A 1/13th scale model of a sail boat

A 1/13th scale model of a Stevenson Weekender

Tallulah is a "metric inch" model of the "Weekender" built from the actual full size plans purchased fromStevenson Projects

I decided to make a study model of the Weekender before building the full sized boat.  The study model quickly evolved into a remote control pond yacht, which is what you see here. 

Metric Inch Scale

Tallulah was built to a funky "metric-inch" scale using the 50:1 side of a three-sided metric architectural rule and reading the decimeter markings as if they were inches.  The resulting model is about 1/13th scale, which works out to be almost 18 inches in length for the 19 ft long Weekender.  

19ft * 12in/ft * 1in/2.54cm * 10/1 (dm as in) * 1/50scale = 17.95in

( 17.95in / 19ft ) / 12in/ft = 1/12.7scale  ~ 1/13th

Why the funky scale?  The dimensions on the Weekender plans are given in inches and fractions of inches, not the feet, inches, and fractions usually marked on an English architectural rule.  Using a Metric rule eliminates converting measurements given in lots-of-inches to feet and inches.  For instance, the 154 & 3/8ths inches of length along the top of the keel reads directly off the 50:1 metric decimeter scale as 154.375 decimeters.  No mind-bending error-prone mental gymnastics are required to find the correct mark.  By comparison, 154 & 3/8ths inches would be 12 feet, 10 & 3/8ths inches on a 1/12 scale English rule. 

Construction

The hull was constructed from 1/16th 3-ply and 5/32nds 5-ply aircraft grade birch plywood obtained from Al's Hobbies in Elmhurst, Illinois.  The lofting lines were laid out directly on the plywood exactly as described in the full-sized Weekender plans with centerlines, perpendicular station lines at scale 12 inch intervals, and offsets marked out from the center line along each station line.  Push pins substituted for nails at the offset marks, and a 24 inch long 1/16th square strip of balsa served as a limber batten to fair the lines.  Obviously, no splicing of plywood panels was required on the model as the entire hull was cut from a single scale 14ft by 20ft sheet of plywood, which can be seen in the first photo at the top of this page.  

Very flexible 1/16th thick birch plywood was used for the hull sides.  It bent around the curve of the hull so easily that the surface tension of the glue was enough to hold it in place.  Unfortunatly, it was a little too thin, and flexed under light finger pressure while handling the hull.  So a second layer of birch plywood was laminated over the first, and short frames installed inside the hull to stiffen up the sides. 

The cabin roof was constructed as a sandwich, with curved deck beams glued to a flat bottom base.  After theses photos were taken, two layers of the 1/16th birch plywood were laminated to the top of the deck beams.  The resulting laminated top is lightweight and very stiff, and snaps into place on top of the cabin sides. 

The mast, spars, bits, deadeyes, transom, rub rails, hatches, grab rails, cockpit combings, ship's wheel, rudder, taft rail, boom crutch, and display stand were all fabricated from mahogany stick and sheet stock manufactured by Midwest, again purchased from Al's Hobbies.  The companionway hatch slides on waxed rails and locks onto the drop board, and the front hatch snaps tightly onto its combings to keep the interior dry while on the water.  

Eyes were carved into the mahogany trail boards and painted to give the boat some personality; reminiscent of Jason's Argo.  

All of the mohogany bright work was finished with marine spar varnish.  No stains were used on the mohogany so the colors that you see are the natural colors of the wood.  The hull was masked off and spray painted in enamel (Rustoleum American Accents if my memory is correct.)  The colors were Hunter Green for the bottom and Heirloom White for the between-the-rub-rails topsides strip, cabin and deck surfaces.  No attempt was made to replicate the non-skid surfaces of the real boat.  

Tallulah's mahogany cradle was made to similar proportions as the stand that comes with the paper model of the Weekender.  The construction method was inspired by a trestle table with a tenonned main cross beam supporting mortised uprights, and the whole shebang held together with a pair of wedges through the tenons.  Self stick felt on the upper and lower surfaces of the cradle preserves the finish on the boat and the coffee table. 

The green mat forming the background in most of the photos is one of the wife's self-healing sewing/cutting mats manufactured by Olfa, which is conveniently marked in a one inch square grid.  This is a great surface to cut small parts on using a hobby knife as the plastic is just grippy enough to prevent the parts from moving.  

R/C Conversion

About half way through the construction, I decided there was enough room in the hull for radio control via standard sized servos.  So I fitted the hull with three servos for controlling the rudder, main sheet, and jib sheet.  The sail trim servos were modified with external trim-potentiometers to increase the control arm travel from 120 degrees to a full 180 degrees of throw.  To produce the greatest mechanical advantage and reduce servo current draw, the sheets were arranged to lead off the servo arm in-line with the arm axis at the fully trimmed and fully eased sail positions. 

The steering cable was fashioned from fishing line running in a stiff nylon sleeve (from an airplane control rod) to form a cable guide ala bicycle brake cables.  Warming the nylon sleeve with a heat gun or boiling the sleeve in water softens the thermoplastic nylon enough to allow permanent reshaping.  The pull-pull steering cable leads from the servo arm athwart-ship to the port cable guide where it is turned 90 degrees to run under the port cockpit seats, and into the lazarette, where it is turned another 90 degrees, leaves the guide, and is secured to the end of the tiller.  The cable then continues on to the starboard side to complete the circle back to the servo arm through a mirror image cable guide.  

The mahogany rudder box turns on gudgeons and pintles made from a nylon aircraft hinge with a removable hinge pin.  The rudder blade pivots just like on the real Weekender to avoid damage during an accidental grounding.  

Sails and Rigging

The sails were sown up from individual panels of nylon cloth with stiched-together seams.  The main sail has a yacht-cut seam pattern with the panel seams arranged perpendicular to the leach.  A miter cut stay sail, with seams perpendicular to the leach and foot, fills the foretriangle. 

The nylon cloth used for the sails came embossed with a fine square grid pattern, which made measuring and cutting the panels a snap, and helped tremendously in tapering the seams to give proper draft to the sails.  The seams were assembled as simple S-fold lap joints with the inside of the seam overlap painted with diluted Elmer's white glue.  Hitting the seam with a warm iron set the thinned glue, which held the cloth together for sewing.  The diluted glue in the seams also performed like starch, giving mild stiffness to the finished sails for when Tallulah sits on display upon the mantle in the family room. 

Stays, sheets and halyards are made of a manila colored extra heavy three strand cotton yarn from the embroidery section of the local fabric store.   The running rigging turns through brass blocks manufactured by Proctor Enterprises.  

Launch day!

Here we find Tallulah sitting in her cradle on the boat ramp of Lake Cosman awaiting her first taste of the big water.  

I was a little concerned that due to the placement of the servos, receiver, and the battery pack in the forward two thirds of the hull, Tallulah would sit in the water nose-down, and not level.  This turned out to be the case.  I hoped that at worse the extra wetted surface under the bow should induce a little more weather helm. 

My original plan was to adjust her trim with some lead ballast on the rear of the cockpit floor, but she had so little freeboard that I decided to just sail her as is.  At launching time, I guessed that I would eventually have to cut the four cell battery apart and place two cells under each of the cockpit seats.  

The radio control worked well, and I was able to easily sail Tallulah around in figures of eights.  I arranged the controls with the rudder on the right stick (left & right) and the sheets on the left stick (Main sheet left & right, Jib sheet up & down).  The left stick was set up so that both sheets trim in with the stick in the lower left corner and trim out with the stick in the upper right corner. 

Tacking was a breeze, and most likely helped by the extreme weather helm induced by the nose-down trim, which is clearly visible in these photos.  Tacking was also eased by the ability to ease the Jib sheet independantly from the Main, which helps the boat weather-vane quickly into the wind.  Pushing the left stick forward to slacken the Jib sheet and right stick over hard to swing the rudder starts the turn.  As the bow swings through the wind, pulling the left stick back retrims the Jib for the new course.  

Shortly after these photos were taken, the wind picked up considerably, and Tallulah suffered a knockdown from which she did not recover.  Apparently, some things do not scale well.  The rig on the model is proportionally much heavier compared to the weight of the hull than on the full size boat, which plays havoc with the righting moment of the boat.  I suspect her stability curve looks more like a sine wave with negative stability starting in shortly after 90 degrees of heel.  Also, judging from her load-waterline displacement, the boat is carrying about 4000 scale pounds of gear in the form of batteries and servos located very high up in the hull.  While she did not turn turtle, she could not break the suction formed when the water touch the sail cloth.  As a concession to stability, for the next sail, I intend to remake the battery pack into a long cylinder and mount it externally down low underneath the keel just in front of the rudder, which should increase the hull's righting moment and simultaneously help with the nose-down trim. 

If anybody else wants to try an RC Weekender, I would suggest doubling the size of the model and executing the lofting in 1/6th scale, or use the 25:1 side of the metric rule for 1/6.35th scale.  Doubling the length, width, and depth increases the displacement of the model hull by a factor of eight, so that 4000 scale pounds of radio gear should reduce to about 500 scale pounds, which is a much more realistic load for a Weekender hull.  The resulting larger sized hull should allow the servos to be mounted on their sides, which will lower their center of gravity significantly and improve the stability of the model.  The expanded hull would also leave room for installing a small six volt airplane fuel pump to be controlled with a fourth RC channel via a proportional electric speed controller.  Connecting the input side of the pump to a tube drilled forward and downward through the center of the keel, and the output side to a tube drilled downward and backward through the keel to exit a little in front of the rudder, will result in a mini jet-drive to allow maneuvering thrust should the wind fail altogether.  

Folding Rig

Finally we come to one of the operational features of the full-scale Weekender that I find very appealing.  Setup and tear-down time for the hinged-mast gaff rig is measured in seconds, not fractions of hours.  Loosening the turnbuckle on the forestay allows the mast to fold down and backwards into a boom cradle for the ride home.  Of course for the full scale Weekender, the sails have to be lowered until the gaff jaws clear the mast tabernacle before the forestay can be unhooked and the mast laid back.  But on the model, we only have to loosen the staysail halyard and untwist the forestay turnbuckle to stow the mast.  

Very cool. 

This last photo was stolen from the Stevenson Projects web site and shows Mike setting up the mast on the full scale Weekender.  Click (here) to go to theStevenson Projects Pocket Yachts page.  I have watched skippers at the local boat ramp waste most of an hour setting up similar sized rigs. With the full sized Weekender, I expect to be in the water and sailing in less than 15 minutes.

My appologies for the execution of the photography, as it is not my best work.  I was shooting the pictures with a Minolta 400si on a mini tripod located on a sloping concrete boat ramp and did not notice that the horizon is not always level in the outdoor shots.  I guess the excitement of launch day was not proportional to the scale of the model !!!