foam cores

[Thad Van Gilder]

OK, lets pretend one wanted to build a dinghy with a foam core with epoxy layup.

now, what if one were to use the blue or pink extruded foam that the building industry uses for insulation.

would said person be looking at an instant failure?

-Thad

[Dan McCosh]

You could make it work, or it could eventually fail. Foam-core laminates generally fail in sheer, and if the foam itself is weak stuff, it crumbles, making the structure two hollow sheets with nothing in between. Structural foams are strong enough to resist this sheer, as is end-grain balsa, even some corrigations in paper and aluminum. If the covering laminates are stiff enough, you can also eliminate most of the sheer loads, and the only issue becomes excessive weight.

[Thad Van Gilder]

would it help if there were wood stringers between the foam sheets?

-Thad

[JimConlin]

Even the structural foams are pretty soft in compression. A-500 Core-Cell (5#/ft^3) has a cpmpression strength of 115psi. So, to withstand a point load such as would be encountered on a rocky beach, you need a much stiffer skin than is needed for strength.
Balsa core, which is end-grain, would be better in this respect, but the decay resistance of balsa is nil, so i'd have my doubts there, too. For a dinghy that's expected to take some abuse, I think that a lightweight plywood such as okoume. cedar strip composite or cold-molded cedar veneers, all with glass structural skins are the lightest practical methods.

[Thad Van Gilder]

well, it's like a proof of concept deal. make a dinghy, give it to my friend's kids to beat up, and maybe make a larger boat for a friend.


-Thad

[Joe Lambert]

I've seen numerous one off car bodies made from blue foam and polyester/glass skins. Depending on the abuse the boat's intended for I'd go for it. What do you have invested, next to nil right?

[Dan McCosh]

Small boats are kind of funny. Generally, they have to use materials that are much stronger, stiffer, etc. than needed for their size, only because they take a lot of impacts. You don't usually drop a 40-footer on a rock on the beach, for example. Solid glass or ply work fine for a dinghy, and the saved weight from the foam is not going to be much.

[Todd Bradshaw]

Just the fumes alone from polyester resin will melt styrofoam, so you probably want to stick with epoxy or pick your blue foam very carefully.

[Dan McCosh]

Styrofoam, the most common, dissolves in polyester. Epoxy works with most common foams. Can't think of much that works with polyster, altough Corcell might.

[Thad Van Gilder]

I was gonna do a test layup this weekend with Polyestermite resin and one with epoxy.

-Thad

[Gary E]

Why dont you make a hatch cover first?
instead of giving a risky contraption to your friend's kids ...

got insurance?

[erster]

Yes it works with epoxy only and a grid reinforcing the structure with some restrictions. The glass is important in this application. If you wish to contact me offline, I will give you some specifics of this myth busting job that I did for the heck of it in 1993.

[Thad Van Gilder]

Gary,
Do I have insurance? yeah, their dad gave me the idea and asked me to do it for them.

Him and I have been close friends for a long time and they, like me, don't follow the lawsuit trend. WE take responsibility for our own actions.

My responsibility is to not hand over something that looks like it isn't strong enough, and his responsibility is to see that the product looks like it might be safe.

I may be idealistic, but it has always seemed to me that If 2 people do that, and they don't believe a lawsuit is a quick means of income, this world would be a better place.

This crazy idea needs to start somewhere, and I didn't start it... I simply followed in the footsteps of those wiser than I.

I don't associate with those who follow the "Lawsuit is better than my own judgement" mindset anyway.

Thad

[JimConlin]

I would make up some test panels.
If you want to try Core-Cell, contact me off-list. I have some scrap.

[Thad Van Gilder]

Jim,
I PM'd you.

Thanks for the offer. I appreciate it.

-Thad

[mmd]

Polyester and vinylester resins will dissolve the blue construction foam; epoxy won't. One difficult part is getting the foam core to wrap around the quick compound curves of a small boat like a dinghy. Another is as mentioned above: to get adequate impact resistance the outer skins have to be much stronger than they need to be for structural strength, so weight savings become minimal. There is, however, the advantage of few or no internal structural members - the structure of the hull is usually adequate in and of itself.

One method to build such a boat is to build a building jig similar to that used for strip-cold-molding, strip it with foam "planks", fair it with a surform tool and longboards with coarse paper, then 'glass it. Pop it off the building jig and 'glass the interior and, presto-bingo!, you have a hull. The down side is that there is a lot of fairing compound and elbow grease required to get a shiny smooth hull surface. But if groundings aren't a big issue, the weight savings can be substantial. Dave Gerr's book gives reasonable scantlings calcs for skin thicknesses. Put hardwood blocks in place of the foam where you want to fasten things like oarlocks and cleats. Last word of advice: be sure to apply adequate resin for the bondline between foam & reinforcement - the foam tends to wick resin away from the interface creating a dry bond which will delaminate with the slightest provocation.

I'd buy a cheap shop-vac and vacuum-bag the bugger.

[Thad Van Gilder]

hmmmm.

I wonder how much glass I would need for an 8 foot pram...

[mmd]

Of the top of my head (I'm away from my boat-y office), I'd say the laminate schedule would be 1.5 oz mat/1808 biaxial/1.5 oz mat on the outside (overkill for puncture resistance) over 1/2" foam with 1.5 oz mat/10 oz. boat cloth on the interior. About 50 sq. ft. per laminate totals about fifteen pounds of reinforcement which would require about two US gallons of resin to lay up. The foam will weigh about twenty pounds, the resin about eighteen, so the all-up hull weight without fittings will be about fifty-three pounds. Completed boat should be under 75 lbs. Considerable weight savings can be had at more expense (spacier materials) and less local impact resistance.

[Ron Williamson]

You could try the urethane foam that signmakers use.
Its compressive strength is greater than extruded polystyrene,but it is much heavier as well.
They glue it with Gorilla Glue or epoxy.
R

[erster]

Well looks like MMD addressed it with great authority and knowledge. I will add that I do use a slurry mix of epoxy and cabosil after using 36 grit to scuff the cheap stuff. I also have found that I use about one gallon of epoxy for 1808 wetout for one side of a 4x8 sheet of foam board finishing up with a 4 or 6 oz finishing cloth that really is fairly simple to wet out and little fairing is neated for a decent finish job.

[George Ray]

Get some Airex or equiv and then at the end of the considerable effort (vacuum bag sounds good) you will have a vessel that your great grands will cherish and your can build it light weight instead of having to go heavy to protect the foam to glass skin interface from flexural failure. But having said that any foam core you do will be a good and interesting endeavor. Do try to read some of the old literature an boats built with Airex ..... AMAZING how they flex and go, flex and go.

[erster]

I have still found that the same glass is used, the same reinforcing and basically the same layup for the same boards such as Divinicell. . One technigue that differs in flat surfaces and in hull designs in small hulls is using a simple heat gun to conform the foam keeping some of the factors of stress cracks to a minimum in the building process on the jig. This takes some finesse but not hard at all.

[Jim Mathieson]

OK, lets pretend one wanted to build a dinghy with a foam core with epoxy layup.

now, what if one were to use the blue or pink extruded foam that the building industry uses for insulation.

would said person be looking at an instant failure?

-Thad

The problem with your insulation foams are they are not closed cell and will absorb moisture making for eventual failure.

Your Boat building foams are closed cell and have stiffness,especially Corecell.
I'd go with 18 oz biax glass ,but skip the matt depending on your supplier.If it's really soft silky glass then use matt,if not for example the glass Noah supplies (and I use) is usually best without matt.
For scratch resistance three strips of hard wood and some care is less weight than the extra matt for me.

[JimConlin]

...One technigue that differs in flat surfaces and in hull designs in small hulls is using a simple heat gun to conform the foam keeping some of the factors of stress cracks to a minimum in the building process on the jig. This takes some finesse but not hard at all.
Cove&bead strip planking also works well and goes quickly.

[erster]

Cove&bead strip planking also works well and goes quickly.


Correct but this was not part of the original request for information. Consider one thing though, the choice of woods is very important or weight does become an issue in small craft. FWIW, I have not found blueboard to absorb water. I think MMD did a great job on describing what I personally have found to be a pretty good method, but found discussing radical alternatives to be very controversial on here. So I think I will bow out of this one. There are times that there are advantages to using the stuff for the average guy as long as its done what I considered to be proper, which has also come from a working application of abuse in my own boat for a great experiement which seemed to have worked for me.

[ssor]

Extruded styrene foam is certainly closed cell and does not absorb moisture. I have used it successfully for building outrigger pontoons. I glue it with canned urethane foam shape it with knives and disk sanders. I cover it with epoxy and double knit polyester cloth.

[Jim Mathieson]

PU (Poly Urethane) foam gets soaking wet like a sponge and has terrible properties in most areas. This is why PU foam should be non existent in boat building, and almost is too. PU foam is open cell foam. It’s the same stuff you can buy in "spray" cans for house building purposes, like insulation around window frames.

[willmarsh3]

This thread reminds me of a dinghy I saw at the Woodenboat show in 1997 in Mystic. I was able to grab and lift one end with one finger. It looked nicely and professionally built. Unfortunately I don't remember who built it.

[mmd]

I'm surprised that no one has started screaming, "Blasphemer!!" and tried to get the thread Scotted yet. <wink, grin>

[Figment]

I'm not coming from the "Blasphemy" angle, but I really must wonder about the practical benefits of this academic exercise, particularly in light of the recent success of s&g plywood Optimist dinghies.

Why polystyrene? Because it's cheaper than plywood?

[Gary E]

I'm amaized that someone has not gatherd up all those used foam coffee cups and used them...
must be a bazillion of them available for FREEEEE.

[Cuyahoga Chuck]

Since Figment brought it up I'll jump in.
I sail the D4 pram. 8'X46" and 65lb. It was overdesigned to be able to function as a sailboat dinghy. Mine is made from ¼"-3/8" HD plywood and has the sailboat options so it's on the heavy side. With BS1088 the weight could be dropped 5 lb.or more. If the ply was reduced to a 4mm-6mm you could go even lower although the hull might be a little flimsy to support a large spread of sail. So, if the foam core dinghy/pram were to have a weight advantage over S&G it would have to produce a practical 8' boat that's less than 50 pounds. With epoxy at 9¼ lb. a gallon that looks like a difficult target.
The guy who designed the D4, Jacques Mertens, has unending requests for nautical foam based versions of his larger boats. The answer is always the same. The hull will cost twice as much with no weight benefit because of the heavy lamination schedual required. There can be a weight saving on some interior structures because the lamination schedual can be lighter. And building over foam is a lot more difficult than ply.
In other discussions I have seen on the use of insulating foam there is an unending line of hopefuls, particularly in the kayak field, who have tried to make this work and, so far, there are only a couple of one-offs that haven't translated into any kind of nich.
"Hope springs eternal" but, I'll bet there are educated discussions on the web somewhere as to why this won't ever be a fruitful building technique.

[Dan Lindberg]

Lots of good ideas here but,

What's the overall goal of this?

To build a boat light, or cheap or quick or maybe a combination of things?

In the canoe world, it's tough to get lighter then kevlar with foam cores, which are fairly common. But even with the kevlar, they tend to get punctured easily on sharp rocks. And in outfitting use, the Outfitters try to get rid of them after 1 season.

I have heard of (home?) builders making canoes using foam (instead of strips) and they are very light but a bit delicate. You sure don't want to drag them over rocks.

Dan

[Andrew]

I google PU foam and most sites are referring to it as closed cell.
This site is advertising it of boat floatation:
http://www.shopmaninc.com/faq_foam.html#3

[ssor]

I did some informal testing of half inch corecell and polyester/glass composites vs. northern white cedar. Same size samples (3x8 inches) and same weight. The cedar was thinner than the composite. Supporrted the samples on the ends and loaded them in the center of the span with a five gallon bucket. then started filling the bucket with sand. they both broke at about the same load. I think that it comes down to what is most available where you are. I guess the composite boat would tolerate more neglect than a wooden boat.

[mmd]

I don't have time to go into a lengthy discourse on wood vs FRP at this time, but hopefully it will suffice to say that each material has its strengths and weaknesses and the proper use of either is predicated on carefully evaluating what properties are most important to the finished product and basing the material selection on that. To offer a blunt example, I can build you a cored FRP dinghy that will be half the weight of a similar boat in wood, but it will not be easy, cheap, or puncture-resistant. Conversely, I can build you an FRP dinghy that will be stronger in every way than a wooden boat, will last four times (at least) longer, and will be no more expensive than its wood counterpart, but it will be considerably heavier. Then there is the whole aesthetics thing, both in the construction and the final product.

But the bottom line remains that you have to evaluate the requirements before selecting the appropriate material, not try to adapt the requirements to meet the needs of the material.

[Dan McCosh]

Expanded polyurethane as used in Old Town canoes is the best dinghy material.

[Figment]

Expanded polyethelene? The crumbly white foam composed of a jillion little spheres? Dunkin' Donuts coffee cup foam? That's interesting.
Are those canoes laid up in fiberglass, or are they polyethelene (or whatever igloo uses to make coolers) plastic shells?

[erster]

What the heck, and then there was those other nutcases...............................

The Birth of Fiberglass Boats http://www.boatus.com/goodoldboat/images/Vanguardsailingbw.jpg
Jeff and Nancy Larson enjoy their 1965 Pearson Vanguard, Nordhavn, the 32-foot big sister of the Triton. The Vanguard was introduced in 1962.

By Steve Mitchell

Despite the popular notion today, fiberglass and plastic resins were not "new" technology in the mid-1950s, nor was Clinton Pearson the first person to use them to build sailboats. This begs the question: who did build the first fiberglass sailboat?

According to Dan Spurr, editor of Practical Sailor, and the author of a forthcoming book on the history of fiberglass sailboats, Heart of Glass, "It probably was a fellow named Ray Greene in Toledo, Ohio. He built a fiberglass and polyester sailboat in 1942, probably a Snipe. So a sailing dinghy was the first fiberglass sailboat." After a pause he adds, "But you have to watch your terms."

It turns out there were several earlier boats made of fiberglass and various plastic resins, but most of them were too brittle for practical use. Dan says it was the development of polyester resin that started the fiberglass boat revolution. In part, this problem of terms revolves around the separate, but parallel, developments of fiberglass and plastic resins.

The ancient Phoenicians and Egyptians made glass, and are said to have used glass fibers as decorations and to reinforce pottery. (To add to the many coincidences of the history of fiberglass boats, the Phoenicians were the master shipbuilders of their day. One can only imagine what they could have done with fiberglass construction.) Through time, many other civilizations made glass strands, primarily for decoration. In 1870, John Player developed a process of mass-producing glass strands with a steam-jet process to make what was called mineral wool for insulation. A patent was awarded to an American named Herman Hammesfahr in 1880 for a type of fiberglass cloth also woven with silk.

Fiberglass experimentation continued into the 1920s, with the first actual fiberglass fibers we know today being made in 1932 - by accident. A young researcher for Corning Glass named Dale Kleist was trying to weld together two glass blocks to make a vacuum-tight seal when a jet of compressed air inadvertently hit a stream of molten glass. The resulting spray of fine glass fibers turned out to be what researchers had been trying to make for years.

In 1935, Corning Glass joined forces with Owens-Illinois, which also had been experimenting with fiberglass, to develop the product further. The word "Fiberglas" (note only one "s") was patented in January 1936, and the two companies merged to become Owens-Corning in 1938. Research showed the glass fibers to be light, yet very strong. On an equal weight basis, a strand of fiberglass is actually stronger than a strand of steel.

Development of plastics began in the mid-1800s, in part due to a challenge from a billiard ball company to find a new material to replace ivory for its chief product. Patents were awarded for a variety of plastics by the late 1800s. Research speeded up in the 1920s, and again with the approach of World War II, due to the shortage of many natural products. Carlton Ellis of DuPont was awarded a patent for polyester resin in 1936. The Germans furthered the manufacturing process of this early polyester by refining its curing process. Early in World War II, British Intelligence stole these secrets and turned them over to American firms. American Cyanamid produced the direct forerunner of today's polyester resin in 1942.

This early polyester resin quickly ended up in a number of manufacturing hands. Owens-Corning had been experimenting with fiberglass cloth and resin combinations to create structural elements for airplanes. By 1942, the company was turning out fiberglass and polyester airplane parts for the war effort.

Back in Toledo, Ray Greene, who had studied plastics while a student at Ohio State, had been working with Owens-Corning on fiberglass composites. He had made composite boats as early as 1937, but was searching for just the right plastic to use for boats. He received a shipment of the polyester resin in 1942 and produced a daysailer.

Others followed suit. Dan says, "B.B. Swan made a small fiberglass catboat in1947. Carl Beetle built fiberglass boats at a GE plant in Pittsfield, Mass. He exhibited his fiberglass boat at a show in January 1947."

The first sailing auxiliary made from fiberglass appeared in 1951. "It was called the Arion, a 42-foot ketch." states Spurr. "It was a one-off design by Sidney Herreshoff. Then Fred Coleman's Bounty II came out in 1956."

Dan goes on to explain that Ray Greene was not finished either. "He formed his own boatbuilding company and produced a 25-foot Sparkman & Stephens design in 1957 called the New Horizon," says Spurr. "He built 175 of them. That was a pretty good number of boats, and right before the Triton, too."

Tom Potter, the driving force behind the Triton, agrees. "Ray Greene did bring out a fiberglass boat before we did, at least what you would call the first sailing yacht," he says. "It was kind of an odd looking boat, though. The Triton certainly was the first mass produced boat that sold well."

Bill Shaw also acknowledges Ray Greene as the first to build a fiberglass boat. "And I worked at Sparkman & Stephens when we designed the New Horizon," he says. "I remember Ray Greene very well."

How the Pearson cousins came to be viewed as the fathers of the modern fiberglass industry is not clear, given the many boats that preceded the Triton. Nevertheless, it was the Triton that captured the buyer's heart - and pocketbook - in 1959. In the end, that's all that matters.
Article taken from Good Old Boat magazine: Volume 2, Number 6, November/December 1999.


What I find interesting is that many people thought that all the other stuff was junk and had no place in boats and the water, overbuilding some of the first production hulls. Now we have also learned that its just not the case now, especially in the canoes that some of the major manufacturers are making. If some of the new methods are good enough to be subjected to abuse of yahoos, then within reason, why should other alternatives not be used, especially given that in this case its not just some yahoo off the street asking this in this thread.

[JimConlin]

Where did that topic go?

[stef]

I seem to recall a web site from Chile or Argentina of a chap who built a 26+ foot boat with epoxy and foam. I have to dig the link out of my archives (or brain ).

He did not bend the foam but shaped the curved sections of the hull from steps.

I do not recall the glass layup schedule but 2"or 2 1/2" minimum of foam sticks in my brain. I do not think the glass was to exotic like maybe 2-3, 9 oz layers biased 45 degrees.

I belive it had a flat bottom much like the Elver.

He built it open as a day sailing boat for parties.

He used a recycled J24 mast and sails.

He was careful to say "the boat was intended for sheltered waters only".

A photo or 2 was included of the finished boat with 5-6 people on board.

Darn, I will have to find that link just to convince myself it was not my imagination.

Best regards,

Stefan

[Dan McCosh]

Expanded polyethelene? The crumbly white foam composed of a jillion little spheres? Dunkin' Donuts coffee cup foam? That's interesting.
Are those canoes laid up in fiberglass, or are they polyethelene (or whatever igloo uses to make coolers) plastic shells?


Expanded polyethelene is a very tough structural foam, which skins over in a mold. Injected molded, it creates a very tough, resiliant structure that is not particularly stiff. For a small boat, you end up with a structure that has a smooth, tough, colorfast exterior and interior, can bounce off sharp rocks, is sufficiently bouyant to not need flotation. One ad has a pickup crushing it against a tree, and it just bounces open again. The interior floor is smooth, and very foot-friendly. Old Town finishes off their canoes with maple caned seats, which is a nice touch, and helps the non-wooden-boat guilt. Unless you have a die shop handy and a molding press, it isn't a do-it-yourself material, but I think would make a terrific small tender, as well as canoes.

[Dan McCosh]

I was in error. The stuff is a three-part laminate, with cross-linked polyethelene skins and a foam core. It is rotomolded, rather than injected. A bit about it here:http://www.oldtowncanoe.com/canoes/anatomy/materials/superlink3.html Anyway, stuff like this makes it tough to think you can do better with hand layups.

[Wild Wassa]

Most of the boats that I repair are foam cored, racing dinghies and sports boats. Foam cored boats are not sturdy work boats by any means, nor can the types of boats I see, take the slightest of knocks.

Over the construction of a boat, different core types are used because of their different advantages and ease of use.

This Flying Fifteen below has used as the core a very flexible nodule sheet to allow easier moulding/shaping in the tighter curves.


http://www.imagestation.com/picture/sraid216/p75c07e6c28a7a5246bf50d0e3d8e4cde/ecafac3f.jpg


The hull of an Australian Lighweight Sharpe uses 20mm end grain Balsa (Balsa was mentioned earlier).


http://www.imagestation.com/picture/sraid201/p4f2260a5d1e59ad9cad55bacb8e2f723/f00bdd8f.jpg


Nidaplast honeycomb. Is excellent stuff to use. It is a closed honeycomb that just need sheathing in glass, carbon or kevlar. Below is a damaged 2mm Aeroply deck on an I14, that was replaced and modified using Nidaplast. The hoop, for the spinnaker tube, is foam core sheathed in carbon.


http://www.imagestation.com/picture/sraid218/p05afb117a094a7e913778d338846eca0/ec3457fc.jpg



http://www.imagestation.com/picture/sraid218/p935eb52a9296f9eb9fe4499c9f87ecb3/ec2e94dc.jpg


10 mm Nidaplast honeycomb core. The cloth is sheathed straight onto the thin surface skin (on both sides) with epoxy.


http://www.imagestation.com/picture/sraid223/pae1635c97f27722340d63dc4b59abb8e/eadbce44.jpg


I'll photograph different foam/core types today, and post the shots this evening.

Warren.

[Todd Bradshaw]

I am not aware of Old Town using polyurethane foam as a canoe core material at any time and the foams that they do use have nothing to do with coffee cups. They have been using Royalex as a building material since the early 1970's or so when Lew Gilman closed his own company (Indian Brand) and joined Old Town, bringing the technology with him. Royalex is a sandwich of ABS structural skins on either side of an ABS foam core and covered on the outsides with a vinyl skin (mostly for UV protection). It comes in sheets, made by Uniroyal in Warsaw, Indiana and the boats are vacuum-formed.

Their more recent developments (SuperLink and PolyLink)were in direct response to the popularity of lower cost, roto-molded polyethylene canoes (Coleman in particular) and are three layers of cross-linked polyethylene, the middle layer being a foaming variety. They are also roto molded, but the layered construction using a foam-core between the load-bearing skins generates greater stiffness than a single layer does and eliminates the need for the crappy aluminum interior structure that companies like Coleman have had to stuff their canoes full of to get them to hold their shape.

Many of Old Town's fiberglass or composite boats have used core materials over the years, end grain-balsa was the most common and is still used today. K-mat (which I believe is some sort of Divinicell foam-based coring material) is another that they use.

[kulas44]

The best of the "home builder" type of cheap insulation to use for core material is called R-Board, used for roof and outer wall sheathing. It is considered a structural component in stick built houses, unlike the R-Mat, and almost all of the other types of insulation that have no structural value. It's also much stiffer than the R-Mat P.U. insulation.

[George Ray]

I think a good approach to blue or pink foam would be use it as structural ribs inside a lite skin vessel. Think longitudinal half rounds faired into the inside and glassed in place and then the same thing fitted in like transverse frames again faired in and glassed. The result is a stiff grid that helps support the thin skin and because the foam is divided into small self contained compartments any one can delaminate or crack and get moisture in it and it is not a huge deal. In this case the small compartments place less stress on the foam glass interface which is the weak point of these foams. The peel strength, the resistance to damage from small crushing blows and the recovery from small crushing bows is LOW in these foams. Bend then and they break, unlike Airix, Klegecell, Divinycell etc.

[Wild Wassa]

Divinycell cores. These offcuts are about A4 size. Left to right, H 80 GS, Density:6lb/ft3, H 80, Density:6lb/ft3, and H 100, Density: 6lb/ft3.


http://www.imagestation.com/picture/sraid223/p1eac38c71f2295b4258ab27cb65880b0/eada7c91.jpg


H 80 GS core are scored tiles on a glass backing.


http://www.imagestation.com/picture/sraid223/p7e352e11d89cf06dafba1a9e57a65199/eada7ca0.jpg


Below, H 60 showing the pores. H 60 core is the most open cell foam of the cores that I've seen. Millimetre scale.


http://www.imagestation.com/picture/sraid223/p96c99d7495a8ebaeb5f71d71d460a0d0/eada7cb3.jpg


The next two photographs are damage to a foam core and polyester hull of a Flying Fifteen that I'm repairing at the moment. The ground out area is about 20 cms long (so far). The foam core is 1.5 - 2mm thick with both the outer hull the inner hull sheathed in chop strand mat, the gel coat is the thickest part of the sandwich after the foam ... all in all, it would be lucky if the total composite thickness is 2.5 mm or 3 mm at the most.


http://www.imagestation.com/picture/sraid223/p3bd679195bab4a3bec16393b5526067b/eada6344.jpg


http://www.imagestation.com/picture/sraid223/pb5b5532fca0a0f3be84e397313924f1a/eada6335.jpg


Warren.

[stef]

After my brain became unstuck if found the link: http://www.magallanesboatbuilding.com/

He uses a urethane foam ~10 cm thick, polyester resins, roving and mat. So much for my memory.

Stefan

[erster]

That site has a virus in it.:eek: I had just updated my settings and it kicked it out.

[Fretz]

I suggest you use polyester resin instead of epoxy. what you $ave will cover the cost of a structural core like corecell. A fridge compressor will allow you to vacuum bag which is fun.

I rebuilt a balsa cored scow and used foam and polyester. It was a learning experience and turned out better than expected.

here is a link to a thread with pictures of the job.

http://www.sailinganarchy.com/forums/index.php?showtopic=28354&hl=

Any questions just ask.

[Ron Carter]

"Mississippi" Bob Brown had a 2 or 3 part article in MAIB a year or two ago about such a dinghy he built. He went through several iterations and when all was said and done he was dissappointed with the result. His conclusions verified the coments above about light and weak or heavy and reasonably srong. Net result no saving in labor or material cost and no weight advantage.

[kenjamin]

Has anyone else heard about Tuf foam? I haven't been able to find a vender for it but it's supposed to be more environmentally friendly than the Clark foam with which they used to make surfboards. Tuf foam was originally developed to shield delicate electronics of nuclear warhead triggering devices. Here's an article from Surfer Magazine about Tuf foam– http://forum.surfermag.com/forum/showflat.php?Number=923648

I think John Gardner's 9'6" pram in his book "The Building of Classic Small Craft" (I think that's the title) would be a great design in foam.
His sturdily built ply version came to 125 lbs. A foam version could easily be under 100 lbs. with no worries of rot in the closed foam-filled seats. A very capable, good rowing boat for its size.

[Dan McCosh]

I've seen numerous one off car bodies made from blue foam and polyester/glass skins. Depending on the abuse the boat's intended for I'd go for it. What do you have invested, next to nil right?


I think what you are looking at are one-off concept car bodies. Current practice is to develop new designs with CAD programs that translate into 3-axis NC programs that run milling machines. The milling machines can either mill clay prototypes or foam. Both can be used to splash-mold epoxy molds that then can turn out low runs of body panels. The foam core can be skinned and the result is a reasonable facsimile of the car. These aren't runners, however--if the car is to be tested, molded temporary panels usually are formed, either from fiberglass, or sometimes steel. In fact, rather than being a reinforcement, the foam core can be dissolved easily, leaving a formed fiberglass piece. I've seen carbon-fiber spinnaker poles made using this technique.

[Dan McCosh]

My favorite composite panel is a sandwich of 1/4 ins. ply and aluminum beer cans. It can support an elephant, and is very light. Haven't seen it used in a boat yet, though.

[htom]

You could take sheets of foam, apply fiberglass with epoxy on both surfaces, then cut into planks and use them for glued lapstrake construction. When the hull was glued together, you'd use fiberglass tape and epoxy to cover the unfiberglassed edges.

Not going to try it.

[Dan McCosh]

There also is a composite, tubular linear cellulose matrix which makes a decent hull. Commonly known as wood.

[mmd]

Maybe I should just publish my curriculum for the course "Introduction to Composites Materials" that I teach here at the College... <wink, grin>

[Uncle Duke]

Maybe I should just publish my curriculum for the course "Introduction to Composites Materials" that I teach here at the College... <wink, grin>
That is actually a very nice idea. You could allow WB to sell it as a downloadable PDF from their site for some small $$ (small U.S.$, of course - it would look bigger in Canadian $$ <Grin!>). No need to worry about printing or distribution.
I'd buy one...

[Thad Van Gilder]

I'd buy one. Unfortuneately, my grad school doesn't offer that course!!!

-Thad

[htom]

There also is a composite, tubular linear cellulose matrix which makes a decent hull. Commonly known as wood.

Ha ha ha ha. Should have left them guessing!

[mmd]

"That (selling the Composites Fabricator Technician Program curriculum on-line) is actually a very nice idea. You could allow WB to sell it ..." - Uncle Duke

Unfortunately the curriculum, although developed & written by me, is in fact the property of the College so I am unable to do other than joke about distributing it. You could, however, come and take the program in whole or in part. We are working towards modularizing the program for the 2007-08 year so that individuals or businesses can "buy" seats in discrete courses within the program. For instance, you could come to the college and take just the course in resin infusion or prepreg carbon fibre laminating or laminate materials repair techniques. Lotsa slick technology to learn.

[ssor]

There also is a composite, tubular linear cellulose matrix which makes a decent hull. Commonly known as wood.

Unfortunately some brands are short term biodegradable.

[Dan McCosh]

I did have a conversation with a friend who has done considerable research in composites and ran the same line by him. He said that they attempted for lots of years to duplicate the properties of wood (mainly stiffness to weight ratio) in a synthetic composite, and never managed it. Oddly enough, both the Corvette and Peterbilts are using balsa-cored floors at the moment.

[mmd]

In compressive strength - vs - weight - vs - cost endgrain balsa is top of the heap; in shear and moisture resistance it is crap. Once again it is an exercise in determining the best material given the application parameters.

[mmd]

Thank you, gentlemen, for this discussion; I presented the questions posed to my Composites Fabricator Technician class as an exercise in answering real-world problems. It made for some lively discussion and made them go back to their notes to find answers. So much more interesting than my "what if" problems.

[erster]

Thank you, gentlemen, for this discussion; I presented the questions posed to my Composites Fabricator Technician class as an exercise in answering real-world problems. It made for some lively discussion and made them go back to their notes to find answers. So much more interesting than my "what if" problems.

I have another excersize for you folks there.;) Just out of curioisty, the area covered is 90" x 60" with simular layup schedule. Tell us what it weighs. I will weigh it when the weather breaks in the next few days. Let compare engineering numbers to real life for the heck of it. It would be another fun excersize.

http://img.photobucket.com/albums/v356/Bateau1/DSC00924.jpg

[mmd]

I'll play...

(Note to Erster, though - I'm making some big assumptions here. I'll assume that 1.) the layup is the same as I proposed in my earlier posting about the pram, 2.) that the epoxy resin that you used is about the same weight-per-volume as the one I am calculating (MAS resins), and 3.) that your core is 1/2 inch Dow styrofoam BlueBoard that weighs 2.5 lbs per cubic foot - mmd)

...the panel weighs about 21.5 lbs.

[paladin]

My apologies if I miss speak....as I haven't read each and every posting on this topic.....sorta spot checked them...get too tired lately...
Referring to actual construction of an object such as cored structures using Klegecell, Divinycell or balsa, two other problems will arise. The shear strength between the two skins will be a major problem in some conditions and the "cure" or "partial cure" can be resolved in attaching the two skins to each other. When you prepare the core, run a narrow saw blade along the cuts, or make cuts, so that there's a 1/16 th inch channel every two inches. The resin can be thickened with fibers and squeegeed in the crevices, then longboarded before attaching the outter skins. Then when you roll the hull and lay up the interior skins, they will bond to the webs created by the cuts. This will also localize the damage in balsa cores if the skin is punctured, and makes it easier to clean out localized areas to add wood laminated in for load bearing areas.
Sorry would write more...gonna go take a pill or two and lie down...

[mmd]

Chuck, some of the newer foam cores made for resin infusion have that feature built in. Diab has cores that have perforations every few inches that allow a thin column of resin to bridge the foam between skins; NidaCore has a foam core manufactured with a surface layer of fibreglass cloth on each side that is knitted through the foam, creating a fibre-reinforced column that is integral with each skin layer. Sometimes it is a bit daunting just keeping up with the advancing technologies and materials. Fun, tho'...

[erster]

MMD, thanks as its just some idle time killing but I will let you know FWIW, the glass on the reverse side is 18 oz. sticked woven. The top is 1808 and 6 oz finishing cloth. Keep in mind that I also incorporated a grid into the decking of 1/2 x 1 1/4" which is included in the weight. I faired it with microlight from west system. It should be interesting to find out. If I recall correctly, a sheet of fir plywood, bare is about one and half pound per square foot. Does that sound about right? I do not recall right now what the okume weighs.

[paladin]

4 hour nap and I'm back.....
Michael..I haven't built anything with balsa or foam cores....or more or less fiberglass construction in maybe 20 years. I find that laminated wood, strip planked or cold moulded has all the characteristics that I like, is easy to work, easily repaired and repairable just about anywhere.....also I dunno like the smell of the other stuff......I guess I may be spoiled.:D

[mmd]

Don't get me wrong, folks; I'm as big a fan of wooden boats as the rest of you, but if you want to be a professional designer and actually make money you have to become familiar with the stuff that makes up about 90% of the pleasure boats in North America. Actually, it is really nice material to design for...but I agree that it isn't the most pleasant stuff to work with. The smell of polyester doesn't bother me, it's the itch that gets me. I lived, breathed, and ate the stuff for a few years when I ran the boatshop in St. Vincent and never did get used to it. Just a sensitive guy, I guess.

[Clif]

Todd Dunn built a blue foam dinghy... you can google it.

http://www.geocities.com/TheTropics/8005/bfd/update.jpg

[StevenBauer]

Hey Thad, there was a story in Messing About In Boats Magazine a few years ago about a styrofoam dinghy. Mississippy Bob, maybe? His was more of a punt, actually. Anyone remember this?

Steven

[rbgarr]

This thread reminds me of a dinghy I saw at the Woodenboat show in 1997 in Mystic. I was able to grab and lift one end with one finger. It looked nicely and professionally built. Unfortunately I don't remember who built it.

I wonder if that may have been a carbon fiber dinghy built by Lyman-Morse.

A couple of years ago a guy named Richard Tate was selling plans and instructions online for building a planing nesting dinghy out of biaxial S-glass over Weskor foam-filled honeycomb. It was called the Abaco 11. Interesting idea. It was kind of a garvey shape and would plane two guys with 4 hp (8 hp max) at about 10 knots.

[JimConlin]

Michael-
The specific engineering problem i'd worry about in a dinghy built with a foam core would be the trade-off between the stiffness of the skin vs. the compression strength of the core. When the boat is set upon a pointy rock, what bears the load? The softer the core, the stiffer the skin needs to be. How do you approach this in a formal engineering way?

[mmd]

Caveat: Little boats are usually either overbuilt or built to previously-proven scantlings (probably overbuilt) because the cost involved in engineering the structure is so overwhelmingly greater than the possible return on the sale of the boat.

To determine the local hull strength (assuming that there is no scantlings formulae such as ABS Rules), first you determine the probable loadings (how much weight at what speed landing on how small an area to get impact psi), then calculate the panel strength of the unsupported panel (area between internal stiffeners), then calculate the tensile strength of the fibre/resin matrix to determine if the point loading will exceed the outer skin strength, then calculate the deflection of the outer skin to determine if it exceeds the core's ability of return from deformation (don't want the core to dent and leave a void between skin and core). If any of the above calcs shw that the material in question will fail, add more or stronger material and run the calcs again. If the calcs show that it is strong enough, assume that it is overbuilt, reduce the material quantity or strength and run the calcs again until you find the "just enough" combination. Add a factor of safety according to the anticipated use and level of risk, calculate again, and you have the required scantlings.

Simple, eh?

[erster]

Layup schedule. 18oz. woven on the back side against a slurry mix of thickened epoxy. The top is a slurry mix, followed by 1808, then 6 oz finishing cloth, followed by microlight fairing compound, followed by two coats of primer and several coats of topcoat enamel paint. The results are in from a cross section which measures 12" x 24" with a cross section of the wooden reinforced grid system. I used my scale that I weigh out my shrimp on, which does a pretty good job when I freeze them in packages for portions for dinner. The results for this cross section is a tad below the 3 3/4, for the two foot square piece. actually the deck structure that tapers to the bow, in my measurement is 2" less than the widest width, but is pretty consistant for the running length. You can actually see that the bond is not that bad, considering that I used a four foot crowbar to remove it, damaging some of the areas of the glass.

http://img.photobucket.com/albums/v356/Bateau1/DSC00934.jpg

http://img.photobucket.com/albums/v356/Bateau1/DSC00933.jpg

http://img.photobucket.com/albums/v356/Bateau1/DSC00925.jpg

[JimConlin]

Thanks, Michael. I'm becoming a believer in scantling rules.

[G Jacobson]

FWIW, I built a pair of boogie boards for the kids (and me) about 8 years ago using blue construction foam sandwiched with epoxy between sheets of 1/8" Lauan. The have taken much abuse over the years and held up great. In addition to being very light, they are also VERY strong and can easily support standing weight.

So much so, I have often thought this would lend itself very well to the construction of small flat/rocker bottomed craft such as prams or even mini-drift boats. The punch thru and structural strength attained by the 2" dimensional gap between the sheets of 1/8" Lauan would seem to preclude the necessity of using heavier material (1/4" and up).

Also, my understanding is that unlike conventional styrofoam, the blue construction foam is hydrophobic.

[few3]

Extruded polystyrene ( pink and blue foam ) are permeable, they do not repel water in any way. Water migrates through the stuff, but at different rates depending on the thickness. 2 inch thick EPS doesn't dry out as fast as 3/4 inch, but all of it does allow moisture to pass through it.

[erster]

Extruded polystyrene ( pink and blue foam ) are permeable, they do not repel water in any way. Water migrates through the stuff, but at different rates depending on the thickness. 2 inch thick EPS doesn't dry out as fast as 3/4 inch, but all of it does allow moisture to pass through it.
Really? Interesting, Tell us more or provide us some evidence that supports this for us. Have you heard that even painted wood absorbs water, too?;) Just ask your off the street home improvement guy. Have you also heard that plywood instantly rots when subjected to moisture?;)

[Figment]

Few, are you sure you aren't confusing polystyrene with polyisocyanurate?

[Paul Scott]

One problem you guys haven't discussed yet is the outgassing problem of bluefoam (or XTR, or XPS), which can be dealt with by controlling exposure to heat (the sun), or by building heavier, which is it's own can of worms.

Pufferfish comes to mind, as a metaphor. And you never know when or if.....

It is fun to work with.

Paul

[few3]

Few, are you sure you aren't confusing polystyrene with polyisocyanurate?

Polyisocyanurate foam is the insulation that is covered in foil scrim, tar paper, etc. The construction type is off-white. It has a higher r-value, but is brittle ( reason for the foil or tp ). On it's own, it has very little compressive strength. PI also absorbs water readily. However, it has an added benifit in that it smolders, with a better fire classification.

[ion barnes]

Well I had experimented with a piece of blue foam, door skin ply and West epoxy some years ago and was very impressed with the tuffness. 2" blue foam with door skin both sides. allowed to set with a ten pound weight in the middle of the span, neting a crown of about 3" on 24". I wont jump onto it but it will support my weight of 230lbs. As for its water absorbtion, negliable as much as I can tell. I have some of the stuff by the shop take has been soaked since last fall and not any heavier. I think some truths get a little stretched when it comes to servicability and lifespan. Just build something and enjoy the experiment.

Example; I saw a small boat in Nanaimo harbour built of rough sawn 2X2 cedar boards, 4ft long, laid brick fashion with Liquid Nail and galvanized nails. Incredably crude and cheap but it worked and the guy was on the water.