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There are the newer epoxy saturated cold molded and older rescorinal glue cold molded hulls. The epoxy are far superior. In my opinion, if properly done, and covered with glass: are as good as most glass boats--and better than many. The older boats did have maintance and possiable dry rot issues...Not so the new ones.
I think the best cold molded boats are terrific - better strength to weight ratio than FRP, and low maintenance too. Not all cold molded construction the same though for sure.
Check out these construction series of photos (a dozen) of the guys over at Six River Marine making a cold molded West Pointer skiff. They are a real class outfit. http://www.sixrivermarine.com/Westpointer.htm
Here is the finished product:
__________________ When blithe to argument I come, Though armed with facts and merry; May Providence protect me from, The Fool as adversary. Whose mind to him a kingdom is, Where reason lacks dominion; Who calls conviction prejudice, and prejudice opinion.... ;-)
I beleive Buddy Davis has been building composite out of molds for the past few years. When done properly as most pedigree sportfish builders do, cold molded boats are outstanding. They are quiet, sweat less below waterline, and usually vibration free. This is old school boat building with modern technology.
I WORKED FOR BUDDY IN THE MIS 80S WHEN HE SWITCHED FROM CUSTOM TO PRODUCTION, WHICH WAS THE TIME HE WENT FROM COLD MOLDED TO MOLDS. THE COLD MOLDED BOATS WERE A LOT HEAVIER & SLOWER. THE KEELS HAD TO BE REDUCED ON THE MOLD BOATS DUE TO BOAT WANTING TO RIDE UP ON THE KEEL @ TOP SPEED.
Most boatmakers using cold-molding use thin plywood to speed up the process, but the result is not as strong. If you look at the way the guys at Six River Marine are doing it, they are using *thin veneers* of dried cedar - a lightweight, rot resistant, and porous wood that can easily be formed into shapes and also soak up epoxy resin readily. Alternate layers are laid on a bias, and saturated with epoxy that is vaccum bagged to eliminate air and voids in the sandwich, making a single layer of uniform strength.
The result is something like having a machine that magically makes a single perfect sheet of plywood, encased in resin, already in the shape of a boat hull. Or, you can view it as being analogous to hand laid glass, with the stronger wood fibers substituting for glass fibers.
If you look at the edge of the 18&1/2 foot skiff after it's first taken off the male mold, it's only about 1/4" thick. The finished skiff only weighs 1100lb.
__________________ When blithe to argument I come, Though armed with facts and merry; May Providence protect me from, The Fool as adversary. Whose mind to him a kingdom is, Where reason lacks dominion; Who calls conviction prejudice, and prejudice opinion.... ;-)
This may sound like a stooooopid question, but, please consider the source. Could "Cold Molding" be considered another form of coring? After all, isn't it simply epoxy or glass impregnated marine plywood that is then encapsulated in 'glass? I know it is not as thick and usually much lighter..........
steveyacht - 3/7/2006 1:45 PM
This may sound like a stooooopid question, but, please consider the source. Could "Cold Molding" be considered another form of coring? After all, isn't it simply epoxy or glass impregnated marine plywood that is then encapsulated in 'glass? I know it is not as thick and usually much lighter..........
I am not the expert on cold molding, but here is how I understand the material they are making at Six River Marine - I don't think it's like plywood coring. Here are some of what I see as key distinctions:
[*] I suspect the glues used in making plywood are different than the expoxies used in cold molding[*] If we cut through the material, the cold molded laminate will be much 'wetter' than plywood, that is, have a higher resin content, with a significant amount of resin infused right into the cellulose matrix of the wood fibers, instead of just lying on top and surface bonded as in plywood.[*] Plywood can't be readily bent, because the polymer strands and cross linking in the glue adopted an orientation during curing so as to be at lowest energy when the sheet is planar. If you cut it, you have weak areas at the joints, seams, and kerfs, and even if you bend thin plywood and layer that, you have introduced a molecular strain energy into the plywood's layer's of polymer matrix - not helpful.[*] In the cold molded hull, the polymer cures right into the shape of the hull, as it does in a glass fabric reinforced hull. The most stable configuration of the polymer molecule strands is the same as they adopt in the hull, because they were allowed to equilibrate in that configuration.[*] If you look at the two types of reinforcement though, the wood veneer "fabric" is both stiffer and stronger than glass[*] So, higher strength to weight ratio than either wood or glass reinforced plastic (GRP).[/list]
I guess I didn't talk much about coring, *lol*, but coring involves essentially spatially separating the two strong GRP layers with an intervening bonded layer of support to make a sandwich. The loads are still primarily carried by the outer GRP layers (aka skins) though, but additional stiffness, and to a lesser extent, strength, is provided by the lightweight coring. The stiffening effect arising from the spatial separation of the skins is often likened to an "I-beam". The core material is normally much less dense than the outer skins, and so for equivalent weight (but increased thickness), a stronger, stiffer layer can be made using a coring sandwich than with continuous GRP.
P.S. I will try to find a nice online illustration of polymer molecular structure and energetics
__________________ When blithe to argument I come, Though armed with facts and merry; May Providence protect me from, The Fool as adversary. Whose mind to him a kingdom is, Where reason lacks dominion; Who calls conviction prejudice, and prejudice opinion.... ;-)
steveyacht - 3/7/2006 11:45 AM This may sound like a stooooopid question, but, please consider the source. Could "Cold Molding" be considered another form of coring? After all, isn't it simply epoxy or glass impregnated marine plywood that is then encapsulated in 'glass? I know it is not as thick and usually much lighter..........
I have to say that the answer to that is "it depends on who is doing the building, and how it is used."wood can be used in many thin layers, with nothing but glue, and then very thin glass skins, just for abrasion resistance, or even no skins at all. In that case, the wood is the structure, and nothing else. This is the originalmethod of cold molding. First used on aircraft, and then applied to boats.Another method usesthicker layers of lightweight wood, and then much heavier glass skins bonded to both inside and outside. In that case, the wood is primarily a core. The real strength comes from the fiberglass skins.Or then again, you can use alternate layers of glass and wood. In that case, the wood is both structural, as an actual part of the laminate schedule, with it's own strength properties, and also a core because it is seperating the layers of glass to give the truss effect of a thicker laminate without the weight of all that glass and resin. This is where the method really shines.As an extra added bonus, when it's layered up this way is when the wood is most protected from water and rot.edit: man, am I a slow typist, yankeeboater just said everthing I just did, only he did it better. I hate when that happens.
So I am going to try to explain a little bit the polymerization and energetics - I couldn't find all the illustrations I'd like, so if this is confusing, send me an email or just drink heavily and forget what you read
Polymers (many units) are formed by reactions that link up many monomers (single units) with strong covalent bonds. The monomers can link end to end to for chains. If they are of appropriate structure, the chains can also form covalent "cross-links" to form networks of bonded atoms. All of this bonding at the nanometer scale gives the material it's strength at the macro scale. Here's a schematic picture of epoxy monomers forming cross-linked chains:
Hopefully you can envision the material increasing in viscosity and finally, rigidity and strength as this polymerization process (curing) occurs. Now, what's not shown in that picture is that the position and orientation of the atoms that aren't bonded to one another is also energetically constrained. The diagram makes it look like empty space between atoms, but that's not true, they are intereacting electronically. One important form of interaction in plastics is called "Van der Waals forces", plotted here. The plot shows the Van der Waals energy as a function of interatomic distance. You can see that there is a "happy medium" of greatest stability at a particular separation:
The reason that's important is that during curing, the molecules also move relative to one another to optimize these kinds of nonbonding interactions for maximum stability, then essentially get frozen in those low energy positions by all the polymerization bonds that form.
If you bend the polymerized material to the shape of the boat hull (like in the glue layers of bent plywood), instead of actually form it in that shape, you will destabilize the material (weaken it). The reasons are that you will:
1. Cause suboptimal Van der Waals interactions between molecules (move the away from the equlibirum interatomic radii).
2. Induce what is called intramolecular strain energy within covalent bonds in the chains and crosslinks - it turns out there are also optimal geometries for covalent bonds - both rotational and scissor like angles.
The resulting destabilized material is much weaker. Hope that helps.
__________________ When blithe to argument I come, Though armed with facts and merry; May Providence protect me from, The Fool as adversary. Whose mind to him a kingdom is, Where reason lacks dominion; Who calls conviction prejudice, and prejudice opinion.... ;-)
So I am going to try to explain a little bit the polymerization and energetics - I couldn't find all the illustrations I'd like, so if this is confusing, send me an email or just drink heavily and forget what you read
Polymers (many units) are formed by reactions that link up many monomers (single units) with strong covalent bonds. The monomers can link end to end to for chains. If they are of appropriate structure, the chains can also form covalent "cross-links" to form networks of bonded atoms. All of this bonding at the nanometer scale gives the material it's strength at the macro scale. Here's a schematic picture of epoxy monomers forming cross-linked chains:
Hopefully you can envision the material increasing in viscosity and finally, rigidity and strength as this polymerization process (curing) occurs. Now, what's not shown in that picture is that the position and orientation of the atoms that aren't bonded to one another is also energetically constrained. The diagram makes it look like empty space between atoms, but that's not true, they are intereacting electronically. One important form of interaction in plastics is called "Van der Waals forces", plotted here. The plot shows the Van der Waals energy as a function of interatomic distance. You can see that there is a "happy medium" of greatest stability at a particular separation:
The reason that's important is that during curing, the molecules also move relative to one another to optimize these kinds of nonbonding interactions for maximum stability, then essentially get frozen in those low energy positions by all the polymerization bonds that form.
If you bend the polymerized material to the shape of the boat hull (like in the glue layers of bent plywood), instead of actually form it in that shape, you will destabilize the material (weaken it). The reasons are that you will:
1. Cause suboptimal Van der Waals interactions between molecules (move the away from the equlibirum interatomic radii).
2. Induce what is called intramolecular strain energy within covalent bonds in the chains and crosslinks - it turns out there are also optimal geometries for covalent bonds - both rotational and scissor like angles.
The resulting destabilized material is much weaker. Hope that helps.
What a Precise, Cogent explaination................Too bad I didn't understand one darned word! Thank you so very much. The depth of knowledge available on this site never ceases to amaze.
Thanks guys - does my heart good to see people enjoy chemistry.
__________________ When blithe to argument I come, Though armed with facts and merry; May Providence protect me from, The Fool as adversary. Whose mind to him a kingdom is, Where reason lacks dominion; Who calls conviction prejudice, and prejudice opinion.... ;-)
See, that's the problem. I never enjoyed chemistry. To bad my HS teacher didn't explain it in the context of boatbuilding--then maybe I would've enjoyed it. I think I get the gist of it, though in a away I feel like Maxwell Smart (I understand everything up to "I'm going to try to explain a little bit...") Best thread I've ever read here. Thanks YankeeBoater and others.
Cold Molded Hulls? 
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Thank you so very much. The depth of knowledge available on this site never ceases to amaze. 
