Hello all,
As a project for school I am making a realistic model of a nacra a2 and plan on using materials similar to those that Morelli&Melvin use to make the A2's. I found nacra's site the Infusion process powerpoint and tried to follow along, but my lack of knowledge of any form of boat building really didnt help me out that much. basically, i have not the slightest idea what is going on. I know this is just for a project, but I really wanted to have a realistic mold made and use carbon and everything to make the hulls...Since the rest of the boat shouldn't be that hard, (mast, boom, sail, rudder, d-boards...etc.) I'm really focusing on getting the hull shape and design made correctly and accurately......but, I am absolutely stumped as to how to make a mold and how to create the hulls. Here are some questions I have...

-I know that a female pruduct is needed to make a mold, but what is that normally constucted of, fiberglass?, plaster?, foam?

-Also, Once the female cast is made, what is normally used to make the actual mold, I researched and found multiple products which all look the same to me, so which one do i use?

-After the mold is complete (if i can get that far), is there a special process that is used to create the hulls?, I know gelcoat is applied first, then I guess Morelli&Melvin use carbon cloth and resin(?) and after that a "core" is laid in, which is again layered in carbon fiber, which becomes "infused"....

I doubt that i will be able to find out the actual "infusion" process becuase thats probably the secret to the design, but i'll try to get as close as i can to the actual making of the boat....
that is really as much as i know...so if anyone could help out, or throw some tips in, (maybe some of you home builders) or if you have any ideas or input as to what materials to use, or could direct me to some books or something, that would be greatly appreciated.

thanks in advance for your help. <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Vinny_M,

You can start here:

http://www.fibreglast.com/contentpages-Free+Technical+Brochures-23.html

Good Luck

Better make it an A3... things change fast in A-cat land. <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

http://nacra.us/A2/A3.html

There is no reason to go through the same building process if you are building a model. The only reason you would want to build a female mold is if you plan on making multiple iterations of the same thing. If you were going to build a female mold, you would first have to build the hull plug. The plug would be polished to a fine sheen. Then you would form the mold(s) around the hull. Again though, if you are just building one, build two hulls and stop there.

Getting the shape right will be tricky depending on how carried away you want to get with it. You can go about it several ways. You could possibly ask for technical drawings from Performance Catamarans (or maybe M&M) and use those to establish some dimensions. You could use some photographs from several angles, scale them, and come up with some plans there. You could take an actual boat and measure it using a coordinate system to establish the major key points and build from there.

As far as mocking up a hull, there are several different ways you can do that too. I recommend strip planking with balsa over formers. There's plenty of information about how to do this on the web. Also I've got some information on my website about mold making. We're making a one meter R/C boat and about to get ramped back up on the project again. Link HERE

Infusion is no secret process. It's is a process where the fiber and reinforcements are laid dry inside the mold. Then they are sealed inside a plastic bag. A high vacuum is pulled inside the bag (compressing the components) and then resin is "infused" into the vacuum area through several ports through the plastic bag. The resin then travels through the fibers and reinforcements and is allowed to cure while under vacuum.

What scale are you making it? Is it for display only, or do you plan to sail it R/C?

Building a plug / mold only makes sense if you plan to make multiple copies. It's very labor intensive.

Otherwise, make it out of a tight, fine-grained wood. Maple is too hard. Basswood is probably the best bet - virtually no grain and easy to shape.

A method I've seen repeatedly mentioned with respect to multihull modeling is to use blue board insulation foam. You glue layers of it together (roughly cut to the hull form), then sand it down to match the lines of the boat. Then vacuum bag a layer of glass over it. This can become a mold plug itself, or the hull. Depending on what needs to go inside the hull you can either scoop out areas of the foam, leave it all in, or use acetone to melt it all out.

The foam is supposed to be very easy to work and cheap to buy. If other structure is needed that can be accomodated (for instance, glueing thin ply between the foam blocks before fairing).

As you don't have as much time in a hull as you would from strip planking, you can more easily experiment with hull shapes.

Some foam may not be compatible with polyester resins, but it sounds like most are compatible with epoxies. If you're going to leave the foam in, you may not even need cloth on the covering, just a layer of resin to seal and fair.

Something else to try...

The "infusion" process has been used for several years by other boat manufacturers. I think J was the first to start using it mass production, they called the process SCRIMP. I heard that part of the reason they went to it was b/c the office of environmental management was requiring them to lower their VOC and HAP emissions. However as an added side bonus, they got a stiffer lighter hull with fewer voids that was less prone to blistering. I could see PC using this process for their boats in an effort to reduce their VOC and HAP emissions as well, esp since they are in CA.

Interestingly enough, the core has TONS of small holes in it that were designed to let resin through. They called these "resin rivits" It help join the three layers of material and decreases delamination. I would suspect that it's pretty similar to the process the PC is using.

Here is a short little bit on it: http://www.jboats.com/j109/j109scrimp.htm

Apparently, they could tell you the quantity of resin in a J109 hull down to the teaspoon!!!

Good point with the foam...you probably want to use epoxy on blue foam - not polyester resin (it will melt it).

You may want to cut a lite-ply plywood profile of the boat from the line drawing side profile (get this thin plywood in hobby shops). Glue foam to either side of the ply and sand to shape. The plywood will make a good reference point to sand to on the top and bottom and then you shape the sides by hand from there.

My 8 year old son and I got bored one weekend,
We downloaded a boat design program and exported offsets of our design and.....











[img]http://qcm.dns2go.com/gal/albums/ftp/50007/normal_catamaran_plans_009.jpg[/img]

[img]http://qcm.dns2go.com/gal/albums/ftp/50007/normal_catamaran_plans_012.jpg[/img]

That looks like a Zipper I or did you draw it up yourself?

My buddy just finished planking a modified Zipper III and should be fiberglassing it this weekend. I'll be making a mold and building several. Question though, what did you use the foam for in the pictures?

Hello again,

Jake, in response to what you said, I did get pictures from multiple angles and scaled them all up and drew the hull design from a side and top view. It looks about the same with some minor deficiencies.

Matt, The model will only be used as a display and will not be R/C or anything like that, and is about a 7:1 scale (about 30" long)

Based on what you all said, making a female mold is a bad idea unless I plan on making multiple copies, which I dont....Obviously, the infusion process is not a secret, but i doubt il be using that process, so I guess i'm down to what Jake said with strip planking with balsa wood, what Matt said with using basswood, what Keith said with using blue insulation foam and sanding it down, or using the program that Erez used.

I am leaning a bit towards the blue insulation foam idea, but what is meant by ?? I understand how to glue the foam together and sand it down, but what is involved with vacuum bagging a layer of glass,....why not just use gelcoat or fiberglass cloth or carbon?

Also, Erez, what program did you use to create your model? I might be interested in that so i can be able to get all the details correct for the hull shape

thanks again for all the imput, i'll be sure to post pictures when this is finally completed

I don't remember that specific program, it was a long time ago, how ever I found a great program that you can download and use here: http://www.freeship.org

you can start with a f16 design that I'm working on right now and change it to what ever you like, it will save you time.
download the file here:
http://www.cat-sail.co.il/1000.zip
and open it with the program

good luck

I sprayed the foam between the bulkheads and when it expanded and dried I cut it with a long knife while the bulkheads created the desired shape of the hull

I used this method in another project:
http://www.qcm.co.il/mini/p.html
The text is in hebrew but the pics are multi language

Hmmm...that interesting. I might have to try that sometime. It looks like you used the spray foam from a can - I wonder if using a stiffer mix-n-pour foam might give you a better and more consistent shape. I've tried using the spray foam in some other, but similar, situations and it seemed to suffer from a lack of dimensional stability.

Vinny, you don't need to vacuum bag the foam...in fact, if you put standard vacuum bag pressure on the regular blue foam, you'll crush it. You would only need to vacuum the fiberglass if you have some features in which the fiberglass does not conform to easily or if you are looking to get an extra bit of lightness and strength out of your laminate. You can easily lay up the hulls by hand once you have them shaped. There will be a bit of sanding and fairing involved after the fiberglass to get a smooth finish.

Glueing pieces of the foam together:

Typically the foam comes in sheets, ranging in thickness. Depending on the size of the model you're making, you'll probably need to glue some together to get the full size of the hulls you're making.

But, there's another aspect of doing this from the sources I've seen. Basically, you get the stations like Erez did. Then you glue pieces of the foam together with the wood stations in the proper locations, then fair the foam down to the wood stations. This give you a fairly easy way to get fair lines with out having to constantly be checking with a template.

You could also do it length wise - cut your wood to the full profile shape, and glue the foam on either side of it. You could also use the longitudinal lines from the hull profile (if you have those) in a method similar to above - in this case you'd have wood down the middle, a piece of foam on either side, wood on both sides corresponding to the lines, then foam on the outside.

You could also just glue the pieces of foam together length-wise, cut to the lines, then fair down.

In the end you might want to use varying thicknesses to get the stations in the right place.

Again, once you cover the hull whichever way, if you like the shape it can become either a male mold or a plug to build a female mold.

Another interesting technique would be to use the hull you've made as a male mold, and draw a heated sheet of plastic over it - it will conform to the hull shape, and when it cools you have a molded plastic hull. This technique is also used in modeling to make a variety of parts, big and small. If you come up with something good, do this and sell a bunch of them....

Normally I don't like it much when people send people away from this forum, but... Check out this thread on Sailing Anarchy:

SA R/C Boat Construction Thread..

There's a lot of cool stuff, but scroll through and you'll a discussion of foam hulls, and you'll see a picture of a trimaran with foam amas under construction.

Here's the link to the site that first got me thinking about this:

Multihull modeling site

Specifically the section on building techniques:

Building Tips

Check out the link for building a foam epoxy hull...

Cheers!

Wow, talk about recourcefullness, I'll be sure to check out all those sites, but i think im gonna just use the foam and shape that according to the program Erez provided and my drawings and just glass that. Its just a display so, I'm not gonna use carbon, but Keith, I really like your idea of using the male mold and drawing plastic over that, but which do you think would be quicker?

thanks again for the bombardment of input from everyone!

You also could go directly to the to designers and request some assistance from them, both technically as well as with the actual lines for the hulls. They can also explain clearly what changes were made between the A2/A3. I have found both Pete and Jeremy to be very helpfull in the past. http://www.morrellimelvin.com/ & http://www.askeland.net/ are the web addresses. Good Luck

Is there an R?C cat available?