Sandwich composites, also known as core composites, can be used to fabricate a vast variety of products, including boat rudders. The centre of the composite boat rudder is known as the core and is often made of a foam, such as polystyrene. The skin of the rudder is made from a composite fibre, usually carbon fibre or fibreglass, and an epoxy, such as West System. With the use of sandwich composite materials, you can fabricate a rudder with a very strong strength to weight ratio.
- Skill level:
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Things you need
- Safety glasses
- Nitrile gloves
- Pore-less peel-ply
- Masking tape
- Vacuum bag
- Sealant tape
- Polyester breather/bleeder
- Resin flow medium
- Composite core (synthetic foam)
- CNC mill or CNC hot wire cutter
- Fibre (fibreglass or carbon fibre)
- Binder (epoxy)
- Polythene cup
- Wooden spoon
- Epoxy spreader
- Twist lock aluminium vacuum cup assembly
- Vacuum pump
- Vacuum tubing
- Tube clamp
- Methyl ethyl ketone
- Utility knife
- Chemical respirator
Put on safety glasses and nitrile gloves. Nitrile gloves protect your hands from chemicals that would usually dissolve latex gloves.
Prepare a clean, flat work surface. Lay pore-less peel-ply (a thin layer of epoxy-resistant plastic) on the table. Tape the edges to the table for a smooth work surface. Peel-ply will keep your table clean and make clean-up easy.
Take a vacuum bag (a folded sheet of plastic used for vacuum-bagging composites) and cut a piece 6 inches larger for all edges of the rudder that you plan to fabricate.
Cut a piece of sealant tape slightly longer than each edge of the vacuum bag. Seal all edges of the vacuum bag, leaving only one open side. Place tape on one edge of the open side but do not peel off the waxed paper protecting the sealant tape. You should have what resembles a large plastic bag with one open end.
Make a slit that is approximately 1/2-inch long on one side of the vacuum bag. Your twist lock aluminium vacuum assembly will connect through this slit to vacuum the air out of the bag.
Cut two sheets of breather/bleeder about 1 inch longer on all sides than the size of your intended rudder. Make one side on both sheets about 6 inches longer. The breather/bleeder will be on each side of the rudder during vacuum-bagging and will collect the extra epoxy from the composite rudder.
Cut two sheets of resin flow medium to the same sizes of the breather/bleeder. The resin flow medium will be on each side of the rudder during vacuum-bagging and will allow for an even airflow, preventing wrinkles in the final product.
Cut the foam core with a CNC mill or a CNC hot wire cutter to your rudder's dimensions.
Place a sheet of fibre (carbon fibre or fibreglass) on one side of the rudder. Do not wrap fibre around the rudder as it does not conform well to curves.
Mix epoxy in a polythene cup with a wooden spoon or stirrer. If bubbles form, place the cup into a vacuum system to remove the bubbles. Spread epoxy over the sheet of fibre with an epoxy spreader. Make sure that every fibre is saturated to ensure a strong bond. Place a second sheet of fibre over the first sheet. Again, coat this with epoxy. Repeat until the desired rudder skin thickness is achieved.
Flip the rudder over and place a sheet of fibre on it. Again, apply epoxy to the fibre. Place a second sheet of fibre onto the first sheet. Apply epoxy to saturate the fibre. Repeat this step until the same thickness as the first side is achieved.
Take the rudder and place perforated peel-ply on each side. The peel-ply will peel off of the final product and allow excess epoxy to drain through it during the vacuum-bagging process.
Place the pre-cut resin flow medium over each side of the rudder, on top of the perforated peel-ply. Make sure both sheets of the resin flow medium align so that the rudder fits into the vacuum bag.
Position the pre-cut breather/bleeder onto each side of the rudder, over the resin flow medium. Make sure that the lengths of breather/bleeder align with each other so that they fit in the vacuum bag.
Place the rudder system into the vacuum bag. Adjust the materials accordingly to remove any wrinkles.
Position the twist lock vacuum cup onto the slit before closing the bag. The twist lock vacuum cup should lie on top of the longest length of the breather/bleeder and the resin flow medium so that it is at some distance from the rudder. If the twist lock vacuum cup is too close to the part that you are fabricating, it could suck up epoxy and become clogged. Peel the protective waxed paper off of the sealant tape and seal the final side of the vacuum bag.
Connect one end of vacuum tubing to the twist lock vacuum cup and connect the other end to the vacuum pump. Pump the air out of the vacuum bag. You will see epoxy saturate the breather/bleeder material. After a few minutes, you should see no more progress, and the vacuum pressure will remain constant. Clamp the vacuum tubing with a tube clamp and turn off the vacuum pump.
Open the vacuum bag and remove the rudder once the designated curing time has passed. The perforated peel-ply should have kept all of the other materials from sticking to the final product, and the peel-ply will peel off of the rudder.
Peel the peel-ply off of the table and discard. The peel-ply should have kept most -- if not all -- of the epoxy off of the table. Discard all other materials, except the rudder and the vacuum bag which can be used again.
Clean up the table if any epoxy did leak onto it. Pour methyl ethyl ketone onto the table and scrape it off with a utility knife. It is advised to use a chemical respirator during this step.
Wash your hands and arms with soap and water immediately following cleanup. Any epoxy, methyl ethyl ketone, fibres or other materials that contacted your skin can cause irritation.
Tips and warnings
- Experiment with other fibres. There are a wide variety of fibres, including natural fibres and Kevlar.
- Use a chemical respirator when dealing with chemicals that create fumes. Chemicals, such as methyl ethyl ketone, can be hazardous to your health.
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