Carbon Fiber Rookie

[modhydro]

A couple of more thoughts on cockpit sides....

I just came in from rolling on a finish coat of epoxy on a hydro and have a couple more thoughts on the sides of our boats.

1. Whatever fiber you choose for whatever reason, laminiate it on the outer faces of the part to be stiffened. I've seen some guys put the fibers in a sandwich between two layers of plywood. This does very little but help puncture strength. The center of a symmetric laminate sees ZERO bending stress. I don't care what you put there, it is really just adding weight. You could argue that no plywood is exactly symmetric and that is true, but put the fibers where it will do the most good. Remember also that the stiffness goes up with the cube of the thickness. That means that a panel that is twice as thick is actually 8 times stiffer. Again this is a theoretically figure for a homogeneous material, but the point remains true: adding a little thickness goes a long way, especially with the trend towards "billboard" sides.

2. Add some curvature to the sides when looked at in plan view. To test this theory, pick up a piece of paper. It will bend down limp unless you curve it slightly. Try to remove the geometry of the cockpit side to deck junction from being a hinge to this same bent panel that will resist bending loads by itself without needing the cantilever support of the deck and resulting stress concentrations.

This stuff may sound complicated, but is really just simple principle that works.

Steve Roskowski

[epugh66]

If I recall the UIM rule on cockpits correctly ( I know we're APBA, but really, who does more crashing?) The outer laminate should be an aramid fibre (kevlar?) and needs to be continuous on to the flat surface of the deck for about 6 inches. Perhaps the fiber overlay helps keep the coaming from collapsing in on the driver.

[pro350hydro]

I could be wrong but,

Currently, the only US built Stock, Mod or Pro boats that follow this guideline for this UIM rule are Matts Carbon boats.

Jim Apel has built a few complete carbon fiber boats. I think these boats may meet UIM guidelines, but I am not a boat builder. I know for a fact that they are carbon and kevlar with a foam core, as I purchased all the materials and got the very first boat built. And I also helped/watched during the construction of my boat. And I know Jim did a lot of research before we started anything.

Since the construction of my boat, I know that there is at least 2 other boats for a total of three. Mine is a 350cc laydown, one a 700cc capsule boat, and a FE laydown.

Mike Sattler

[hydroplay]

Steve and Mark are arguing about sandwiching a reinforcing fabric between layers of plywood. I would add that both are incorrect and both are right. The dilema comes from the confusion between stiffness and strength. In some ways we think that something stiffer must be stronger yet that is not always the case. The stiffer sample may have a lower yield point and bend or fail with less load than the stronger one.

Putting a reinforcing fiber between two thin overlays of plywood will not do much for the bending stiffness of the panel because as Steve rightly notes, it is on the neutral bending axis so the fabric is neither in tension (as desired for max stiffness) nor in compression. The panel will be only slightly stiffer because it is thicker and Steve also noted that stiffness is essentially proportional to the cube of the thickness. The panel is stiffer but only because the plywood has an added "core" of reincorcing fiber. In real practice, this is a poor engineering decision as the core material should optimally be a less dense material as it is very lightly loaded.

However, Mark correctly notes the panel would be noticably stronger because of the fiber layer, even though it is not much stiffer. It is capable of carrying heavier total loads before it fails. At some point the wood will fail slightly on the tension side of the panel and the neutral axis will move so that the reinforcing fiber is carrying a tension load. This panel will be stronger and absorb more loads, especially in an impact situation.

The problem for cockpit sides is that we would generally like to increase both the stiffness and the strength. To accomplish this with plywood and fiber, the best engineering solution is to put the fiber on the outer surfaces so the individual fibers can be in tension as much as possible with the anticipated loads. Ideally fiber orientation comes into play rather than just slapping a layer of woven fabric on the plywood. Putting it on at a 45 degree orientation is best but not the most efficient use of material.

But then if you've gone through all that trouble, the core material comes into play. Since you're getting all the strength and stiffness from the fiber surfaces, the core isn't doing much, save for holding the surface apart. A lighter density material than plywood becomes a better option from an engineering standpoint but possibly not from a budgetary point of view.

It must have been back in the late 70s that Del Snyder and I started playing with a composite cockpit side, because Hank Menzies was still alive. We made a fixture to lay it all up on and took it over to the basement of his dental office. Henry and his dad built their boats there as well. We tapped into the vacuum system he used for the dental needs and vacuum bagged some sides. Some time later Del and I were at St.Louis for the big tunnel boat race and asked Bill Seebold and Bebe if they ever thought of using a foam core panels for the sides of a tunnel boat to save any weight. Both of them looked at us like we were crazy for even thinking that there was something better than wood. How times change! We gave up on the project back then because Stock/Mod has a minimum weight and it was pointless to make things lighter and more expensive only to add weight. Our panels worked but weren't cost effective. And Seebold eventually saw the light.

[Matt Dagostino]

Theory vs. Reality...............

The late model B&H we have is a good example of the light weight foam core cockpit sides that decrease weight and add strength. In a early season crash our AXSH hull was broadsided and the throttle side combing withheld most of the impact and my young J driver walked (swam) away with minimul leg injuries. Although the material was splintered and needed to be 'sandwiched' back together it did do it's job.

I surmize that a traditional plywood side may not have provided the strength and/or protection of the 'foam core' and may have resulted in greater injury................

I am wishing my new(er) B&H AXSH Hull had the reinforced sides !!!!!

Happy Holiday

[jsilvestri]

Next month I'm planning on starting my new CSH and I would like to make the cockpit sides as strong, light and cost effective as possible. I'm thinking of sandwiching a piece of 1/2 foam between two pieces of 3mm plywood. However, could I sandwich a piece of 1/2 foam between one layer of plywood and one layer of fiberglass? Is the fiberglass strong enough to be used this way? Would I save any weight making my panel this way over two layers of plywood? How many layers of glass would I need to build up? What kind of glass would I use? Would the glass side of the panel have to be vacuum bagged? Thanks.

[hydroplay]

Joe,

You've reached the point where a little knowlegde is dangerous. In playing with composite panels, you're dealing with a very large number of different core materials, a large number of fiber materials, weaves and weights, different laminating resins, so it is impossible to say best because a small user will probably not have access to some materials as he is buying such a small quantity.

You need a more in depth understanding which could come from books or seminars or seat of the pants experience. And then take that knowledge and make samples and compare to what you think an acceptable wood side. Make test strips of uniform width and clamp one end to a bench and see how much they bend with a uniform weight at a uniform distance. See how much weight it can support before it breaks to get some comparison between stiffness and strength.

All that said, call Baltek and ask about Duracore panels. They come in foam or balsa core with wood or fiberglass on the outside. You can use these just like plywood and not have to laminate anything. The current issue of the PROPELLER has a pic of John Palmquist in his Hall of Champions ASH which has the greenish foam/fiberglass panel sides. There is also a pic of Valerie D'Agostino on the cover in her J/AXS hydro which has balsa core/fiberglass sides. Both core materials work well but the balsa is heavier and stronger. Cost was about $6-7 a square foot for the balsa core and $10 a square foot for the foam. Not exactly cheap when you look at 5mm plywood at $1.50 a square foot. But effective and available.

[Brian10s]

Sorry and Thanks

Sorry to all for starting a thread and then not getting back to it. Just got back from my in-laws for Xmas and they have dial up and one of the 1st computers ever made. It was like going back to the days of rotary phones and party lines. I will never curse my DSL provider again.

To answer a couple questions:

The reason for this project is first and formost to protect me. My main concern is to restrict/prevent puncture/penetration of the cockpit walls. That being said I also don't want to be replacing these every weekend becasue they are so rigid that they just snap off or, on the other hand, have them so stiff/hard that the never give, no matter what and the sides are like a brick wall.

With that being said, I want to thank everyone for their input on this. Any and all opinions are greatly appreciated.

I am going to start work on the boat this weekend and if possible will post some pics of the sides and why I called this a safety improvement. Just got a digital camera for xmas and am still playing with it.

Thanks,
Brian 10s

[Dave M]

One Point

One point you need to consider is where to draw the line at how strong it needs to be. You can make it very strong at the direction of these folks here, or as weak as you want. There are so many rights and wrongs with composites that cancel each other out and it boils down to do you need it that strong ? Personally, sandwhiched between wood has proven effectice for my uses. I have been t-boned at around 75MPH in Coldwater MI race in FEH. The other boat hit me because they missed a buoy and came back into the course at the apex and there I was, kaboom. My Roper not only stayed upright, but the sponson that hit on the left side simply busted the cockpit side at the decklineand never fully broke away. It deflected the hit and the other boat flipped and was damaged badly. It was missing a sponson I believe. I had some west and wood and made some rather easy repairs that day and raced the next day. Now where the re-enforcment stopped the cockpit cave into the boat, back near my feet when stretched out. That is my experience, and I am sticking to it. I bet the ways that others do it for shear strength are better, and maybe it looks nice to.

In school I was taught the Kiss theory, and I try to stick to that.

No offense meant to anyone here, just relating my experience. I think you all have enough knowledge to be dangerous with composits.

[jsilvestri]

Dave,
You make a good point about a cockpit side possibly being to strong. I want my sides to be strong enough so that when I hip check them, they stay intact. However, when I go out of the boat I want the side to break because if it doesn't, then I have a good chance of breaking something on myself. Good thread here, I've learned a lot and always enjoy that.

[Brian10s]

Joe,
You are 100% correct in that this has been a big time eye opener! I know I had no idea all the different schools or individual process that each builder has come up with based off of education, experience and trial and error. For some reason, I thought there would be a uniform process that most people used, with the same tried and true materials used and that would be that. However, it seems that everybody is doing twists and variations with composites and each is making it work to suit their needs and wants.

I originally wanted to learn how to make a better cockpit side, however I should mention that my old sides did pretty well under the cir***stances. The outside was hit by another hydro at almost top end speeds and held together with only a small puncture and the inside blew out upon my ejection. Other than the puncture (which could have been a ton worse) everything performed better than advertised. My main goal in doing this is to create a new set of sides that would preform exactly as the old, with more puncture resistance. I had not thought about all the variables that come along with adding these type of materials. Change 1 item and you change 10 different aspects that you might not have wanted to change.

I know I have had an education based of this thread and as Sam says "A little knowledge can be a dangerous thing."

Thanks all,
Brian10s

[Dave_E71]

The U.I.M.s take on this

At the risk of opening a giant can of worms..........

http://www.uimpowerboating.com/vsite...v-list,00.html

click on "circuit rules" to download a copy of a UIM rulebook (dial-up beware)

you will need acrobat reader to look at this file, avalable here
http://www.adobe.com/products/acrobat/readstep2.html


The following sections may help......

Page 147 Reinforced cockpit
Page 150 Pickle-forks
Page 167 Racing outboards
Pages 169 - 171 reinforced cockpit on outboards


Dave

[HYDRO21Z]

one more opinion

This past winter I did research and learned how to vacuum bag, and work
with Carbon Fibre. I wanted to improve the strength to weight ratio on my
coamings for my new CMH. What I wound up with is this-- I like a natural
finish on my boats and I learned the shear strenght of carbon needed to
be on the outside of the coaming for best effect, so I laminated a coaming
panel with the inside layer being Carbon, then a 3mm okume panel, then
another sheet of Carbon, and finally another 3mm okume for the outside
finish. Overall thickness was around 3/8" and the weight was much less
than our usual reinforced plywood coamings. We tested the panel in the
shop and it had remarkable flexibility and strength. I tested it at Millville
in the first turn with a barrel roll at the exit pin. No breaks!
Anyway my opinion is this is a reasonably cost effective method to make
a reliable set of coamings.
The real costs in my efforts was the vacuum pump and related materials
to do the vacuum bagging.
Now that that cost is absorbed I can make panels fairly reasonably.
True or not the Carbon gives me extra peace of mind over the standard
coamings I had before.
Just my 2 cents worth.
Dennis 21Z

[Brian10s]

Dave

Dave,
About time you show back up here. Thought the Maryland wilderness swallowed you up. Was going to send out a search party.

Thanks for the UIM Rules. I have been looking for a way to get them.

Thanks,
Brian10s