Coldmolding
Make your own Plywood
and get a more sophisticated hull shape easily
by Jim Betts

What I really don't like about sheet plywood is: 1. It limits the shape of the boat: 2. It is limp as a wet noodle unless you can force some shape into it. and, 3. It is heavy as hell! A sheet of 4x8 3/8" weighs 38 pounds. Now that wouldn't be so bad if it were a small thing you could lift with both hands, but a sheet of the stuff really takes two people to handle. And it gets worse - 1/2" weighs 50 pounds and I" (if you ever needed it) is right at 100 pounds. Even in small pieces it is heavy. It is said that the only thing that benefits from more weight is a steamroller. (A designer once said. "Add more lightness.") A lighter boat moves faster with less sail area or less engine power, is easier to transport, and costs less to build.

So Make Your Own Plywood as You Go

Yes, you can make your own plywood in any shape you need and in small pieces that weight only a few pounds. This is called COLDMOLDING. (I like this as one word and will save more time. effort and space by hereafter calling it CM.)

CM is faster, easier and - thanks to epoxy - stronger than sheet plywood. It is structurally stronger because the plys run in different directions and it is ultimately stronger because the boat will have a monocoque shape.

For those not familiar with this building method, let me explain. (For you old salts, please remember that we are reaching a lot of newcomers to the area of amateur boat building.) CM is simply a method of making your own plywood by laminating thin strips of veneer. This is somewhat like using layers of fiberglass cloth, but it is done with wood. In the Old Days. when glue was made from horse's hooves rather than modern chemicals, such a process was called "hot molding" and required heat and pressure. Today, epoxy generates its own heat and the pressure comes from staples. Besides, epoxy does not
require pressure because it is gap-filling.

You Build a Boat-like Mold That You Throw Away

CM boats do not build themselves. In place of frames, you make a mold over which you build the boat. This is a sort of chicken coop and can be made of rough wood. This will be a number of forms, depending on the nature of the design. Over these, you put stringers spaced as needed to achieve the desired shape.

Over this, you apply layers of veneer. These are at 45 degree angles to each other. The last layer is usually applied parallel to the waterline so any show through will not look odd.

A Boat So Light (in parts) That a Child Can Do It

These thin strips of veneer are cut in various widths depending on the amount of curvature in the hull shape. These are easy to handle, very light in weight and can be bent and twisted with little or no effort. Where you have a need to taper the pieces to fit, you can do this with a small saw. plane or by double-cutting. This is a method where you lay one piece over another and cut both with a power saw set to depth that will cut through the two pieces. Veneer comes in various lengths. Where necessary, simply butt the pieces together.

Over your frame, you put plastic wrap or waxed paper so the layers of veneer do not stick to the framework. (In some boats, there are parts of the framework that you want to stick to the veneer, but that's a simple matter of following the directions.)

After the first layer of veneer is in place you will want to fair this a bit. Not to a piano-smooth Finish, but just knock down the high spots. This is time fora power sanderor power plane. Now vou fit and cut the next layer of veneer. The best way to do this is piece by piece and number each piece. (Yes, yes, you could lay them out in order, but what if someone comes along and kicks the stuff around? Number the pieces!) You do not have to do the entire boat, just a goodly area of say six feet or so.

A hull shape such as this is certainly impossible in plywood. It is also difficult in frp because of the tumblehome shape. It would require a split mold that can be opened. So the solution is to build the boat over a form that can be removed.

It is best to do both sides of the boat as you move along. That is. do say three feet on one side and then three on the other. The reason is that there is always the danger that you will put more pressure on the hull if you do one complete side. This may pull the hull a bit out of shape. And it is better if you start in the middle and work toward the ends. For one thing, the middle is easier to do and will give you some learning time and practice.

Now you actually start to CM. Brush on epoxy and make it fairly thick. You can wipe up any that squeezes out, but you cannot put it into places that didn't get enough.

You will use a power stapler. There is no manual staple gun that will give good results. (Besides, you'll be using hundreds of staples - maybe thousands - and you will wear out your arm.)

Now comes the debate: Leave the staples in or pull them out? There are two sides to this question and I'll address both. You may leave them in if you use stainless steel that won't rust. Or pull them out. Even regular staples that may rust are not a big problem because the epoxy and paint will cover them. It's up to you.

How to Remove Staples the Quick and Easy Way

Way one: Put strong string under each staple. This is a long piece of string that will be under maybe 50 or so staples. When the epoxy has dried (see drying time on the can), you pull the string and at least part of each staple will come out. You can get the rest of the staple with pliers.

Way two: Use very strong cloth (old auto seat belts from the junkyard are very good) and when you pull this the entire staple will come out. (On the downside - you will have to use a new piece for each application or spend time pulling the staples out of the belts.)

Speaking of staples, you will want them with legs long enough to almost go through both layers of veneer. If they are too short they will not have enough holding power. If they are too long they will protrude inside the boat and you'll be cut to ribbons when you rub up against them.

And So On and So On Until You Have a Boat

It depends on the hull thickness, but you just keep doing this until it is finished. On small boats, use thin (1/8") veneer. On bigger ones, use thicker. (The designer will tell you what to use.) Much will depend on the complexity of the hull shape. When it's all done, sand the hull fair. Use body putty (like used on cars) or epoxy thickened with sawdust or other Filler to till low spots and the good old belt sander to knock down the high ones. Then fiberglass the hull if you wish and paint the boat. All done!

A Few Tips and Cautions

Epoxy may cause allergic reaction. Do your building in a well ventilated area. Use fans to exhaust the air from the building. Apply barrier cream and wear plastic gloves and eye protection. If epoxy gets on your skin, wash off immediately with soap and water. White vinegar is also said to be good for this. Do not put brushes and such with uncured epoxy on them on surfaces. (You'll never get them off) Wipe off any epoxy that squeezes out of the work. If you let it harden, it's hell to sand or scrape off. Put drop cloths under the project to protect the floor. See curing time on the epoxy container. It is best not to move the boat for several days during the cure time.

Jim Betts