Hybrid Construction

You've described a (similar) method for building what is known here in Maine as a 'West Point Skiff". The West Pointers are generally pine strips thick enough to edge nail using bronze ring nails. The frames are added afterwards, so tensile strength comes from the shorter nails and the continuous frames (of steamed oak).
No glassing is done, this is old school stripping like the Amphibicons and a few one-off boats done that way back in the fifties and sixties. Such boats tend to last well though they are a bit hard to repair.
Your method depends on the frames alone for cross-grain strength, but spaced correctly, they should work as well as the West Point skiffs in terms of holding together. They will just need enough frames, which is more of them if you're not edge nailing.
The quality of the wood is vital; quarter sawn wood will shrink/expand at half the rate of plain sawn. A wood like cedar, and in particular like eastern white cedar (soft and light) is important too. Cedar "springs" back when crushed while most other woods don't so well.
I assume the method of attaching planking will be rivets or clench nails?

 

Assembly is entirely by glue - no nails or rivets, and the glue takes the place of edge nailing. Tensile strength comes entirely from the ribs, as it did for the wide plank and batten method that I have studied where the battens were used primarily to keep the plank seams aligned and sealed. Compared to 4 mm marine plywood planks the ribs have half the tensile strength of the center veneer, double the cantilever strength and much greater stiffness. I depend on the ribs - not merely for strength - but for accuracy; they define the hull shape since no building form is used. I found a West Point Skiff site; the ribs look to have similar proportions to my design - allowing for the different size of boat.

As far as repair is concerned, it should be easier than for a conventional strip-built boat as there is no glass to contend with, and also easier than glued lapstrake.

Your comments on wood quality are noted. I may have a problem in this area as I am only able to get hardware store quality cedar at present. However it’s not too bad and I can take slash-cut planks and cut off strips that approximate to quarter-sawn. The cedar is too dry and rather brittle; for the ribs where I need sharp bends I use pine. I look forward to getting something better such as ash later.

Later I can get out to a decent wood-yard and hopefully obtain boat-quality wood; in the meantime it is a good test of whether the average DIY boat builder using readily-available wood can do this.

 

I've been working on the stems lately and progress has been slow as my ignorance and inexperience is starting to show. Finally I have a decent-looking pair complete with rolling bevels.

I threw away the first pair as I did not realise that, with the bevel rolling a full 90 deg around the stem, I needed to make the stem foot wider to give enough glue area for the strips. I tried laminating them at first - I don't want to talk about it!

Cutting the rolling bevels was also a learning experience. I worked my way through several of my power and hand tools and eventually found it was easiest and quickest to use a simple chisel. It just seemd to roll around like it was programmed. My chisels are Japanese and cut wood like cheeser.

So now I'm back to mass-producing ribs; I have 20 and need another 16. I find they take less than 10 minutes each fully finished so it's not working out too bad time-wise.

If I do another version of this boat I may make the entry narrower and let the strips twist, so the bevel doesn't have to roll so much. I am wondering if it is practical for the stem to be beveled at a constant angle so a router can be used: it would have some kind of impact on the entry and exit shape.

 

Here is a link to a traditionally stripped (non-epoxied) bit of a boat from Weston Farmer. I'm sure you've run acrossed it before, but there might be a tidbit of information in the text that you'll find useful with your current build.

http://www.svensons.com/boat/?p=Utility/DollyVarden

 

I gotta admit at first I thought ole Daniel was some loony tune with a hammer but the more I read the guys stuff the greater respect I developed for him. I cant wait to see him finish his house boat. Maybe if we all play nice he'll come back and entertain us with his ever present wisdom.

cheers
B

 

LP: thanks for the link: a bit too olde-fashioned for me - must have pre-dated epoxy and color photography

Some good info though, and I made a note of it for future refence. Some of the methods are similar to those in a book I have on Wood-and-Canvas canoes and it echos some of the late 19th century methods recorded in John Jennings seminal book "The Canoe"

 

I haven't done much lately, I took a step back and reviewed what I have so far. The stems are nice and I am keeping those but I am unhappy with the quality of the ribs, so I plan to junk them (or perhaps keep them for a SOF later) and explore new ideas. My overall objective is still to come up with good methodology rather than just build a boat ...

There have been two problems with the ribs. The shape is not exactly what I wanted as there is a pressure point where the curve changes to a straight section and there is a tendency to failure and distortion there. Also the clamping arrangements are insufficient to keep the laminations pressed together over the entire length while the glue sets. So, while the ribs can be used they look crappy, or at least not up to the standards I aspire to. I still hang on to my delusions of adequacy ...

I think there has to be two features in my new approach. First, the shape must have a gradual transition from curve to straight which I can achieve by bending a batten to a fair shape rather than using ruler and compasses in an attempt at a geometric ideal. Secondly, I believe if I stop applying the glue before reaching the ends - and make the strips a little longer - I can clamp the ends and achieve some friction between the strips as the three strips are bent. This should create considerable and uniform pressure between the inner and outer strip that will be as effective as lots of clamps or ties, as is usually used. It is not practical to use large numbers of clamps when mass-producing ribs as I wish to do.

I also feel the bending jig is unnecessarily complicated and time-consuming. I plan to try out a new design and will report back in a few days. I may actually know something about laminating after this exercise!

 

I haven't gone away or given up, but my health has been lousy lately, heavy cold which led to hacking cough which led to bronchitis which led to gasping for breath, so I didn't think a cold garage full of wood dust was a good place to be. The idea for a simple rib-bending jig is looking good. Should be able to resume working on the canoe soon ...

 

Sounds like my last few weeks, except the antibiotics they gave me for the mild bronchitis is not working and tomorrow I go hound them for something else

 

late

I know this is a bit late but may be useful. I built a skin on frame rowing boat two years ago. it was built by eyeball with no molds at all. the ribs were laminated inside temporary ribbands. I had access to 3/4" thick Alaskan Yellow Cedar, so I ripped it to 3/16" thick and laminated three pieces in place using a bunch of c clamps and dozens of clamps made out of PVC pipeI got a pretty fair hull that was very slow to build. Not recomended. The cedar bent and laminated beautifully with no steaming at all. Maximum beam was 50" with a hull depth of 14" midship. The very fine bow sections required that the ribs be two piece with a solid piece to joint them and attatch to the keel. If I were to do it again, I'd take the time to loft and get molds to work from.

 

I thought Constant Camber was a Jim Brown invention.

 

I have also been under the impression that constant camber was a Jim Brown/John Marples/Dick Newick invention.
Steve.

 

I expect to return to work tomorrow. I am moving at a reduced speed but will post pics as soon as it's worth it. In the meantime thanks to all of you for your help and suggestions, your warnings too!

I had to search for a description of the constant camber method as I hadn't heard of the term previous to this thread. It does seem to have originated with Jim Brown.

Although the details are different the method shares the ideas of using standardization to minimize work, and reducing non-boat material with my concept. As with Jim's method, the key to success with my concept is ensuring the profile is indeed constant. In addition it must have a substantially circular radius to allow the strip bevels to be constant end-to-end and the same on all strips - not as simple as I thought.

The ladder jig for forming ribs would be the way to go for speed, given a good design, but I gave up on it - at least temporarily - until I gain experience with laminating, as it represents a lot of work to invest in something I am not sure about. Instead, I took a simple piece of thick ply and attached small wood blocks to define the rib shape. I played with that until I was getting an acceptable shape, and then I expanded it to have four rib-forming stations. As is usual in boat building, I am limited by my clamps.

So currently I am limited to producing 4 ribs at a session instead of the 10 I had with the ladder jig, but they are smoother in shape and - I hope - more nearly identical. I need 30+ ribs; at only 2 sessions a day and 4 ribs per session I need more time to finish them and move on to the next phase.

The original plan was to work on other bits like cutting the cedar strips and shaping stems in parallel with making the ribs but ...

“the best laid plans of mice and men gang aft aglay’ - Robbie Burns
“Only a fool makes plans for something he hasn’t done before” - me

 

"Skira Single Frame Curve Method of Designing and Constructing Hulls"
Patent Number: US 6,564,737 B2

 

Par: thanks, that is the same concept. Interestingly the patent was filed in Aug 2002 whereas there are references on the web to the basically identical Constant Camber technique being pioneered by Jim Brown back in the 1970's. It seems likely that Daniel - and I for that matter - arrived at the same idea independently; it is called convergent evolution by geneticists.

It is not the first time this has happened to me; I "invented" the Bruce foil around 2004 ... it was very disappointing to discover it had been around for 30 years. No wonder a full patent search is so expensive - it is much easier to find a patent from the filer's name or patent number or title than from a description of the basic idea.

When it comes to patents timing is all; being too early is as bad as being too late. As an example the clock timing circuit used in most computers was developed by me at Plessey laboratories in 1968 and patented. However computers did not appear in great numbers until years later and Plessey, which owned the patent, had self-destructed by then so it did neither of us any good. Sigh.