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Old 08-05-2014, 11:08 AM   #1
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Cold Molded

A cold molded boat is about the most sophisticated hull made. Extremely strong and light. There have been many high tech very high performance sailboats made this way.

I had a Sumnercraft that was wood and glass but it was not cold molded. It was of "sandwich" construction. In the past it was common to FG a wood boat but that didn't make it cold molded. My Willard's cabin and deck is glass over plywood and she's not cold molded either.

But I'm not explaining it properly either as I'm not sure what the "cold"has to do w it. Must mean that no heat is used to cure the plastic but I know of no boat that used heat for curing. Also I don't know any cold molded boats that didn't use very thin veneers for structural rigidity. Only remember sailboats. And only extremely high performance sailboats. The method is a bit shape limited. Veneer laminated would seem a better name than cold moulded. And I wonder if they were actually built over or in a mold or over a framework. One would think mold per the name.

Anybody really know?
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Old 08-05-2014, 11:41 AM   #2
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This is a pretty fair explanation from Wikipedia and explains why small-volume, high performance sportfish builders like Merritt and Rybovich pioneered this technique in the mid-60s:

Cold-Molding is a composite method of wooden boat building that uses 2 or more layers of thin wood, called veneers, oriented in different directions, resulting in a strong monoque structure, similar to a fibreglass hull but substantially lighter. Usually composed of a base layer of strip planking followed by multiple veneers, cold-molding is popular in small, medium and very large, wooden super-yachts. Using different types of wood the builder can lighten some areas such as bow and stern and strengthen other high stress areas. Sometimes cold molded hulls are protected either inside or out or both with fiberglass or similar products for impact resistance especially when lightweight, soft timber such as cedar is used. This method lends itself to great flexibility in hull shape.
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Old 08-05-2014, 11:52 AM   #3
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Eric, I posted this link on the other thread. There are some pictures and videos on the link that show Jarret Bay's process. They build some very expensive boats.

Custom Sport Fishing Yachts & Full Service Facility | Jarrett Bay Boatworks
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Old 08-05-2014, 11:56 AM   #4
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Hi Eric,

Many (most, all?) Luders 16s and 24s used a were hot molded process to form their hulls. Also many, many of Uffa Fox's boats (Fireflys, etc.) immediately post-WWII were also hot molded. Not sure of the details of the process, but believe they used urea-formaldehyde based glues in those days. Equally unsure as to whether or not the hot molding cured the glue, or simply formed the hull shapes. This required a permanent mold, similar to those used for fiberglass work today. Good for production boats, not so fine for one-offs.

Steve Rander at Schooner Creek Boat Works in Oregon has made numerous one-off cold molded powerboats, using his take on the cold molding process, which includes a foam core inside the laminations. Here's an example:

2001 Schooner Creek Downeast Power Boat For Sale - www.yachtworld.com

Cold molding, of course, refers to the laminations being laid at room temperature, using staples and epoxy to afix them until they cure. The laminations are laid onto a male form, which typically includes the frames, some intermediate removable forms, and numerous longitudinals to properly define the hull shape. Very labor intensive, possibly the most expensive process used in boat building today, but capable of forming very complex shapes, with a resultant hull structure significantly lighter and stronger than strip planking, or carvel, or ??

IMHO, wood cold molding of one-off power or sailboats has been superseded by various techniques to used to execute light weight structures in composites these days.

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Old 08-05-2014, 12:54 PM   #5
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Thanks Pete and Don,
Yes I remember some of that history now. US Molded Shapes. I'm sure they were hot molded boats w a male and female heavy form using probably hydraulic power to press the forms together. I'll bet the heat helped the wood take the mold shape a bit like steam bending.

How are ABS plastic boats like canoes made? With a hot mold?

Yes the Schooner Creek boats are probably well suited to cold molding and would be much stiffer in the center of the bottom than a reg FG boat. And the "built down" Lobster types would do well too.

The Jarrett Bay boats are another example of why I've got to come east and see many many fabulous boats that I've only see so far in pics. Thanks Don.
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Old 08-05-2014, 01:21 PM   #6
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Thanks gents, I have learned something today and I thought I was too old!! Sounds a lot like a cored hull only with stranded wood so that it ads strength which ordinary cored hulls do not do as they are primarily just to reduce weight. Am I close? Could you have a cold molded boat with no outside or inside glass or other protection? Would that not just be a plywood boat? Interesting discussion.
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Old 08-05-2014, 02:36 PM   #7
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here's something I clipped from another forum...I thought some prototype PT boats were tried this way and later just double planked...maybe Marin knows as he is a PT enthusiast I think.

One big [and I mean that literally ] disadvantage of hot-molding vs cold-molding is that hot-molding is hot: an autoclave large enough to hold the hull you're building is a pre-requisite. According to the Classic and Vintage Racing Dinghy Association, Fairey (who invented the technique for aircraft and adapted it to boat building in the post-war years) involved pressurized steam:

Faireys method was somewhat similar to the “vacuum bagging” method used with cold moulding today, but Faireys method was rather more drastic – the hull was laid up over a male mould, using a system of pre-fitted slats, rather than staples, to hold the veneers in place. It was then covered with a fitted rubber sheet and steam was injected into the autoclave to give a pressure of 50psi at 100 degrees C which was maintained for 12 hours.

An autoclave that large, even without steam and/or pressure, is not something that would be easy, practical or possibly even doable to fabricate in the back yard for a one-off project. Add that much pressurized steam and you'll almost certainly be needing to license your boiler and earning your steam engineer's license just to fire it up.

Here's a hot-molded hull going into the autoclave at Carver Boat in Milwaukee, c. 1955 or so:
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Old 08-05-2014, 04:44 PM   #8
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Had a Luders 16 that was hot molded. I believe that resorcinol glue was used. Held up extremely well. Eventually, there was some delamination near the keel which we fixed using cold molding (peeling back a few of the old layers and epoxying in some new layers). Not my old boat, but here's a pic of an L16. Pretty, but not as fast as it looks, wet and uncomfortable seating. But a joy to look back on when rowing ashore.
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Old 08-05-2014, 07:48 PM   #9
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Would it then be a misnomer to call the boat I plan to build "cold molded"? It is a ply on frame design with epoxy joining and fiberglass covering. The screws used in construction are incidental and can be removed after epoxy cure is achieved.
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Old 08-05-2014, 08:25 PM   #10
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Would it then be a misnomer to call the boat I plan to build "cold molded"? It is a ply on frame design with epoxy joining and fiberglass covering. The screws used in construction are incidental and can be removed after epoxy cure is achieved.
Take a look at this thread: Cold-Molded Boatbuilding
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Old 08-05-2014, 08:54 PM   #11
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Keep in mind, CP, if you are going to remove the screws your bond is with the inside layer of the plywood only. Good epoxy and the best marine grade plywood can work. But many builders will leave the screws with plywood construction to add strength thru all the plywood layers. Go bronze and if you want to be meticulous, you can encapsulate each screw as explained in the "West System " book (Gudgeon Bros? forget how to spell their name). That book is offered as a free download on their website and covers just about everything. (I want to build a bolger 'Sneakeasy' for lake running! it's interesting learning)

What boat are you thinking of building?
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Old 08-05-2014, 09:03 PM   #12
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Would it then be a misnomer to call the boat I plan to build "cold molded"? It is a ply on frame design with epoxy joining and fiberglass covering. The screws used in construction are incidental and can be removed after epoxy cure is achieved.
I think cold molding is pretty much where you make the plywood out of layers of thin veneers.

You are just building a ply boat with a belt and suspenders approach if you leave the screws. Unless the fiberglass covering is so thick to add structure as opposed to just a surface finish/abrasion protection, then it's just a hybrid or composite construction depending on who wants to call it whatever.
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Old 08-05-2014, 09:22 PM   #13
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Yes, I picture 'cold molded' as much different than plywood on frame. I may be wrong, but i see cold molded as making your own 'layers' where plywood offers all the layers in one shot. I think they both can work well depending on the boat and intended use. There are many ways to skin the cat since epoxy came to town.
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Old 08-05-2014, 11:06 PM   #14
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Thanks guys, though the screws are not needed structurally beyond construction phase as per the NA I'll be leaving them in to avoid patching holes. Some time back I purchased about 5 sets of small boat plans from a designer called Jeff Spira.

My youngest son and I plan to pick one and build it this winter. It's more for father son bonding than anything else. Have sourced a local supplier for cabinet makers who assured me he can supply the marine grade ply and specialty hardwoods I'm requesting.

I just spoke with Jeff the other day and decided to commission a new John Boat design he was considering drawing. If the boats do not work out as we plan they will be donated to be used as play props for local youth groups.
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Old 08-05-2014, 11:51 PM   #15
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Boat to the left is cold molded. Two layers of okume plywood in alternating layers, bottom skinned with 1708 biaxial and West. Then flip boat and take out temporary jigs where permanent bulkheads go. Install the bulkheads. Then take out the rest of the jigs and glass the inside with 1708 and West.

You end up with something similar to an I-beam in the structural sense. The glass skin provides the tensile and compressive strength, the wood holds them together and at a distance, and give some impact resistance that a balsa or foam core would not. And the whole thing is LIGHT and STRONG compared to other methods.

And yes, it is labor intensive to build.

No point at all in leaving in the screws. Unless you wait too long after laminating and the dang things break off!!!

I filled all the screw holes with a syringe. Since I had nothing better to do, I counted them. Just under 10,000 holes filled.
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Old 08-06-2014, 12:09 AM   #16
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Originally Posted by Ski in NC View Post
Boat to the left is cold molded. Two layers of okume plywood in alternating layers, bottom skinned with 1708 biaxial and West. Then flip boat and take out temporary jigs where permanent bulkheads go. Install the bulkheads. Then take out the rest of the jigs and glass the inside with 1708 and West.

You end up with something similar to an I-beam in the structural sense. The glass skin provides the tensile and compressive strength, the wood holds them together and at a distance, and give some impact resistance that a balsa or foam core would not. And the whole thing is LIGHT and STRONG compared to other methods.

And yes, it is labor intensive to build.

No point at all in leaving in the screws. Unless you wait too long after laminating and the dang things break off!!!

I filled all the screw holes with a syringe. Since I had nothing better to do, I counted them. Just under 10,000 holes filled.

If you ever have to do a lay up with epoxy again,and want to remove the stuck screws,here's how I do it.I use a soldering gun,an industrial commercial unit.I heat the stuck screw head for 3 to five minutes,and then try to back it out with an electric,plug in the wall style, 1/2 inch drill with a screwdriver bit in a quick chuck.If you need to grab the screw,use gloves.That little ba$t!d is gonna be hot as all h3ll.As me how I know.


Here's a unit similar to the one I used.can't remember the wattage right off.Seems like 240w and 120v.
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Old 08-06-2014, 01:58 AM   #17
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My Dad gave me my first boat in about 1962. He said it was "molded plywood" .
They had actually built the plywood in the shape of a boat by laying the sheets veneer in a mold. I don't know if it was cold molded or hot molded but it was a very pretty little skiff about 12 feet long. It had soft chines and a roundish bow. You couldn't have bent a sheet of plywood to that shape. The finished hull was about 1/4" thick. No fiberglass anywhere on that boat.
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Old 08-06-2014, 10:09 AM   #18
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When we were living down in New Zealand I looked at a few cold molded boats.. the Kiwi's are really the Premier builders in CM wood boats. Many of them are laminated using black plastic staples that are ground off flush between lamination's and left in the hull. The hulls if bright finished had little black spots the were barely noticeable and not a issue. A lot of those boats used Kauri which is sort of like a cross between Cedar and Mahogany.. and very beautiful.

I would own a CM boat in a heartbeat, they are strong,light,pretty,quiet and just felt right. A well built CM boat is totally indistinguishable from a GRP boat. A friend that lost his Moody sailboat on a reef in the Tuamotu's bought one as a replacement and it was fantastic.

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Old 08-06-2014, 10:20 AM   #19
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Ski,
Sounds like you've got a plywood boat glassed on the outside and inside. You could say it's a sandwich construction whereas the plywood is the core material.

I had a Sumner Craft that was made in a similar manner. Started out strip built. Douglas Fir planks (1"X1") were attached to forms (like bulkheads) to form the hull ... then glassed. It was not double planked. Turned over and the forms taken out. Then glassed on the inside. I considered this a sandwich boat w the 1X1 fir as core material. The boat was 29' and powered by a 120 Sabre (same block as the Lehman). It was light at 8000lbs.

Sounds like the boat you describe is very similar. A stressed FG membrane to take the place of frames and stringers ect. Very tough boat but it seems to me one could make a plywood boat w/o the glass and plastic that would be lighter. It would have less puncture resistance but overall stronger.

Seems to me I remember sailboats being made that were basically wood veneers laid 45 degrees off. Just a wood boat w no cores. The end result would be molded if you could consider the forms a mold. And w no heat involved .. "cold molded". These boats had very curvey soft chines and looked much like a Thistle sail boat. Many traditional cruising sailboats were made this way and had varnished hulls.

But it seems cold molded boats can be made w veneers or plywood. And the "mold" part is the structure that holds the hull skin in place while it's covered w cloth and resin on the outside. Seems to me I have a book that deals w the same type of construction but w foam instead of wood.


Scott,
Re the Faireys boat building efforts was that related to the contemporary Carver boats?
Must have been considered extremely high tech at the time.
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Old 08-06-2014, 10:30 AM   #20
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The issue I have with CM boats is many designs wind up with areas of low ventilation and accessibility. Unless painstaking care is made sealing these areas and providing access to make sure later additions allow proper sealing they will rot...and pretty fast.

In New Jersey there was a bulge of 25-40 footers built here and down in the Carolinas bach 15-20 years ago. I wound up putting electronics on quite a few that had major issues within 5-10 years of being new.

I just sold my cold molding and strip planking books thinking I would build either my retirement boat or at least a smaller interim boat. The idea never panned out but I did quite a bit of looking and research. While I think it's a viable method...it definitely has it's own quirks.
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