Braided Kevlar/carbon sleeve application

Hello, I’m a new reader of this site and have already learned very much from searching these discussions but I already have a question.

I’m wanting to build a canoe similar in design to a Geodesic Airolite by Platt Monfort, (See http://www.gaboats.com/). For those not familiar they are essentially skin on frame constructions similar to Native American or Inuit boats but using modern materials. I would like to take the construction one step further and replace the wooden frame with a completely composite one.

What I want to do is form each rib and stringer of the canoe with a 1” carbon/Kevlar braided sleeve over a foam core. This would create a network of carbon/Kevlar tubes forming the frame, over which I would shrink fit a Dacron skin and seal watertight.

Now the ribs of the canoe are of greatest concern to me, around that I have many questions.

Does anyone have experience using fabric sleeves on curves?
Will a braided sleeve of carbon/Kevlar make a smooth radius?
How tight of a radius is realistic?
How many layers do you think would be required to achieve the required/equivalent strength?

Thanks for any input on my idea.

 

snowman_fs

I have been working on the use of carbon braid over mould foam core for a number of components on the ROCAT, and it's a good way to go. We are infusing in closed moulds, but it is possible to bag the outside - just doesn't look so pretty.

"Does anyone have experience using fabric sleeves on curves?"

Depends a lot on the weave and weight and size, but get those right and braids work fine on curves.

"How many layers do you think would be required to achieve the required/equivalent strength?"

How long's a piece of string?! How strong do you want it? We just got some braid and experimented. What resin are you planning to use - you don't mention that?

Have a look at www.rocat.co.uk and see if what we are doing answers any of your questions.

atb ... Christopher

 

Thank you Christopher,

Your ROCAT site has been very helpful. I’m still reading the site but so far it looks like my ideas and application of carbon sleeve are well within the limits you have pushed.

The weight of sleeve I’m considering is 7.5 oz and the curve is the contour of a canoe hull. The most demanding curve is obviously the bow and stern rib which I will have to test before constructing the whole boat.

The layering/strength question was in reference to a 1/3” x 1/2” wooden rib as seen on the referenced website. I think I will have no problem with just a single sleeve layer. There are 20 ribs in the canoe which will work in parallel to take the load.

As for resin I have some West System epoxy in my garage from other projects that I would try to use first. If that is not acceptable I will have to consider other systems.

Once again thanks for your help and I will be checking this site regularly as I’m now hooked.

-Jordan

 

Jordan

I wonder if the braid on foam core is not a bit of overkill in your case, unless you could get some ready-made extruded (preferably D-shaped) foam profile. If I understand right, you are looking to make some strong, light hoops ... I presume they don't need to be hugely stiff as long as they won't break.

Suppose you were to make monolithic hoops out of uni-directional carbon tape; that wouldn't be difficult. You could cut the stations out of 18mm MDF, or such; then, having given the edges a bit of draft and painted, polished and released them, you could sandwich the 'mould' between two flat pieces of glass or plastic, (to give you nice clean edges) and wind on some wet-out uni carbon tape till it's about 4mm thick. When that's cured you would have an extremely strong, light hoop. Join twenty of those together with a few good stringers and you've got a structure!

Yes, I would certainly use epoxy for this kind of application.

I don't know if that's any help?

atb ... Christopher

 

Christopher,

I’m actually trying to have a little overkill in my application. The foam profiles will be very easy to mill out from a foam sheet on a mill I have access to and the ease of slipping a sleeve over the rib makes life much easier.

I have tested the wrapping method similar to what you suggested, (albeit with bi-axial glass) to form a helical type structure but I found that at the vertex of the rib it would fail in compression quite easily, where the layers of wrapping would delaminate. Not good as compression will be a main load when providing buoyancy.

I thought a braid would be stronger, more uniform and easier to apply; the thing is I just found out about sleeves this past week so I never considered it before and have no experience with it.

Vacuum bagging will unfortunately be the most sophisticated I can get on this project as it is in my garage and I cannot build a mould for every rib and stringer. I’m hoping to make some sort of vacuum table where I can put multiple ribs on at once, the problem for me will be the cost of such a table and its ability to form the 550 cm long keel line. Hand lay-up may be the only option for the keel and other stringers.

You have been more help than I can stress. Before this I was not going to proceeded with the construction as my trial wrapping method had failed but now I’m prepping my garage for trials again and have more confidence that it will work.

Thanks,

Jordan