FRP vs CF

[Seafra]

I've recently become interested in boatbuilding, but I've been interested in working with advanced composites for a long time.

Would any of the knowledgeable among here care to add their personal opinions on FRP vs. CF in specific regards to:

-Cost(assuming an epoxy resin)
-Ease of work. I assume it's fairly similar though CF is tougher to cut.
-Performance advantage per $
-In a boat hull...is stiffer always better?

Additionally, my understanding is epoxy resin is 100% UV proof. Has anyone laid out a hull in CF and left it unpainted? There are too many white/light-coloured boats in the world.

Any good online CFRP/epoxy suppliers to recommend?

[SeaSpark]

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[marshmat]

Cost: CF is more than FG.
Ease of work: Depends how many years of experience you have with each.
Performance: Depends on boat. When CF is used it gives slight gains for big bucks.

[frosh]

Hi Seafra, welcome to the forum. I will assume that CF is carbon fibre?
I have built boats in wood, glass fibre and wood, carbon fibre/glass and wood, carbon fibre foam, carbon fibre/glass foam. Always epoxy resin.
The differences are not that huge compared to the cost differences. It also depends a hell of a lot in the particular application. If you are doing a high performance kayak, or an outboard runabout, it is completely a different world between the two. You need to be a bit more specific about what type of boats you are particularly interested in, and then we can progress.
PS. Just lately woven carbon fibre has become scarcer and more expensive!

[Tim B]

I have found that Carbon is actually just as easy to cut as glass fibre as long as you have a sharp pair of scissors. A good reason for boats being white is that a dark surface when left in the sun for any period of time can get very hot. I don't know if it would be hot enough to cause problems with delamination, but you should certainly consider the fact that the material will be working at an elevated temperature (prob 50 deg C or more) and consequently the resin properties will change from standard room temperature properties.

Dark boats look great in the marina but are hard to see at night at sea and tend to be incredibly hot inside.

Tim B.

[Splint]

Hi Seafra,
personally I think unless you're building a hull for racing purposes you should stay away from CF. Mostly due to the cost but you also need to be aware of the performance characteristics of CF, it is strong but has very limited impact resistance so if your hull hits rocks you're in trouble. Sheets of CF are very easy to snap with your fingers, much easier than woven mat or even chop mat fiberglass, CF is good if used in the right methodology and in the right application but appart from that it's a not all that the average punter on the street thinks it is. Also keep in mind that the directions of the rovings are criticle to load exposure. Here's a couple of pictures to demonstrate how easily CF can break. This was an experiment to sample different surface and core materials. A hammer was used to punch the holes in the CF, it took minimal effort to do the damage. CF works well where the load is spread over a large area (think of aeroplane wings).

Cheers
Splint

[marshmat]

CF is incredibly strong and incredibly stiff, but it is also very brittle. As Splint says, it doesn't like point loads. It can't flex to absorb them, without shattering. As several have said now, CF is for specialized applications where weight is of paramount importance. It needs really careful engineering of the laminate schedules in order to work. Unless you know exactly why you need carbon, you probably don't need carbon.

[fiberglass jack]

why dont u go with a kavlar carbon hybrid u can get a 2x2 twill and it has a nice look on it this way u have the best of both worlds

[bntii]

Originally Posted by Seafra

Additionally, my understanding is epoxy resin is 100% UV proof. Has anyone laid out a hull in CF and left it unpainted? There are too many white/light-coloured boats in the world.

you have it backwards....

Epoxy is not at all UV proof. In about 2 months the stuff will go south if left in the sun. All epoxy laminates must be painted. Also the thermal transition temp is low enough that the solar gain on a black CF surface will be too high.

Just paint the hull a nice light green and with some bright blue spots

[Tim B]

There are special UV blocking agents to add to epoxy. Personally, I think the heat will be the biggest problem. Even with high-temperature resins, the inside of the boat will still get far too hot.

Tim B.

[bntii]

Never used blocking agents.

Do you have a link to a commercially available UV stabilizer for epoxies?

Thanks

[Seafra]

Yea, my prior experience with carbon fiber comes from motorcycling. It's great for the fairings and non-load bearing parts. I've seen some pics of spectacularly delaminated carbon fiber wheels...high speeds and rotational stress can do that I suppose....


I understand one of the key differences between FRP and CF is in terms of flexibility vs. stiffness. CF is the most brittle when it's made with a poly resin, but never has the flexibility of FRP.

In my initial question, I wondered if stiffer was always better(in terms of sailboat hulls). Would using carbon fiber to reinforce an otherwise FRP hull produce favorable results IYHO? In terms of motorcycling, stiffer is not always better as a certain amount of lateral flex is necessary to act as a tertiary suspension (wheels, dampers, (sub)frame) when leaned over. That is why Carbon Fiber frames made only a brief spark in MotoGP.

Fiberglass Jack, tell me more about Kevlar/Carbon hybrids. Kevlar's used in riding gear for motorcyclists, but it's typically blended with other fabircs to increase abrasion resistance. I suppose abrasion isn't much of a concern in a sailboat. From what I remember Kevlar degrades rapidly in UV light- I had kevlar brake lines on my bike but they were coated with a thick plastic to shield them.

So whatever, this is a boating forum...not a bike forum.

I think for hull color I'll just paint it soft pink...with little flowers running along the gunwales.

[Tim B]

Kevlar is has a lower modulus than Carbon, but much higher tensile strength. That is what makes it useful within a (mostly Carbon) laminate. The failure will not shower little bits of (sharp) Carbon fibre all over the place.

For Yacht hulls, stiffer is always better. It is a necessity for good handling while sailing. Carbon is a fantastic material, and great for highly loaded beams (mast supporting beam) and the like. However, since boat hulls tend to be pretty stiff anyway when they have a full-length deck, it is only really needed in highly loaded areas of the hull. For a small racing skiff (Moth or I14) you may choose to use Carbon because of the weight reduction. Not because it couldn't be made stiff enough from GRP.

Tim B.

[John ilett]

If you build a boat in CF using the same weight of fabrics you will have a much stronger stiffer boat that is very unlikely to explode, snap or be brittle.

When people make the change to stronger materials like carbon they tend to use less of it in comparison and have a much lighter boat.

[Seafra]

John,

Do you think it's common that a boat built out of Carbon Fiber is likely to have less material thus be lighter, stiffer, but also more brittle?

In ocean cruising situations, it seems almost disadvantagous to use carbon fiber for the either the mast/spars and the hull. However, for dinghies and racing scows I think it seems the best option.

You don't get much lighter than pre-preg carbon fiber layup.