easier to visualize the  required angles.

The edge of the plank keel has been routed to create a solid landing for the first plank.  At the ends, the plank edge is curved with a constantly changing angle.  This needed to be done carefully.

Carefully fitting 2 inch wide by 0.21-0.24 inch thick planks (not quite quarter inch).  I picked two inch wide planking because that is the thickest wood my table saw will willingly cut, and that is the widest that many of my clamps will span.  No fasteners used; only epoxy adhesive.  The planks are falling into alignment quite nicely; much better than when I used plywood.  To get the length I need, I am scarfing together shorter lengths using a 7 degree bevel on my chop saw.  Perfect results using a simple jig, and it only takes seconds.

Using real planks have given me insight into the design of the original Guideboats.  Upswept sheer in the ends of the boat facilitates easier planking.  The greater length of curve from keel to sheer spreads out the bending stresses and provides a better landing for plank ends.  That end curve had to be a conic projection in order to fulfill all requirements, although the first builders I am sure were not thinking of mathematics but instead just ease of planking.

I am enjoying the nice fair curves that the planks follow.  Relying solely on epoxy adhesive means that I have to let the bonds mature on each plank before I start the next row.  Slow, but I am not in a hurry. 

With this triple chine design, the hull shape appears to be that of a nicely rounded hull form.  Very pleasing.  If I had used narrower planks, as in strip planking, the curvature would be even smoother.  
  

                        First coat of paint

                            Second coat of paint

I had a quart of red on hand, so that is the color.  It will need three coats.  Then I get back to finishing the trim, the stem decks, and interior.  I built two oars recently which will need varnish as well.

Close to completed; all it requires is a few more coats of varnish.  I really like the carrying handles placed on the stem decks.  They are bonded securely and allow convenient carrying or the securing of lines.  All I started with were two scraps of 2x4; initially shaped with saw cuts, then a belt sander, and finally fine sandpaper.

Next to make are the removable seats.

You should know that I have already shaped the keel for a planned next boat.  It will be slightly wider with a wineglass-shaped stern.  Trying to decide if I should include features for sailing.

Finishing Up the Guide Boat

    New oars on the left; old oars on the right.

My latest guide boat is essentially finished; just adding varnish.  I also built a new pair of oars for the new boat.  Using published formulas for proper oar length, standard oars would be about 80 inches long according to the boat beam, but I also read a note, "Guide boat oars are usually 7 1/2 or 8 feet long."  I have a fairly large stack of scrap wood which I need to use.  From the scrap pile, I found some nice straight pieces to bond together creating 92-inch long oars with the inboard ends left with a chunky square profile to help counter balance the somewhat longish outboard shafts and blades.  I am not going to go into oar construction because there are already plenty of Google instructions posted.

Taken on the US Air Force Academy.  We are still discovering more trails in the Colorado Springs area; although we also took the bikes to Arkansas and Montana this summer.  They are a great source of exercise and fresh air away from crowds of people (and COVID).  Building boats is more enjoyable when the weather turns cold.

I want to apologize for the slow progress in recent months.  Progress has been slow to non-existent during the better weather of Summer and Fall because my wife and my own infatuation with the new e-bikes we purchased.  With the mountain e-bikes we feel confident to go further and steeper on our outings than we would with regular bikes.  It has been a godsend letting us travel forest trails with fresh air, ample exercise, and no crowds.

The hull ends are symmetrical and the oarlocks are set about a foot ahead of the hull midpoint. When rowing with two people onboard, the rower sits ahead of the oars.  When rowing solo, the rower sits at the hull midpoint facing the other direction.

    Seat positioned amidships for a solo rower.  Yes, it is snowing outside.

Now that winter is here, I'll be looking for a project in my wood shop to keep me busy.  Still working at the clinic, but only 2-3 days per week.  My present thought is to build another guide boat using what I have learned building this one.  Always trying something new; I anticipate using a 14' length (more easily cartop-able) and a wider plank keel. I was able to buy a length of flat lumber 12'2" long and 10.3" wide. I'll see how the wider keel changes the hull stability. 

Finishing the planking

I put off making choices for planking.  Previously I have always used a plywood initial sheathing to define the surface shape and provide a substructure for bonding exterior thin planks; it works well with developable surfaces.  I had some marine plywood on hand.  Also had some  mahogany planks left over from my last build, but there was a reason they were left over.  The planks had flaws; they were the rejects.  This new boat is somewhat of an experiment; didn't want to invest too much in materials; so I used those rejects.  And I have been reminded how important it is to keep focused and not compromise at any step.  Later on it catches up with you.

Now I am doing extra sanding and using fairing putty to make up for those inferior materials used.  Next time I will spend more time and money to produce high quality planking at the very beginning.  Even the garboard would be better with solid planking than the altered four-ply plywood I used.  I would also omit two of the intermediate stringers in the frame work; they have not added much to define the build.  A stringer at the initial chine and at the sheer would be enough framework. 

 

Getting to the final touches.  Need to finish all the trim, build some seating, and create oars.  I painted the interior because the planking is not uniform; thus, not all that visually appealing.

Creating a Developable Surface

This has nothing to do with any computer program and its underlying algorithms; instead, let's consider basic geometry, some algebra, a touch of trigonometry, and perhaps some optional calculus.  Developable surfaces cannot include curvature in multiple directions at a single point.  A straight line must pass through any point on such a surface; these are called "ruling lines".  A unique line can be defined by either two distinct points in space, or one point and a defined slope.  Surfaces can be created by projection from points: parallel in two dimensions (flat), parallel in three dimensions (think of a cylinder), or conic- radiating from a single point which I will call the focus or focal point (FP).  Multiple projections can be connected to create a fair surface as long as those projections are linked by common ruling lines.

 In this sketch of the topsides of a previous boat, I used four projections. I used a parallel entry for only a short distance.  Then I switched to a conic projection (using a common ruling line) to create a flaring bow.  Next, I moved to a different conic projection for a transition to stern tumblehome.  Finally, a parallel projection was used to finish the tumblehome.  You can see how projections are combined, using common ruling lines, to create varied surfaces and the desired shape.  All projections were done from defined coordinates along the chine or extensions of the chine.

First, let's concentrate on ruling lines.  On a segment of any line between two points in an X-Y-Z-defined space, the change in X is proportional to the change in Y and the change in Z according to the slope of the line.  The slope can be calculated as (X1-X2)/(Y1-Y2)/(Z1-Z2) if we know the coordinates of two points on the line.  We can calculate the coordinates of another point (or multiple points) on that line (X3,Y3,Z3) using (X1,Y1,Z1), the calculated slope, and any one of the X,Y,or Z coordinates for point 3.  Let's assume we know X3, then the formula for Y3 would be the following:

Y3= Y1-(X1-X3)(Y1-Y2)/X1-X2)
Z3= Z1+ (X1-X3)(Z1-Z3)/(X1-X3)

In words, the change in Y is proportional to the change in X, and that change is then subtracted (or added, depending on direction) from the initial Y value.

Here comes the big concept which makes this whole system work:  In order to make this work, we need some defined points in virtual space to start describing our desired surface.  We can't just draw a line on paper and say that this defines one edge of our surface.  We need numerically exact discrete points.  A mathematically defined curve provides the solution.  I generally use a form of trajectory curve, also called a parabolic curve, for this purpose.  An example below:

Y=14.4-(72-X3)squared (14.4) /5184          (5184=72 squared)

Z= 4.8+(72-X3)squared (5.76)/5184

The X-Y slope at any point =2(14.4-Y3)/(72-X3) where X is measured from the bow and Y from the midline

If you integrate the curve (which I will not do here), you can calculate the length of the curve or a section of it.  I actually did the integration calculations for the hull I am building.  It eliminated the need for a strongback frame as the parts were self-aligning. 

Using these particular curves, I insert values of X3=66,60,54,48,.... etc. and solve for Y and Z values at each of these X intercepts.  This provides a table of exact coordinates, spaced every six inches along a chine curve.  I could calculate values every three inches if needed, but the extra accuracy is unneeded.

Let's say I am designing a guide boat with a frame every 12 inches (which I did).  We have the chine; what should the bottom look like?  Displacement, stability, and construction considerations help decide this.  I decided on a midships deadrise slope of  1:3 and a plank keel 7.2 inches wide (can use standard 1x8 lumber).  Now for the projection.....

By setting Y=0  (width=0), we can solve for X and Z (length and height) and plot the bow profile.  Note that as the focal point (FP) is located nearer to the surface being described, the resulting projected curvature increases.  This is generally true.  Note also that the ratio of Y to Z at the FP is the same as the midships deadrise, z/y=1:3.  This has to be true to create a common ruling line.  Shifting the X coordinate fore or aft also affects the slope.  If the corresponding X coordinate matches the stem half angle (defined as Y/X), it will create a plumb bow.  (Y/Z ratio is fixed by the midships deadrise ratio.)    

By setting Z=1.2, we can solve for X and Y (length and width) and create the plank keel profile with a width of 7.2 inches.  Using a conic projection results in a longer keel with slightly more abrupt entry profile.  

We have a choice of projections for creating the frames at X=,12,24,36, etc.  This drawing was created using a projected parallel profile, X:Y:Z= 6:2.4:0.8.

These frame profiles were created using a conic projection.  The FP is located at (-20,-9,-3).  Recent experience suggests that the conic projection may be superior in this application; it depends on what characteristics you value most.  A conic projection appears to shift some of the surface curvature near the stem from the Y-Z plane to the X-Y plane.  At least that is my current best guess.  The parallel projection creates a more aesthetic bow profile curvature, but a shorter waterline length.

Posted to answer a question asked:

 

Demonstrating the alignment of frames using the plank keel, and the calculated length chine and sheer as references.  These pieces will only fit together in one relationship when aligned.  No strongback needed.

Because this hull is designed as a developable surface, compound curvatures are avoided when planking.  By using a triple chine design (not including the plank keel edge), plus narrow planking (2" wide), the result closely simulates a rounded, non-developable shape.

   

Solving the hull sheathing conformation

Spring is here but Pikes Peak still is snow covered.

Wow! Has it been so long since posting previously?  Over six months?  That has been time for three vacation trips and a major bathroom renovation.  It is nice to stay busy.  Now with the pandemic, things have slowed down some, and it's back to the guideboat project.

In the back of my mind has been that failure of the garboard sheathing to conform to my design dimensions.  The plywood when bending aligned itself with a different curvature, lower stress pattern.  Today, I did a simple investigation.  By laying a straight edge (I used a four-foot level) on the hull sheathing and rotating around a tangent point it until the entire edge contacted the surface, I was able to discern some of the actual (approximate) ruling lines inherent in any developable surface.  I had designed the hull bottom to be a parallel projection; the X:Y:Z ratio was 6/2.4/-0.8.  It appears that, instead, the plywood adopted a conic projection toward the hull end.

Ruling lines marked on the sheathing plywood.

I marked some of the ruling lines on the hull surface.  As you sequentially view the ruling lines from midships toward the ends, The first line is consistent with the design slope.  The second line converges with the first line toward the hull midline.  Converging lines indicates a conic focal point in that area.  Subsequent ruling lines at the hull ends only slightly converge but with steepening deadrise (Y/Z slope).  Looking at these lines and viewing the hull surface from various angles suggests to me a conic projection, or several conic projections, with focal points located forward and across the midline (keel).  On my previous guide boat design, I had used a conic projection in that area.  I used a parallel projection on this hull, expecting that it would be superior, and it is for general purposes.

Initial convergence toward the keel of the ruling lines from midships proceeding toward the ends.

Slight convergence with increasing deadrise for marked ruling lines.

I think I have solved this puzzle.  The plywood was thin enough, and with only a four-ply unbalanced stress resistance, to relieve stress by distorting slightly at each of the frames creating an unpredictable conformation with a lower induced-bending-strain pattern; at least in this situation of a long, comparatively slender hull panel.  I will make sure that I never face this situation again.  I want predictability; not repetitive cut and fit construction.          

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.