Rin Tin Twin-
A Tale of Two Dinghys

Materials List and Instructions for Building an Aluminum Two Piece Dinghy

Materials List

1 each	2.0mm x 1200mm x 4800mm 5034-H3 sheet
2 each	2.5mm x 1200mm x 4800mm 5034-H3 sheet
1 each	5.0mm x 125mm x 350 mm 5034-H3 scrap
3 each	2.0mm x 25mm x 5M 6061-T651 square tube extrusion
2 each	3.0mm x 25mm x 5M 6061-T651 equal angle extrusion
2 each	3.0mm x 25mm x 5M 6061-T651 flat strap
7 meters	4mm aluminum wire (used for the 'stitching' of the bottom panels
2 kilos	5325 filler rod
1 each	6mm x 1200mm x 4800mm BB/CC Exterior Glue plywood
1 each	2" x 2" x 20' fir
1 each	1" x 10" x 2" fir plank
1 each	2" x 6" x 6' hardwood
1 each	2" x 4" x 8' fir (construction 'tool' use)
1 box	#10 x ½" Phillips pan head sheet metal screws
1 box	#10 x ¾" Phillips flat head sheet metal screws
1 box	#8 x ½" Phillips pan head sheet metal screws (either cheap steel and pitch when finished or stainless and retain for future projects)
8 each	1/4 -20 x 2" stainless hex head bolts
4 each	1/4 -20 x 3/4 " stainless hex head bolts
2 each	¼-20 x 4" stainless flat head bolts
2 each	¼-20 x 2" stainless steel 'u'-bolts
18 each	¼-20 stainless hex nuts
25 each	¼" stainless flat washers
2 each	7/16" x 1" Stainless hex bolts
1 each	7/16" x 2.5" Stainless hex bolts
10 each	7/16" Stainless Flat washers
3 each	7/16" Stainless hex nuts
1 each	¼-20 x 3' cheap threaded rod (cut in half to use for clamping)
1 each	5/8" x 5" stainless shaft
1 each	4" boat trailer roller, 5/8" mounting hole
4 each	5/8" stainless cotter rings
1 pair	Edge mount oarlocks
1 pair	Small brass hinges
1 pair	Perko cabinet closers
1 each	4" (or thereabouts, I make my own) cleat
4 each	1-½" x 5/8" x 6" refrigeration tubing insulation
1 yard	4 meter wide tarpaulin material
40 feet	#4 purse seiner twine
250 ml	Epoxy glue
1 liter	Epoxy sealant
2 liter	Closed cell pour-in foam kit
1 tube	5200 sealant

Construction Differences from Mr. Greene's Plans
PLEASE NOTE THAT BUILDING THIS DESIGN WITHOUT BUYING THE PLANS FROM Mr. GREENE MAKES YOU A THIEF!!!!
Further, my instructions must be matched to his drawings.
He can be reached at:
Mr. Danny Greene
Off Shore Design Ltd.
PO Box GE213
St. George's
Bermuda GE BX

1.	You can choose to layout the aluminum pieces on either cheap plywood, masonite, or gib board (sheet rock in America) either true size or with ¼" offsets to use as a cutting template with an offset router bit or plasma cutter. Alternatively, you can layout directly on the aluminum with a scribe. The 25mm flat strap makes an excellent batten for the curves
2.	Lay out and cut the bottom panels, center bulkheads, bow and stern transoms, and skeg doublers (drawing A) on the 2.5mm sheet
3.	Lay out and cut the side panels, cargo bulkhead, floatation chamber sides, rowlock doublers (drawing B), and center transom pieces (drawing C) on the 2mm sheet
4.	Lay out and cut the cargo hold top, floatation chamber tops, hatch cover top, and seat tops on the ¼" plywood. Please note that the aft seat should be two inches longer than shown on the drawings
5.	Copy the curve of the stern transom to the 2x4 and cut with a jig saw
6.	Lay out and cut the reinforcing tabs for the outboard bolts on the 4mm plate
7.	Rip the 2x6x6' hardwood into ½"x2"x6'. Plane to 7/16" nominal thickness
8.	For the fabrication of the bulkheads and transoms (steps 7-9 see drawings D-G), it will pay to clamp the piece to preferably a flat piece of thick steel to act as a heat sink to keep the bulkheads from warping
9.	Cut, tack, then stitch weld (I use this term for a line of beads about 4" long) a piece of 25mm strap to the top curve of the center bulkheads
10.	Cut, tack, then stitch weld the 4mm bolt reinforcing plates to the center bulkheads
11.	Cut, tack, then stitch weld the square tubing and equal angle as indicated on the center bulkheads and transom as indicated
12.	Mate the mating bulkheads (no wisecracks)
13.	Locate the mating bulkhead joining bolt holes, drill with a ¼" pilot
14.	About 1.5" from the bottom of the mating bulkheads, drill a pilot for the #10 pan head screws. Separate the bulkheads, the open a clearance hole through the pilot on one side for the sheet metal screw
15.	Mate the bulkheads together with the ¼ hex bolts and sheet metal screws, using three ¼ flat washers between the bulkheads as spacers
16.	Tack weld the forward bottom to aft bottom panels together as indicated on the original plans
17.	Mate the starboard and port bottom pieces together and mark where the aluminum wire will be tack welded. Also mark where the bow transom clamp is to go. (A red 'Sharpie' marking pen shows up well for construction marks and can be cleaned with solvent when finished)
18.	Separate the port and starboard pieces and tack weld the aluminum wire to the bottom mating seam (in lieu of the strap shown in the photographs)
19.	Cut two, 3" sections of the 25mm flat strap and drill a 5/16" hole on one end. Tack weld to the top portion of where the transom is to go
20.	Cut 12, 2" long sections of the flat strap. This will be temporarily used to ensure alignment of the mating bulkheads and will be later reused. Try to cut as close to 90° angles as possible
21.	Mate the port and starboard pieces again. Twist the wire (no more than 2 turns) together. Insert a section of the ¼" threaded rod through the holes on the 3" long strap, install a flat washer and nut on each end. Hand tighten the nuts until there is a space between them a bit larger than the width of the bow transom at that point
If you haven't already, read steps 21-44 carefully BEFORE going further. These are the key steps to ensure that the boat has a fair shape when finished!!!!! A second, and possibly third, stout person will be of immense aid for this stage.
22.	Set the now joined bottom sections vertically, with the bottom seam oriented downward. Starting from the bow, start evenly separating the panels until they have a 6" gap. Use a thin screwdriver and/or scribe to keep the edges from overlapping as you are expanding.
23.	Force (I'm not kidding) the bow transom into place. If necessary, tighten the twisted wire beneath it. Place a single tack at the junction of the bow transom, port bottom, and starboard bottom pieces. Using a pair of clamps, lightly secure the middle of the bow transom to threaded rod.
24.	Tack weld perpendicular to the bulkhead seam of the bottom panels the 2" long alignment pieces cut in step 19
25.	Force the mating bulkheads into the gaps between the 2" flat straps. Hold in place with either a steel strap clamp or two pieces of 2x4x5 with ¼ threaded rod
26.	Lightly clamp the 2x4 aft transom mold cut in step 5 at the stern
27.	Proceeding from the bow, tighten the twisted wire, threaded rod at the bow, and clamps at the stern together to form a nice seam, again taking care to avoid overlaps. Patience is a virtue. Overlaps and gaps up to 2mm are functionally insignificant, but will result in more work grinding later. They will also detract cosmetically from straight lines
28.	For longitudinal stiffing, cut a piece of 25mm flat strap to extend from the bow to 6-8" before the mating bulkhead. Cut a second piece of flat strap to extend between the transom and 6-8" before the mating bulkhead. Cut or grind the straps to have the same general shape of the hull standing centered and perpendicular to the center seam
29.	Tack weld the mating bulkhead to the bottom pieces, spacing the tacks no more than 3" apart. The tight spacing will lessen distortion during the final welding of the seams
30.	Working alternately at either transom, tack the stiffening piece to the bottom seam, again spacing the tacks no more than 3" apart. Continue past up to the stiffener to the mating bulkhead
31.	Tack weld the bow transom to the bottom
32.	Remove the mating bulkhead temporary alignment 2" flat straps by using a cutting wheel on the welds. Clean up at least 10 of them for constructing the floatation chambers
33.	Starting either port or starboard, center the tack welded side seam in the gap between the mating bulkheads. Working from the mating bulkheads to the transoms, tack weld the sides to the bottom working the edges together as in step 26. You may have to slice out some material from the side with either a plasma cutter, or grinder, or jig saw to fit.
34.	When both sides are tacked, tack the sides to the mating bulkheads
35.	Tack the bow transom to the sides. Don't worry about the overlap at the top
36.	Remove the stern mold and tack the stern transom in place perpendicular to longitudinal centerline in a 'best fit' between the bottom and the sides. Again any excess will be cut off.
37.	Double check your work and repair if necessary
38.	Turn the dingy over
39.	Beginning at the mating bulkhead center seam, weld (TIG is preferred here) towards either transom, untwisting the wires as you get to them
40.	Again beginning at the mating bulkhead, weld both side seams
41.	Trim the sides and bottom to plane with the bow and stern transom
42.	Weld the transoms in place
43.	Flip the dinghy back to normal and weld fillets on all of the inside seams. Work no more than 6" of fillet before going to another seam to keep heat (distortion) down
44.	Remove the ¼ bolts and sheet metal screws from the mating bulkheads
45.	Invert the dinghy (catch the ¼" flat washers as they fall out for reuse later). Using a jigsaw or a close-quarters hacksaw cut the tacks between the bow and stern sections.
46.	Weld the sheet metal screw holes closed. Grind flush
47.	Test welds for porosity. Seal the ¼" holes in the mating bulkheads with some silicone under the ¼" flat washers or make a rubber gasket. Fill the bow and stern section with fresh water. If there are no visible leaks, add about ½ cup of a bright food coloring to the water in each section and allow to stand at least overnight. Any porosity will be visible as a dried color on the outside of the dink. Before emptying, this is a good time to scrub the welds clean with a wire brush and get rid of the accumulated gunk in the bilges
48.	Invert the each dinghy section, cut, tack, and stitch weld a piece of 25mm equal angle to protect the center seam (provides greater rigidity and protects from impacts).
Rue the day you were born if you didn't read ahead first. You will now fabricate the stern center rib.
49.	Measure a line athwartships 22 ½" from the mating bulkhead across the bottom and side panels. Cut and trim a pair of flat straps to fit on this line on either side of the longitudinal stiffener. Gaps are preferred here to allow for bilge drainage. Allow a for a drainage hole on either side of the stiffener. Tack in place.
50.	Cut and trim another pair of flat straps to fit along the same line on the sidepieces. Cut a slot on the outside of the straps to accept the rowlock doublers. Tack in place
51.	Stitch weld the rib to allow for drainage
52.	Slip the rowlock doublers into the slot between the rib and side and tack weld into place
53.	Locate the skeg doublers on either side of the center seam in the aft section and stitch weld into place
54.	Cut four pieces of 25mm equal angle to fit on the top edge of the floatation chamber sides. Using a bezel, take an offset from the floatation chamber top to get the needed angle to mate the pieces. Tack, and then weld the sides of the floatation chambers together. The forward sides of the floatation chambers are a great place to add fishing pole holders
55.	Fit the floatation chambers into place. You will need to cut a slot in the middle piece of square tubing to accept them. Tack, then stitch welds to the bottom, side and transom pieces.
56.	Clamp one of the alignment pieces that you used for the center bulkhead to one end of an offcut of either of either equal angle or square tube. Clamp the other side of the offcut to the equal angle on the top of the floatation chamber side aligned with the dinghy side. Tack weld in place, remove the alignment tool, then stitch weld in place. Place a vertical mark above it on center. Make at least two tabs on each side
57.	Fit the plywood floatation chamber tops. Drill pilot holes for the pan head screws through the top into the equal angle along the sides and also through the tabs mounted in step 52. Remove the chamber top and open the pilots to clearance holes for the sheet metal. I chose to glue fiddles on the chamber top to keep from loosing my pipe tobacco. Seal the plywood with epoxy. Apply a finish
58.	Invert the dinghy. For the skeg roots, cut two pieces of equal angle 24" long each and drill 4 9/32" holes in each piece, centered on one leg. Locate in the center of the doublers welded in place in step 49. You will need to bend the extrusion, two blocks of wood and a determined clamp works wonders. Stitch weld into place
59.	Cut the wooden skegs, locate and cut the lifting slots. Fit to the curve of the hull along the skeg root. Locate the mounting holes and drill as appropriate. Leaving in a coral and toredo worm infested area, I chose to wrap a piece of flat strap around the 'impact zone' of the skeg to give them a slightly longer life. Except for the seat, outwales and knees, this completes the stern section
60.	On the forward section, measure on square from the mating bulkhead of the stern section 25" towards the bows. Mark a line athwartships perpendicular to the center longitudinal seam. Fit the cargo bulkhead to this seam with the square tube side facing forward and at right angles to the center seam (parallel to the top of the transoms and mating bulkheads). Tack, then stitch weld into place
61.	Measure a line on the forward transom parallel to and 4" down from the top of the transom. Mark the center point of the line. Mark another line 1" further down, parallel to the first, and also mark the center point. From the intersection of the sides to the transom, measure and mark towards centerline 1". Measure the distance between the centerline and the last mark. On the cargo bulkhead, find the centerline and measure outward the same distance as just marked before.
62.	Using a bezel for offsets, measure and cut 2 pieces of 25mm square tube to run from the square tube on the top of the bulkhead to the forward transom. Weld into place
63.	Using the same technique as the tabs on the floatation chambers, locate 2 tabs per side on the bottom for the forward floatation chambers. Insure that you align these to the sides of the square tube that face each other.
64.	Using the remaining plywood cut two longitudinal bulkheads to fit facing each other. Drill pilots through the plywood into the tabs (bottom) and square tube (top). Remove and epoxy seal. Apply a finish if desired. Re-install.
65.	Fit the plywood cargo hold cover.
66.	Athwartships, at right angles to the floatation bulkheads, measure forward to the forward and leading edge of the hatch for the cross members made of square tube. Using a router, cut notches to mate the cross members with the forward floatation chamber square tube.
67.	(This part is an adventure). Unscrew the flotation bulkheads and lay them flat in what will be the cargo compartment. Weld the cross members into place. Cut and weld a piece of 2.5mm sheet between the uppermost line drawn in step 57 and the most forward cross member (this piece is a backing plate for the bow cleat and roller). Re-erect the floatation bulkheads and screw into place
68.	Cut two 8" long pieces of equal angle for the bow roller. Cut a notch at the center of each piece to bend into the angle formed between the backing plate and the bow. Predrill two 9/32" holes on the leg opposite the bow transom. Measure a 4-¼" wide slot on centerline of the bow transom. Place a small scrap piece of ¼" plywood over the backing plate. Clamp the bow roller holder to the bow transom with the plywood wedged between the holder and the backing plate. Tack, and then weld, the bow roller holders into place. Remove the scrap plywood.
69.	Refit the cargo locker top. Drill #10 pilot holes through the top into the square tubing beneath it. Drill four 9/32" holes through the pre-drilled holes of the bow roller holder through the plywood and backing plate. Locate and drill the mounting holes for the cleat. Remove the top, open the #10 pilots to clearance diameter
70.	Fabricate and glue the hatch lip to the cargo cover. Seal the cargo cover with epoxy. Finish as desired
71.	Fabricate the cargo hatch top. Epoxy seal and finish as desired. I chose to use a bit of my offcut hardwood for the edges and it set the paint off nicely. Because of the angle of the cargo locker top, mounting the hinges on the side of the hatch will keep the hatch from bonking your head or back when trying to find something inside the locker
72.	Join the bow and stern sections together with the ¼" bolts. One at a time, clamp near the outboard mounting bolt, remove the bolt, and open the hole to 29/64". Insert and bolt with the 7/16x1" bolts.
73.	Remove the center ¼" bolt. Using a ¾" holesaw, drill towards the mating bulkhead through the transom facing pieces of square tube. Insert a 23mm long section of 18mm round tube and weld into place (keeps the tube from possibly being crushed by the bolt). Open the hole to 29/64"
74.	As per the stitch and glue construction, using plenty of clamps, fit the outwales to the sides. Through drill #8 pilots from the inside to the hull into the outwale.
75.	Cut the knees from the scrap 2.5mm sheet. I cut the knees so as to allow beverage holders. The only critical dimension on the knee is on the mating bulkhead-to-side of the aft section (if cut too large, the dink will not nest). Very carefully tack into place.
76.	Remove the outwales and weld the knees into place. Open the #8 pilot holes in the hole to clearance dimension
77.	Sand the outside of the hull with #220 aluminum oxide paper. Clean thoroughly with a non-residue solvent such as triclorethylene. Mask and apply 5200 to the outwales with a serrated trowel. Refasten the outwales and allow to cure as per the manufacturer
78.	Fit the inwales. As the inside curve of the forward section is pretty radical, I medium strength clamped pieces rough cut for length overnight to take the set of the curve before final bending. In the stern section, locate and route an inset to allow the rowlock doublers to fit. From the outwale, drill a #10 pilot from the outwale into, but not through, the inwale. Remove the inwale. Countersink and clearance bore from the outwale through the hull for #10 flat head screws.
79.	Sand the inside of the hull with #220 aluminum oxide paper. Clean thoroughly with a non-residue solvent such as triclorethylene. Mask and apply 5200 to the inwales with a serrated trowel. Fasten the inwales with #10 flat head screws and allow to cure as per the manufacturer
80.	Cut plugs from scrap and bung the holes in the outwales
81.	Trim bungs. Flush and fair the sides above the inwale/outwales. Mount rowlocks 22-1/2" from the mating bulkhead. Apply appropriate finish as per manufacturer's instructions
82.	Construct the seats as per the stitch and glue plans. You can get very creative with these. I chose to build a drawer under the aft portion of the aft seat. In addition, I also glued in another 2"x2" athwartship piece, then cut a ¼" deep rabbet into the underside of the seat and glued in another piece of plywood to create a box section and give the seat more buoyancy. On the bow seat, I used another athwartship piece with a 1" space between the end of the seat and the second piece. I then used a 2" holesaw to bore a hole to accept the mast (if sailing is desired). My mast is the same as my boat hook pole: Two sections of foam filled bull float handle screwed together, with an 'EZ-In' broom thread boat hook head. It was suggested by Scott Bannerot that a hole be cut into the seat to allow a cooler for fish. Let your conscience be your guide
83.	Tape the seams of the floatation chambers with electrical tape. Mix the pour-in-place foam and pour into the chambers. HINT: MIX NO MORE THAN ABOUT 4 OUNCES (100 ML) AT A TIME. THIS STUFF CAN GET OUT OF CONTROL FASTER THAN A MONSTER IN NEW YORK CITY!
84.	After the foam cures overnight, trim off the surplus with a serrated knife
85.	Using the rest of the 5200, install the floatation chamber and cargo locker tops with #10 pan head screws. Use a dampened finger or tongue depressor to force the sealant into the joint.
86.	Install the bow roller.
87.	Invert the dingy and mount the skegs. Use one of the bolts on each skeg for a sacrificial anode.
88.	Drill the top 25mm square tube of the transom with a 9/32" drill and mount the ¼" 'u'-bolts with the eye outboard for lifting eyes, towing, stern mooring line, etc. If you are going to mount an outboard, ensure that you allow adequate clearance for the outboard bracket between the 'u'-bolts. At a greater expense, ¼ eye nuts can also be used
89.	The topsides can be left bare, but if to stay in the water for any length of time, prime and anti-fouling paint as per manufacturers instruction. Please note that aluminum is very fussy about bottom paint.
90.	Construct the fenders with the insulation foam. Cut notches out of the corners to fit
91.	Construct the fender covers. These are drawstring 'skirts' on the outside and lashed to holes on the inside
92.	Paint name on stern
93.	Uma lava pisupo (an old Samoan adage, loosely translated, everything is finished, even the tinned corned beef)

Enjoy
Michael Homsany
S/V 'Shangri-La'
Originally written whilst enroute between Pago Pago, American Samoa and Savusavu, Fiji Islands

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Rin Tin Twin-A Tale of Two Dinghys

Materials List and Instructions for Building an Aluminum Two Piece Dinghy

Rin Tin Twin-
A Tale of Two Dinghys