How does one design a stitch-n-glue boat?

[Matt Middleton]

I've got this nutty idea in my head that I'd like to try to design a small boat, sort of a double paddle canoe, for stitch & glue construction. Who knows if I'd ever build it, but I'd like to go through the design process so I can learn something.

How are stitch & glue boats designed? I have a basic understanding of how to design a hull, but how do you make sure your design can constructed using plywood panels? Is the basic design arrived at first, then adapted to S&G, or do you start by seeing first what can be done with bent ply panels?

Thanks,
matt

[paladin]

get a software program called "Plyboats"...it will do the calculations and even layout the panels for a model or a full size boat...google "Plyboats"...it is an inexpensive program..

[Stiletto]

You can also play around with cardboard and a hot glue gun once you have the general idea worked out.

[Bruce Hooke]

It is not really as bad as it seems. Plyboats is certainly one way to go. The way I did it was to draw the boat out on paper and then test it using first cardboard and then scale plywood. The key thing you need to watch out for is a design that calls for excessive twist in the plywood.

As I understand it, as far as the actual design goes, there are not really any restrictions on the shape of a stitch-and-glue boat beyond the restrictions on any sheet plywood boat. Plus you have the advantage that on a stich-and-glue boat you generally can let the plywood take up a curve along the frame (station) lines, which it will generally want to do (this is the whole issue of "developable surfaces"). On a boat where you build the frames first you either have to figure out how much curve there should be in each frame or design the boat so that this issue does not arise. It is most likely to arise in areas where there is twist in the plywood.

The key "trick" with designing a stitch-and-glue boat is that you have to figure out the correct shape of the panels before you build the boat rather than picking up these shapes from the building frame. I did this using my (carefully made) scale model. It sounds like Plyboats might be an easier way to go.

[Woxbox]

Well, you can do that and have fun, but you'll get a way better boat if you buy plans from someone who's studied naval architecture and benefited from having made all the mistakes. Will your boat sit level, have the stability you want, will it track straight, will the bow dive into the smallest waves, or will it sit high and get blown sideways in the slightest breeze? There's all sorts of ways to screw up. But yes, it would be your own boat! ;)

[Wes Kisting]

Just thought I would echo what WoxBox said...

I know there's a certain charm and romanticism to the thought of designing and building one's own boat from scratch, but really, I think the same satisfaction (probably better satisfaction) can be derived if you carefully select a well-established design that fits your needs and then build it with care, modifying the usual things (colors, comforts, etc.) to "make it your own."

In the end, if you've done your research before choosing a design, you'll end up with a much better (i.e., better performing) hull shape than even most "advanced novice designers" could design. In fact, a lot of very experienced designers will tell you that they don't often have success with the first build of a new design... it's something that is always being refined, hence the wisdom of choosing a proven (and previously built-and-tested) design over designing anew.

I'm sure you could very easily design your own craft and probably do a decent enough job to come out satisfied with the results. Partly, you wouldn't even realize what you were missing unless you compared it side-by-side with a professional design. If you do take the risk, however, as I have sometimes been known to do myself, I would highly recommend that you build a VERY cheap prototype of your boat the first time around. For a canoe, make a cardboard model first as others have suggested, then perhaps a scale model in balsa. When you go to build it full-size, I would throw it together cheaply out of a few $6 - $8 sheets of Luan ply and a thick coat of acrylic latex paint (wouldn't even bother with fiberglass or epoxy on the prototype... except to join the panels). For about $50, you'll have a boat that will last about one season (years, in some cases, though not likely) and give you a very good idea of whether you really want to build the boat out of finer materials (marine ply, epoxy, etc.). It will also give you an excellent opportunity to think about what you would like to tweak, and what doesn't meet your satisfaction (stability, speed, maneuverability, etc.)

There are other ways to approach this, of course, but for a newbie designer, that's what I would consider the "smart" approach if you're absolutely dead-set on designing your own.

Also, to be clear... I'm not trying to burst your bubble. I honestly believe it can be great fun to design and build your own simple boats... The mistake I am cautioning you against is the story you hear every now and then: a first-time designer designs his "ideal boat," then builds it out of thousand-dollar-materials with years of painstaking labor, only to find that it's a complete performance catastrophe. Keep it simple and cheap, and you'll keep it fun!

[Lewisboats]

If you were proposing building something big or complicated, I would agree with the above, but on a simple ply canoe I think you can take the chance ;) . Plyboats, Hulls, Carene50 will all give you developable panels. All you have to do is get the shape you want. Plyboats and Hulls you can still get on the web, but email me for Carene50. It is an older shareware program that isn't available anymore (that I have found). I have built 5 boats that I have created using it (and subsequent versions) and each has performed to the level that I expected it to. FreeShip will give developable panels but the learning curve is a bit steeper for the software.

Steve
numbaoneman@aol.com

[Bruce Hooke]

Originally posted by Wes Kisting:
I know there's a certain charm and romanticism to the thought of designing and building one's own boat from scratch, but really, I think the same satisfaction (probably better satisfaction) can be derived if you carefully select a well-established design that fits your needs and then build it with care, modifying the usual things (colors, comforts, etc.) to "make it your own."I wouldn't argue at all with the point that choosing a proven design by a professional is a safer route to go and that designing your own boat is a somewhat risky venture. What I do disagree with is the idea that taking that safer route is as satisfying (to someone with a strong desire to design their own boat) as designing your own boat.

It is hard to put into words, but there is something intangible but very satisfying about knowing that it is your own design. I tend to raise caution flags when people start talking about designing their own boat, but having gone that route myself I am also very sympathetic with the urge to do so.

At the very least, since Matt has said that he is not even sure he will go through with building the boat but just wants to try designing it, I would very much say GO FOR IT, especially since we are talking about a double-paddle canoe here!

[Todd Bradshaw]

The vast majority of the successful canoes designed over the last century were not designed by naval architects. They were designed by canoeists who decided they wanted a better, or faster boat. Most of the top production canoe companies of the past five decades or so got their start just that way (Mad River, Sawyer, Jensen/We-No-Nah, Lincoln, and many more). Naval architects don't generally want to mess with designing canoes because there isn't any money in it. The few who have designed canoes probably have a better understanding of the interaction between their hulls and the water, but that doesn't mean they're winning races.

I'm not saying that the better canoe designers have no knowledge of naval architecture, but most of them were already messing with canoe designs when they decided to start studying it as a means to improve those designs. I say go for it. You never know where it will lead you. If you're unsure of your design abilities at first, I offer you this bit of wisdom from the Voyageurs of the past:

"De Wind she blow on Lake St. Clair,
She blows an' blows sam more.
If you don't drown on dis big lake
You bes' keep close to shore."

http://www.imagestation.com/picture/sraid29/pbed31eb2dc0725d92b385e84e504d4db/fd60f08f.jpg

[ 03-22-2006, 03:44 AM: Message edited by: Todd Bradshaw ]

[Matt Middleton]

Thanks for the responses, everyone! Your responses have been helpful and encouraging!

I guess I had it in my head that it was a complicated thing to make sure all of the panels were developable, but maybe the CAD programs help out in that regard. My worry had stemmed from the fact that I have been making paper models lately, sketching panel outlines by eye, cutting them out, and taping them together. As you may expect, the results were less than successful. I suppose that it's one thing to build a boat out of many wood strips or smaller planks, and quite another to take a few larger flat panels and tack them up into a boaty shape.

I had initially thougt I should do a design by hand to get a more authentic or complete design experience, but I like the idea of using a CAD program to supplement the process. I have played with FreeShip some, enough to have worked through a couple of tutorials. Maybe I'll give that a try.

If my attention span is long enough to make it through the initial design phases, I will definitely build a model. (Todd, I like the method that your photo illustrates- thanks!) I also like the idea of a cheap luan hull to use as a mock-up to illustrate the difference in a paper/screen hull representation and the real thing. (Again, that's if my attention span is long enough...)

Thanks again everyone!
Matt

[Bruce Hooke]

Developable surfaces have unfortunately been very poorly covered in most of the books about boat design, which I think may have given them their somewhat mythic status. I've read the discussion of developable surfaces in Skene's Elements of Yacht Design many times over and it still leaves me scratching my head. Fortunately, there is one clear, concise discussion that I have found, which, at least for me, very effectively clears away the fog surrounding this subject. It is in a book called Problems in Small Craft Design: Selected Papers by Members of The Society of Small Craft Designers and the paper (chapter) in question was written by Samuel Rabl. This book was published in 1959 so it is LONG out of print, but there appear to be plenty of cheap copies on Abebooks (http://dogbert.abebooks.com/servlet/SearchResults?sts=t&y=12&tn=Problems+in+Small+Craft+Design&x=60).

With the advent of software like Plyboats this may all be superfluous information, but I still like to understand the principles of the matter even if software will take care of the math.

[Wes Kisting]

Geez, some of you guys took a pessimistic view of my post smile.gif

Again, I wasn't denying the rewards of designing one's own boat, just cautioning against the manifold dangers which (more often than not... though we can all think of "sucess stories") cause no little frustration and prompt the building of 2, 3, or even 4 prototypes before the designer finally obtains what he was hoping for. (Or, else, simply settles for the first prototype and some disappointment about "what could have been done").

But I do see the joy of design. I would disagree, (politely, of course) with Lewisboats suggestion that good design is somehow less critical in a canoe or kayak than it is in something more complicated like a big ship. It's true that as long as a boat is fat in the middle and pointed at both ends, it will probably paddle something like a canoe and get you where you want to go. But I think folks who have designed a few canoes and kayaks will tell you that in some respects, it is more critical to produce an accurate, fair hull in a canoe/kayak than in a larger ship.

A larger ship (like a pocket cruiser or moderate-sized sailboat) offers more ways to balance out a few minor design flaws later (shifting the ballast, modifying the rig, etc.). If you plug a canoe or kayak into design software like Hulls, Freeship, or any of those other programs that pop up regularly... you'll see that it doesn't take much alteration to the hull form to affect drag. Small as it sounds, a tiny shift in rocker or the taper from stem to stern can make the difference of a comfortable cruising speed of 3mph or 4mph. That seems very small (only 1mph difference, right?), but as soon as you paddle the "slower" of the two kayaks, you'll realize how BIG that difference is... either having to paddle much harder (drag increases exponentially beyond the comfortable "hull speed") or settle for much slower progress over a long day of paddling.

That's why I advised caution, Matt. Because it's almost impossible to work out those little particulars unless you have a very reliable software package and a solid education in the principles OR you build several prototypes and tweak the problems as you discover them. But still, as I said before, I also think the risks can be very well worth the experience as long as you don't invest too much in the initial experience. Cheapness is the key. Another smart idea is to take measurements off of canoe hulls that you have paddled and enjoy... this will at least help give you a working idea of basic requirements (max beam, amount of rocker, flare, tumblehome, etc.) that will help meet your needs and expectations. Certainly, it's much easier and safer than "designing completely from scratch" if this is your first go.

Partly, my advice was being practical, too... you can find an existing hull shape for a canoe that will do just about whatever you want it to do. (assuming you are willing to compromise... obviously, you can't have a canoe that cruises at 30mph, turns on a dime, portages itself, folds up into a pocketbook, and is self-maintenancing... even if we all would love to have one!) Designing your own hull for anything other than the sheer rewards of designing it yourself (as Bruce points out above), is really unnecessary if your goal is just to have good performance in a self-built boat that meets your needs.

Again, not trying to deflate your enthusiasm, as I have been known to design and knock-together a few boats myself! And it IS fun if you do it cheap, quick, and with reasonable expectations for your first tries.

[JimD]

If you want to reinvent the wheel then you might have quite a job in front of you. If, on the other hand, you are willing to start off with a proven design and modify it then I bet you won't go far wrong. For example I built a tursiops kayak and didn't like it. So I redrew it as a narrower, shallower boat and ended up with this:

http://www.imagestation.com/picture/sraid202/p085ce4b0d6dc2b03420a53621fb675f6/efbf1321.jpg

Compared to the three kayaks I've built to professional designs it's turned out to be the best behaving of the lot and I made no calculations whatsoever. I just eyeballed what I thought needed to be changed on the tursiops and went ahead and did it.

[George Roberts]

Matt Middleton ---

You can make anything out of plywood. Just take some 3mm sheets cut them into 3/4" wide strips and build. (I expect that is a bit different than you stitch and glue model.)

As for designing a good boat ...

I am sure you can find a production boat that better suits your needs.

I am also sure that a boat you design will better suit your needs than most boats would.

---

If you happen to be on the water in "unexpected" conditions, you might be wishing for a different boat.

[Lewisboats]

From what I got out of the tone of the original post, I don't think that the ultimate in performance is part of the criteria.

"sort of a double paddle canoe, for stitch & glue construction. Who knows if I'd ever build it, but I'd like to go through the design process so I can learn something."

This suggests to me that the exercise is more a learning experience but not to the extent of learning conical and cylindrical projection. The resulting boat would only get built if he came up with a design that he felt would be worth building. If in fact the design was a bomb, there is something to be learned there too, isn't there. Still...odds on it would float and move through the water and that may be all that is needed for now. So I still stick to... Go with it!

Steve

[Matt Middleton]

Thanks again for all the replies. I've considered them all to be constructive, and I appreciate that.

I'm no naval architect, and I don't have years worth of paddling experience, but I do have an idea in my head of the perfect boat for me for now. I'm not very inventive, so like most of my ideas, this boat is based on a couple of real world designs, but modified for my favored set of compromises (as some of you have suggested as a good way to start).

So more than anything, this is just a way for me to get my kicks, and maybe get smarter in the process. What have I got to lose? (except for some time, and maybe some pride when i post the design and you guys poke holes in it... ;) )

Later!
matt

[Wes Kisting]

Lewisboats... I wasn't telling Matt not to go for it. Just cautioning him to proceed with care and realistic expenses/expectations.

Your original post suggested that you disagreed with my advice, as you said: "If you were proposing building something big or complicated, I would agree with the above, but on a simple ply canoe I think you can take the chance."

I thought you were disagreeing with my advice to build the boat cheaply and quickly, with little investment. (i.e., telling him to "go for it" and lavish time and expense on the materials of an unproven design his first time out). Apparently, I misunderstood.

If you were disagreeing with my cautions against designing his own, I voiced them in the interests of being prudent. My original post still goes on to admit the appeal of design, to demystify the process, and offer him words of encouragement. Hence, my confusion.

Anyway, it turned out to be productive confusion: He's got some sensible advice to mull over from all of us now. smile.gif

[ 03-22-2006, 08:03 PM: Message edited by: Wes Kisting ]

[WayGray]

I don't see disagreement in the previous posts. Instead, each one discusses a separate aspect of "the truth". I can see the artistry in doing a beautiful job of building someone else's design. For me, the creativity comes from transforming a vision in my mind into a real boat I can touch and use. The risk inherent in a first design is part of the thrill. Do your research carefully. Use proven designs as a guide. But design something unique to your requirements, or you are just 'reinventing the wheel.". Conic & cylindrical projection will get you a stitch-n-glue design and has been a special interest of mine. The basics can be had by exploring the several ways you can curve a piece of paper without creating creases. Then do the same thing mathematically, if that challenge interests you. Or use one of the established programs. It all depends on what part of the process "floats your boat". Good luck.

[Philip Maynard]

Matt, There will never be any shortage of good advice telling you want not to do and then they will argue among themselves about what you should not do. My 2 cents is there is nothing quite like being on the water in something that is yours, that is something no designer can do for you.

[Woxbox]

I used to think I could design a better boat for myself than the professionals, so over the years I've sketched out numerous designs for sharpies, catamarans and trimarans. It's a learning experience - because when you start to try to figure it all out, you learn more than anything else why successful boats look the way they do. And you also learn that, short of spending all of your time on the study of this stuff, it's unlikely you'll top the good designs out there. I wouldn't say don't do it, just that you've got to approach it as a self-educating experience. And wear a life jacket first time out! ;)

[JEM]

A simple plywood canoe could be designed by trial and error. Plyboats is a great prgram for this.

You could also find a design that is close to what you want, build a model, then make the custom changes you want, and see how it works.

[Dave Hadfield]

I did exactly what he says.

I wanted a simple flat-bottomed canoe, rockered just right to have the stems touching with my weight plus the weight of the hull plus lunch on board. (A unique, personal, individual design criteria.)

Using PLyboats, I was able to play with the rocker, freeboard, and beam to easily arrive at a hull that matched the above. At every tweak the hull displacement is tabulated, so you can see the effect.

Then it lays out the plywood developement, which I used to put together the boat. (Simple, cheap underlayment.)

Result -- exactly what I wanted. A boat that was perfect for the intended use -- a complete match on all points. I couldn't be happier with the result.