I do not know if you guys are interested in reading this or not.
Preamble
I successfully made a set of what I admit are pretty rough A-Class hulls using a layup of 5.7 oz carbon, 5 oz Kevlar, 3/8 inch Corecell foam, and 5.7 oz carbon going from outside to inside laid up in a female mold using vacuum bagging. On the first version of the hulls, I made the bows too skinny and the boat was scary going out in any breeze. The boat bows would dive when any kind of gust would hit, but it certainly had no trouble piercing waves. As long as the wind was steady, it would go through boat wakes very smoothly, exhibiting no hobby horsing at all. But when it was gusty, the bows would dive very easily. Due to the topside of the bows being almost pointed, the hulls could be driven in a bow down manner without showing any tendency to go under further, and as soon as the gust would let off, the hulls would pop up and we would continue along at full speed. I will certainly use this topside shape again.

I did not like this tendency to dive as I feared for my mast so in the middle of last winter, I dug out my skilsaw and cut off the bottom on one of the hulls. I spread the front by 2 inches near the bow tapering to 1 inch at the main beam . This caused some seperation of the outer skin from the foam due to the high stresses involved in doing the spreading. A carbon skinned hull is pretty stiff, so something had to give. I made new bottoms that are wider than the hull width at the front, and had a completely different shape than the old hull bottom, so had to fit pieces of foam to join everything together. Due to the inability to vacuum bag the layup when applying the final layer on the bottom once the bottom was glued on the top, several areas of the carbon did not attach well to the foam. It took several months of head scratching to figure out how to do the changes, and then once figured out, the second bottom was cut off and the new bottom glued on and finished within 2 weeks. All in all, I like the new hull shape and am considering making a new mold to make a good set of light hulls. My current hulls are over 50 lbs each due to several of the things I did wrong in the building process. I lost about 3 lbs each hull with the new bottoms that I put on. My next hulls will be built utilizing a lot of different design changes, and all the things I have learned, and should weigh about 35 lbs each. On my next hulls, I may use 4 oz unidirectional carbon fabric instead of woven. It is a bit cheaper, and the fibres will all be straight then which will provide greater strength. To get cloth on at 45/-45 degrees, it has to be overlapped 2 inches where there is a join, or you have to purchase fabric that is made on the angles. That proved pretty costly, so I overlapped the cuts with resulting bumps.

So here are some things to consider if you are making a set of hulls:

Try to make sure that you get the layup real dry, especially if you are doing multiple layers. Lots of epoxy means added weight with no structural benefit. When making beams or foils with multiple layers of fabic, the way I get a relatively dry layup is to wet out one layer, get it as dry as I can with a plastic sqeegee, put it in the mold or on the mandrel, and then take a second dry layer and put it over the first layer. If you use your hands or plastic spreader and work it a lot, you can get it to wet out with the excess of the first layer. It took several poorly made laminates with lots of wrinkles in the layup to get this method figured out. If the layup is too wet, the layers will move around easily, and it will be easy to get wrinkles in the layup, plus the excess epoxy gets squeezed out of som areas and into others so you get bumps. If you get wrinkles, you are probably not getting the fabric dry enough, so on the next piece you make, try for less epoxy!

When you are doing a multiple layer layup do not lay the vacuum hose over the layup as it will move the top layers of cloth and form them around the hose. Then when you pull off the vacuum layers needed, you will have a mess, having a nice half round track in the layup where the hose was. Trust me!

When using foam core material, do not put cuts in it to help it mold to the shape of the hull. As you have to fill the cuts in the foam with epoxy, plus the epoxy will fill a minimum of the outer 1/16 of the foam, it will require way more epoxy and make heavy hulls. I used 3/8 inch 4 lb core cell for my core on my hulls and used a heat gun to form the hulls to the shape of the mold. When it proved very resistant to bending by heat gun (too thick), I used knife cuts and then had to fill them with a microballoon epoxy mixture. I tried making a heater box first, with poor results as it took too much energy to mix the air around, and it would have cold spots. It would be possible to do it successfully, but you would need way more air movement than I tried with using 1 8 inch furnace ductto move the air from 1 end to the other. The top of the mold was real hot, and the bottom was cold, so the foam would not mold.

I was the most successful with using a heat gun to mold the foam about 1 sq ft at a time. Once the foam is close to the shape of the hulls final shape, the vacuum will be sufficient to get it the rest of the way. After my first design proved too skinny on the front, I made a new bottom using quarter inch foam and had a way better success molding it with the heat gun. My next hulls will be made with ¼ inch 5 or 6 lb foam.

If you are designing your own hulls, if you have hard chines in them, it adds to the complexity of getting a decent layup. Everywhere you have to cut the foam, it adds places that you have to spend lots of time making sure the core is perfectly fitted to the mold. A way of making a hard chined hull easier is to just glue on one skin at a time. Then if the core moves on you in the first vacuum bagging process, it is relatively easy to fill the gaps with microballoons and put the inside skin on. You will need double the amount of mastic and plastic you use for that though.

Make sure your mold has no pinholes in it. If it does, you will have voids in the layup where the air is coming in. These will not only have to be fixed but will likely leave a bump on the hull where the void was after you fill it with epoxy. Trust me on this!

Make sure the mold is fair before starting to build your hulls. If you are making a Cat, fairing the mold once is better than having to fair both hulls you make with a mold that is not fair.

I made my molds by cutting out frames for every foot, boxing them in with 3/8 inch plywood, and then using 1/8 inch mahogany door skins being tortured into shape of the frames. The door skins plywood did not like this, and would go to whatever shape it wanted between the frames. What I had to do is run a stringer down the length of the mold about 6 inches apart, and try to straighten out the skin. Then when the skin was close, I had to fair out the mold with epoxy/microballoons and sand till smooth. This used a huge amount of fairing compound (costly) and took vast amounts of time (read over a month), but I did not have to do the fairing twice and put more weight on my boat hulls. The Mold leak did require pulling off about 4 sq ft of carbon off the front of one Bow and replacing it. It made a mess of the bow and took more time and money. Do a good mold first thing!

What I would do for a mold now: I would cut out plywood stations every ft, make a box that is close to the size of the dimensions of the hull, buy stiff insulating foam in 2 ft by 8 ft by 2 inches thick sheets, line the box with the building foam, and then use a wood rasp or sanding block to shape the foam to the shape of the hulls between the frames. Once shaped, I would then cover with 3 or 4 layers of fiberglass cloth in epoxy and sand smooth, fairing with microballoons as needed. You would then have a fair, solid boat mold that you could tape a vacuum bag to and make your hulls. It would be a lot of work, but less than what I did, and should not have any leaks. I would also put a face of at least 3 inches wide on the top to use as a face to use the mastic on when vacuum bagging. It is pretty normal for me to get some amounts of cloth hanging over the edge when making a hull half. These have to be trimmed later, but can get in the way if you have made the mold face too narrow, and can cause sealing problems with the mastic. I learned to always have a tube of silicone sealant handy to use to fix leaks in the vacuum bag, and holes in the plastic can be fixed by applying a short piece of packing tape to the hole. For the plastic barrier, I just used heavy duty constuction plastic. It worked fine.

Another thing you have to watch for is getting a good vacuum. The pump is important in that it has to be capable of sucking a decent volume. When you use mastic, and it has a few holes in it, sometimes you cannot tell where the holes are if the pump does not suck enough volume to be able to hear a whistle. Make sure you use a good mastic, too. Sometimes I would use packing tape, and if careful, it can work. I found that 3M packing tape is so much better than the cheaper stuff that I will buy nothing else now. I purchased rolls of mastic from fibreglasssupply and I would do that again. It was real good stuff. When I ran out of that, I used some stuff that I bought from a glass shop that they use to install windshields. That was not nearly as good.

You can use any nylon that is breathable for the peel ply. If it is waterproof, it will also be epoxy proof and you will not be able to get the excess epoxy out of the layup.

For breather layers, I used quilt batting. Walmart prices are okay, but I found better prices at a discount fabric store later on. I sure got lots of funny looks going into the fabric stores for this stuff though!

For most of my layups, I used mastic applied around the mold face and gained a seal against the mold. On the last few things I made, I would just stick the piece in a plastic bag. Bags are easy to make using packing tape to seal off the edges. That sure worked easier as long as the bag has just a few holes in it. It seems impossible to get a bag with no holes in it, so you are always hunting for the leaks in the bag, and sealing them with packing tape. Having a roomy workshop would help that a bit.

When applying the plastic vacuum film, it is quite important to make sure that there is lots of extra plastic in pleats. If there is not enough, or the pleat is in the wrong spot, the plastic may not go into every crevice and then you can have a void in the layup.

I made 4 daggerboard halves before I got one suitable to use for making my mold. At first, I tried to make ones that I could use in a daggerboard. Finally, I made one that turned out good by gluing cedar to a plate glass, and then carving it and sanding it until it was the shape I wanted. I then covered it with one layer of fiberglass, and achieved a shape that was thin enough to be accurate. I then made a mold by laminating 7 or so layers of fiberglass on top of the shape I had made, cut out the foil shape in half inch plywood, and bagged it on top of the laminated fiberglass. When I made the cedar shape, I made it long enough that I could make each end the shape of the daggerboard tip, so I can make each daggerboard half by using opposite ends of the mold. That worked good.

When making something as big as a mold for a hull half, it is imperative that you are extremely accurate in the mold shape. Foam with carbon on each side does not like to bend at all, so any mold inaccuracies are not easy to fix. Even being out by as little as a sixteenth of an inch can make for joint problems., and ugly hull joins. I had thought that a sixteenth or even an eighth should be close enough, but my next set of hulls will have a simpler design and I will try to be extremely accurate. I wound up grinding a lot and adding layers of carbon for the joints.

I used bubble pack on one rudder layup. This is not a good idea. I had all these little bubble indentations in the layup that I had to grind out. I now stick with using 2 or 3 layers of quilt batting for breather, and it works fine.

I made my own beams on a 3 inch round aluminum tube. It is imperative when doing a thick layup like this to make sure that you get the layup dry so that it does not squirm under vacuum, and that you do not get any wrinkles in the peel ply. This will make wrinkles in the tube you are making. You will ether have to fill the wrinkles in later or grind them out. When making my front beam, I made it about 12 layers of 9 oz carbon thick with an additional 5 layers on the top and bottom. It was supposed to be about 10 layers thick, but was so wrinkled from using too much epoxy and other reasons that I had to fill in the wrinkles and put another couple layers on to get it close to smooth.

Getting too much epoxy in the layup seriously weakens the layup. With too much resin between the layers of cloth, the resin will crack and weaken the stucture. With the beams, I made them thick enough that they are okay, but it is way wiser to get the layup real close to the ideal of less that 50% resin content. One guy has suggested to me to weigh the resin to be added and make sure it weighs the same as the cloth, and only use that much. To make beams now, I would add 4 layers at a time, using the second and 4th layer to soak up as much epoxy out of the wetted out layers as I could. I might even try doing 3 layers and use 2 layers of cloth to soak up the excess out of the one layer of wetted out cloth. I have started making my rudders and daggerboards by making the skins first, and then adding the foam core later. To add the foam core, I butter it as lightly as I can, let it harden, and sand it, then glue it in. I think this will make it lighter and absorb less epoxy.

My next set of A-Class hulls will be made by lightly buttering the foam core and letting it harden before the skins are glued on. When using foam core, it soaks up a significant amount of epoxy, penetrating about a sixteenth of an inch into the foam. By buttering it real lightly, I hope to lessen the epoxy penetration, let it harden, and then sand it to make sure the skins will adhere to the foam. I had someone suggest using peel ply on the foam as a means of not having to sand after. That might work. Another means of not having to sand would be to not let the buttered stuff harden totally before gluing on the skins. Epoxy will bond chemically to other hardened epoxy up to a certain time limit. If the skins are glued on before that time limit is reached, the laminate should bond to the foam/epoxy perfectly in a much lighter layup. In talking with Ben Hall some time ago, he said that they made 2 hulls that were identical except for the weight. They took far more care in keeping the layup dry in the second set of hulls and the hull weighed over 5 lbs less.

Another thing to be aware of when making your own hulls is there will likely be a significant number of pinholes in the hulls outer skin. This can easily be fixed before painting by sanding the hulls, mixing some epoxy, and spreading it on the entire surface of the hull using a plastic spreader. If you make sure the spreader has no nicks in it and that you leave no ridges of epoxy behind, you will have a minimum of sanding to do after letting it harden, and it will fill all those pesky holes. If you try to paint the boat without doing this fill, the holes will show up in the painted finish and are almost impossible to fill any other way. So do the hull with epoxy. It is worth it. When you build rudders and daggerboards, you need to do the same thing. It will save you lots of time, especially if you get the layup real dry. The dryer the layup, the mor epinholes by the way.

Hope this helps!