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PostPosted: July 10th, 2008, 12:08 am 
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I read with reasonable care the thread so far, and I disagree with a fair bit of it, or at least look at the subject differently. So I will just lay out my philosphy briefly.

A stripper can be seen as a wooden boat, or a glass boat. The glass boat discusion goes that the strips are a crappy core material, and the tensile structure of the boat is the glass or other fabric.

On the other extreme one can regard it as a wooden boat where the hoop strength is provided from the comp fibers.

In either case there is a lot to be gained from using thicker wood and scrimping on the glass, the exception being where impact loads are the issue, and that tends not to be my kind of stripper.

I tend to lean towards the idea that it's a wood boat, I try to maximise wood structure, this means as much fiber alignment as possible. I don't lay up typically. It also means limiting parasitic weight in th glass layers. You can go bias though I don't know if that helps it gets more fiber working across the grain, but not at 90 degrees to it. Or one can go linear. It's also possible to just minimize the glass since little is needed when the wood is maximized. The wood is stiffer for a given weight than glass by a large margin. And thicker wood will create a deeper sandwich increasing the stiffness of the glass lam also.

Go for quality epoxy. It's a design spiral, meaning one has to give something to get somethign. It is interesting to question whether all the clear epoxies have identical performance to the earlier juice. I'm fine with the original west. Use what one wants, but keep in mind it's a vital part of the mix.

I'm willing to do stuff that eliminates the clear finish. This is boat building not a highschool breadboard project using every contrasting offcut in the shop. Also I design the canoes too, and I am proud of the shapes, Often the strips obscure the true beauty of the canoe, and the finish really isn't seaman like. I don't mind leaving the inside clear, there are a lot less compromises there.

The biggest waster of weight in many plans is the stems. They are just stupid built in most cases. The key is to end up with the design shape without varying hull specs. In most cases the stems are more of a structural liability than a help. Find a structure that keeps hull thickeness the same or similar everywhere, or even go composite. I am considering a light solo stem build with a carbon stem that will be a separate part that everything else scarphs too. That only makes sense because this particular design has a widening stem and is quite wide at the shear, as one finds on modern boats. It's a design that would lend itself pretty well to a carbon cloth and epoxy lay.

You are certainly going about it the right way as far as breaking it all down and keeping a careful weight budget. When it comes to vac bagging, sometimes it is necesarry just to get the quality of layup one wants. In general though I like to look at what is happening on an individual basis. I have to be honest, and say I haven't vacced much on a stripper, though I have vacced lots of wood. I would look at the glass and consider whether it is over or under spec. As an example the 1.2 oz glass mentiioned seems light. I would probably be happy to have it thickened a little with a hand layed coat. Squeezing resin out of standard lays where maxing a given fiber ration is the objective, is not the same thing as a case where no additional fiber can be added or subtracted, and the jump to the next fabric weight may be considerable in percent terms.

In the us I would look into linear carbon scrims they are available and would allow incredible weight reduction in a "wooden" boat.

Also consider where the weight actually hurts you. Excess weight in the ends is nasty. Excess weight in gunnells that is there to allow one to use a material that rots is hard to seal, etc... Is another issue also. Weight that gives the hull the structure it needs is rarely in places it really hurts like the ends, and can be all good.


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PostPosted: July 10th, 2008, 6:55 am 
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Hi Peter,

I consider your comments very good and proper. When i think of BK's goal of an ultimate lightweight boat there does need to be a balance in the goal of the boats use as brought up in some of the posts by GB.

Looking at the balsa cored boat over in OZ, that to me is the ultimate of light. But if someone such as BK whom is not the ultimate of lightweight were to kneel in the boat, he might cause compression damage at the contact points.

To me the design goal of lightweight is for the art of building and I would expect the hull to be a bit tender, structure wise. Especially if it were thin wood and thin fiber. I would dread hitting a tree branch wrong when bushwhacking.

When I get around to building the boat I intend, it will be moderate weight. My intended layup will be with all UNI cloth laid at bias, the same way I have been building aircraft wings. It will be vacuum bagged.

I expect vacuum bagging the outside of a stripper to be a nightmare. For one it needs an inner bag, this needs to be against the strips otherwise only a very light vacuum can be applied. Getting the bag between the forms and hull will be the interesting part. The bag is of little value full of nail holes. I have a technique of external clamping that may work for me but is not proven. It is using both the internal as well as external forms. The external are obviously moveable for working under them. Clearly not a standard technique but may be what is needed to work with a sheet of poly inside the hull.

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Last edited by Awetcanoe on July 10th, 2008, 2:53 pm, edited 1 time in total.

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PostPosted: July 10th, 2008, 11:51 am 
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PeterPan has done an excellent job of bringing some much needed perspective to this discussion. While a close look at the ingredients in a recipe can be beneficial, a close look at how they interact is also necessary. Further, an outstanding recipe for hors d'oeuvres is not relevant when roast beef and potatoes are called for, and vice versa.

Several of his comments suggest to me that he and I are on the same page of the menu, at least some of the time. I'm sure some have noticed that my Lassie in the picture posted by Awetcanoe is painted. I chose to use an aerosol can of auto enamel instead of several coats of UV absorbing spar varnish in order to save a good chunk of money, a bunch of weight, and the need for frequent refinishing. It doesn't offend my eye because I can't see it from my side of the gunwale. And if there are others to see it I've chosen my route poorly. The reduction in weight helps me get more quickly to waters without such offendable eyes.

Re. PeterPan's comments on stems, I agree wholeheartedly. When getting ready to build my first stripper many years ago I looked at the recommended stem construction and asked myself "Why so much lumber?" I concluded that the stem had to meet two requirements: first, it had to hold the two sides together and, second, it had to withstand accidental ramming of immovable objects. The first was easy: a bias strip or two around the stem. The second was taken care of by the orientation of the strips in the sides; direct columnar loading. The only remaining concern was procedural; how could I go about 'glassing the inside? The solution I chose was a fillet of epoxy filled to putty consistency with WEST System 409 low density microspheres. I troweled the fillet to a concave inner surface fairing into the two sides prior to 'glassing the inside, then lapped the inside 'glass over the concave surface of the fillet. Years of use and abuse left me 100% satisfied. I did the Lassie the same way and am equally happy with the results but the next generation will use a procedure that I hope will be easier: I will trim the inside 'glass to just shy of the fillet and then apply a bias-cut strip over the fillet and overlapping both sides. The hope is to get a neater job and less mess. Unmentioned above, I strip directly to the stem mould, overlapping the strips from the two sides log-cabin fashion, then carve and sand the leading edge to a nicely rounded shape leaving all end-grain and no easy way to tell whether a given strip is butted to a strip from the other side or extending over the end of the strip from the other side.

I notice that while vacuum bagging has been discussed to some extent, nobody has mentioned whether they lay up all layers at once or separately when not vacuum bagging. Never having wet out more than one layer at a time, I wonder if there is a difference in the total amount of resin used. My procedure has been to apply localized reinforcement first, allow it to cure enough to be able to sand the edges to fair into the hull, then apply the overall layer. Since my next build will use much more localized fabric and a thinner overall layer, I'm curious to know how others apply multiple layers, and the consequences in weight.

bob

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PostPosted: July 10th, 2008, 6:59 pm 
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If you rely on spam filtering by your ISP and on topic notification from CCR you might be interested to know that Postini.com, the filtering service provided by my ISP and others, is trapping notifications of activity on this thread, probably because of the word "stripper" in the thread title, which appears in the notification. :tsk: :tsk: :tsk:

(((....and you thought 1984 was history. :doh: )))

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PostPosted: July 11th, 2008, 9:43 am 
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I don't see the point in vacuum bagging a stripper. Soft woods that are porous enough to absorb resin will become impregnated by the resin to a much higher degree if it is subjected to a vacuum. This could hurt more than help as far as weight reduction with no real increase in strength

I also don't see why balsa would be used on the sides. The increased resistance to bending that a thicker sandwich provides are better suited for use on the bottom. That is what has become standard in the industry for producing ultralights, only they usually use foam.

The sides of the canoe can be made quite thin. Most Kevlar boat have extremely thin sides that flex significantly when pressed with just the thumb. Maybe the ideal boat would have wood on the bottom tapering to no wood in the sides, only cloth. How do you decide where a stripper leaves off and a reinforced composite canoe begins?

People with advanced skills and knowledge in composites will always look for answers within their areas of expertise. I am a wood worker, so it makes sense that I view the whole thing as a wood management problem. The way to go to achieve ultimate weight reduction is to eliminate all the wood from areas where it is not needed. As long as you are using very light weight cloth (3 oz. or less) and doing a fair job of removing the excess resin I can't see that you will save more than a couple of ounces. Besides, we're talking strippers here. The composite folks have already shown what is possible with their methods.

Anyone who is into sculling knows about the legendary Poc**k shells. Last year there was an article about Poc**ks in Wooden Boat magazine. They were made of 2 planks (veneers) of steam-bent WRC 3/32" thick! Stiffness was achieved by strategic bracing, just as is done in an acoustic guitar. Eventually, they went to glassing the hulls, but the glass used was only 0.56oz./sq.yd. These boats had decks and additional bracing around the c**kpit to support the sculler and the sliding seat assembly. In spite of all that, Poc**k was able to deliver a 26' boat that weighed about 30 pounds.

Apparently, you can't use the letters "c**k" in sequence on this board:-?. "C**ks" and "Strippers", my this thread has gotten obscene :lol:
Marilyn, can we do anything about this?


Now, I'll say right now that I'm not going to be putting my chunky butt in a hull with 3/32" planking and go over any beaver dams. However, I am not aiming at a canoe for my own use but rather for the type of smaller paddlers that made the original Rushton designs famous. No one over 175 pounds has any business inside a 10' pack canoe, and a 9' canoe shouldn't see more than 125 fully loaded.

The original Sairy Gamp weighed 10 1/2 pounds with 5/32" NWC planks and 5/32" elm ribs every few inches. Plus, it had oak stems and keel (I think anyway; Dan Miller, where are you?) and maybe a pound of copper nails. That proved to be enough wood without the addition of any fiberglass. A bit less wood should be possible with just a small addition of glass.

The secret to traditional boat hull stiffness lies in the ribs. Note that the Sairy Gamp's ribs were paper thin but numerous. Partial ribs covering only slightly past the turn of the bilge and placed on top of a lightly glassed interior could be installed only along the most flexible (i.e. widest) part of the bottom. Port Orford cedar would shine here, and it would be a nice and sparing use of this hard to find/expensive wood. Featherlight quarter thwarts could be fashioned from this incredible wood as well.

Stems... why leave these out? The inner stems on our 11 footer are of laminated old growth WRC and weighed only 3 oz. each straight from the bending form. I'm sure they lost at least an ounce in the tapering and trimming. Eliminating stems to save 4 ounces total is folly IMO. Where we went wrong (not really wrong since our objective with this first canoe wasn't an ultimate lightweight) was in the addition of cherry outer stems. They look spectacular, however, and make an excellent battering ram for those beaver dams. Besides, they allow for a narrower entry angle into the water. An ultralight I would make would have light inner stems and no outer stems.

GB, I never weighed a canoe before and after varnishing, but an entire quart of Spar varnish only weighs a couple of pounds and it is at least 50% volatiles. At up to 400 sq.ft. of coverage per quart I can apply 8 coats without sanding, inside and out, and only add a pound to the weight of a finished pack canoe. Did you calculate the solid content of the paint you used for your canoe? Whatever, it weighs more than zero. And paint isn't forever on a hard used canoe. The main reason for using paint IMHO is that the lines on a well designed canoe are infinitely more beautiful when painted than that "cutting board" effect previously mentioned. Best color to show off these lines? Hey, I'm a traditionalist - any color... as long as it's white. :wink:

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PostPosted: July 14th, 2008, 10:05 pm 
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BK wrote:
Quote:
The secret to traditional boat hull stiffness lies in the ribs.

That statement intrigues me. I'll neither agree nor disagree with it until I understand what stiffness it refers to and how the ribs are presumed to contribute to it. I have always assumed that the role of the ribs was to tie the planks together and prevent them from splitting. As far as I know, builders like Rushton had no reasonably waterproof glue available to them, and no means of caulking compatible with the light weights he was aiming for. He therefore (my assumption) attached plank edge to plank edge with copper tacks but was still left with the weakness of his planks perpendicular to the grain and a tendency of the copper tacks to split the cedar because they concentrated loads on quite small areas of contact between copper and wood. If two adjoining planks were allowed to slide longitudinally relative to each other, then the hull would flex longitudinally in use and the tacks would split the cedar. Well-fastened ribs would prevent this sliding, (again, my assumption) thereby stiffening the hull longitudinally. When I first gave thought to their role, I guessed that they would also help hold the cross-sectional shape of the hull but the more I thought about that the more I thought that they would do quite the opposite--that the planking held the ribs to their curve rather than the opposite. (This, then, is the second kind of "stiffness" involved.) The third "stiffness" that would no doubt result from the ribs is resistance to local flexure normal to the hull surface, the flexure common to thin structures with no curvature. My hunch is that Rushton's planking thickness already addressed that potential, and that it's possibility never even occurred to him.

On the paint versus varnish question, I don't consider it to be of any great consequence either way. The can of spray paint hefted in the hand seems much lighter than the quart of varnish and I suspect has a higher percentage of volatiles. It may or may not scratch more readily but is easier to touch up and won't deteriorate in the sun. A benefit not yet touched upon is that it doesn't draw onlookers with thousands of questions, which allows the owner to get on with the business of launching and paddling. That advantage for fuzz-faced old farts may, of course, be a disadvantage for handsome young........

b

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PostPosted: July 15th, 2008, 11:17 am 
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GB,

The third type of stiffness is what I am talking about. Because the planks aren't glued together they will flex dramatically at the laps and deform. Even if the laps were glued with something like epoxy, they would crack at the edge of the plank since this is the stiffest part of the section. Rushton's "smooth-skinned" hulls would be less prone to this and would fair slightly better but would be even less stiff in cross section so they would need ribs even more.

No, they didn't have epoxy glue back then, but thickened varnish (or shellac) between the laps was a very common building technique and my friends who have done a lot of restorations on these boat can attest to it's tenacity. Sometimes a plank is pretty much destroyed trying to separate it from the lap for repair.

You are well aware that I have only a single boat's worth of experience with lapstrake construction, but from my observations during the ribbing out of that boat, I can say that there was a truly remarkable increase in cross sectional hull rigidity after we put the ribs in place... even when they were only clamped in place and not yet nailed through the planking. The combined effect of 48 1/2" wide x 1/4" thick ribs on the hoop strength of the boat hull was truly amazing.

Keep in mind that Rushton didn't pioneer the use of ribs inside of small boats, nor was he the only or even the greatest of makers. His success was primarily due to the exposure that Sears' writings brought him and he was wise enough to capitalize on it. Remember, too, that we as strip builders are putting thousands of miniature ribs into place when we glass a hull. Even using epoxy glue and 1/4" thick planking, a stripper would be a pretty flexible beast without some sort of additional stiffening.

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PostPosted: July 15th, 2008, 1:41 pm 
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Battenkiller wrote:
.... Even using epoxy glue and 1/4" thick planking, a stripper would be a pretty flexible beast without some sort of additional stiffening.

Indeed it would, but I'm not sure we have identical understandings of why strippers are as good as they are with the addition of glass layers inside and out.

Wood has great strength, both compressive and tensile, in the direction of the grain but comparatively poor strength across the grain, as you know well from your experience with stringed musical instruments. Plywood compensates for the cross-grain weakness by orienting roughly half of the wood fibers perpendicular to the other half. Those with little practical experience with plywood frequently consider it much stronger than solid wood, which it is not. It simply spreads the available strength in two directions. That makes it better for some applications and lesser for others.

Continuous compound curved surfaces with uniform strength in all directions are very rigid, making excellent use of all of the available strength. An egg is the classic example. As long as high, localized stresses can be avoided, the strength of an egg boggles the mind.

Builders of much bigger wood boats sometimes combine the advantages of plywood with the advantages of membranes with compound curvature by laminating veneers into what can best be thought of as boat-shaped (or egg shaped) plywood. Problems arise, however, with scaling these laminated hulls down to canoe size. One problem is that there are limits to how thin veneer can be cut and handled; another is that as the veneers get thinner and thinner the weight gain from glues gets out of hand.

I view a strip-built boat as a way of sidestepping these limitations on scaling down the hull lamination technique by using wood only for the longitudinally oriented veneers and fiberglass for all remaining veneers. There are other differences, of course, but this way of looking at strippers leaves me with the legacy view of a stripper as an egg, a membrane in compound curvature. That implies limitations. The further the hull design departs from compound curvature, the less suitable the construction method becomes. The same limitations apply to all composite constructions currently used in boats, of course, but our focus here is on strippers. For me, if a design tends to oilcan a bit the solution is not stiffening it with more structure but rather to work out a design that performs as well (or nearly as well) while incorporating more curvature in the area subject to the oilcanning. The same holds for floppy cheeks.

This thread is about light weight. That is a narrow focus. The narrower the focus, the more other aspects of the boat will have to be compromised. The ultimate lightweight certainly won't be the most indestructible and it probably won't be the fastest though the average paddler on a trip involving a lot of portaging may find it the fastest overall. I'll be happy with the weight of my canoe when when it floats overhead, with all my gear aboard, led by a kite string serving as the bow painter.

b

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PostPosted: August 6th, 2008, 12:44 pm 
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I've spent a fair amount of time trying to build a light weight tripper.
The 2ed hull was 40 lbs, the 3rd and current is about 42/43. (no trim)
Do to this, everything that goes in is weighed on a scale to the oz.

I believe and subsribe to George Robert's theory's re; light weight building.

With that said, I also believe that the lightest boat you could build would be one that got rid of all the core materials, and added ribs for stiffness, ie, a "kevlar" boat.

Folks building kevlar canoes are approaching Wenonah canoe weights, off hand I don't know what their solos weight, but their trippers, 18', are in the low 40's.

Building a light canoe is easy, building a tough light canoe is very hard.

Dan


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PostPosted: October 3rd, 2008, 9:07 am 
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In my experience a lot of the weight gain occurs with the...

1) Trim. Keep all structures to an absolute minumim. Reduce using hardwood to a minimum. Make the seats detachable. (In my plywood canoes, I don't build in seats. I use simple bench seats that can be moved around.) Keep the inwales and outwales to a minimum. Scupper the inwale and cut down on it's cross-section. Use spruce and cedar instead of ash, or laminate with a cap layer of ash or cherry over cedar. With Trim, labour can save weight.

2) Epoxy. Squeegee ruthlessly. Fearlessly! Push the cloth down and get rid of the excess. Then before it's cured completely apply another layer that just fills the weave.

I know most of you guys are way beyond these tips, but they're the ones that usually trip-up beginners.

Dave


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PostPosted: October 21st, 2008, 5:14 pm 
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The next canoe I build, I'm going to use 3/16" wood on the bottom and 1/8" on the sides. Should save a bit of weight, and 1/8" is plenty stiff for the side. Just a thought.

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PostPosted: October 21st, 2008, 5:57 pm 
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Bryan Hansel wrote:
The next canoe I build, I'm going to use 3/16" wood on the bottom and 1/8" on the sides. Should save a bit of weight, and 1/8" is plenty stiff for the side. Just a thought.
Plan to take your time, especially if the design has any moderate to tight curvature in the sides. 1/8" thick strips don't allow much stock for fairing.

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PostPosted: October 23rd, 2008, 5:32 pm 
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No, 1/8" strips don't. I built a canoe out of 1/8" strips once. As long as you take time it works out just fine.

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PostPosted: October 16th, 2009, 10:22 am 
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Found this while trying to look up info on vacuum infusion:

Quote:
New Vacuum Infusion Method:

After nine years of R&D, I have received a US patent for a new method of hull and fuselage construction. The method uses perforated architectural wood veneer with layers of carbon, aramid or hybrid reinforcements. Each piece of veneer is overlapped with adjacent piece about 3/8” to ¾” depending on the specific project. The perforations in the veneer and the small continuous triangle that is formed by the overlapping veneers allows the hull to be vacuum infused without the need of expense of infusion media. The overlap of the veneer greatly increases the stiffness of the hull while adding little weight.

I have built solo canoes based on a stretched “Wee Lassie”. I increased the length from 10’-6” to 13’-6 to increase its capacity. Raw hulls can be as light as 10.5 lbs and are strong enough to pull form the mould and paddle without gunnales or thwarts. My lightest finished 13’-6” canoe to date weights 14.7 lbs with wood gunnales and varnish.


His patent can be viewed here:

U.S. Patent 7,273,576

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