Hybrid Construction

Doing the frames is probably going to take you as much time as doing extra strips. You'll most likely need four laminations in each frame to keep the springback minimal. You have to align them and clamp them while they're slippery with glue, then you invariably have to do some cleanup on them afterwards. I think that by the time you've done 18 of those you could have sorted quite a few strips.

For the topsides, why not just do the plywood section as a lapstrake? Strong and simple join to the strips and will look good if lined off nicely.

 

- it's possible, but I hope not.

I think that would look great, especially in the water, and it solves the joint problem too. When/if I get to the top of the stripped bilges I will take a look and see how I feel about it - I haven't any experience in lapstrake yet.

 

Laminated frames are strong and look cool so if you're into them for the coolness factor then go for it. They do tend to be a bit messy and time consuming to make though, so I wouldn't expect to save time that way. Having only one form required for all the frames will help but you still have all the gluing, clamping, cleanup and sanding to do on them.

Doing a lapped sheerstrake would be easy. All you really have to do is cut it much the same shape as it would have been if flush, but with a bit added to the bottom for the lap. No need to fair the joint flush either. Piece of cake.

 

The ribs sound like a challenge. One approach is to make ultra-wide ribs and slice them into several ribs but I don't have a bandsaw; another is the multi-rib mold, incorporating clamping at one end and stapling the other end of the ribs. My Christmas gift to myself was a bench belt and disc sander which should help cleanup. I haven’t installed it yet as The Wife found it and gift-wrapped it for me, then I got sick after Christmas so it’s still in its box.

At least I don’t have to bevel the outer edges of the ribs to fit the planks since I can install the ribs at right-angles to the planking; this is possible as the ribs are not full-width. I believe I can also calculate the rolling bevel of the inner stems precisely enough to save some time there, too.

For a typical full-size first-time stripper about 200 hours seems to be average for a moderately equipped amateur, inclusive of sanding and finishing, but 160 hours is probably more appropriate for this small solo canoe. The design approach should save some time during stripping, but that is unproven. Half the strips are being replaced with ply which in my experience goes about 4 times faster, which should save 3/8 of the time or 60 hours.

How long will the ribs take? Your projection of 4 laminations is probably right, thick laminations will crack and I don't want to have to steam AND laminate. My workshop is fairly well sealed from the weather so steaming would rust half my tools ...

There will be about 34 ribs, I’m guessing 16 hours plus 4 for the mold, which projects a 40 hour overall saving. Gonzo predicted 20 hours a few posts back, if he thinks in pro hours we are in the same ballpark. I need to to do way better than that to convince the sceptics!

We'll have to wait and see. Sorry to keep everyone on tenterhooks like this, but I don’t want to start until I am fit, to make it a fair trial.

 

They wouldn't really be a challenge. Just a bit of messing around. There's nothing particularly tricky about doing them if you want to.

 

Get the chronometer out and an official timekeeper

 

I tried bending cedar and it's too brittle for the rib lanimations, at least not what I have, although it is nice clean stuff. Even ripped to 3/32" thickness it creaks and splits out at the edges. I tried clear pine and that is much better, at 1/8" thick it bends easily so I should be able to get away with only 3 laminations. I'll keep the cedar from the strips.

 

Might pay to overbend them slightly. I remember the Gougeon Brothers book had a formula for springback vs number of laminations (in the back of the book). They got it from another source but I don't know which one.

ETA: Found a couple of links for ya. http://www.woodweb.com/knowledge_base/Calculating_Springback.html and http://www.richardjonesfurniture.com/PDFs/LaminateSpringback.pdf

It's funny how one link says the formula is awesomesauce and the other guy says he's found formulae unreliable. Hey ho. Anyway it gives an indication of how rapidly springback can decrease when you add an extra lamination. Try one and see what happens.

 

I think the formula may be a little off - I seem to recall seeing it as 1/(n62-1) instead of 1/n^2 but it is fairly close either way. I find it reliable.

My jig will preform the bend to 90 deg, and the springback - about 7 deg - will be about right for the sheer flare angle; nicer looking than vertical sheers and it should result in a nicely-raked stem.

 

Terry for your radius, mold up for a 10% smaller radius and it'll spring back to what you want.

 

Thanks PAR, that has turned out to be spot-on. I built the rib-forming jig with 10% smaller radius as you suggested and a rib made of three 1/8" pine laminations bends comfortably, provided I don't rush it, and springs back as expected.

The test rib was bent to 90 deg and the springback provides a flare angle of 9 deg. With the rocker that should give a nicely curved rise at the stems of nearly 3" - I will probably add a bit more in the sheer planks.

I am keeping track of time spent, the rib-forming jig has about 4 hours in it. Finding the optimum clamping arrangement took some time. I am keeping track of tests and experimentation time separately so I can be completely honest.

 

The first 10 ribs turned out well; the springback was fairly consistent between them. It may have been affected by clamping pressure variations - I made notes for the next batch. The pictures show the rib-forming jig with 10 ribs clamping in place and the jig with a partial load to show its construction.

The third image shows a "stack of ribs" (french fries with that?) - the barely visible pencil line marks the position of the bottom plank's edge. This batch looks like it will produce a fair hull, there is less than 1/4" variation along the left-hand end where the sheer line will be, which will be faired by the gunnel.

The ribs have not been cleaned up yet; I will probably need to made a simple jig to hold them in place while I plane the edges. The time to cut, glue and bend the 10 ribs so far is 1-1/4 hours.

 

When I have ribs like that, the first thing I do is run them through the table saw. It's a bit weird at first, feeding the curve through the saw and installing a really tall fence can help a lot, but it will square them up and machine the edges precisely enough to skip the bother of tearing up your plane's blade on them. Ease all the edges slightly so paint or varnish will stick and it relieves edge stress too.

 

Great stuff Terry. I hope you keep us up to date on your build progress.

Sometimes, I can only manage a vicarious living. You efforts are much appreciated.

 

I have more finishing work to do on this batch of ribs than I anticipated, because my saw blade was out of alignment which left the strip width poorly controlled. They'll be 1/16" under width because of that, but I went ahead with them to see if any problems cropped up. This part of the work went very easily apart from the booboo.

I normally prefer to do my own work but I don't have a table saw and a buddy of mine suggested running the ribs through his thickness planer, several at a time.

I am tempted to take him up on his offer; is that a safe thing to do? I thought material fed through a thickness planer had to have one side run through a jointer first.