Strip-Building on a Cylinder Mold

Sure, but it starts with a cylinder section.

 

Right, but in the method of Cylinder Molding, nothing is glassed until after it leaves the mold. Also, nothing is screwed to the mold. The bag goes around the entire stack of plywood you drop (with gravity) into place. The layers go:

-Bag
-Breather
-Outer 3mm Okoume Skin
-Middle 3mm Okoume Layer
-Inner 3mm Skin
-Bag

ALL of that is put on the cylinder mold before it is bagged. You drape the bag on, open, then put down all your scarfed plywood panels. After your plywood and breather is in place, you close it all up and suck it down until the epoxy kicks. Then, you have a good panel that is a close approximation to the hull form, but needs lots of wrestling to get it all the way into the proper hull form.

Ok, I'm out. That PDF should help the thread readers, I think.

 

Catbuilder,

Your description of the process is exactly as I understood it 20 years ago. Clarify one question - does the cylinder mold (Hughes invention) have a solid surfaced mold?

Ancient dude wants to stay off the side trip so that's enough for me.

Marc

 

It does not have a surface at all. It's an open mold. You just stick your plywood in the lip on the front of the mold (which holds it down on the hard bilge curve) and throw it over the back. Because the plywood sheet is wider than the spaces between the stations, it can't fall through... it spans more than one station, always. Here is a picture from the PDF...

In this picture, the guys are dropping the final layer of the 3 layers of 3mm plywood onto the cylinder mold. The surface you see in the foreground is the dry, final layer of 3mm ply. The darker surface you see them dropping the plywood sheet onto is the wet, epoxy laden surface of the middle layer of 3mm ply.

In about half a second from when this picture was taken, they just let go of that sheet of 3mm and it falls nicely over the back of the mold, taking the form of the stations it wraps (by gravity). The bag gathers the 3 layers together and pulls the scarf joints together and it all takes the shape of the mold.

You can also see the scarf joints and the bag coming out over the lip, but tucked under the mold (it is raised off the ground a bit by feet).

 

Ok, I would like to also add that Ancient does understand cylinder molding. I had posted on this thread because so many people were not understanding what cylinder molding is, yet poking at his attempt to do strip planking on a cylinder mold. It's a valid thing to explore, though IMO, it's going to be a bit harder than doing it with plywood. Maybe cheaper though... who knows? We'll have to see what he comes up with.

 

Plywood is cheaper than solid lumber of comparable quality. If you add the amount of glue between the strips and the labor, the price difference increases a lot.

 

- but correct about my - and perhaps others' - lack of experience. I welcome and actively solicit all NEW comments including the negative ones expecially from our experienced folk here on the forum. I don't know how this will turn out but either way I will be honest about it.

Gonzo: if CM is safe and practical with only one ply layer then I think you are probably right that it can be done cheaper than stripping - that would halve the core cost. You seem to be in a minority on that - a situation I am all too familiar with . . .

 

Sorry...I am still struggling to see the advantages of your method.
A cylinder mold is used to essentially divide the process of bending flat panel material into a non cylindrical shape, into steps that are intended to simplify the torturing process. The strip method requires no such simplification and can be built over the half mold shape of the hull and then reversing the mold, allowing you to build the other half and providing a fixed shape that when joined together will provide a perfect hull without any bulkhead torture.

You do understand that when these panels come off of the cylinder mold it takes quite a bit of wrestling to push them into shape? That is why there is no glass on the ply during initial molding. It really would be great to put it on while it was on the mold with the vac bag there but the glass would restrict your ability to push ply out into shape.

Why not just start with a mold half that is already shaped correctly?

 

That is exactly my question as well, Dgreenwood.

 

Yup...now that I go back and read more carefully I see that you did point out the problem with this.
I think maybe cylinder molding is being confused with "Constant Camber Molding".

 

Agreed.

True for ply panels, but stripped panels will acquire their final shape after being bent on the mold and hold it after being glued - no wrestling expected.

I am sure some folk do that. Of course, with a pre-shaped half-mold the hull must be symmetrical. The flexible mold is a bit more . . . er, flexible about that.

There is not a lot of difference between that and what I am proposing here. When the strips are applied to a “final shape” mold they must either be done one at a time using clamps while the glue sets or held in place with staples.

When applied to the flexible mold, my hope is that the strips can be arranged while flat taped into a sheet which can hung on the mold as a whole. Then it can be bound to the mold and stapled to the center station form only before being bent into shape and glued. IF it works this will eliminate 90% of the stapling and allow the strips to be handled faster. The whole thing is now down to the binding; if that doesn’t control the strips, or enough of them that only a few staples are required, then it isn’t going to be any use.

- actually the design I am using in the demo is a scaled-down constant camber design I did for an earlier project. The midships profile pre-determines the profile of the stem in that design which is a bit limiting. I believe the limitations on stem shape can be freed up considerably in practice but I haven't got to that point yet. If the scale demo works I may have a go at exploring that aspect on a full-sized boat later.

 

I'll be watching your results with interest. Let us know how it works out for you. Some photos of the mating of the two halves would be great. ;?)

Actually I see where you are trying to save labor in the stapling process.

Good Luck

Skeptical

 

I treasure the interest of skeptics . . .

 

Sorry things are moving so slowly at present: it's yard cleanup time . . .

Ancient chinese proverb (also reportedly found in Japan, Byelorus, UK, Mesopotamia, Pharaonic Egypt, Europe, Scandinavia, the Aegean, Mayan S. America, S. Pacific Is. . . .)

Give your wife a flower, make her happy for an hour,
Give a garden to your wife and have a job for life.

 

Finished Mold: Pic

Finally all the yard chores are done! Back to the important work. . .

- oops! The significance of your request just hit me. I hadn’t planned on making both sides, but I should do so for a convincing demo. That has implications I hadn’t thought about. Since I am only building from midships to one end of a scaled-down boat for this demo, it is asymmetrical, so the second half cannot be built on the same mold.

I modified the mold so I can take off 2 hull-half, with a stem on either end of the mold, and fixed other shortcomings I noticed during the preliminary bending test. The new binding system consists of foam pipe insulation over neoprene tubing with nylon cord down the center, to hold all the strips firmly against the station molds, and in case it doesn’t I added softwood blocks to some of the station molds so I could add a staple or two if needed. The station mold edges have been painted and waxed to permit gluing if the experiment gets that far.

Looking at the mold I realize that it can be used to build boats with different beams and lengths, though I’m not sure how much use that would be in practice.