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PostPosted: July 6th, 2008, 11:12 am 
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Here is the article I refered to above re. the 18 and 20 foot stripers made with 1/8" strips.

http://www.smallboatforum.com/PDFfiles/ ... Canoes.pdf

also, another re. using the boat on the Bowron lakes circuit.

http://www.smallboatforum.com/PDFfiles/ ... alPark.pdf

Interesting reading.

Moonman.


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PostPosted: July 7th, 2008, 9:25 am 
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Bryan Hansel wrote:
You should seriously consider changing plans for the next one.

Bryan, you may be right, but first I think we need to give this design a good tryout. I can't turn my back on what may turn out to be a superior hull design. If it proves to be a dog, is unreasonably tender or oil cans badly the next will definitely be along the lines of a shallow arch hull.

Interestingly, this weekend I was at a retailer that had a couple of Placid Boatworks canoes in stock. I was surprised how much the bottoms flex on these otherwise very tough canoes. The sides are extraordinarily flexible. Gives me even more faith in wood strip construction as our little Nymph is vastly more rigid than the PBW offerings.

Seems to me that there is an inherent limit to how thin you can go with a canoe bottom without sacrificing stiffness and that limit is not necessarily dependent upon materials used. PBW canoes still flex even though they have five layers of high-tech cloth on the bottom because they have no ribs or foam. They might get much greater rigidity by introducing a 1/8" layer of balsa crosswise along the bottom and getting rid of a layer of Kevlar.


I was at the Wooden Boat show in Mystic, CT last weekend. I spoke at great length to one of the reps from System Three about weight reduction. He pointed out two very bad things about basswood as a boat building material. One is that is contains an extraordinarily high amount of unbound water when green. The spaces left over inside the wood after the free water dries up make the wood very susceptible to soaking up resin. He also noted that the wood basically lacks long fibers (one of the reasons carvers love the stuff) and is not as strong on a strength-to-weight basis as other woods like Sitka spruce, northern white cedar and Port Orford cedar. Plus, the short fibers have a stronger wicking effect on the epoxy and pull more of it into the wood surface.

So far I have determined at least a few things I will need to consider on the next boat:

- A shallow arched bottom may be necessary

- I will need to switch to cedar, preferable northern white as it is light enough that I can go with a thicker and therefore stiffer laminate and still not add too much weight.

- A graduated thickness construction is still desirable, but I should try 1/8" at the bottom and go to 3/32" on the sides

- Strips should be only 5/8" wide rather than 3/4". This will enable me to eliminate planing rolling bevels on the gluing edges and will leave more wood in the curved areas of the hull as they will need less fairing. The danger of sanding through will be reduced by this as well.

- Multiple layers of 1.25 oz. glass may save more weight than the 3.2 oz. I used on the last one.

- Gunwales should be thinner, made of northern white cedar and glassed over for protection from dents. 1.25 oz. glass should suffice here.

- Seat should be a molded composite one rather than a woven cane seat.

- Outer stems should be eliminated

- Breast hooks should be replaced with small carry thwarts.

- 3/32" on the bottom may be possible but stiffening ribs may be needed. I like the idea of 1/16" thick ribs 1/2" wide spaced 2" on center and long enough to reach just past the turn of the bilge. These would only add the net equivalent of 1/64" extra wood weight but would place the orientation of the grain 90º crosswise to the hull bottom making it stiffer.

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PostPosted: July 7th, 2008, 10:57 am 
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BK; A few comments based on admittedly limited experience:

Be cautious in trying to limit resin absorption of the wood. Maximum shear stresses occur at the wood/'glass interface. I'd suggest making multiple test pieces, testing them to destruction, and carefully examining the break. You may find tensile failure in the fabric, compression failure in the wood, buckling of the fabric on the compression side, etc. but if you find any sign of fabric delaminating from the wood at the break point after sealing to minimize absorption then you might want to reconsider.

Sawing strips thinner is the simplest and by far the most common way to minimize the weight of wood in the boat but it's not the only way. You could also fair and 'glass the outside, thereby strengthening the hull, and then sand the hull thinner before 'glassing the inside. I've found that 60-grit, open coat, abrasive paper backed up by a styrofoam block shaped to the curve of the hull, and used vigorously at an angle to the grain direction on white cedar is a very fast way to remove stock, and therefore weight. Depending on the shape of the hull, a lot of blocks might be required but they are quickly made by using the hull itself as a backup for the abrasive and sanding the foam to the shape. The problem is avoiding sanding right through the cedar to the outside 'glass. I do that by drilling right through the hull at strategic locations, measuring remaining thickness with a depth gauge, and filling the holes with epoxy when done.

On estimating weight, I've come quite close by estimating the wood weight based on weighing samples of the actual stock to be used and calculating for the actual square footage and thickness of the hull to be built. For the 'glass I've found that the rule-of-thumb that resin for a thorough wet-out weighs the same as the fabric is fairly accurate. I haven't found a good rule-of-thumb for filler coats.

I draw the designs that I use in a simple, old, 2D CAD program that allows me to easily read off offsets and lengths of spline curves. I plug these dimensions into a simple spreadsheet that gives me estimated hull weight as well as other useful information. Email me if the spreadsheet would be helpful to you.

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PostPosted: July 8th, 2008, 12:47 pm 
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Graybeard wrote:
Be cautious in trying to limit resin absorption of the wood. Maximum shear stresses occur at the wood/'glass interface.


I'm not trying to eliminate absorption, just to limit it to the surface. Turns out that may be hard to do according to the guys from System Three. Better, they say, to find a wood that is both light weight and low on absorption and live with how much it soaks up to achieve maximum peel strength. Apparently, basswood is a poor choice for that.

Quote:
I've found that 60-grit, open coat, abrasive paper backed up by a styrofoam block shaped to the curve of the hull, and used vigorously at an angle to the grain direction on white cedar is a very fast way to remove stock, and therefore weight. Depending on the shape of the hull, a lot of blocks might be required but they are quickly made by using the hull itself as a backup for the abrasive and sanding the foam to the shape. The problem is avoiding sanding right through the cedar to the outside 'glass. I do that by drilling right through the hull at strategic locations, measuring remaining thickness with a depth gauge, and filling the holes with epoxy when done.


Man, that sounds like a lot of work! Here's a photo of the pile of shavings my aggressive scraping on the inside of the hull produced:

Image

All those shavings plus vigorous hand sanding produced only a 12 ounce reduction in weight. Removing a uniform 1/32" (two pounds) from our basswood hull would require sanding away for hours and hours inside the hull, a tough place to sand in the first place. I think using thinner strips would be lot less work and it would be much easier to achieve uniformity in hull thickness.

As far as measuring hull thickness, I used a musical instrument maker's thicknessing caliper to reach most of the hull for Nymph. I will be making a much larger version out of Baltic birch and a simple dial indicator. There are other even simpler gauges that can be made from scrap that will do the job fine.

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For the 'glass I've found that the rule-of-thumb that resin for a thorough wet-out weighs the same as the fabric is fairly accurate. I haven't found a good rule-of-thumb for filler coats.


I don't see how that is possible as the wet out coat is the one that soaks into the wood adding extra weight. In our case, the cloth we used was 3.2 oz. I weighed a carefully measured square foot of the stuff on a gram scale (gee, what am I doing with one of those :roll:) and it weighed 10 grams (just about exactly 3.2 oz./sq.yd.). With about 28 sq.ft. of surface area, we should have had about 10 oz. of cloth/layer.

Well, the first 12 oz. batch of epoxy soaked right into the wood in no time flat. It covered less than 1/3 of the hull after carefully squeegeeing it out. I mixed up 45 oz. altogether and recovered about 5 oz. through squeegeeing (plus whatever dripped onto the cloth overhanging the hull). Even if it was possible to get 15 oz. back out of the cloth we would have added 30 oz. during wet out - three times the weight of the actual cloth. Our solitary fill coat on the other hand only used 24 oz. of resin and a lot of that sheeted off onto the overhanging glass. It was plenty thick enough to sand the entire hull down without going into the cloth anywhere.

I'd really love to believe that it was possible to achieve a 50/50 glass/resin ratio upon wet out. On a 10' pack canoe, that would mean a 5.5 pound bare hull (stripped in 1/8" NWC) with only 36 oz. of glass (3.2 oz.) and resin, inside and out. I'd be at 7 1/2 pounds, with no need for extreme reduction in the scantlings. Going to 3/32" planking would get me down to just a shade over 6 pounds. :o

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PostPosted: July 8th, 2008, 4:37 pm 
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A couple of tidbits from my learnings.
Resin
A 1-1 resin to fiber ratio is nowhere even close to filling the weave. In order to get minimum weight as far as resin goes the boat will not be show finish.
One example that you have looked at are the Placid hulls, they have full exposed fiber on the inside of the hull. In just a few hours of use they have plenty of Kevlar fuzzies under your heels.

With the aircraft I have built we would use enough resin for structure and then fill with lighter materials till smooth. This may be fine for a painted finish but obviously will not show the beauty of wood.

A question, Is the varnish lighter than epoxy?

Wood,
I am giving thought on my future build of using NWC in the lower structure and balsa up the sides.
Since I have full vacuum bagging equipment I may take the added time to bag my boat. This should reduce some of the absorption into the wood with the benefit of great clamping of the fabric to the wood reducing how much the fabric floats in resin. When working with foam cores this makes a major difference both in weight and strength. With honeycomb it is a must do. I expect it has similar value with a wood core.
In the sailboat industry bagging has been done even with the low pressure of a vacuum cleaner, I have three different size vacuum pumps that pull to microns so full clamping is available.

To get any value in using multiple layers of thin cloth you will need to bag the layup to clamp the layers to eliminate the fabric from floating.

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PostPosted: July 8th, 2008, 4:50 pm 
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BK; It sounds like the Sys3 guys were as concerned as I was about shear stresses when they advised going for peel strength. It occurs to me, though, that the Sys3 Clear Coat itself may be part of the problem. I haven't used it, having always used WEST stuff, but I've been hearing a lot about how well it wets out the fabric and intended to give it a try on my next boat. Perhaps it wets out the wood as aggressively and deeply as it does the fabric :doh: You could test four samples, two of bass and two of cedar, one of each with Sys3 Clear Coat and the remaing two with WEST 105. If you're really going for the ultimate lightweight stripper, the only other species that I find in the Forest Products Lab's Wood Handbook that might be a serious contender is Balsa, and that would be tantamount to laminating hundred-dollar bills to the required thickness.

You're right, of course, about sanding to reduce weight being a tad labor intensive. I mentioned it for its advantages, not its disadvantages; the advantages being that you can tailor thickness to the specific area and that it's low-tech. Doing it by hand with coarse abrasives is comparatively quick and keeps the air clear. If you think sanding the inside of Nymph was tough, wait until you tackle something with serious, low-radius tumblehome. Clearly, sawing the strips thinner is the more efficient route---right up until you reach the practical limits. When you reach the point where aligning the strips requires a plug instead of moulds, then the whole equation changes. While on this subject, I'd love to see a sketch of a suitable thickness gauge made from scrap that could be used to measure hull thickness while under construction.

Keep pursuing this!! With every passing birthday, yesterday's "lightweight" seems more and more overweight.

b

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PostPosted: July 8th, 2008, 5:04 pm 
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Awetcanoe wrote:
A 1-1 resin to fiber ratio is nowhere even close to filling the weave.

Regardless of the weave?????

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PostPosted: July 8th, 2008, 6:08 pm 
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Yes. if you have a very light and open weave a 1-1 will not even be watertight. A very tight weave will provide the best results but are very difficult to wet out at atmospheric pressure. A very slow cure helps. Either way it will still show a print through in the finished state with a very light layup.
All fabrics flex when being squeegeed with a tendency to lift after the tool has passed. This lifting is can not be prevented without clamping the fabric.
I have heard of many people with techniques claiming the fabric will not lift or float when working atmospheric. This is BS since the fabric still floats when doing a wet layup under full vacuum. 15 PSI is not enough to get the resin out.
This will always leave more resin than desired to achieve minimum weight and much more than a 1-1 weight ratio..

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PostPosted: July 8th, 2008, 9:23 pm 
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Resin goes four places (not including places where we don't want it, like the floor)
1. Into the wood.
2. Into the interstices between individual fibers in the fabric.
3. Into the voids between yarns in the fabric.
4. Into depressions in the surface that result from yarns going over and under each other.

My understanding is that the term "filler coats" is used for #4 and really needs to be considered separately since many builders don't use filler coats on the inside in order to provide better traction for the paddler. In my next build I intend to skip filler coats on the outside above the design waterline in order to save weight.

My understanding is that the term "wetout coat" includes both #2 and #3.

Until BK brought up the the question of how much resin his basswood was soaking up, I always thought of that resin as part of the "wetout coat" but if that varies widely depending on species of wood then it probably ought to be estimated separately.

If yarns in various fabrics are twisted to approximately the same tightness, then it seems to me that #2 will be a function of fabric weight.

It seems obvious to me that #3 will vary from weave to weave, perhaps quite widely.

In the last few posts I commented that estimating resin for wetout as about equal to fabric weight has come fairly close for me. I concede that I was not using an overly precise scale. But BK's concern about unusual wood absorption would question the usefulness of the "rule" anyway. Awetcanoe commented "A 1-1 resin to fiber ratio is nowhere even close to filling the weave." But the ratio that I mentioned was not for "filling the weave" but for wetting out.

I would really like to see:
1. Data on wood absorption of resin for specific species with specific resins.
2. Data on fabric absorption of resin for specific weaves.
3. Data on resin required to "fill the weave" for specific weaves.
I don't really expect to see any of the above.

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PostPosted: July 9th, 2008, 9:59 am 
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Bob, you see it a lot like I do.

Denser weaves will be thinner for a specific weight and will hold less resin. Thinner epoxies will wet out this weave much better but obviously will penetrate the wood better. This is not a problem unless you are pursuing the limits of lightweight construction. Adding a pound or two on a tripping canoe might even be desirable, but an extra pound on an experimental ultralight... well, that's just a no-no.

I'm sure that the thinner resins penetrate more, not sure how much. Epiglass by Interlux is touted as the best penetrating wood sealer on the market. It is even thinner than Clear Coat. Maybe the way to go is to seal with regular viscosity resin and then do the wet out with the Clear Coat or Epiglass.

One thing that you didn't mention is the resin that gets trapped underneath the cloth. Like Charlie mentions, there is no practical way to to reduce this. The Clear Coat is so thin and slow setting that it literally runs underneath the cloth and pools in the low spots. Even if you eliminate the fill coat, you will have to live with the entrapped resin.

When we glasses the tops of our gunwales we took great care to get the cloth tight against the wood. They have the slightest crown to them, almost imperceptible. Still, the Clear Coat flowed down this crown and raised the cloth so it was now actually higher than the center. A few swipes with the sanding block confirmed this to be true.

I should take the time to make up some test panels and start to amass some raw data. I can epoxy them with the excess from various operations during construction. Maybe folks can send me samples of other epoxies and glass to get me more enthused (no, Bob, I don't want a sample of that twenty year old stuff you used on your last canoe :doh: :lol: ).

Most glass has a number that specifies it's properties. I used Style 1648 from Thayercraft. He has many other types available and seems to know about them. He is a bit hard to understand due to his heavy southern accent (he pronounces his own business "Thigh-ar-cry-ift") but seems to be a real helpful sort.

http://thayercraft.com/Style%201678.htm

To be honest, I bought it because it was recommended by some on the Bear Mountain builder's board, but also because I could use 44" cloth on a small boat and it was dirt cheap. The original intent on this first boat wasn't to make an ultralight but to make the boat that my wife wanted out of the materials she wanted. Looks played a big part in her decision making process. I, on the other hand, will get great satisfaction in building a boat for myself that is both longer and lighter than her "showroom quality" little gem. :P

Here's a scan from Bob Benedetto's guitar making book with a drawing of his thicknessing gauge. It can easily be adapted for canoes:

Image

I'd still go with a dial indicator since you can get one for a few bucks on eBay. Better yet... use a 500W halogen work light on the outside. As the wood gets less than 1/8" it starts to become translucent. You can easily see (trust me :oops: ) the areas that are getting too thin. :wink:

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PostPosted: July 9th, 2008, 5:17 pm 
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Battenkiller wrote:
.......Adding a pound or two on a tripping canoe might even be desirable, but an extra pound on an experimental ultralight... well, that's just a no-no.

I wouldn't carry that line of thought too far. If you're really going for the limits of ultralightweight construction then lighter fabric is an obvious candidate. I know I've seen 0.75 oz. fabric on a vendor's website but don't recall the weave. Whether that's too light depends on the criteria. Trippers on big, fast rivers very far through trackless wilderness from any kind of help such as in Northern Canada wisely carry boats that are both very tough and field repairable. A BWCA trip of equal length and duration but on placid waters on frequently used routes with lengthy portages might suggest more weight savings. And the aging, bushwhacking, daytripper determined to continue exploring small ponds a mile or more from roads, trails, or navigable waters might demand the lightest boat possible--even one 'glassed with a single layer of 0.75 oz. fabric.

While on an afternoon paddle with Awetcanoe and Documania I took my Lassie, sheathed with a single layer of 2.25 oz. fabric, over a couple of low beaver dams without bothering to get out. I charged the narrow, shallow, opening and after hanging up about a third of the way across I poled myself and the boat over. I was intentionally testing the layup. I sustained minor scratches and that's all. I'm convinced that reducing fabric, and therefore resin, can be a fruitful area for saving weight. But I wouldn't have done it without the two paddling companions standing by. If I remember correctly, Awetcanoe took some pix of the dam fool. Gen-2 of the Lassie will probably use 0.75 oz. glass, doubled up to a couple inches above LWL, and tripled along the keel, at the stems, and at the turn of the bilge. I'll fill the weave only below the LWL. I keep reminding myself that Rushton used no 'glass or resin and Sears took his boats through some unfriendly passages with no serious harm.

Quote:
When we glasses the tops of our gunwales we took great care to get the cloth tight against the wood. They have the slightest crown to them, almost imperceptible. Still, the Clear Coat flowed down this crown and raised the cloth so it was now actually higher than the center. A few swipes with the sanding block confirmed this to be true.

At what stage did you squeegee??? I find that if I wait until the resin has begun to stiffen up, both the fabric and the resin behave themselves more "decorously."

With regard to 'glassing gunwales, consider biaxial tubing over thin strips sandwiching the top edge of the hull and spacing the inwale with short blocks of cedar. I've been quite happy with my first experiment using this construction on the Lassie. If done with carbon fiber tubing, the bold, black line at the sheer could be a very attractive accent. One nice aspect of the procedure is that tension on the tubing pulls it tightly to the wood core during cure.

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.....(no, Bob, I don't want a sample of that twenty year old stuff you used on your last canoe :doh: :lol: ).

BK!!! I'm crushed that you don't want a sample of my vintage 105. I'm sure you wouldn't turn down a generous sample of a highly reputed 20-year-old single malt.
b

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PostPosted: July 9th, 2008, 5:49 pm 
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PostPosted: July 9th, 2008, 6:20 pm 
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BK!!! I'm crushed that you don't want a sample of my vintage 105.


That is the specific resin for coating Basswood.

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PostPosted: July 9th, 2008, 6:32 pm 
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Thanks for the picture, Awetcanoe.
At this point in the crossing, jerks of body inertia were more effective than poling. Note the waves well ahead of the canoe; progress was in relatively small increments. Immersion fore compared to aft gives an idea of the amount of water over the high point. Note also the shoreline in the background; Awetcanoe pays attention to details when taking a picture.
b

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Last edited by Graybeard on July 9th, 2008, 6:34 pm, edited 1 time in total.

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PostPosted: July 9th, 2008, 6:33 pm 
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Awetcanoe wrote:
Image


Charlie, don't let GB get away with that lie. I've seen that posture before and I know for a fact that he really had too much Jamison and was actually passed out on that dam.

Greybeard wrote:
BK!!! I'm crushed that you don't want a sample of my vintage 105. I'm sure you wouldn't turn down a generous sample of a highly reputed 20-year-old single malt.


No, but I wouldn't do an experiment with it. I carefully dispose of the vile stuff, ever so slowly, one dram at a time. :wink:

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