Carbon vs. S-glass for '74 Sol-Cat

I have a Sol Cat 18 in desperate need of a new hull and was thinking about laying up a set of CF hulls but I have heard that carbon fiber tends to be brittle and that S-glass offers much more resilience with comparable strength and only slightly more weight. Any input you guys can offer would be greatly appreciated.

 

Cant speak from any boat building experience. I have used both materials in my car parts though. And your statements are correct.

A big problem with carbon is handling it. The edge tows pull away really easy. And the weave pattern is easy to disturb.

Im a big fan of S glass, just dont think any manufacturers make large woven S glass. Only seen your typical 6871 type.

If you have the money go for the carbon layup. All things considered 19oz carbon is pretty cheap.

 

Thanx for the response JRL I really appreciate it.

Well money isn't that big of a concern, I mean I don't want this to be a 10k+ project but 3-5k doesn't seem to bad considering what it would cost to replace the whole boat. (parts are no longer available and even if they were you'd still be looking at 5k) My main concern is just picking the right material for the job, making it lighter/stronger would be nice but not at the risk of thrashing a hull midcourse.

 

Something else I was curious about was UV. What, if any effect does it have on CF or S-Glass, and the resin or epoxy used to laminate them? Texas sun can destroy most things in a summer or less. Also, I have heard of a number of methods for creating molds, what would you guys recommend for this?

Thanx in advance, Jon

 

If use epoxies, paint it with an epoxy paint that has UV inhibitors built-in. They sell uv for epoxy to mix, but I find easier to just paint after

 

What my Dauphin said.

Carbon and S-Glass arent effected by UV rays. Its the resin that is effected.

 

This link has detail on various composite reinforcements. You need to go to the very end to get the information your seeking:
http://www.fgi.com.au/products/reinforcements/Reinforcements.pdf

CF has higher tensile strength and is much stiffer than E-glass. It has relative low elongation at failure meaning it is not able to share stress well so will tend to suffer brittle failure. (I have only ever seen fibreglass fail due to osmosis and I am now using CF for the first time so I have never seen it fail)

So if you want high strength, stiffnes and light weight then CF is best. If you want impact resistance then E-glass or S-glass are better.

In terms of your boat you could make a faster sailing hull using CF but you would need to be more careful with it. The water is unlikely to cause high stress but you need to be careful around fixing points to avoid stress concentration.

There is a lot of hype with CF to the point where it is hard to get in the most recognisable weave because it has become a selling point for all sorts of "high tech" machines.

Unless your are doing a very careful design and prepared to take care of the boat, glass is the best choice. It will groan and crack before it gives up. THere are warning signs. The data and various reports on CF failures suggest CF just goes bang.


Rick W.

 

Thanx for the link Rick, I will check it out shortly. The failure tendencies in CF are really my only concern with using it. I have snapped a fiberglass hull while underway before and its more exciting than I care for, CF's tendency to "just go" sounds like even less fun. Since the boat isn't currently safe to sail I have no way to get any data on the forces that the chainplates and other attachments are subjected to so any design in that area would be purely SWAG which could result in a weak hull or an overbuilt hull which would of course defeat the purpose of using CF in the first place. I guess its either trial and error or go with S or E-glass. Unless someone knows how to figure the stress that a 165 sq. ft. sail on a 30 foot mast would place on the various stays and shrouds? Either way the design will be done carefully because I want to update the hull to a more efficient form.

 

I would be interested to know how you snapped the fibreglass hull!

There is some good discussion on the first of the "similar threads" listed below.

Generally if you have a good handle on the forces you can be surprised by how little material it actually takes. Your boat actually limits the stresses on the rig unless you overdo the preload on the stays. You would probably prefer to capsize first, break rigging second and last of all fracture a hull.

In practice it is most often the indeterminate forces that cause things to fail like hitting something solid, creating a stress concentration through a build defect or surface damage in operation.

Rick W.

 

The Sol Cats made pre '74.5 had a flaw in the design of the hulls just ahead of the forward X-memberthat will allow the hull to fail under high loads, i.e. flying a hull in heavy water. My current Sol Cat has had both hulls replaced at different times in its life due to this defect.

 

Nifty! I haven't seen the "Similar Threads" thing before!

 

I have made lightweight boats using thin aluminium ranging from 0.6mm to 2.1mm and have a range of methods for fixing. There are some very good glues around for the thinner sheet.

The properties of alumium and CF mate reasonably well. Aluminum has a higher elastic modulus but it has a much higher elongation to failure. So mating the two should give a more progressive mode of failure around stress points such as chain plates.

I am presently building a new HPB using CF over full foam core and intend to embed 3mm aluminium plate into the CF layup to provide fixing points.

I have not looked around to see if others have done this. The bond might deteriorate over time but I use the boats only sporadically and usually in fresh water.

Rick W.

 

I was reading about that earlier, and found an interesting bit of info on the reactions CF creates when combined with metals. Apparently CF creates enough of a static charge to cause a cathodic reaction when in direct contact with metal accelerating the corrosion process. they recommended using a layer of fiberglass or aramid ( I assume any non-conductive material would do) between the metal and the CF to insure they would not come into direct contact.

I was thinking of using aramid patches at each attachment point, slipped in between the layers of CF. And possibly a layer of aramid along the bottom line of the hull to help protect against scrapes and such, since that part of the hull seems to take the most abuse from beachings and trailering. Can you reccomend any good sites for the actual lay up process?

 

There are a lot of sites that cover glass layup. Some good ones on surfboards. You should also look at vacuum bagging as well.
http://www.fiberlay.com/howto/Fiberglass-Epoxy-Basics-Training-Guide.pdf
This one has the basics covered - things like gloves and other safety advice are good.

I am told that working with CF is more difficult because it does nopt sit as well as glass and the weave tends to fall apart. I have a particular way to overcome these issues but am yet to test them with CF.

My main hull that I am now working on has a length of 7.2m and beam of 242mm. In your units 24ft by 9.5". I am making it from a solid core of polystyrene foam layers that are cut to waterlines 1" apart. I will fair this out so it has soft curves even over the gunwale. With a narrow hull like this I can completely encircle it with 1m wide cloth. See the photo of the unfaired block.

I am aiming for a boat that will be unsinkable even if holed but also very light. The forces are easily defined based on buoyancy. A hull this narrow and with so little reserve buoyancy does not experience much additional load from waves.

I intend to use an aluminium strip inside the layup of carbon fibre along the keel and a 'T' section along the centre of the deck. The 'T' provides a solid point for clamping the cloth to while laying up.

I have found that if you want a good job in glass using minimum layers then you need to be able to hold the cloth firmly and minimise the number of pieces of cloth in each layup. You also need to start with a nicely faired core with no sharp curves other than the bow and stern.

There are various ways to hold the cloth in place while it is wetted out. I have tried 3Ms spray on "90 High Strength Adhesive" on polyurethane foam and it is OK until the glue is soaked. I guess you could stretch the cloth out and leave the glued sections unwetted while the wetted section sets. Then mix up another batch and wet out the glued sction.

With the present boat I will use only one layer of 250g/sq.m of CF cloth and cover it with a smoothing layer of polyester fabric. If necessary I might use micro bubble to fill any imperfections after the first layup.

It is possible to vacuum bag this hull but I have plenty of time to work the epoxy in and take care with volume. I usually get close to the recommended resin/epoxy weight providing the cloth is stretched out and a single piece over a nicely faired core.

Rick W.

 

I have also heard that not disturbing the weave can be a real pain, as yet I haven't come up with any practical ideas on the subject. I would be very interested in your thoughts on the subject.

On one of the sites I visited a guy was using vinyl electrical tape wrapped sticky side out but there was some trick to not getting ridges and something about perforating it to allow excess epoxy to squeeze out. I'll see if I can find the site again and post a link, there was some discussion about bonding aluminum to CF on there as well. I know you can get vinyl tape from 3M in 12cm widths and it may be available in larger sizes.

Well it's midnite here and work tomorrow so I'd better sign off for now, J.