Is this a bad idea?

[pandelume]

I'm thinking about using some software to generate expanded plank shapes and sending them to a CNC routing shop to be cut. These would then be used in glued plywood lapstrake construction. It seems like this would save a lot of time and space (at the possible expense of flying in the face of all that is holy). I'm also not convinced that it would cost all that much, although I'll know if I quote the parts.

I'm not an experienced woodworker, and I've never built a boat, so hopefully some who have can clue me in on why this is or isn't a crazy idea.

[Yeadon]

What are you building?

[pandelume]

It isn't set in stone, but I was thinking of the sailing skiff here:

http://www.woodenboat.com/forum/showthread.php?t=94736

Mainly for 3 reasons: 1) I think it looks nice, 2) it'll fit in my garage, and 3) I've already done some work towards developing the planks (as mentioned in that thread). But although I had that skiff in mind, I didn't mean to limit the discussion to just that.

[willmarsh3]

Iain Oughtred's book shows how to make patterns and cut the lapstrakes to build a boat.

http://tinyurl.com/chfxnr

I don't know that much about using CNC but I think Iain's method would ultimately be easier.

Edit: That skiff's going to look really nice. Be sure to post some pictures.

[Bob Cleek]

Well, it's an interesting idea, but I'm not sure it would be worth the effort. I'm no CAD expert, but I would expect you would have to be dealing with an extremely complicated program in order to generate the compound curved shapes necessary for planking. If you are planning on using CNC cutting equipment, I presume you aren't thinking that you are going to just "rough them out," but rather that you will get exact cuts the first time. Now, I'd think it's really doubtful that such a plan would work because the accuracy of your planking would be dependent upon the accuracy of your framing and backbone set up. If you could cut EVERY part in the boat EXACTLY to a PERFECTLY programmed measurement, in theory, it would work, but it's one thing to do that sort of thing with simple square-edged Scandanavian knockdown furniture from IKEA in a production environment, and quite another to do it in a complex shaped item like a boat. Frankly, I'd expect that it would be more effecient to employ the traditional lofting techniques and "shave to fit" your planking than to try to train a computer to do it. Not to mention that an error in cutting too small in one spot or another would result in very costly materials waste.

[pandelume]

Bob: that's pretty much what I was worried about. I was thinking that I'd have to cut the stem and sternpost on the router to get them to fit right, although this is another aspect I'm not too sure about. I thought that it might work to have the stem and stern made from 3 pieces of 18mm marine plywood:



one beveled piece each side of a non-beveled piece. All the pieces (pre-bevel) would be cut on the router. Similarly for the knees:



Doing this would leave the plank ends exposed, but I suppose they could be sealed with a fillet of glue. Or maybe cut full at the ends so that they could be trimmed to lay with the outer edge flush with the surface of the center piece? Or maybe it would be better to have patterns cut and make the stem, sternpost, and knees from solid stock?

[JimConlin]

It ain't rocket surgery. CLC manufactures a line of glued lapstrake boats using CNC and 6mm okoume. There are others.
I would undertake it only if I was already good at using boat design code, a CAD system and the interface between them AND if my CNC equipment was capable of cutting proper bevels. Apparently CLC's cutting machinery can't cut bevels and they use a much weaker ship-lap joint between planks. An unacceptable compromise, in my opinion.

[David G]

There is CNC equipment available to cut bevels. The real problem is the difference between a mfgr. who's setting up to do multiples and a home builder who's setting up to do one boat. There's a certain amount of CAD work to be done to make it happen, and a bit of fussing to convert it to instruction that the machine can cope with (G-code). Unless you have the skills to do this programming work yourself, it's not cost-effective.

It's a great idea - for multiples. As mentioned, CLC does it. Bartender Boats kits are done this way. Several others as well.


"Travel is only glamorous in retrospect" -- Paul Theroux

[Yeadon]

... I say there's only one way to find out if you can do it, just do it. Be prepared to screw up and waste a lot of good material on the first round. But it just might work.

I'd be tempted to do to a practice round of two on your CAD, have them fabricated, then see where you are at. You may have to recalculate based on the reality of the situation.

[Bruce Hooke]

I thought that it might work to have the stem and stern made from 3 pieces of 18mm marine plywood
...
Similarly for the knees...

Replacing solid wood parts like stems and knees with plywood needs to be done carefully. Especially with the stem, the problem is that half the laminates in the plywood are running in a direction that is pretty much useless in terms of the loads applied to the stem. So, the stem needs to be re-engineered to account for this difference. If the knees are designed to be made of steam-bent wood or wood laminated to a curve then the same issue applies there. This is why when plywood is used as a gusset to replace a knee the plywood is likely to be much deeper than a bent knee.

Plus you are exposing a lot of additional end grain that will be vulnerable to rot...

[mmd]

Been there, done that...

Pandelume, unless 1.) this is a passion of yours and you don't care how much time and materials you waste, or 2.) you plan on selling a production run of kit boats to pay you for your wasted time & materials in producing your prototype, don't do it. If you are fussy with your work, you can digitally develop the planks for a "tack-and-tape" hull, but lapstrake adds a whole new level of complexity that will most likely put you off boatbuilding for quite some time, possibly forever.

What are some of the appropriate trite lines for this?

Sometimes the old ways are the best ways.

The devil is in the details.

Anybody can make a mistake, but to REALLY screw up, you need a computer.

A computer is a device that enables you to make bigger mistakes faster, with greater confidence.

I predict that it would take you between 100 and 150 hours to define the CNC toolpaths and even then I'd have strong worries about their accuracy. Hanging & spiling & fitting to shape will take you about half of that time once you get going at it, and the planks will be on the boat, not on a stack on the floor waiting to be hung.

Sorry to rain on your parade, but I think you'd better think this ambition over carefully. On the other hand, I hope that you boat turns out well regardless of the method you use to get your planks out.

[Yeadon]

It just occurred to me ... pandelume probably wants to work on this while he's at work. I fully understand now.

[StevenBauer]

This is totally doable, Pande. Jordan Boats sells lapstrake kits for many Iain Oughtred designs. I was talking to some guys at the Maine Boatbuilder's Show about their kits. They make the kits for the US and Canada under contract for Jordan Boats. They make the WoodenBoat kits, too.

http://jordanboats.co.uk/JB/


Steven

[pandelume]

The plans call for a hog-piece or cheater along the keel so that you don't need to cut a rabbet there, only a bevel. I thought that something similar might work ok for the stem and sternpost, but maybe not. I understand that much the same idea is sometimes accomplished by using an apron.

Originally the stem was spec'd at 2" thick oak, and the sternpost at 3" - I think mostly to account for the much wider planking angle there and the need for an adequate land. The instructions say to make a template and have both of these parts cut to shape at "the local sawmill", but I don't know that I coud do that now. If 52mm wide plywood (at the full-width part of the stem and sternpost) is likely to be too weak, what's the alternative? A laminated stem?

On preview:
Yeadon: Sort of. I am using software available through work, but most of this stuff has been done as a sort of idle winter project - something to fool with in the evenings.
MMD: I do care how much time and material I waste, but I'd also like to give it a try if it winds up seeming feasible. Judging from your remarks, it may not be. I can generate plank patterns and make a scale model - do you suppose that would go very far in identifying problem areas?

[pandelume]

Sorry, Steven, I missed your post. Thanks for the link to jordan boats - I'll have to take a look.

[G. Schollmeier]

I’m guessing that using Carlson Hull Designer you will get the plank shapes. They would be easy and not very expensive to cut. Putting the bevels on those planks in where it gets tricky. They change constantly from end to end. This requires 3D software to draw the bevels; high end CAM software to generate the code for the surface milling or a 5axis CNC router to cut them. This can and is done daily but the skills and equipment needed are not cheap. If you have worked with 3D CAD and have played around with hull shapes you can appreciate how difficult this is. It makes my head hurt. ;-)

I'll go with, bad idea,
Gary

[Bruce Hooke]

Originally the stem was spec'd at 2" thick oak, and the sternpost at 3" - I think mostly to account for the much wider planking angle there and the need for an adequate land. The instructions say to make a template and have both of these parts cut to shape at "the local sawmill", but I don't know that I coud do that now. If 52mm wide plywood (at the full-width part of the stem and sternpost) is likely to be too weak, what's the alternative? A laminated stem?

Lamination is likely to be a good option but to really sort this out and comment on it I would want to see the plans. The local sawmill part has me a bit puzzled. Any decent bandsaw can cut 3" thick oak so I am not sure what a sawmill would be needed for. The point may have been that you were supposed to get a piece of wood that had some natural sweep (curve) to it to follow the curve of the stem. If that is the situation then lamination is likely to be a good alternative (but educate yourself on the issues around white oak and epoxy if you plan to use white oak). If you have a local sawmill that is familiar with working with boatbuilders they may have some stock with sweep in it around.

[pandelume]

The instructions are posted as a series of scans from a copy of "Practical Boatbuilding for Amateurs" on Gavin Atkins'a inthebaotshed.net. The link below is to the index, and the picture is the relevant page for the stem. I think that this is the only description.

http://intheboatshed.net/2007/08/27/...e-ended-skiff/

[TerryLL]

Having helped put together a number of CNC-cut boats in aluminum I have to report that the cut and fit is something less than perfect. These were larger chine hulls with a lot fewer panels than the lapstrake skiff considered here. If you're committed to this technology maybe consider a simpler design to work out the process, perhaps a three-plank dory. I have no doubt that this process could be used, but expecting it to work perfectly the first time is asking for grief.

[John Meachen]

Judging by the colours used in the illustrations that pandelume provides,I have an idea that he may be familiar with a high end CAD program.This would make determining the plank shapes comparatively straightforward.Bevelling the centreline structure would be more or less achievable if you don't mind doing some clean up work.A 5 axis machine would be greatly preferred but would need a sufficiently capable CAM program.The part that might pose the greatest challenge would be cutting the scarphs in the planking as one section would need to be flipped in order to allow the bevel for the land to be cut on one side and the bevel for the scarph to be cut on the reverse.You could probably use a fine scribing tool to mark the outline of the plank on the spoilboard and to determine the machine offset to use.The same technique could be used with the stem.It seems to be an interesting project and I think a lot of us would enjoy watching it progress.

[Bruce Hooke]

The instructions are posted as a series of scans from a copy of "Practical Boatbuilding for Amateurs" on Gavin Atkins'a inthebaotshed.net. The link below is to the index, and the picture is the relevant page for the stem. I think that this is the only description.

http://intheboatshed.net/2007/08/27/...e-ended-skiff/

My guess is that this route was suggested because of the curve of the stem and the fact that it would be better to get such a shape out of a piece of wood with curve to the grain, but that is just a guess.

Were it me, I think I would laminate the stem (or try to find a piece of oak with the right curve to the grain). However, if I were shifting to glued lap for the planking I would definitely NOT use solid oak. I would be worried about the oak moving to much with changes in moisture content. Traditional construction can handle this better than epoxy. So, for glued lap I think I'd laminate the stem.

[StevenBauer]

The glued lap boats I've built have an inner and outer stem. The inner is beveled the planks run by and are trimmed off after. Then the outer stem is glued on. Lap bevels would of course be planed as you go after the plank is hung. Not part of the CNC process.

Steven

[pandelume]

Unfortunately, I don't really have access to the appropriate CAM software to to the lap bevels on a 5-axis machine, but getting the expanded profiles for a 2 or 3 axis router or a lasercutter is less of a problem. So I'd have to do the lap bevels as Steven says - as the planks are hung. I think this is probably the better way anyhow. I can provide a scarfed 12' panel to the cutters along with a nested pattern that spreads the scarf out among the planks as widely as possible. After they're cut, I can cut the plank end gains with a jig.

I can see that having the planks extend past an inner stem and be trimmed later might make things easier, but I don't know quite how to do that on the lower portion of the sternpost where the rabbet runs across the stern knee. Maybe make the sternpost and knee from one piece, with a mating outer piece? It seems like those would be complicated parts to laminate. But if solid stock and plywood are off the table, what alternatives are there?

[Cuyahoga Chuck]

It ain't rocket surgery. CLC manufactures a line of glued lapstrake boats using CNC and 6mm okoume. There are others.
I would undertake it only if I was already good at using boat design code, a CAD system and the interface between them AND if my CNC equipment was capable of cutting proper bevels. Apparently CLC's cutting machinery can't cut bevels and they use a much weaker ship-lap joint between planks. An unacceptable compromise, in my opinion.

CLC is using the patented "Lapstitch" method that was developed by it's founder Chris Kulczicky. It allows for building without a mold and the allowable angles can be greater so hulls can be done with fewer planks.

[James McMullen]

Which do you enjoy more? Planing winding bevels using your own wits and skill or sitting in front of a screen typing? I think you are not going to save the slightest amount of time or money by figuring out how to get the computer to do it for you--in fact, I bet you will spend double the time it would take to just build that boat the conventional way. You'd only see time savings if you were to build multiples and could amortise all that programming time over several hulls.

Now if your real passion is actually programming and you want to exercise your computer programming hobby by using it to make a boat, then I can sympathise with that. But from a woodworker's perspective, there is NOTHING more enjoyable than handwork using edge tools like planes, spokeshaves and chisels, and CNC-ing your parts will rob you of all the funnest parts of boatbuilding. Seriously, as a professional woodworker I often have to pick up the router to get things done on time and under budget, but on my own stuff I use a plane whenever I possibly can.


Now if you could rig up a CNC sand-and-varnisher, then you'd really be talking!

[Eric Hvalsoe]

Well, it's an interesting idea, but I'm not sure it would be worth the effort. I'm no CAD expert, but I would expect you would have to be dealing with an extremely complicated program in order to generate the compound curved shapes necessary for planking. If you are planning on using CNC cutting equipment, I presume you aren't thinking that you are going to just "rough them out," but rather that you will get exact cuts the first time. Now, I'd think it's really doubtful that such a plan would work because the accuracy of your planking would be dependent upon the accuracy of your framing and backbone set up. If you could cut EVERY part in the boat EXACTLY to a PERFECTLY programmed measurement, in theory, it would work, but it's one thing to do that sort of thing with simple square-edged Scandanavian knockdown furniture from IKEA in a production environment, and quite another to do it in a complex shaped item like a boat. Frankly, I'd expect that it would be more effecient to employ the traditional lofting techniques and "shave to fit" your planking than to try to train a computer to do it. Not to mention that an error in cutting too small in one spot or another would result in very costly materials waste.

And I also agree with the sentiments of MMD and James. I don't understand exactly what Jordan Boats is doing, but getting the ENTIRE kit would be a different kettle of fish than extracting plank patterns. And I question if Jordan Boats has a kit for quite as demanding a build as you have chosen. You could not have picked a more challenging basic hull design to plank - wide, fat, double ended, somewhat squat, with many strakes. Not saying it aint pretty - she is beautiful. And quite challenging. There are a thousand ways to introduce small variations with the backbone, molds, and initial set up, and planing the lap bevels. Perhaps plywood lapstrake is slightly more forgiving than cedar on oak. Small variations compound themselves. I suggest you take this puppy one plank at a time.

P.S. I have plank patterns for my traditionally planked Hvalsoe 13 and 16. I tend to use used them as spiling guides, maybe the first couple of planks I'll zip right off the patterns (after double checking on the boat). After that, it seems to me that even resetting up the strongback, molds, bracing, etc, every time introduces small variations, despite all my backbone patterns.

[djtil]

I'm thinking about using some software to generate expanded plank shapes and sending them to a CNC routing shop to be cut. These would then be used in glued plywood lapstrake construction. It seems like this would save a lot of time and space (at the possible expense of flying in the face of all that is holy). I'm also not convinced that it would cost all that much, although I'll know if I quote the parts.

I'm not an experienced woodworker, and I've never built a boat, so hopefully some who have can clue me in on why this is or isn't a crazy idea.

I did what you are suggesting here when I started building Iain Oughtred's Fulmar. I am an experienced woodworker, but a first time boatbuilder. Iain's plans are very helpful in that they include full scale sections showing the position of the plank laps at every station. This made modeling up the plank shapes much easier than trying to line off the already developed hull shape, but then I am no CAD expert, so maybe for some it would not be a problem.

I used Rhino to do the modeling, because it allows you to unroll the plank shapes once developed. I then exported the shapes to AutoCad because the CNC needed DWG files. I scarphed my plywood using a hand router and jig. I used the CNC to then cut out the planks, molds, and stem shape. I did make test planks first using junk plywood in order to prove to myself that things were going to work. Everything fit surprisingly well, except for one mold that had lost a small section of curvature during the transfer from Rhino to AutoCad. A change of setting solved the problem, and I just cut out and fit in the new correct section of the mold.

I did let the planks run long at both ends, and trimmed later to the transom and the inner stem. The outer stem was added after. I cut the plank bevels with a router jig on the boat, and I cut the lands by hand.

For me at least, the work up to this point was the easiest part of the build. The finishing and fitting out has been much more challenging, and is not yet done.

Good luck.

[boylesboats]

Are you willin' to put -up with tech support?
boat from next boat isn't exact.. even if you set both molds, strongback exactly the same.. each pre-cut planks is gonna be thrown off a bit.. even it is perfect to began with..
Every builder are not alike.. you'll hear it almost every hour of day, those complaints gonna drive ya insane..
It best to lay-out, line-up the forms and use old school skill of spilin'..

[captainconrad]

Let me suggest that learning to build a boat is one of the most rewarding activities a man can undertake. It will tax your intellegence, your soul, your knowledge of why boats are the way they are and not the least, your pocketbook.

Taking supposed shortcuts is only shortcutting yourself. The satisfaction of setting a properly cut and beveled plank is one of the highest rewards a boatbuilder can achieve. If you only want to let someone else do the work, farm out the hard stuff and make end runs around the tough jobs you might as well go buy a plastic boat. It will be safer, cost you less and more pleasing to the eye than your subcontracted "project."

This is not a personal attack, just the facts. Learn to do by "doing." Good Luck.

[Yeadon]

I think pandelume has a fighting chance of pulling this off.

But thinking about Hvalsoe's comments ... I wouldn't trust the dimensions from your plans to represent the relationship between the backbone and the garboard. I'd remeasure your backbone once it was set up, then figure out your plank line-off. The de facto backbone is likely to be close, but not close enough to the original plans to simply trust the original offsets.

Conrad has a nice point about the experience of traditional boatbuilding ... but I think this method is every bit as novel. You really can't place a value judgement on pandelume's learning curve. He's in his comfort zone, and I think he's looking forward to the challenge.

Me, personally ... I'd spile every plank, use a stanley 78 with a fence to carve out my gains, and carefully fit every templated hood end to the fore and aft stems. That's just me.

[boylesboats]

Me, personally ... I'd spile every plank, use a stanley 78 with a fence to carve out my gains, and carefully fit every templated hood end to the fore and aft stems. That's just me.

That the way it should be Yeadon

[pandelume]

I did what you are suggesting here when I started building Iain Oughtred's Fulmar.

I'm glad to hear that someone has successfully done something like this. I've been using software from work, but I'll take a look at the trial version of rhino and see what I can do.

One thing that makes me worry, especially in light of Yeadon's and Eric's comments on error in the backbone, is that the plans call for everything to be set up upright on a no-frills 2x6 (or therabouts) strongback directly on the floor of the shop [in my case a small garage]. No other bracing. The molds are set up and temporarily fastened to the hog piece and a batten reaching from stem to stern. According to the plans, the next step would be to start planking.



I don't know that this would be a rigid enough arrangement, even if the backbone has minimal errors in and of itself.

One other thing: I don't want my interest in this to give the wrong impression - I'd love to build this boat traditionally according to the plans, but as is often the case there are limitations on my skills, time, etc. that make it a more difficult undertaking than it might otherwise be. If I can build something nice with an alternate method, it may be more suitable to my current skills and circumstances, and I assume I'm not the only one like this. I have the greatest respect for people who build boats traditionally.

[John Meachen]

I believe it is entirely possible to create a lattice of slotted ply or MDF to hold the moulds in place and locate the backbone.While I respect the comments about traditional boatbuilding,I see no reason why the process cannot evolve in parallel with available technology.Indeed I would suggest that it has always done so for those of us that avail ourselves of machinery,rather than pitsaws.The possible inaccuracies in a table of offsets would show up in the creation of a 3D CAD model.Having spent a little time working with the evaluation version of Rhino myself and using the function that applies a mirror finish that allows the model to be revolved and the reflection to be checked for unfairness,I have no doubt that blemishes could be spotted and eradicated.Extracting plank shapes should be achievable and the other steps may still require a small amount of hand finishing.The project is feasible and will be observed with considerable interest.

[James McMullen]

You really, really don't want to assemble a glued lapstrake boat right side up! That way is possible for some forms of traditionally planked and fastened lapstrake boats, but you want gravity's help from the other side to keep your glue dripping in the right direction. A far better way to assemble a glued lapstrake boat is upside down over a strongback.

Perhaps you could use the CNC to cut out all your station molds and then plank it up in the conventional way that would allow you to cope with all of the inevitable tiny variations. I know of several strip-canoe builders who had their sets of station molds cut out for them by CNC router.

[Eric Hvalsoe]

Once again James is pretty much on the money. When I think small boat, I usually think upside down for pretty much any construction. I am not making an aesthetic or moral argument about tradition vs technology - if you are still talking about a fat double ender I am saying you have a bear of a planking job in lapstrake or carvel ahead of you, and if you intend to mix computer and manuel technologies you are asking for trouble.
You can strip this hull, not as satisfying in my opinion , but less of a hurdle. I believe a transom ended boat would tend to be somewhat easier to plank, although you will have more backbone work.

[davebrown]

i read this post with interest. i am finishing my fifth boat right now. i think that makes me a little more than a beginner. maybe an advanced beginner. i think you should pursue using the computer to build lapstrake. i think it woudl be a great tragedy if you didn't also learn how to do it the traditional way, including the tedium of lofting. you will acquire skills and knowledge that will make the copmuter part of this more successful. it reminds me of using a power plane without knowing how to use a hand plane. you certainly can, but...there is a process here in which blocks of knowledge build to each new level. just the opinion of a beginner.

[pandelume]

I want to take a second before I go on and thank everyone for their contributions to this question. I think it's wonderful that everyone is so open with their opinions and expertise, and however this project turns out, I hope everyone can take some interest in it as it goes along.

Another thought occurred to me yesterday: is anyone interested in a parallel build, using whatever method they find most congenial? I'd be happy to share any models or information I have that might be useful. If we pick different building methods, we could almost call it a contest !

Back on topic, is it a bad idea to laminate the knees, stem and sternpost (or any combination) using solid 1x4 or 1x6 stock as in the picture below?



Doing it this way has the advantage that every part can be cut on a router, per the original idea, and also wouldn't need much in the way of a laminating jig. The sweep of the rabbet can also be cut on the router, so that during assembly only beveling of that shoulder would be needed - although this would leave the plank ends exposed. The plans call for leaving an exposed edge along the keel hog-piece, and call for caulking there. Is there a preferred modern method apart from making an inner and outer stem or sternpost?

As for building upside right side up, I suspected that this might not be the best way. It seems like a simple jig much like the one in the plans could be used - just flipped over, with the station molds lengthened to sit on the floor. Maybe someone has a better idea?

[John Meachen]

It's fascinating to see the development of the concept occurring.I would throw in the suggestion that a stem assembly could be built up from a number of components cut oversize and then machined to final shape.The planking bevels could also be cut on the router,one side at a time and using location fixturing.The ends of the planking can be covered by adding a false stem.You can choose whether to laminate over the stem and planks or whether to produce one by machining.
The building jig could be made by slotting the hull moulds to accept longitudinal locators,maybe sited nine inches or so from centre and these in turn could be slotted to accept the moulds,thus guaranteeing alignment.Upside down would be my choice and you could either extend the station moulds to the floor of the workshop or designate a vertical datum plane and stand the assembly on trestles.

[Eric Hvalsoe]

The planking bevels could also be cut on the router, one side at a time and using location fixturing.

Wow, what does that mean? I confess with the last HV 16 I mostly cut the bevel of the keel apron with a router and support batten. 2 1/2 hp. A transom stern boat. The apron was Apitong, not fun to work with a plane. I just can't see doing laps with a router, not to mention NOISY . . . but then I'm old fashioned. Why knock together structural complexes with multiple layers and thickness (instead of a single thickness, stem, gripe, forefoot, etc) - well, maybe you can make an argument for stability. The actual building material is important, and gluing is not an entirely brainless operation, messy too. How much time are you going to spend setting up router jigs and fixtures versus good ole basic hand eye coordination. Of course we understand you are very interested in the machining process, be it more or less efficient. Consider looking for a somewhat easier build. Or . . . just go for it.

[pandelume]

Eric, I think John meant the CNC router table, rather than a standard router - certainly that's what I meant when I was referring to cutting parts for lamination on a router. In that case a set of jigs wouldn't be necessary for cutting, although maybe for gluing. As for material, I probably need advice about that too. Off the bat I was thinking of something like 1x6 finish lumberyard DF, which I had understood was suitable for laminations.

Will post pictures of concepts for sternpost, stem and building jig soon.

[neilm]

It's obvious you have the CAD skills so it might be practical and fun for you. But for normal folk buying a kit is a good option for your first boat. I bought a kit boat from Chesapeake Lightcraft and I learned allot about boat building and using epoxy from it. Now I'm ready for my first real boat.

You could also try making model boats from your CAD drawings. Print them out on the plotter 1:1 and use Model Aircraft Plywood or cardboard.

Neil

[Gary E]

I'm thinking about using some software to generate expanded plank shapes and sending them to a CNC routing shop to be cut. These would then be used in glued plywood lapstrake construction. It seems like this would save a lot of time and space (at the possible expense of flying in the face of all that is holy). I'm also not convinced that it would cost all that much, although I'll know if I quote the parts.

I'm not an experienced woodworker, and I've never built a boat, so hopefully some who have can clue me in on why this is or isn't a crazy idea.

These folks do it... why not you?
http://www.mysexyboat.com/

From their site....

In response to their request, MySexyBoat.com was born. We realized that we had the technology to design, cut and build the coolest small cold-molded power boats in the world. After all, we did it everyday with the larger yachts. We discovered that we could design a new small boat model on sophisticated computer software, cut that design on a five-axis CNC router and assemble the cut components on a pre-cut jig. After assembly, we were able to refine the design through rigorous sea trials, and then make these designs available to the public. No other kit boat builder can offer the quality craftsmanship and attention to detail as MySexyBoat.com.

[John Meachen]

"The planking bevels could also be cut on the router, one side at a time and using location fixturing."
Yes I was referring to the CNC router.It would take a little work to create a location fixture that would allow the stem to be flipped in order to cut both sides.It is fairly fundamental to CNC routing that you need to provide a fixture offset at the head of the program so that the machine knows how far and in which direction the component is located relative to the machine's home position.

[Eric Hvalsoe]

Location fixing, ah hah. Thanks fellas. All interesting. I think about CAD now and then but not had the opportunity to study it.

[bob easton]

I'm curious about a different question. Instead of "Is this a bad idea?," I would like to know why you (pandelume) thought it a good idea? Is it because:

1. Routers are the only tools available?
2. Lamination is required due to the scarcity of thick stuff, or because you really really really want to use a router?
3. You're working in Norm's shop and there are no tools without motors? (and nearly every tool is some variant of a router)
4. You're gearing up for mass production where all the sunk cost in setting up automation and custom jigs can be made back by volume?
5. You really enjoy CAD?
6. You really enjoy jig making?
7. Some other reason(s)?

By the way, don't interpret any of those as criticism. I really am curious.

For what it's worth, I'm at the other end of the scale, building a boat with traditional techniques and almost entirely with hand tools. I know that some would think me crazy for resawing planking material with hand tools and dimensioning lumber by hand.

[pandelume]

Bob, the answer to your question is slightly complicated, but more or less mundane. I should say that I don't own a CNC router or any router of any kind, really - so it isn't that. The idea was born like this: I ran across the plans for this skiff a while back, and started playing with it as a model for fun. I had an idea that it would be smart to figure out how the planking laps and whatnot would work with an eye towards building in glued lapstrake, but it wasn't too serious. When I started to think about shop space and other logistics of actually building, I decided that I really didn't have the space to do it...unless there was some way to take operations out of the assembly space. So long story short, I started trying to figure out how to do as much preprocessing as possible. I also thought that doing much of the work on a machine would speed up the build process, which didn't seem like a bad idea. In a nutshell, that's why I thought it might be a good idea.

As I said before, I'd love to build this skiff (or any boat) traditionally. Hopefully I'll have the chance someday, but until then I'll have to make do with other methods.

I also have a major advantage, to paraphrase John Gardner: I'm an amateur, so my time is worth nothing. Whether I spend it figuring out the details of the model or in the shop doesn't really make much difference; either way, I'm doing it for enjoyment, so I don't have any investment to make up.

By the way, don't interpret any of those as criticism.

Never in life

I appreciate that approaching things from this perspective isn't for everyone. But it might work, and if it doesn't it'll at least serve as a cautionary tale.

[bob easton]

Thanks for the answer. For awhile there, I thought you were flush with routers.

Yep, it sucks having a shop that's too small. Hope you find a way to build the dream boat.

Gardner got it right about the value of our time. Since it is already zero, I don't try to add up the boat building time. Just enjoy it instead.

[pandelume]

Sorry for the delay in posting, but I've finally got some new concept pictures to show for the jig, stem, sternpost, etc.



I've drawn the building jig much as John Meachen suggested: The station molds and the strongback planks (2x6) are slotted to receive each other. I'm thinking that fastners would then be installed diagonally through the mold and into the strongback. Maybe we'd need some horizontal diagonal braces to prevent the jig from racking? The molds will be temporarily fastened to the hog-piece and keel, but maybe I'll also need diagonal bracing for them as well?



The stem knee is pretty straightforward. It doesn't need any bevelling, so it can be a simple layup of 3 sections of 1x6 material. Later it will need to be modified to have a mast step, but I figure it would be better to have that as a separate part, and install it after flipping the hull.







The stem, stern knee and sternpost are all variations of the lamination concept posted before, but with 4 layers instread of 3. This way, the unbeveled inner layers are the same thickness as the keel, which I was planning on being 2x3. This simplifies the garboard strake, taking out a joggle between the keel and the stem/sternpost. The stem has two sets of bevels - one for the planking lands, and one for the cutwater (not sure it's called this) or pointy bit on the font of the stem.

For those interested in router vs laser, here's a picture of mold B showing how each interior corner has to have clearance for the router:



The planking joggle on the right of the picture could be cut by a laser, but not by a router.

So far I've been looking at making each peice of the backbone individually and putting them all together with some combination of adhesive, bedding compound, and fasteners. If I need to replace anything, it would be a bummer if it were glued in place, but I don't know if it's a bad idea to just fasten laminated parts the same way you would solid ones. Anyone have any ideas about this? Should I just go ahead and glue everything up? If the backbone is just bedded and fastened, the planking lands would have to be bedded and fastened as well, although the planks would be glued to one another.

Another question: if I can find solid stock for say, the sternpost, would it be a bad idea to use it with glued plywood planking? I'm thinking of dimensional stability here.

[pandelume]

Please excuse the double post, but I forgot something I meant to ask:

The original instructions say I should fit the risers and inwale before removing the molds, but that was for an upright build. I think I can do this upside down, but I'm not sure that it's necessary. Should I?

[John Meachen]

I would have grave doubts about the possibility of removing the moulds from the hull unless a vertical relief is provided for the risers and inwale.As far as diagonal bracing is concerned,a rectangular panel tightly fitted between the two larger moulds and aligned withthe edges of the longitudinal 6X2's would do much of that.I would be tempted to add some diagonal bracing to hold the moulds vertical.
A solid sternpost sized for a small boat should not give any trouble with plywood planking.I have a friend with a fifty year old Merlin Rocket which has plywood planking and a solid transom and stem,it has survived so far.