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Waljojo

Barrels winter project

29 posts in this topic

Hello all,

 

I'm am interloper from the left coast and I'm glad I wandered in. This board's alot more applicable to my fishing than the Southern California boards since I've moved (it's cold up here! [Portland, OR]). Striper fishing is limited but we got a tremendous fishery. Right now I think I am the only SOT kayak fisherman in the city. Lots of kayakers, lots of fisherman, but no kayak fisherman. Actually it does kinda figure, but that's another story.

Anyway, I have been dying for somebody to start this train of thought. I've been thinking about building a boat for a couple of years. Epoxy and glass is definitely the lick, but after reading the "Kayak Shop" (a really good book on stitch and glue building) I'm thinking foam sheets as opposed to carving out a plug. Approaching it more from the kayak builders perspective than a board builder. Something along the lines of Cobra's expedition but with a tad more beam.

Stitch and glue in 1.5 to 2" thick foam panels instead of wood. The panels lend themselves to fair lines and relatively easy shaping. Other than that, building it should pretty similar to Barrels (by the way, I have the link for a step by step of a guy in San Diego who built a boat exactly as you described it. Be glad to email it to you.) Fair it and smooth it out with lite weight filler, then glass it. Hull lay-up schedule similar to a conventional composite kayak hull for strength and a light stiff deck. I think I'll vacuum bag it as I'm too lazy to do the finish work and I got some big mylars and a pump hanging around.

Open interior leaves room for a live well, fish storage, and storage in the rear (or, God forbid, a motor wink.gif ) Another bonus is it should still float pretty well completely swamped. I built a sorta proof of concept model out of foam meat trays and it seems workable. Big hatches, flush rod holders, recessed gripper cleat, flush mounted fish finder. I miss anything?

See any screamingly big flaws before I run out for some foam sheets?

 

 

------------------

Wali

 

[This message has been edited by Waljojo (edited 04-01-2002).]

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Welcome Waljojo! The only obvious "flaw", if you could even call it that, is the belief that foam panels will "lend themselves to fair lines." While they may be easy to fair (by sanding or hot-wire sculpting), they will not have sufficient homogeniety (SP?) to curve smoothly on their own. In addition, the manufacturing process lends itself to building in waviness or thickness variations that, while not important for the intended construction usage, will make getting out a fair shape harder.

 

Chris

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My only question, and it is a question, is if after fairing, some sections might wind up a little too thin. They could be patched from the inside if you could find them. I would bet you could find them with a really bright light.

Just thinking out loud.

Ken Lyons

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Welcome Waljojo HappyWave.gif

 

Glad to see we have another guy to keep JimW and Porter going with the cononefficent drags controled yaw and pitch and copolymer resin sand bagger wood stripping stuff cwm31.gif scary stuff for me.Dont really get them all the time.Ya know I am a little slow cwm15.gif

No really these are the guys you want to talk to .You will like it here.

JoeV

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Thanks yall for the warm welcome.

Jim, that's the guy in San Diego. I didn't post the link because I wasn't quite sure about board policy. Thanks for posting it.

Chris, I'm looking at fairly hard chines and no really big curves (tight radii (?)) to follow. I've played with some sheets and they "appear" to hold smooth lines. Initially I was going to use a hotwire. But I couldn't wrap my head around a set of templates for a compound curve. I figured that a long board and lite filler would eat up any waviness. Am I setting myself up for an excessively long row to hoe?

Ken, I really like the idea of being able to look at the relative thickness with a light. But I'm not counting on the foam for any structural strength. It's just holding up the cloth while it dries (or better "catalyzes"). I do plan to glass the inside so it will add to the overall stiffness (and protect the foam), but won't do much for the "strength".

Yall, I'm extrapolating from a background of building composite model sailplanes. I've played some in epoxy and glass but I have not built anything with this kinda structure so all of your input is greatly appreciated.

But then again, the spring Salmon are in and I'm in the Willamette(river)tomorrow. Spring has sprung (least it has out here) so I guess this is no longer a "winter" project.

 

------------------

Wali

 

[This message has been edited by Waljojo (edited 04-03-2002).]

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That's why I was thinking about S/G plywood for the hull. It'll go together fair and fast, and it's pretty durable and light. IMHO, By the time you get thru laying up enough glass inside and out on foam you're going to be a lot heavier. I think yr right about not gaining much strength from the inside layer of glass, the foam would be too compressable and strength of bond is suspect to me. Foam under the cockpit and watertight hatches would be plenty of flotation. More/less build a std sink S/G but remove part of the deck and build in box beams along both sides of the cockpit to make up the lost strength. There are also lot's of hulls around with known performance characteristics, you're thinking hard chined anyway...

Jim

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There is no way to get the shape I want out of strips. Only a solid block of foam and help from an experienced surfboard shaper friend of mine is going to get it.

Barrell

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Barrell, unless you're thinking of something incredibly complex (i.e. multiple compound, convex sections with very tight radii) it can be done with wood strips. Almost all the production kayak manufacturers (composite and tupperware) build prototypes of wood strips and use them, after fine tuning, as male molds for the production female molds.

 

S&G (stitch and glue) plywood on the other hand will only allow slightly hollow lines at the stems and simple curves (slight compounding is possible w/ "tortured" plywood construction.

 

Chris

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JimW,

 

Just wanted to point out that from my days in radio control, a lot of stregth is obtained by sandwiching a core material like foam or end grain balsa between fiberglass. When one side of fiberglass is compressed, the other side is being stressed. This is where you get your stiffness from because the fiberglass on the outside will resist stress greatly. The core material just prevents the two sheets of fiberglass from collapsing.

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Mrsinbad,

You are right on, but you need that core to be non-compressable. I think foam or balsa cores are also used a lot more to provide stiffness, as in preventing flat bottoms from oil canning. I have no idea if the foam they use to core boats is similar to extruded polystyrene or whether it is treated some how to improve the bond to glass/epoxy.

 

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Jim W, the foam doesn't have to be non-compressible. The forces acting to compress the foam are only likely to do so after the fiberglass skins have failed in tension or compression. Under all but the most unusual circumstances failure will be caused by bending stresses. One side will be pushed and the othe pulled. At the same time don't underestimate the additional strength added by only having foam on the inside. Essentially, without the fiberglass skins, one side of the foam has to resist compression and the other tension. With the skin most if not all of it will be resisting only one of those while the skin holds off the other.

Porter, your the structural engineer, if I remember correctly. Maybe your input would be clearer than mine

Ken Lyons

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My input may be clearer, but I'm not sure I agree with you. wink.gificon15.gif

 

Composite technology (not just resin/glass composites but all types including steel reinforced concrete) is a pretty advanced science and introducing the enormous multitude of forces involved in a boat only makes matters worse.

 

Let's start simple with simple bending: picture a square solid beam supported on each end with a weight in the middle. This causes tension in the bottom fibers and compression in the top (the forces being proportional to the distance from the centerline, this is why composites put the strong stuff on the outside face). The fibers in the center experience mostly shear forces.

 

Now for the complications (keep in mind that I'm making generalizations here)...

 

Steel reinforced concrete works by having the steel accept all (effectively) the tensile forces and the concrete all (for the sake of this example) the compressive forces. This is pretty easy to do for most structures (i.e. buildings) because the forces involved are known/assumed or can be modeled in some way approximating reality. The concrete will generally be asked only to accept simple bending and, as such, will have steel only near one face of the beam (depending on which direction, +/-, the bending is). If it may experience either positive or negative bending, it will have steel on both faces.

 

Boats get tossed around, lifted on waves by the middle or either end, twisted, racked, pitched, supported dry (slings, rollers, racks, stands, etc...), run into docks, and generally abused. The combinations of forces exerted are exceedingly high and any or all pieces of the boat may be in bending (+ or -), tension, or compression at any given moment, or some combination of the above.

 

If you could create an application where you knew that simple bending in one direction was the only load condition that your composite need withstand, I'm still not sure that a foam and one-side-glassed assembly would work. The 'glass is great in tension and relatively poor in compression (as are all thin shells). The foam, depending on which you choose, may be so-so in compression, but you would have to find a real specialty product. Of course, you'll never find this ideal condition in a boat.

 

So, what do you do? You 'glass both sides of course! This construction (foam-core or foam-sandwich composites) is very effective because it lets the foam do what it's truly good for; provide shear resistance by connecting the two faces of 'glass. To do this, of course, the 'glass to foam bond must be very good (it's the most stressed shear plane) and you should select your foam well. This assembly will now allow positive or negative bending and provides sufficient support to the compressive face of 'glass to overcome the thin-shell problem mentioned above.

 

Now you get to the last important point: compressive strength of the foam turns out to be important after all because bending, tension, and compression are not the only forces the hull will see. Impact resistance is, as I often demonstracte when I paddle, highly important. A foam product with low compressive strength will allow the 'glass face to collapse into the sandwich when subjected to (low) impact loads.

 

Too much? icon15.gif

 

Chris

 

[This message has been edited by Porter (edited 04-03-2002).]

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