A Plywood Canoe

I built this canoe 10 years ago.
It was fun but various design flaws has limited it use.
This project is about a salvaging the canoe.

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My Canoe
It works but not that stable.
Upon reflection there were some design flaws.
I propose to build an outrigger for it.

Plywood Construction

The canoe uses stick and glue plywood construction. This is how it is done:

The main trick is to use copper wire as it can be removed when heated with a gas blow torch. You buy the fibre-glass tap, epoxy and epoxy filler (micro balloons) from a boating shop.

I hate fibre-glass so for this project I bought a roll of rather expensive dynel tape. Not as strong (about 40%) but sure nicer to work with.

Here is another method that I really like that I have only just discovered:


Some Canoe Construction Photos

Here is the initial butt join of two sheets of 6 mm plywood. The wooden clamp just makes life a bit easier, but it is not the only way:

Here is the finished join (before sanding off the sharp fibre-glass tap edges):

After the join has cured, the other side needs to be taped as well.

After sanding, marking and cutting out the pieces:

Here the pieces have been joined, sanded and ready for painting:

And another view:

The 6 mm plywood is not strong enough for the middle span so I reinforced it with wooden strips.

And the finally painted:

Design Flaws

The first issue is that because the bottom of the canoe is wide, if you slide to one side you will tip! It would have been better to have a narrower sole that helps center your "seat" like this one:

The second issue that there is no foot rest to help move your weight around to maintain balance. Not ideal.

The final issue is that because canoe rides higher in the water (less than 2" displacement) it is less stable. You cannot use an elevated seat. Not ideal.

The Big Fix


  • foot rests
  • buoyancy tanks
  • an elevated seat
  • and an outrigger

The Outrigger

I am going to use a 1/2 size mini-version of the canoe.

The bridge(s)/spar(s) will be detachable.

Here an image of a trimaran to give you an idea of what I have in mind (but less one outrigger):




A DXF version of the updated lofting layout

AutoCAD DXF - 189.95 kB - 04/01/2017 at 05:23



The original DeltaCad file of the lofting layout

dc - 6.35 kB - 04/01/2017 at 05:22



A macro to export a sorted list of offsets for lofting

bas - 1.52 kB - 04/01/2017 at 05:23



Yep, the lofting offsets (load into a spreadsheet for printing).

ms-excel - 6.07 kB - 04/01/2017 at 05:22



A DXF version of the plywood cut-out shapes.

AutoCAD DXF - 158.17 kB - 03/31/2017 at 13:16



A guide for how to use the following macros.

document - 244.80 kB - 03/31/2017 at 13:06



An Excel workbook inputting the Hull Offsets Table and a macro to export them to a CSV file for the DeltaCad macro. Also contains some basic hull calculations.

12 - 106.93 kB - 03/31/2017 at 13:06



The DeltaCad macro to import the Hull CSV file and to convert the 3D hull to 2D cut out shapes.

bas - 38.58 kB - 03/31/2017 at 13:06



The DeltaCad design file for the plywood cut-outs.

dc - 14.75 kB - 03/31/2017 at 13:06



Basic Canoe Design Metrics and Calculations

application/vnd.openxmlformats-officedocument.spreadsheetml.sheet - 18.05 kB - 02/23/2017 at 07:53


View all 13 files

  • Cross-Beam Design

    agp.cooper04/14/2017 at 09:26 0 comments

    The Pontoon Bridge/Spar(s)

    I have been playing with various options. The torsion maths says a single 6 mm plywood box (bridge) about 150 mm x 150 mm square will work (also 180 mm x 100 mm). The plywood can also be designed to take a curve. Otherwise a single 90 mm x 90 mm solid wood spar. Attaching the bridge/spar to the pontoon is straight forward. Attaching to the canoe is problematic. I am considering a wooden knee(s) (i.e. angle bracket) between the canoe outside and the bridge/spar.

    At the moment the bridge/spare is forward of the paddler (on the right) but I think it would be more out of the way on the left. The pontoon has to be clear of the paddle stroke which I calculate as about 1 m from the canoe sheer and 1.5m forward of the paddler:

    The knee(s) will require longitudinal reinforcement on the canoe inside/outside (perhaps another set of knees):

    I will have to look at the option for the bridge/spar behind the paddler, and the lighter twin spar options as well.

    Plywood Bridge

    I had trouble finding suitable timber for the spars and knees. The plywood box is relative easy to make and would be attached with fibreglass tape. The box section is 180 mm wide and 100 mm deep with a minimum thickness of 6 mm. Likely I will use 18 mm thick pine for the side faces and 6mm plywood for the top and bottom:

    I am still having design problems with the plywood bridge. The main problem is the stress levels on the canoe hull (circled red below) are far too high:

    Basically the bridge is like a can opener on the side of the canoe hull. I think I will have to go over the top like I did for the pontoon.

    Basically I need to get the stresses directly to the outer skin.

    I was a bit worried that I was over-designing the bridge so I checked out (reverse engineered) some designs on the Internet. The keyword here is "cross-beam" rather than bridge or spar. There are a number of designs (for bigger boats) that match my loading estimates after scaling.

    I have been trying to rationalise why most of the design on the Internet don't have the stress problems that I have. I did notice that some designs did have pretty heavy duty saddles for the cross-beams. Eventually I noticed that the wale and skin thickness for most of the designs are pretty heavy duty! More than enough to just boat or lash on (with a cross-member and bulkhead backup).

    I have gone back to a hardwood cross-beam with a saddle for distributing the load:

    I have been going around in circles with the cross-beam design. The problem is that I am trying to avoid the need to sanding the interior paint back to wood for epoxy joins. My fingers will not like me if I go down this path. Still the best option is to install a bulkhead or two to bolt the cross-beam to.

    Checking the Internet the method of choice seams to be a heat gun and a scraper. I am not going back to chemical strippers (the modern stuff is pretty useless and the stuff is just as awful). Not keen to use screwed in frames/brackets. The heat gun may also work with removal of the copper tie wires. For A$65 worth a try. I have a bathroom ceiling that needs stripping anyway (I stripped it with paint stripper a few years ago and never again).

    Here is the next proposal:

    I have reduced the cross-beam to 100 mm x 64 mm using four 64 mm x 18 mm hardwood DAR. I have added two 12 mm plywood bulkheads to attach the cross-beam to the canoe. They are only 75% of the required design strength so rather than increase the thickness I will sheath them in fibre-glass.

    I have looked at some designs on the Internet and the bulkhead seems to be the preferred method although I did see two half frames (similar to my orignal knee design).

    The bulkhead options allows me to add a buoyancy tank (or two).

    Before painting I have to attach the cross-beam and I am still struggling to determine the easiest way of doing this. I had a look at some timber at the hardware store yesterday. Not cheap! The simplest solution is a 90 mm x 90 mm solid pine but it really looks heavy...

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  • Lofting, Cutting Out and Gluing Together

    agp.cooper04/02/2017 at 06:34 0 comments


    Bought some marine plywood yesterday. I could not get 4 mm so the skin thickness is now 6 mm. Formatted the lofting offsets in Excel and printed them out:

    Along with a plan:

    After 2 hours (half done), time for a coffee break:

    I will say it was worth redigitising the layout design to align with the 100 mm offsets or sections.

    Lofting Done

    Complete the lofting in 200 minutes excluding the coffee break. That is about two offsets per minute. A useful statistic for next time.

    If I had a suitable CNC machine (I can dream!) then I would have designed the wiring holes and perhaps a toothed edge for seam alignment.

    Cutout, Trimmed and Sanded

    Took about 3 hours to cutout, trim and sand the panels.

    For the amount of work spent on the pontoon I could have built a full size kayak!


    The next task is to drill the wiring holes. I should get away with 150 mm hole spacing. I can always infill if necessary.

    I will assemble and glue the "harpins" (i.e. the two outer thin crescent shaped pieces and the two triangles) first, then the deck using the harpins and bulkheads as temporary forms to get the right shape. After that the harpins are used with the bulkheads for the main hull. Finally the deck and hull as glued and screwed together.

    Stitching the Hull

    Made up a template that drills 100 mm spaced holes 7.5 mm from the edge. I start in the middle of the panel and work my way to the ends. The blue pin in the image below pops into the last hole drilled to keep everything properly aligned:

    I taped the panel in pairs to reduce the drilling effort:

    Here is the bottom and side panels wired up:

    Copper wire works best as it can be heated with a propane torch to allow removal (this trick does not work with steel wire). Unfortunately the copper wire is a bit light duty so I need to be gentle when tightening the wire to close the gaps.

    All done (about five hours later):

    A close up of the front:

    The wires need to be tightened before being epoxied. I am only going to put dynel tape on the outside, so the bulkheads will be epoxied at the same time as the seams.

    The Deck

    I could join the deck with copper wires as well but I want to try nylon lacing instead:

    (Source: "Graefin 10" by Will Graef (Science and Mechanics Magazine, May 1964))

    The nylon lace is stretchy so the join and be opened. More holes to drill and fill but less issues with heating the copper wire to get it out. Also easier on the fingers (the copper wire ends are sharp). I suspect getting the string tension just right will be important.

    More Seams Done

    I made up two batches yesterday and most of the inside of the hull is done. About 90 minutes to mix and place. The main problem is that the pontoon is just a little too small to easily place and smooth/finish the filler and I can't get my head in to see what I am doing. The filler is very sticky and hard to place/finish, you need room to work. Still two more batches should finish the inside seams. Here a examples of the work:

    Finished the inside seams. Tomorrow I will try the heat gun on the copper wires to see if they will come out. After that a slightly more runny mix of epoxy filler to fill the outside seams and the wire holes.

    Epoxy Safety

    I don't use polyester resin as it is not safe without the proper breathing gear. Epoxy is pretty safe but you can become hyper-sensitive to it (i.e. that would mean the end of my boat-building) so I now use rubber gloves. I once used acetone to clean-up but now I use white vinegar. It deactivates the epoxy allowing it to be washed off with detergent. It is not perfect as it still leaves a residue but good enough. I don't try to reuse bushes etc. I reuse metal spatula/scrapers by grind off the epoxy after it has hardened. The filler is a hazard to your lungs so I would recommend a face mask when mixing it with epoxy (or at least hold your breath not to breath the dust!). I have swore off fibre-glass tape because sanding the (sharp) edges a pain (lots of sharp fibrous dust). I will be trying...

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  • DeltaCad Macro Completed

    agp.cooper03/31/2017 at 13:05 0 comments

    DeltaCad Macro Completed

    All I can say it was a bit of a marathon getting the code working reliably. The issue is that the underlying processes (wire-framing) is not unique/deterministic. Asking the macro to sort out lazy chine offsets was a dead end.

    Why migrate from the spreadsheet version previously presented? After all it works! The reason is that even simple designs take forever to code and it is just too hard for more complex projects. The new DeltaCad macro version handles simple hulls easily and the more complex designs are slow but doable.

    Design Process

    The process consists of two macros/files:

    1. BoatOffsetTable.xlsm
    2. BoatOffsetTable.bas

    The Excel file and macro allow you to enter the offset table and then to export the design to a CSV file for DeltaCad.

    The DeltaCad macro imports the CSV, draws the design and unfolds (develops) the hull.

    Note: DeltaCad can be purchased for US$40 from


    DeltaCad does not have a suitable table entry process which is why Excel is used. Below is the Excel offset table for the “Mini-Kayak”.

    “Mini-Kayak” is an adaptation of work by Bruce C. Anderson ( The actual design is too small to be of practical use as a Kayak (refer to Anderson’s webpage).

    The above offset table has three additional features over an offset table:

    1. Chines have a colour for easy identification.
    2. Chines can be invisible (and ignored) if the colour is “0”.
    3. Chines can have a “break” or a sharp bend.


    • The design is in millimetres.
    • The stations are rounded to the nearest millimetre.
    • Any duplicate stations are deleted.
    • Stations within 5 mm of each other will have “breaks” automatically added.
    • Colour 0 is not processed.
    • If an interpolated value appears wrong or wildly off then you will need to add “breaks” to the chine stations near the problem area.
    • No curvature checks are made, the design may not be developable (i.e. the plywood may break).

    The offset table is exported to DeltaCad as a CSV file. The name of the CSV file is the same as the Excel WorkSheet name. To execute the macro just click the blue “Make CSV” arrow as shown above.

    In DeltaCad the macro (“BoatOffsetTable.bas”) is run to import the CSV file and draw the design. For complex designs, the actual process is iterative (i.e. chine by chine). Below is the imported and unfolded “Mini-Kayak” showing the main drawing components.

    Note: The unfolded panels are the cut-outs for the design and only one side is shown.

    Macro Options

    When you run the DeltaCad macro, it first presents a file manager window. It starts in the DeltaCad macro directory. You will need to navigate to your working directory (i.e. where the Excel file is located) and select and okay the CSV file. For the “Mini-Kayak” it is called “Mini-Kayak.CSV”, as shown below.

    The macro then presents the “Hull Sections” options box. Set the number of frames to 7 and zero the remaining entries as shown below. This option adds additional frames to the hull model.

    You should see the following design.

    Other Options

    If the “Frames” entry is set to zero then the offset table as entered in Excel will be drawn as below.

    The other option entries, create different sections (cross, long and plan) through the model. For example the following options, shown below, also draw a series of cross-sections, long sections and plan slices.

    More Complex Designs

    The program is capable of more complex designs but the offset table entry process is rather time consuming. Shown below is “Heart’s Desire II” a design by William Atkin.

    Back to the Pontoon Design

    Okay, I have generated the pontoon design file in DeltaCad, what next? No big deal, digitise "shapes" over the pieces I want (delete the all the segments when done) and lay...

    Read more »

  • Enclosing the Pontoon

    agp.cooper03/15/2017 at 07:28 0 comments

    Enclosing the Pontoon

    This has been a difficult problem to solve. You cannot just fibreglass tape the outside seams as it will leak. Not good. Here is an ideal join (source unknown):

    Note how the yellow filler seals the joint.

    One option is to cut holes in the last plank/panel in order to gain access to the inside seam and then patch the holes when done. I did this once and I can say it is still not that easy to tape the inside seam and patch a curved (stressed) panel afterwards.

    Another option is to add a chine log/stringer/batten and screw/glue the last panel after bevelling as per this example (source unknown):

    Image result for kayak chine stringer

    In the end I decide to "lap-strake" the last panel. Here is the unfolded panels (one side only):

    The magenta panel is a copy of the blue (top) panel but shifted 50 mm up and trimmed to the blue panel. Instead of using the blue (top) panel, the magenta panel is used instead. After all the inside seams are done, the blue (top) panel is glued/screwed over the magenta panel.

    The main problem is that the panels do not fit on a half standard plywood sheet (i.e. the black box) so I will have to shrink the pontoon a little

    Updates to the MiniKayakTable Spreadsheet

    More updates to the spreadsheet for the above closure method and the inclusion of some DXF export code. The DXF file is as simple as can be but I know not all CAD programs will not be able to read it. As they say: "Not my problem!" as it works with DeltaCad:

    I need to get the data into DeltaCad so I can re-export it for laser cutting, if I decide to build a model. I originally intended to migrate the excel macro to DeltaCad once I had "ironed out" the bugs. I still may if I can workout how to add a table input in DeltaCad.

    Here is the central pontoon bulkhead:


  • The Pontoon

    agp.cooper03/05/2017 at 13:33 0 comments

    The Pontoon

    The pontoon design is based on work by Bruce C. Anderson, have a look at his webpage:

    This is what it looks like:

    Here is one side of the unfolded (cutout):

    And the table of cutout offsets (this may be revised):

    I have yet to workout how the how to epoxy the inside of an enclosed kayak?


  • Unfolded Offsets

    agp.cooper03/05/2017 at 07:07 0 comments

    Unfolded (Cut Out) Offsets

    In order to cut out plywood pieces for your boat/canoe, the design needs to be "unfolded" from 3D to 2D. Now there are some very good programs on the Internet that can do this, my favourite is Carlson Design "Hull Designer" or "Hulls" ( The only problem with this program is that the program needs to be run in compatibility mode (otherwise the behaviour is frustratingly strange).

    The original canoe was unfolded using a spreadsheet (i.e. formula based). The problem is that building a design is a painfully slow process and there is not much hope of explaining its use. About three years ago I wrote a macro that reads a Table of Offsets (what you will often find in a boating books or magazines) and calculates the unfolded offsets directly. Like most home brew programs there are probably bugs that need to be fixed and improvements that can be made and no documentation.

    The Offset Table

    Here is a typical offset table for a canoe:


    Although there is everything you need here (that is the above image) to physically build the canoe, it is still a tough job for a program to decode. Below is the offset table for my canoe:

    Other than the offset table being rotated, there are two additional fields:

    • Break: If TRUE then the "line" or "chine" can have a sharp bend
    • Colour: Having colours helps to identify the "plank"

    Two other comments are that although each "station" or "section" above have the same "X" co-ordinate, this is not a requirement, and although I have filled in each cell, again this is not a requirement.

    It helps a lot if you run the "lines" or "chines" all the way though to a common point at each end of the table.

    Running the Macro

    After checking that you have filled out the yellow cells, click the blue arrow. A minute later (yes it is slow so don't panic!), it will update the "Unfolded Offset Table":

    It will also update the 3D drawings:

    The "Unfolded Offset Table" will need to be moved around to suit the plywood, so another page allows this. The "plot" button on this page will update the unfolded drawing:


  • Basic Canoe Design

    agp.cooper02/23/2017 at 07:52 0 comments

    Basic Canoe Design

    Before considering the pontoon and bridge design here is the basic canoe design. I have uploaded a spreadsheet with all the following calculations.

    Basic Canoe Measurements

    Canoe Basic Metrics
    Length Overall (LOA) 3.930 m
    Beam Overall (BOA) 0.650 m
    Length Water Line (LWL) 3.600 m
    Beam Water Line (BWL) 0.550 m Actually the bottom width
    Depth Water Line (DWL) 0.075 m
    Rocker 0.025 m
    Amidships Deadrise 0.000 Degrees Flat bottom
    Amidships Freeboard 0.200 m
    Forward Freeboard 0.325 m
    Rear Freeboard 0.325 m

    Note: Bold numbers are inputs.

    Design Pressure

    Now some basic calculations but most importantly the design pressure:

    Basic Calculations
    Mid-Section Area 0.041 m^2
    Plan Water Line Area 1.320 m^2
    Displacement Volume 0.088 m^3
    Displacement Weight 90.200 kg
    Prismatic Coefficient (cp) 0.593
    Displacement Length Ratio (DLR) 42.080
    Hull Speed 4.605 kt
    Design G Force 3.500 g Light duty
    Design Pressure 2.346 KN

    To calculate the design pressure I have assumed the canoe is loaded 3.5 time the rated displacement of 90 kg.

    Bottom Plywood Thickness

    Bottom Plank Design
    Design Pressure (P) 2.35 kPa
    Span (L) 550 mm BWL
    Allowable Stress (S) 14000 kPa F14 Plywood
    Plank Thickness (t) 5.03 mm t^2=P*L^2/2/S, ~fixed sides
    Design Plank Thickness (t) 6.00 mm
    Modulus of Elasticity (E) 8400000 kPa Factored 80% for wet condition
    Moment of Inertia (I) 18000 mm^4
    Deflection (d) 3.70 mm d=P*L^4/384EI (2% max)
    Deflection Ratio 148.74
    Maximum Concentrated Load 0.50 kN =S*t*t

    Here I calculate 5 mm but the nearest larger plywood thickness is 6 mm. Although this is okay for water pressure it is too thin for an adult to stand on. The middle section of the bottom of the canoe needs to be reinforced.

    Bottom Reinforcement

    Upon reflection it would have been easier just to double up the plywood in the middle of the canoe or that fibre-glass both sides with 4 oz/sq_yd fibre-glass cloth. The calculations assume a "T" section across the hull (beam-ward) with plywood strips (see image). It is also assumed that two "T" sections share the load as they are quite close together:

    Hull Centre Reinforcement
    T-Section Modulus
    Maximum Rib Spacing (Flange Width) 256 mm Fw<36t+w
    Design Rib Spacing 150 mm
    Plank Thickness (Flange Thickness) 6 mm
    Rib Thickness (Web Height) 6 mm
    Rib Width (Web Thickness) 40 mm
    A 1776 mm^2
    cy 3.8 mm From top of T
    cx 0.0 mm From centre line of T
    Ixx 10474 mm^4
    Iyy 8420608 mm^4
    Design Point Load 1.00 kN ~100kg
    Span 550 mm
    Allowable Stress 14000 kPa F14 Plywood
    Bending Moment 69 Nm
    Section Modulus 2749 mm^3
    Working Stress (per rib) 25013 kN
    Distribute Load (over two ribs) 12506 kN
    Safety Factor 112%

    Here is an image of the reinforcement:

    If you look carefully you can see the filled wire holes below the single strip of 4 oz/sq_yd fibre-glass tape.

    Side Plank Calculations

    If the side plank is the same thickness as the bottom plank then no calculations are necessary but here they are anyway:

    Side Plank Design
    Design Pressure (P) 2.35 kPa
    Span (L) 275 mm
    Allowable Stress (S) 14000 kPa F14 Plywood
    Plank Thickness (t) 2.5 mm t^2=P*L^2/2/S, ~fixed sides
    Design Plank Thickness (t) 6.0 mm Okay

    Hog and Sag Calculations

    So put 3.5 big guys in the canoe and get two even bigger guys to lift the canoe up by the ends. Is it strong enough (not actually required)?

    First the Load Calculation:

    Hull Section Modulus Triangular Load & Free Ends
    Design Pressure 2.35 kPa
    Width 550 mm BWL
    Length 3600 mm LWL
    Allowable Stress 14000 kPa F14 Plywood
    Required Section Modulus 99547 mm^3 SM=PsL^2/12/S

    Now the Strength Calculation (assuming a channel section):

    Channel Model
    Chine Width (web) 550 mm BWL
    Side Height (flange) 275 mm
    Deck Width (lip) 50 mm
    Thickness (t) 6 mm
    cy (from bottom) 86 mm
    I 75400372 mm^4
    Rg 102 mm Radius of gyration...
    Read more »

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