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Thread: Designing your own plywood hull, but mostly just screwing around...

  1. #1
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    Default Designing your own plywood hull, but mostly just screwing around...

    I turned 50 last week and owing to being bored and retired, I'm building a boat. I've contemplated, prepared, and abandoned this idea at least 2 times now in the last 3 years. But given my recent purchase of various materials, to include epoxy, plywood, what have you, it looks like my level of commitment this time is a bit more sincere.

    I've purchased various plans, put together a small library of books, collected enough articles and other information to fill 3 gigabytes on my network server, among other efforts. While I am not a proficient sailor (with sailing) nor have I ever built a boat, I've spent enough time on the sea, whether on a kayak, small craft, and similar, or my years navigating ships (yes, I know how to use a sextant!) to at least have some time on the water.

    So here's the rub, I'm really just screwing around but have a design in mind. Nothing spectacular, 16 feet LOA, 4 foot beam, a fairly deep hull, built with plywood.

    The issue I am experiencing revolves around determining panel sizes for the hull as well as the bulkhead dimensions. I've modeled this mentally and have a fairly good idea on how to cut the panels to provide a given hull shape. I downloaded "Hulls", "Freeship", and "Delftship" and am having a heck of a time understanding CAD. This is from a guy who has programmed in C and Perl, as well as administering various UNIX systems, go figure.

    How did the old timers do this before the advent of reasonably low cost computing? I've thought about cutting out the bottom and fitting to the panel dimensions I have put together, adding the top panels, and then measuring the "void" to cut corresponding bottom panels (it is a single chine design). Am I on the right track? I've never done this before and find myself looking at Mount Everest, metaphorically speaking.

    I'll take advice, encouragement, even harsh language, but submit myself to the wisdom of the crowd...

    Garry

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    Your question is a little bit confusing. Have you already drawn up plans? If so is your question how to loft the lines from that plan? Or are you trying to build by eye at full scale as you go along? Either way maybe something in this video will help.

    https://www.youtube.com/watch?v=z6Fi...=RudyWoodcraft

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    Models
    build models

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    I used to build simple plywood skiffs by making a mold frame to go somewhat in the middle, a transom, and a stem. I'd eyeball a shape for the sides, depending upon if I wanted a planing hull for power use, or more of a displacement model for sailing or rowing. Once assembled, I'd trace the bottom panels, cut them, and attach them. The boats floated and did more or less what I expected. If the bottom edge of the sides (chine) is straight, you'll get some rocker as it's bent, depending upon how much flare the sides have. More flare equals more rocker, to the extent that boats like dories with a lot of flare wind up with a reverse curve when laid out on the flat. I fooled around with one of those boat design programs (I think it was Freeship), and it would show the expansions for the plank shape. The questions are- how much rocker? How much flare? I study a lot of boat designs which seem like they will work for my intended purpose, and copy the elements into a fresh design. In short, a lot of my 'new' designs look a heck of a lot like existing designs. I've built crude models of some of my designs, and they look OK, but of course, that doesn't predict what they'll do out on the water when rendered full size. Obviously I an a rank amateur, but it's gotten me out on the water at minimal cost. I guess I'm lucky in that I can look at a model and see if it 'looks right'.

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    I used Freeship to design this. It is well worth persevering with it. You will need to preprocess the inputs, so do as Bruce advises, build a rough model, measure it and build the input file. Then go at the fairing process. I then used a simple 2D cad programme to nest the planks.

    Quote Originally Posted by Peerie Maa View Post
    This is the plank expansion of a 16 foot boat I designed, nested on two 16 x 4 ply sheets
    Attachment 1282506 strake developments.jpg
    She is a small coble, so a tad extreme.
    Attachment 128251Bow quarter (2).jpg
    Last edited by Peerie Maa; 01-29-2023 at 06:56 AM.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    Hello Garry,
    Produce all the line plans and offsets. Build the moulds or permanent bulkheads/frames from these from the stations and go from there. Set up the bulkheads or moulds run stringers at the chine and gunwale. Make templates off this structure. You could start with the bottom panel if you have the curve of the chine right. That's one way, I also suggest making a model first for many reasons. Sam Delvin talks about scaling up panels from directly from a model in his S&G book.

    You said you have a bunch of books, but if you want to know how some of them did it before computer software. Read the two below, they are great pieces on how to design by two people who knew how to do it. 16'x4', is this a power/row boat or sailing?


    https://www.abebooks.com/Albert-Stra...30345879210/bd




    C079A76C-AE24-42F1-9FB1-B47A16BE63FF.jpeg
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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    The old dos-based program PlyBoats was great for hard-chine designs like this. You didn't have to invest a week of study just to learn a computer program.

    Is there a replacement for PlyBoats -- a simple-to-use program that allows you to play with a boat design, and then give you the cutting-numbers: the distance-in from the edge of a plywood sheet every foot so you can fair a curve?

    I had very good luck with PlyBoats.

    Build A Lightweight Plywood Canoe Dave Hadfield


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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    It's pretty simple really - just very time consuming.

    Start by drawing a Profile (at the centreline). Mark in the datum waterline (dwl) roughly where you want the boat to float, and a chine line if a chine design. Divide the waterline into 10 equal spacings (so you will have 11 station lines usually numbered 0 - 10)

    Draw a Plan view (of the sheer), and add in a plan view of the dwl and the chine. Mark in the same station lines .

    Using measurements from the plan and profile drawings, draw the midships section (Station 5)

    Again, using data from the plan and profile, draw two more stations say 2 and 8 to start building up the Body plan

    On the profile, add a waterline above the dwl and below the dwl. Add the same waterlines on the body plan.

    Using the data from the body plan, draw the plan view of the two new waterlines.

    Now you will likely need to make the new waterlines fair. Any changes to the plan need to be also changed on the sections on the body plan. Keep going back and forth until you have both fair waterlines on the plan and fair sections on the body, with the same data.

    Next you have to introduce a buttock or two (in the underwater part) on the body plan and using the data from the sections, draw this out on the profile. Get it to run fair, and reflect any changes on the sections. Then you'll probably have to change the plan view of the waterlines which in turn may change the buttocks. You simply keep going back and forth until you have a small set of waterlines, sections and buttocks that are fair and all agree with each other.

    Then you fill in more sections, more waterlines and more buttocks, all the time reflecting any changes in one view in the other two.

    Once you are looking good, add in some diagonals and draw these on the plan view (measuring down the line of the diagonals). If they run fair then you are golden! If not it's back to tweaking the other three (sections, waterlines and buttocks) until they do. The data on all four lines must be the same.

    Then with a reasonable set of lines, you do the calculations to get the displacement, longitudinal and vertical centres of buoyancy, prismatic coefficient etc. They'll probably also require the lines to be tweaked to get satisfactory numbers.

    The next step is to draw a 20 heeled waterline on the sections and draw the 20 heeled lines and do the calculations again to see how the heel hull compares with the upright hull. More tweaks will likely be needed.

    For a small boat, or a power boat you don't need 20 heeled calculations.

    As I said - time consuming! But that's the pre-computer way to produce a set of lines. And then make moulds, from which, once set up, you can derive the hull panels, planking or whatever.

    Cheers -- George
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    A C Grayling

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    Well, that ^ is how I was taught to do it, in the 1970's.
    It is an iterative process, and so very time-consuming.
    The joy of Freeship is that you can see the hull from any direction, to make sure that it is good-looking. Freeship does the sums for you, which is also a boon. You can test for fairness, and that the planks can be developed, unrolled flat, and then printed out
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    Quote Originally Posted by wizbang 13 View Post
    Models
    build models
    This.

    Graph paper can be your friend.
    "A dogmatic belief in science is contrary to the principle of science itself...."

    Joseph Cropsey (1919 - 2012) 1964

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    Quote Originally Posted by Peerie Maa View Post
    Well, that ^ is how I was taught to do it, in the 1970's.
    It is an iterative process, and so very time-consuming.
    The joy of Freeship is that you can see the hull from any direction, to make sure that it is good-looking. Freeship does the sums for you, which is also a boon. You can test for fairness, and that the planks can be developed, unrolled flat, and then printed out
    Absolutely. And you generally get a better, fairer result, with better hydrostatics and a lot more knowledge about the design – as well as developed surfaces. And because the basic calculations are pretty much instantaneous, you can tweak the lines as many times as you want to fine tune the design – something that in pre-computer days had to be limited to be cost-effective. And of course the final lines had to be lofted to remove scale errors.

    The only thing that hasn't changed is that you still need to know what you are doing, though the ability to do instant calculations does help as there are some figures and ratios that need to be within certain parameters for a successful design so it's great to be able to keep a handle on these as you develop the design. Calculations 'by hand' are, like drawing the design by hand, very very tedious – and generally rather less accurate.

    Cheers -- George
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    A C Grayling

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    While we are suggesting software that might save a few miles of pencil lines being re-done,the old Hulls program from Carlson Design was pretty useful.

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    You might want to spend some time pondering what you are really trying to achieve :
    a) design a boat - fully
    b) build a boat
    c) sail/motor/row a boat
    If you want to achieve b) (which is mainly what I do with occasional c's) then I'd strongly recommend buying plans from a reputable designer such as Oughtred, Gartside, Atkin, Vivier, etc.................
    If you want to do a) then I'd draft up the shapes which you want to see in the boat possibly using CAD, then loft the hull fullsize. This will let you see what the hull will look and hopefully some idea of how it will act in the water. Be prepred tha this may mean the design needs sigificant alteration but that's ok because you want just whitewash the lofting and restart.

    Of course I have never designed a boat so may well be waffling - sorry about that :-)

    Regards Neil

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    I cannot thank everyone here enough for the thoughtful responses! I will delve more into the "Hulls" program, which I have a copy of. I also picked up some more drafting tools from the local hobby & crafts store while out with the wife yesterday.

    The reason for the build is that I need a "purpose" built boat for what I do. I frequently go fishing on Elephant Butte Lake here in New Mexico as well as Caballo Lake, a little further South. I have an Old Town "Discovery Sport 15" but the hull depth is not enough given the occasional rough water, not to mention the fact that after several years, it is now "oilcanning". I figured I might give the Texas 200 a shot as well as I have recently become interested in sailing.

    I've purchased plans for the Glen L "Minuet", the "Otter", among others in addition to picking up "Boatbuilding with Plywood", "Sprits & Lugsails", "Skeene's Elements of Yacht Design", "Preliminary Design of Boats and Ships", and MANY, MANY more... I've been researching this for around 3 years now. These forums are a WEALTH of wisdom and experience...

    Basically, I needed something with a greater hull depth, greater beam, about 16' LOA, and ideally, the portion forward of the cockpit is covered to eliminate spray entry. I was stuck in some bad weather on Caballo Lake last year where I had to use my bilge pump as I was getting a great deal of chop over the bow (yes, I installed a bilge pump in a canoe!).

    So, I'm going to proceed with Hulls and see where it takes me... The replies regarding doing this manually were much appreciated as well, I will research this too for redundancy. I also have a copy of "Freeship" and "DELFTship", but they seem rather difficult to use for me at this time.

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    I guess I'll be that guy, any chance you haven't come across these plans yet? https://duckworks.com/goat-island-skiff-plans/

    15' 6"' LOA
    5' Beam
    Sails very well
    Rows pretty well
    Relatively easy to build
    Lots of info/builder groups
    I think quite a few have completed the Texas 200

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    Quote Originally Posted by John Meachen View Post
    While we are suggesting software that might save a few miles of pencil lines being re-done,the old Hulls program from Carlson Design was pretty useful.
    Have you ever got that to run under linux -without using a dos/windows based VM?
    I'd much rather lay in my bunk all freakin day lookin at Youtube videos .

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    Quote Originally Posted by P.I. Stazzer-Newt View Post
    Have you ever got that to run under linux -without using a dos/windows based VM?
    Haven't tried as yet.My first choice would have been to try WINE,does that not work?

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    I designed and built a 7-1/2’ dinghy as my first build. I did it to save $20! LOL! Boat wound up costing hundreds. After all was said and done, I should have bought plans, though I kinda did enjoy the process. I did it building a card stock model and then enlarged the dimensions to full size.

    Here's Pixie.

    pixie1.jpg
    Last edited by dalekidd; 01-30-2023 at 05:09 PM.

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    Quote Originally Posted by mattglynn View Post
    I guess I'll be that guy, any chance you haven't come across these plans yet? https://duckworks.com/goat-island-skiff-plans/

    15' 6"' LOA
    5' Beam
    Sails very well
    Rows pretty well
    Relatively easy to build
    Lots of info/builder groups
    I think quite a few have completed the Texas 200
    https://duckworks.com/mayfly-16-plans/

    Or the Mayfly 16, another good option for $40. The Mayfly's have good depth, as you mentioned are looking for, I have a 14'.

    A flat bottomed boat, you really are reinventing the wheel. If you are really passionate about it I say go for it, its a fun process. if you don't get good at the software. I recommend again building a model, one you can test in the water with the proper scaled weight, make sure you get the run right. If you are going to sail it you don't want the stern dragging in the water when loaded.

    Is 4' the beam you are going with? If so then designing your own might be needed as most modern ones are wider. You could start with a 48" wide bottom panel, that's a nice small size skiff, 16' long would be nice in that size.

    I sailed a canoe for years on Northern NM lakes, can easily imagine those rough conditions kicking up you write about. I experienced them many times. I think the size boat you are talking about is a good fit, you will have to be careful, as always, when the squalls come. I ended up just dropping the sail and letting the strong ones blow past.
    Last edited by Matt young; 01-31-2023 at 09:18 AM.
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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    As to how it used to be done, glass, epoxy and stitch and glue have changed things quite a bit. I recall my dad putting together a dinghy as this gentleman is from an old, I think, Popular Mechanics article. The stringers don't just define the shape, they're also needed to hold all the screws and nails that fasten the ply panels in place. In any event, as explained higher up, once you have offsets to create the frames you can set those frames up on a strongback, bend the keelson, chine logs etc. into place, and simply lay on and mark the ply panels. to get the shapes.

    boatbuild.jpg
    -Dave

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    Quote Originally Posted by Woxbox View Post
    As to how it used to be done, glass, epoxy and stitch and glue have changed things quite a bit. I recall my dad putting together a dinghy as this gentleman is from an old, I think, Popular Mechanics article. The stringers don't just define the shape, they're also needed to hold all the screws and nails that fasten the ply panels in place. In any event, as explained higher up, once you have offsets to create the frames you can set those frames up on a strongback, bend the keelson, chine logs etc. into place, and simply lay on and mark the ply panels. to get the shapes.

    boatbuild.jpg
    Which probably won't fit if your chosen design process does not employ conic projection or its programmed equivalent
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    Quote Originally Posted by John Meachen View Post
    Haven't tried as yet.My first choice would have been to try WINE,does that not work?
    I've not tried it recently but have had it fail many times in the past.
    Run well in a VM under Windows 98 or whatever else you have handy, the trick is getting the files back into the Linux environment...
    I'd much rather lay in my bunk all freakin day lookin at Youtube videos .

  23. #23
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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    Design individual planks ... No.
    Having decided max length width and draft, I spent hours and hours , going round the hull shape/ buoyancy loop to fit in the box. This was pre freeship all done by hand.

    Satisfied with the shape I designed, the 5 frames and transom, to fit on a strong back.
    Once made and installed, the hog and top planks were installed..
    After that each plank was laid on the hull and marked out to fit against previous planks
    Just an amateur bodging away..

  24. #24
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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    Plans are worth the money. This is especially true when building a sailboat. Many years ago I took an old 8 foot dinghy and converted it to a sailing dinghy. That SOB ran like a scalded dog down wind, but wold not point up at all. Not a bit. All that work for nothing, not to mention nearly getting blown all the way up to Canada on Lake Memphramagog when I found I could not return to where I had started.

  25. #25
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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    I have thought about designing a boat. After all, I am a retired engineer. Then I decided that if I designed and built ten boats, even small ones, about the time I designed and built number nine, I would have a decent sort of OK boat. Life is too short. That is why we have naval architects.

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    Default Re: Designing your own plywood hull, but mostly just screwing around...

    Quote Originally Posted by ahp View Post
    I have thought about designing a boat. After all, I am a retired engineer. Then I decided that if I designed and built ten boats, even small ones, about the time I designed and built number nine, I would have a decent sort of OK boat. Life is too short. That is why we have naval architects.
    This is less a new design as it is a modification to an existing design with a few "tweaks". In other words, there is an express purpose to this endeavor... And the gap cannot be filled without some effort here.

    Unfortunately, there are few, if any, naval engineers in Albuquerque, New Mexico, thus, this effort requires some research on my part.

    I was "nuking" this, and although not an engineer by trade, am doing best, and I am a "numbers" guy. Given that the first boats were likely reeds bound together and/or dugout canoes, I suspect that while there is degree of complexity to this, it certainly isn't "rocket science".

    I'm giving this my best, if I fail or make a mistake, that's ok, I'll get up and try again, for I have nothing else to do...

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