Fred, One easy way to do it is make the wall thickness the same as the aluminum beams you are replacing. This will make them somewhat stronger than needed and about 30% lighter. You could use an inner and outer layer of 10.4 oz./yd cloth with the remainder being carbon unidirectional. 10.4 oz. cloth is very common commercially and comes out to about .014 inches thick per layer. The uni comes in various weights but you can look up thicknesses and other data on the Hexcel website. They have data sheets for most of their fabrics and uni which are pretty standard for most retailers. If you want to do some calculations, wall thickness can be further reduced while still being srtrong enough. For instance the Tornado masts I make have a wall thichness of .052 and the aluminum version is .085 thick. The carbon version was calculated to have the same strength and stiffness as the aluminum one. Carbon is 21 lbs and aluminym 38 lbs. Hope this helps.
I can only refer to the carbon-beams I made for my ventilo. They have a wall thickness of 3.5mm and a diameter of 120mm by a lenght of 3m. there are no dolphin-strikers as the diameter is quite big and the beams are very stiff.
the beams are reinforced at the place where it connects to the hulls and screws. they are made of unidirectional carbon fabric (400g/qm 12K HSC Carbon UD-Gelege 500mm width) from SP-Systems and has crosswoven carbon layer on top only for the optic.
The orginal Ventilo-Beams are also made of carbon, but are shorter (2.5m) and have a wall thickness of 2.9mm by the same diameter.
Fred, As I recall, the P-19 crossbars are mast sections and not round tubes. You could save yourself a ton of work if you used a section of carbon mast. Maybe you could find a broken I-20 mast or an A Class mast and build it up as needed.
Great idea Fred! Were you planning to go 10 foot wide and have a cheap Tornado? I heard there was a carbon mast floating around at Performance. I don't remember the name of the owner, but he supposedly works there. It might be available. I would be interested in your old beams. My front beam has a huge dent in it.
A-class carbon masts are pretty thin walled, thicker in the bottom meter or so: I would not use one for a P19 front crossbar- back- maybe. (My citation: actual observation during repair).
Dacarls: A-class USA 196, USA 21, H18, H16 "Nothing that's any good works by itself. You got to make the damn thing work"- Thomas Edison
I'd think a mast section would have a lot more flex to it than a beam section should have. Masts are designed to take more compression loads and to flex within the limits of the diamonds etc. You basically don't want any flex in a beam.
Perhaps you could use a mast section as a starting point and reinforce it with more layers of carbon to get it stiff.
Mike.
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Fred, As I recall, the P-19 crossbars are mast sections and not round tubes. You could save yourself a ton of work if you used a section of carbon mast. Maybe you could find a broken I-20 mast or an A Class mast and build it up as needed.
Fred, One way to make carbon tubes that is pretty fast is to use a male mold (mandrel). In your case it could be the old aluminum beam that has been stripped of fittings with any holes filled up. Can also make one out of solid wood. After using your favorite mold release wet out all the unidirectional you plan to use on the mandrel and wrap the outside with a layer of Dacron peel ply tape. Next, wrap the wet uni with two layers of polyester heat shrink tape. This is available from Dunstone Industries – they recently added a store front to their website. The polyester can be shrunk with a hair dryer or heat gun and applies a lot of compression to the lay up. Resulting laminate is good quality. Use an abrasive cut off wheel to cut the cured carbon lengthwise so the tube can be pulled off the mandrel in two halves. Glue the two haves back together along the seams. Step two is to remove the peel ply and wet out your carbon cloth around the outside of the carbon uni tube. Repeat the shrink tape routine minus the peel ply. Sounds labor intensive but really it goes pretty quick. The polyester tape leaves a shiny finish surface on the outside that needs little sanding. As someone else mentioned, you need to locally reinforce any holes for fittings or fasteners with extra layers of cloth.
Mike, I agree. Also, beams take some hard knocks from stuff banging into them. A layer of 5 oz. Kevlar besides pure carbon lay up would make a great insurance policy. Kevin
if you can heat the aluminum enough as the carbon cures, the aluminum will expand. when it cools, the carbon will be at the expanded size and just pop off.
Re: compression, not bending strength
[Re: basket.case]
#31097 03/11/0401:34 AM03/11/0401:34 AM
Guys, The front crossbar, along with the dolphin striker and the other two members, form a truss structure. The front crossbar is a compression member, with almost no bending stress. There are shear loads at the hulls. The dolphin striker rod is also compression member (just like mast spreaders) and the other two members are in tension (just like diamond wires). A front crossbar, with dolphin striker, does not require a great amount of bending strength.
An I 20 mast section may be too large to fit into the sockets in the P-19 hulls. I agree that an A Class mast would probably be too thin, that is why I said "an A Class mast and build it up as needed."
Taking an existing carbon mast section and doubling the thickness of the layup is far easier and cheaper than starting from scratch. The mast section already has a slot for the tramp bolt rope.
Kevin, That is a good idea to add at least one layer of kevlar.
Basketcase, A very interesting idea. We have seen how so much work is involved in removing the mandrel after curing. If the wet layup were wrapped around a cold metal mandrel, aluminum or steel , and then heat were blown through the pipe, the pipe would expand tightening the layup , and heat curing the resin. Upon cooling(cold water?) the mandrel would contract, freeing itself.
I've done this - no need to cut the spar in half to remove! Just lay one layer of paper over the mandrel first, and then another layer of release film next. Your layup begins on the release film. The release film will not stick to the paper and it just slides off (but remains inside the spar - but it's only 5 mils thick thus very light). See Photo of 12 foot spar, attached.
Lots of good ideas here. Some odds and ends, Loading on beams: Yes it's true the mast load is converted to compression by the dolphin striker. But there is also significant torsion from platform wracking. Also a bending moment from leeward hull hydro forces wanting to force hull under the boat (reaction to lateral sail force). Like most boat parts is hard to quantify precisely how it's loaded. Cost of materials: For cut yardage expect to pay 30-35 us dollars per pound for carbon. For an entire roll (100 yards) expect to pay 15 dollars. Often you can find a partial roll of 30 to 80 yards at a good price. One piece method: If you can get it off the mandrel great. Just be sure to do a test to make sure it will work before commiting lots of material to a part that is permanently stuck on the mandrel!! Also need to consider the fit of the new beam in existing beam channels in hulls - the two piece method allows you to almost exactly match the original beam size.
Hello Dan, Also check Dupont's manual on Kevlar and you will find that it is 1/3rd as strong as fiberglass in axial compression. You have to use Kevlar very carefully. Years back when Kevlar first came out, some C class cats and other custom one offs were built with Kevlar composite hulls. They all failed on the compression side of the hull. The bows came together. Kevlar is great stuff but you have to be careful how you use it. Bill
Don't use kevlar on the outside. Kevlar has low compression strength, it is difficult to fair, and it is not very UV tolerant. On the positive side it has very high tensile strength, it is lighter than carbon, and it resists crack propagation. Use Kevlar on the inside or as a core in combination with carbon or glass. I use it on the inside of wood composite and as a core with carbon for things that are subject to impacts like rudders and dagger boards.
If you want to use something on the outside for protection, try glass. I use a 4 oz fabric that looks like satin dress material
I heard there was a carbon mast floating around at Performance. I don't remember the name of the owner, but he supposedly works there. It might be available.
