Ply on Frame/Stitch and tape

Sam: designs from the 50/60's will not take advantage of the capabilities of modern materials like marine plywood and epoxy glue, and the revolution in boat design and construction that they have inspired. The ply will be unnecessarily thick to allow for the use of inferior ply with internal voids and poor glue, the frame will be strong enough to withstand bending that thick ply, assembly will require lots of screws and the frame members will be extra deep to retain them and extra wide to keep the screws clear of the fragile ply edge. To cut the planks to shape for a POF the builder will lay the ply on the frame and mark it to fit the frame, so the design will have the dimensions of the frame not the planks.

The construction sequence for stitch-and-glue is quite different and you must have data on the shapes of the planks - called the developments - so you can cut them very accurately. The plank shapes define the shape of a S&G hull - not the frame. Despite thinner ply, as a S&G hull is pulled into its final shape stresses develop that must be taken up by the stitches. The stitches must not pull through the plywood during this process. Keeping the stresses within bounds may require certain compromises in hull design that a ply-on-frame design may not have or need.

As always when questions like your one are asked, I recommend to start small if you want to design it yourself. If you just want to build the boat of your dreams forget about adapting other boat designs, which is a design activity. Buy plans or even a kit, and before you select a design define what you want in a boat, then prune out everything you don’t actually need. Get some time on other folks’ boats to help you understand what you need.

 

me ? something wrong you know that can never happen !

As Mark kindly mentioned, we were comparing 16ft Kayak building.

I am certainly not canning the S&G method, but I was certainly criticising the offhand way some enthusiasts portray the ease of execution. My earlier remark about the catch all phrase "adjust the wires to bring the panels into alignment" still stands. This should be better expressed as "spend an aggravating hour and half with levels, pliers, and hammer to get the hull in 'kilter' before epoxying the chines". Then, after that little exercise, 1 bump before the epoxy goes off, and all the work is undone.

Its just as easy to create some kind of supporting framework in the first place - and be assured of accurate layout.

Exactly my point - but the trouble is determining the "proper execution and sequence of events " when the designers themselves are so offhand with the instructions.

Likewise - thousands of boats have turned out warped and unusable. Sam Devlin himself has a dinghy he built, in his workshop eaves that is so 'bent' that it is unusable, Mr UpChur has a bit of 'hog' in his keel line - and I could put you in touch with people who have ruined their backs trying to manhandle 25ft panels without assistance ( mechanical or personal)

Oh ? I consider it part of very normal for S&G. If you have a 4mm, 4inch wide plank, 16ft long, that you have to present to temporary frames - upwards - before stitching, you get a very floppy event that requires much mucking around with temporary bracing, or if you are in Sam Devlins world - his son helps out by holding the side panel for a 10ft dinghy.

One builder of a 26 footer had to create rolling steel stands to hold the panels in place while the bottom chine stitching was done. On the PT Skiff, they fasten temporary 'arms' to the bottom of the floor moulds to support the first chine plank.

I repeat again - all this effort to cope with awkward handling, why ? - when it takes just the same amount of effort to make female moulds that the planks can be dropped into, and they stay in place with gravities help.

Yes indeed - all the more reason for have adequate female mould support, strongback and solid support - and that applies to any S&G project over 10feet.

You may not need to climb into a ten foot dinghy, but you certainly have to lean over the edge to apply epoxy etc - an event that has to be done with extreme care if you dont have any proper support and bracing.

Many S&G Boats kits ( like the PT Skiff) now also supply the patterns for the building moulds and other support tools.
Thats because they realise that 'freeform' S&G is so fraught with errors.



Mark will enjoy the strip planking exercise because everything is held rigidly in place during execution - and it wont take a bump or bad light to put the whole hull out of kilter.

But, by the same token, I wont miss the horrendous 'fairing' exercise, particularly inside as well as outside, and the sheer tediosity of working with 25mm strips of timber instead of 1 foot wide on strip plank. ( the whole epic story at http://greencanoe.weebly.com/building---the-very-beginning.html )

But, I do still get a kick out of looking at the seductive curves of the strip plank hull long after the pain is forgotten.

For others like Mark and myself that didnt get totally happy results for 'bright' finishes - 2 points

1) If you use West Systems epoxy, 207 hardener is suitable for clear finish - the 205 and 206 are not recommended - ( technical manual page 12 )

2) Dont overwork the epoxy when you apply it to the cloth - the stuff that you take off the surface with the squegee should be scraped into a throwaway container, not re-worked into the cloth.

Long live little boats !!!!!

 

Terry,
Thanks very much for all this info, all very valuable valid points,
I dont intend as a career to venture much above 20' so as a beggining small is deffinately the order of the day, Ive not made any decision what to do anyway, I suspect a first project would be of the order of 10' max,
again, thanks
Sam

 

Mr Watson,

I did not intend to get into a shouting match. You make some valid points but, in the end, fail to make a strong case against stitch and glue construction. All boatbuilding methods require a learning curve that the prospective builder must go through if a good boat is to be the result. S&G is no exception and anyone who holds or fosters the belief that it is a simple cure all where no knowledge or skill is required is living in fantasy land.

As far as female molds are concerned, perhaps the very first boats to built in the taped seam method were built this way with fiberglass and polyester resin in the 1950's in Norway. I redesigned the Windmill Class racing sailboat to be built in a female mold with plywood/epoxy/glass some years ago so am very familiar with the method. In that case, I chose a female mold because of the demand that the finished boat meet tight class tolerances that the home builder would be unlikely to meet outside of an accurate mold.

I have also built or helped build many dozens of S&G boats from 8' to 28' and have handled panels of 3/8 ply over 25' working alone so am familiar with the problems there. Ingenuity and/or proper instruction overcomes all of these. Some kind of cradle, as you suggest, is very helpful in making a butterfly molded S&G kayak sit still and conform to design while seams are epoxied and taped. It is just part of a good building program.

Since I also design a line of S&G powerboats up to 28', there is a serious attempt to foresee, properly warn and instruct the builders in how to deal with them. Some glitches still creep in and are dealt with through communication. It is impossible to know all the interpretations that a novice home builder may reach on even the simplest instruction. Pity the poor builder who gets inferior plans in any construction method and has no contact to the designer. That is where forums like this one have their best value.

Some boats are able to be built in several construction methods, some are not and some even use all of them in the same boat. Choosing the right or best one one for the task at hand results in the best boat for its intend use. In many cases, that best one method is S&G.

 

My first experience of boatbuilding was helping a friend build a S&G canoe. Handling the floppy panels was difficult: the sheer planks were worst as they were very long, and wider at the ends than at midships. They broke the first time he tried to get them in place even with my help. He spent a very long time fairing and sanding the seams, and never finished the boat - years later it still languishes in his garage.

 

Terry,

I have to admit that among all the boats I've built there is not a single wired up multi-side panel kayak among them. Lapstrake boats have either been built over a mold with ribbands or some other controlled method. If there is no anchoring method for these long strakes, I can see how that can get a bit messy. I guess it is a case of weighing the advantages of a S&G boat against the problems that that particular situation brings about. Still, there are a lot of successful kit kayaks built that way. Fortunately most S&G designs don't face that problem to such a degree.

 

When working with my friend on his S&G canoe, as well as the plank handling problems he became frustrated with all the holes that needed drilling and wiring, getting the planks to mate along the chines, glass taping the seams, figuring out how to make the epoxy gunk non-slumping and applying it along the seams, and sanding it down to a smooth appearance. It was about then that he had enough I think; I suspect he had already done all the hard work but whatever, he stopped. I think with better organization (he did not have instructions for the boat - just a drawing set) an S&G boat need not be so hard but I found methods that seemed a lot easier for my boats.

 

Terry,

If any builder is not willing to learn the proper techniques of any method, they would be best to leave it alone and work with the method they are most comfortable. S&G is not as satisfying to work with as working with lumber, no argument there. The benefits often greatly outweigh the effort to learn and some superior performing boats can be built with it that can't be duplicated in lumber. Granted, some experts can equal or come close but then they are experts and their works in not fairly rated against the novice or journeyman builders.

 

I am sorry you thought I was getting into a shouting match, and even sorrier that you thought I was trying to make a case against S&G - far from it !!

I must not have made my points very clear - though it seemed clear when I wrote it.

The 'case' I am arguing is for decent supports and patterns when stitching and gluing - not 'freeform assembly' as some tutorials suggest is good enough.

I will stop there - and keep it plain.