View Full Version : Strength of Stitch-and-glue?
01-05-2005, 10:56 AM
I am in the process of designing a hull for use in the shallow glacial rivers near my home in Alaska. The hull must be light weight, carry a payload of 900 lbs, and be powered by a 65 hp outboard with a jet unit attached (about42-45 output hp). I am at present re-designing the bottom configuration of the Delvin Snowgoose stitch-and-glue plywood boat to be a satisfactory quick planing hull. After re-reading several of the responces to my inquiries for help in such matters as calculations of deadrise and floatation, I have come to question whether a Stitch-and glue hull will be strong enough for the constane flexing and pounding that shallow river runing will produce. How does stitch-and-glue construction compare in strength to plank on frame construction??
These pics from Devlin's website from a builder who beefed up the construction a bit. Add chine logs, sheer clamps, and a few battens on the bottom and it ought to be as strong as anything out there.
PS - after you've done all that you really have a panel on frame boat, which is why I don't take very seriously those who try to make like there's a huge difference between framed boats and stitch and glue boats.
01-05-2005, 01:24 PM
Seems like your asking to much from this design. The Snowgoose has a 950lb payload with a 7" loaded draft and is rated for a 40HP motor. I'm not familiar with the lamination schedule but I would think its more like the Cackler. The Honker is much beefier in its scantlings and will handle an 1800lb payload with a 8-1/2" loaded draft and its rated for a 70HP motor.
I'm not familiar with how demanding it is running a glacial river in Alaska, but I have been in a fair amount of slop in both my Cackler and Honker here on the Jersey shore and Chesapeake and have never had any trouble with hull failure. I did add some deck framing on both of these boats but the hulls were built as spec, and in my opinion they are more than adequate in streanth. I still have the Honker and have trailered it to different locations here in Jersey and MD and love it. Next summer it will have a slip at the Jersey shore at the Great Egg inlet, which is pretty demanding itself.
I remember reading you initial post about this project and wondered then if what your looking to do is feasable with this design. The Snowgoose is rated for a 40HP motor and your looking to use a 65. I know it will probably handle it, however I personally am not a fan of overpowering any design. Is plank on frame stronger? I don't know, I know there are some heavy duty designs out there, Bob Smalser built a very heavy duty punt type design for logging that would probably survive a trip over Niagra Falls but I don't know how suitable it would be for your use.
Exactly what are the conditions up there? Would a Simmons sea skiff be a contender?
01-05-2005, 01:40 PM
Check out the Tolman Standard. It can be built in 18 or 20 foot version or really any size you want.
They've been used a lot in rivers and don't utilize much in the way of frames. Renn Tolman, who designed the boat and sells the books on building them, lives in Homer Alaska. Its a very seaworth, strong, and light boat. try http://www.alaska.net/~tolmanskiffs/
01-05-2005, 02:11 PM
Originally posted by otterbfishin:
I have come to question whether a Stitch-and glue hull will be strong enough for the constane flexing and pounding that shallow river runing will produce. How does stitch-and-glue construction compare in strength to plank on frame construction??
otterFlexing? No properly built S&G boat is going to flex unless it is specifically built in a non rigid fashion. A plank on frame boat will tend to flex more than S&G but I don't think many people will want a boat that flexes. Most are built so that they will not flex.
Built to the same weight/scantlings, my experience is that S&G is stronger than plank on frame. Plywood on frame is another matter but I'd still go with S&G most of the time.
If I were going to be banging over rocks in shallow water, a welded aluminum hull like many built in Alaska for that purpose would be high on the list. Next might be plywood S&G shell with heavy glass non woven fabric like Knytex sheathing inside and out plus a final layer of Xynole on the outside..
How does stitch-and-glue construction compare in strength to plank on frame construction?? The "strength" of a given hull, at least in the way I think you are referring to it here, is established by adequate engineering of the structure, rather than by a particular construction method. Proper engineering will take the loads and construction method into account, and arrive at adequate scantlings. Things like service life, available materials, and workmanship levels will also be taken into account.
With adequate scantlings and construction stitch-n-glue can certainly be as "strong" as plank-on-frame.
Indiscriminate throwing of extra structure into any boat usually ends up creating weak spots, which break over time. It also usually creates an overweight answer, requiring wasted energy throughout the boats life time.
All the best, Tad
Interesting comments by one and all. So I will muddy up the waters with my humble opinion.
What I envision is a white water sled being propelled by a jet outboard, up swift, shallow, rocky rivers, with a lot of gravel beds, sharps rocks, and being banged off of more rocks then you would care to admitt to. About as abusive use as one could put a boat through, but a lot of fun.
I would think some of the heavily welded aluminum boats would excell at this abuse. But if you don't weld aluminum and have the equipment, then buying one would be next. Kinda exspensive if you could afford it.And if you can't, then you are back to building a rough and tough wood or plywood sled.Fiberglass would never take this punishment or abrasion.
Look at the chine logs (where the sides meet the bottom) in the picture above of the stitch and tape boat. The chine logs are plastic, epoxy, and the two edges of plywood-side and bottom- are covered outside by fiberglass cloth. Reguardless of whether or not stitch and tape construction is strong enough for regular use, Imagine hitting a rock at 10 or 20 m.p.h. on the chine, right between the frames.How many times or how much of a blow can the edge of plywood take before cracking or the chine log is going to crack or shatter.As far as fiberglass cloth inside or out, it is not going to add any strength, abrasion resistance yes. But only to a degree, at some point you are going to abrade through the cloth or crack it, allowing water to be trapped between the cloth and plywood. With the water being trapped,that will lead to rot. It is my opinion for this type of abusive use you will be better off with out glass.
I would think a sled from the heaviest possible douglas fir marine plywood would be the best. With heavy frames, wooden chine logs, that can take shock impact. Also white oak runners on the bottom as well as outside chines as well, to take abrasion and impact. Everything flexes, bridges and steel hull ocean liners flex. You are pushing the flex extra hard, by impact. You might be surprised if you compare the weight of a stitch and tape boat covered with fiberglass, to that of a even heavily framed and planked plywood.
I would go with the one that will take the most banging from one rock to the next, and keep ticking, or floating.
Again look at the white water sleds that hankinson designed for just this abusive use. I am sure that if he thought stitch and tape was tougher, then he would have designed them that way. But he didn't, he designed them for heavy plywood on heavy framing, or heavily welded aluminum. So appearantly he thinks that is the way to go for this use. Have fun, and show pictures of whatever you decide on, maybe a report after you used and abused it for a couple of years.
01-05-2005, 04:41 PM
The Fiberglass composite sandwich with plywood as the core will be stronger and easier to build with a saving of weight over a planked boat, but you'll have to use biaxial fabric and tape inside and out to gain the strength. Then for the keel/bottom - there is always the kevlar layer!
Devlin doesn't design in this manner, but you might contact Jacques Mertens at www.bateau2.com (http://www.bateau2.com) , most of his own designs use a composite sandwich.
We can debate later whether the product is a wood boat or not! smile.gif
01-05-2005, 06:43 PM
Interesting question, otterbfishin. I would agree with the opinion expressed above that strength is dependant on things other than the construction method. Furthermore, I should think "stitch & glue" entirely adequate, provided adequate plywood is used.
Here's an idea, if you can spare a few bucks for some competant design work. Phillip Bolger, well known on this forum, and the designer of my Shearwater Yawl, has designed many (if not all) of the "Stitch & Glue" boats written up by Dynamite Payson. Furthermore, Bolger is a recognized talent in the area of power boats. I believe I've read that he cut his design teeth working for Hacker Craft in Detroit. Bolger also appreciates a challenge, perhaps even more than most other boat designers.
You might approach him with a commision to design exactly what you require.
Just a thought, Moby Nick
01-05-2005, 07:06 PM
I may not fully understand this; but are not epoxy (and most glue) bonds stronger that the surounding wood?
If that where the case, then would not the limiting factor be the wood joined by the epoxy?
The stuctural integrety would be limited by the design and materials used, more so than the epoxy bond?
Build a sound designed boat for the waters you need it for and your laughing.
All the best,
01-06-2005, 01:00 AM
To all of you,
Thank you very much for your intelligent input into this project. I must surmise that the stitch-and-glue type of construction for this project can be strong enough with the addition of longitudinal logs, carefully placed bulkheads, possibly the addition of chine logs, sheer clamps and cafefully designed deck construction. Again thank you all.
I realise that the Snowgoose design was rated at 40hp, Mike, but a 65hp outboard with a jet unit attached only develops about 42hp. The added weight requires a little more transom width to support it, but I think it will be ok to make this and a few other changes to the hull.
It might be interesting here for you all to gather a bit of my rough and tumble, rogue, seat-of-the-pants economy boat design history:
My first boat in 1965 was a home designed 8 foot punt constructed plank on frame of ½ inch plywood to be used for hunting ducks in the brackish water estuaries of the San Francisco Bay area. This was a rugged, but heavy punt that tasted much success in hiding in salt grass, and drifting up on sea ducks downwind.
My first river runner here in Alaska , (1973) was a home designed and built 12 foot flat bottomed air boat powered by a 110hp Corvair automobile engine (rebuilt from a derilick on the edge of town) with a 5 foot wooden Banks/Maxwell prop. To this hull I added a galvanized steel bottom aft using of contact cement. The basic hull was regular exterior grade AC 1/2 inch plywood bottom, 5/4 local spruce frames, and 1/4 inch sides covered with fiberglass resin and painted with polypropylene house paint. I ran this boat 4 years before making a fatal (for the boat) error in rounding a turn downstream at high speed. Didn't make it; this produced a survival situation, as this part of AK is true wilderness. I survived with the help of two fine gentlemen who having seen the debris from my crash floating many miles downstream, ventured farther upstream in their outboard jet jon boat than they would have otherwise gone, and found me.
My next homebuilt river boat was of the same construction only 4 feet wide and 20 feet long, powered by a 40hp Johnson outboard with a jet unit attached (approximately 22hp thrust at the jet), found on a sunken hull in the river and resurrected to running condition. Both of these hulls were plank on frame construction. I ran this boat 10 years until the exterior grade AC plywood finally rotted out.
I followed this with a 12 foot duck boat, plank on frame construction that weighed only 115 lbs when completed. I took pics of the construction of this project in stages, and am presently looking through boxes of stored stuff for them. I will scan them and post them on this forum for you to browse through. This hull was plank on frame, lapstrake, 1/8 inch plywood over red cedar framing with epoxy coating over all and epoxy fiberglass bottom. I happened to use birch/mahogany door skin plywood (mahogany on the outside), and the hull was so pretty that my wife and others insisted that I not camo it out, but do it up bright. I ended up trading this pretty boat for a more useable10 foot aluminum skiff with a new Nissan 4hp outboard. The new owner of the bright plywood duck boat has since put it in several TV commercials, one you might have seen last year with Santa Clause sitting in it on a pond casting a spinning rod, advertising cellular telephones.
The present Snowgoose project will provide me with a boat I can use for fall duck hunting, moose hunting, and spring king salmon fishing. It is not my intention to demise in any way the fine hull designed by Sam Delvin, but to tune it to me needs here in Alaska. I contacted Sam with regards to making some changes for me, but the costs were prohibitive for my meager budget; so also, the suggestions that aluminum might be a better hull material for my usage. I am imprisoned by my small budget, but liberated by past experiments with low grade materials that proved seaworthy.
The Snowgoose project will be built of ½ inch fir marine plywood bottom with ¼ inch sides. I’m close to finishing the re-design lines of the hull bottom. I appreciate immensely the input provided by this forum. I apologize for my rudimentary practices in design and construction.
01-06-2005, 10:18 AM
Sounds like you have a better handle on what will work for you than we do. As for the need for chine logs, etc in a S&G boat, I have seen and participated in attempted destruction of sample S&G chine joints with sledge hammers. The plywood outside the joint area always has failed before the joint. I think Sam's glass/epoxy schedule for the joints is plenty strong and rugged enough.
[ 01-06-2005, 10:22 AM: Message edited by: Tom Lathrop ]
01-09-2005, 06:41 PM
Wow! Thats some pretty rough and tumble pastime you got there.
So your a little nuts huh? (only kiddin)
Sam shows 1"x1-1/2" keels and bilge keels on his duck boats that are very effective for abbrasion, perhaps you could add a few more, say an inch or so from the chines, on both the sides and bottom. That would give you five across the bottom and two on each side counting the gunwale. Speaking of the gunwale, in your case I would beef it up considerably, maybe oak. This would give you a sort of ecto skeleton (sp), probably not the most actractive boat in the world but one that could bounce off stuff.
I hope you keep us up to date on this project, sounds neat..
01-09-2005, 07:12 PM
About the only thing I might try is to add a aluminum skin on the bottom the way you did with the galv boat. Stick it on there with 5200 and go.
We used to glue and tack on copper sheets to prevent ice dammage to the hulls in winter.
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