Definition of Cold Molded?

[Capt. Rodbone]

Would a vessel hull constructed of two layers of marine plywood then glassedbe considered a cold molded hull? I seem to recall that cold molding involves THREE layers, specifically angled in three different directions, and also involves vacuum bagging?

 

[jgwinks]

Depends on how it was done. Two layers of ply or timber planking on a vee bottom hull set in mastic, maybe even just paint soaked canvas would be called "double diagonal". They used to do that before plywood was invented. Set them in epoxy or recorcinol on a round bottom and you're closer to cold molding. More, thinner layers at different angles would be stronger though. Vacuum bagging gives more even pressure while the glue dries for a better bond but screws and staples can also be used. There's not much point to cold molding flat areas like a vee bottom, full plywood sheets would do it better.

 

[psneeld]

Would a vessel hull constructed of two layers of marine plywood then glassedbe considered a cold molded hull? I seem to recall that cold molding involves THREE layers, specifically angled in three different directions, and also involves vacuum bagging?

Nope.... can be many more than 3 layers and vacuum bagging not required.

While 2 layers would be iffy in many designs, there are some that might get away with it with a heavy enough outer and inner glass skin. Usually the glass is only for waterproofing the structure but it does add strength to the wood core.

Cold molding is about using resins that cure without heat and built over a mold/frame/skeleton to form a monocoque structure.

 

[Simi 60]

Nope.... can be many more than 3 layers and vacuum bagging not required.

While 2 layers would be iffy in many designs, there are some that might get away with it with a heavy enough outer and inner glass skin. Usually the glass is only for waterproofing the structure but it does add strength to the wood core.

Cold molding is about using resins that cure without heat and built over a mold/frame/skeleton to form a monocoque structure.

This ^^^^^^

 

[DDW]

I'm not sure there is a well defined technical description of cold molded, but what I would call cold molded would have to be done with narrow sheets of wood or plywood, over a form, such that the result holds it's 3D shape when removed from the form. Big pieces of plywood cannot be formed, if two are glued together on a V bottom (not 3D surfaces) I'd just call that thicker plywood, not cold molded.

 

[jgwinks]

I once worked in a shop that built vee bottom plywood boats. The larger ones did get two or more layers but it was full length sheets, not diagonal strips. We didn't call them cold molded, just plywood. We only used 3/8" ply and just added layers till we got the thickness we wanted.

 

[Hippocampus]

Wooden Boat some years back did a review of what would be the strongest for weight and most durable wooden construction. Came up with edge nailed strip plank, then double diagonals of woven glass, or aramid or carbon on either side, then cold molded veneers parallel to the vectors of the forces the hull experiences such as from a rig then mat with gelcoat on top. Think the only thing that exceeds it is prepreg baked carbon with high tech honeycomb or foam. Have seen old school resorcinol ply older than me with no water ingress and as strong as the day it was made looking Bristol. All paint so no brightwork to chase.
Think it’s unfortunate modern wood using strip plank and/or cold molded never gained the market acceptance that grp achieved. Done correctly it’s the same maintenance, stronger per weight and allows complex curves without needing molds and all that tooling. Also stiffer so less dependent upon framing.

 

[LovetoBoat]

So when I first went looking for a boat I found a Composite boat. It was 40 foot drop dead gorgeous boat to me. I paid a surveyor to go over the boat on the hard after it was laid up for a year or two. His words not mine - "I cant let you buy this boat." He showed me where water intrusion hit in the corners of the stern and other places. He told me for every foot of damage we would have to extend the inspection cuts 4 feet out beyond on both sides to ensure integrity. He then showed me where I missed the keel was completely split on the bottom. Cold Molded or Composite boats are more forgiving in the southern states but up in the northeast you have got to make sure any cuts or splits in the fiberglass / resin are immediately taken care of. Water intrusion and frozen temperatures are a bad mixture for a boat and for someone with limited funding. YMMV

I ended up going with a fiberglass hull boat and for me it was the right decision.

 

[Hippocampus]

Ltb can you give more details about the construction? Who built it?who designed it? Properly constructed cold molded has the laminates permeated in epoxy and that includes the ends of the laminate strips. Areas of cross cut will soak up more epoxy than cuts with the grain. Even when I prevarnish wood pieces before assembly I end up putting twice as many thinned coats on the ends than the rest of the piece. Sounds like the builder didn’t know what he was doing. Big advantage of wood in cold places (and very hot) is it’s a great insulation. Doesn’t sweat like grp either. With plank on frame it’s generally a bad idea to skin a boat with fabric as the wood planks move and you can get water between the skin and wood which promotes rot. But given epoxy impregnated strip plank or cold molded wood won’t absorb water you can skin either.

 

[psneeld]

Some of cold molded/strip planked boats I worked on, mostly sport fishing boats of both Downeast and Outer Banks designs suffered from interior wood rot. The hulls were fine but interiors that gave some structure became problematic. Design and wood selection could have been better.

One big Sportfish lost sections of it's bottom from some sort of failure (never heard if the origin was ever identified.) It almost sank once, was salvaged, patched and lost the patches again not to much later.

I like cold molding and strip planking even more, but they can have issues like any other hull. Inspect carefully like any boat.

 

[sean9c]

My brother and I had a conversation a little while back. He is looking for a new boat shaped project and was looking at 2 boats, a Bill Garden and a Ray Hunt, both were double diagonal wood planked, obviously with glue in between. Both boats were built back in the '80's so pretty much before epoxy became the go to, so they were likely glued together with resorcinol glue. The big question was how long does the glue last? If the glue gives up there is no easy fix and without the planks all glued together it's not strong enough. We pretty much concluded that it was a scary proposition

 

[psneeld]

Pretty sure the double diagonal planked boats I remember all were fastened planks.

Glue might have been used.....have read some... I think that red lead or similar sealant/bedding between the layers was common on older builds.

 

[Hippocampus]

Think ps is correct. Advantage of wood is you can steam bend it which was commonly done in the past. Currently glues used in boat building are as strong as mechanical fastened. Problem is with modern non stick built boats you can’t see past the liners so have no idea if it was done correctly so if that strength is there.
Both epoxy and resorcinol with last for just about forever so that’s not a concern. Probably longer than the resin in grp.

 

[Inbreaker]

A John Lidgard 40, built in Aukland. Double diagonal kauri and kahikatea planks, heart kauri stringers, laminated ribs, and the lot bronze thru bolted together. Resorcinol, epoxy, and dynel sheathed exterior.
Launched in 1982.

 

[Bmarler]

My brother and I had a conversation a little while back. He is looking for a new boat shaped project and was looking at 2 boats, a Bill Garden and a Ray Hunt, both were double diagonal wood planked, obviously with glue in between. Both boats were built back in the '80's so pretty much before epoxy became the go to, so they were likely glued together with resorcinol glue. The big question was how long does the glue last? If the glue gives up there is no easy fix and without the planks all glued together it's not strong enough. We pretty much concluded that it was a scary proposition

I’ve been involved with the laminated beam industry all my adult life. Many of those are made using resorcinol glues. Look at any lam beam and if you see dark glue lines it’s likely resorcinol glue. It doesn’t break down. Some of those beams are run through treatment operations and directly put into the ground and used as power poles. We did artificial aging on samples and as long as the glue was mixed properly it doesn’t weaken as it ages.

 

[DaveGibson]

From what I read many years ago, cold molding involves impregnating thin wood strips and sheets with epoxy, and laying subsequent layers on diagonally. Then fiberglassing since epoxy is not UV resistant.

 

[etype38]

Cold Molding

I have never figured out the definitive qualifications as to what defines a cold molded boat. But I have one.

It's a 1999 33' Maine built express with a bunch of varying thickness cedar strips going fore and aft with 2 and 3 layers of 1/8" Okume ply on the outside.

My understanding of the process is that everything is pretty much soaked in epoxy during assembly. The ply on the outside is fastened with plastic T nails for assembly, but the epoxy is where the strength comes from. Then the whole hull inside and out is covered with layers of glass cloth in epoxy resin. Final finish in this case was Awlgrip.

The thinnest area of the hull is from water line up at 1" and the whole thing is fairly light.

It is strong as a rock, but I believe it has to be continually watched to ensure it stays dry.

 

[bshanafelt]

Spend some time on this website for some great examples:

https://coveyisland.com/recent-projects/nancy-lakin/

 

[Hippocampus]

Been to that yard as was interested in FarFar and the Westerman designs. Both are strip planked as the basic method. Edge nailed wood strips that are epoxy impregnated. The edge nailing is mostly to hold the strips in place until the glue sets but does add some strength.