This instructible is to show you how to make small repairs to watercraft eg. cracks or chips on kayaks, surfskis, surfboards etc.

If you have ever paddled or lifted a kayak across rocks like these, you will probably need to do a repair.

This 'ible will work for:
- small wooden boats or kayaks
- fiberglass or carbon kayaks/skis/surfboards
- repairs where the hull is intact and not compromised
- scratches and small cracks

This ible will not work for:
- rotomolded or 'tupperware' kayaks - the epoxy will not bond to this material
- some kayaks which have single-part + hardener finish / old gelcoats
- boat repairs which are structural in nature. One piece of tape will not repair a hole in the hull :)
- high performance craft below-the-waterline hull repairs. This repair will create too much drag. Time for a new boat!

If in doubt, check with a marine engineer for a survey before commencing work. Another option is to try a small patch of the boat (eg. under the seat thwarts on a rowboat) to check the part bonds well.

If you are in luck, this low cost repair will save you the cost of a new boat and extend the lifetime of your vessel by many years to come.

Step 1: Safety First!

Safety First!

This instructible using the following things that are dangerous to humans with short and long exposure.

Some Hazards:

Epoxy Vapours: the epoxy resin gives of vapours which are toxic. Wear a respirator with a gas canister at all times you are working with epoxy.
Epoxy Sensitivity: epoxy resin can cause sensitisation in people with time. Avoid contact with skin and follow the manufacturer's safety instructions.
Epoxy splashes: avoid the wet epoxy touching your body - especially be careful around your eyes (considering this is a mask). Wear safety glasses and gloves. People may have an allergy to latex gloves too! In which case you can use the non-latex gloves or thin allergy free gloves.

Carbon Dust: when you grind away the finished carbon fiber shape there will be carbon dust. Wash it down and away, and wear a particulate or dust filtering respirator / cartridge when you are doing this step.
Carbon Slivers: Avoid getting small bits of carbon 'tow' or splinters caught in your fingers. Again gloves are good here.

Paint fumes: when spraying work in a well-ventilated area and wear glasses/gloves and old clothes, not your tuxedo.

Scared Away? I hope not!

Step 2: Tools and Materials

For this project, you will need the following tools and materials. I have tried to provide a reference in Australia and USA where possible.

Tools:
Dremel or motorised grinding tool - Bunnings / Home Depot / $ shop. For tidying up any 'dags'.
Stanley Knife or Box Cutter with spare blades - Bunnings / Home Depot / $2 shop
Safety Gear - goggles, latex gloves and respirator with gas and particle canisters - Bunnings / Home Depot
Brush - $2 shop - for painting the epoxy
Scissors - ideally these would be for cutting carbon/kevlar. Any sharp scissors are ok (not for kevlar, only carbon). Otherwise you can experiment with the stanley knife if you want to save money.

Materials:

Epoxy Resin (two part) - you can buy these from the same places as the carbon tape, or marine chandleries like bunnings. Another place to get it for 'free' is a local boatyard or if you know someone building a boat. Remember to get the epoxy resin, not PU resin with hardner. If you get any good, they may offer you a job!

Surgical Gloves - pack of 50 - Bunnings or paint shop - $5

Carbon Fiber tape 1" or 2" x 1 meter - $5 - http://www.carbonfiber.com.au/ or http://www.cstsales.com/products.html. It is cheaper to get the tape than a meter/yard of cloth and it is easier to work with in this application. It is better to buy one with a selvage edge so the carbon will only deteriorate in one dimension.

Blue Painter's tape - bunnings or 3M or home depot - $6

Newspaper - to avoid a mess.

Clear release film * 1m $5 - this is to prevent the epoxy sticking to the film. I had some film already which I think was polyurethane. You can buy this from the carbon vendors above.

Clear Varnish - $2 in a rattlecan.

take-away containers - recycled and washed! for holding the epoxy resin.

So for less than $30 or so you may be able to save yourself from a ruined boat!

Step 3: Prepare the Surface

Collate all of the tools and materials in the same place, like a surgeon.
The epoxy will set quickly when activated, so you will not get a lot of time to drive to the shop if you have forgotten something. Planning is the key. You can even practice without the epoxy to start, eg. use a piece of cloth or newspaper.
This may save you money as well.

Clean the surface of the boat with methylated sprits, or detergent and water. Wait for it to dry and ensure any sea water, grime, dust, oil, detergent etc. etc. have been removed. Otherwise the tape will stick to the dust and fall off, not the boat. Simple as that.

Mask off the section with blue painter's tape. this is so that you can remove the tape when the epoxy is 'tack dry' and thus remove any spills.

Lightly sand the affected area with 200 grit sandpaper. This is to prep the surface so that the epoxy / carbon will take to the surface.

For cracks, it is important to prevent the cracks from further propagating. Drill the end of the cracks out! Sounds counter-intuitive, right? http://en.wikipedia.org/wiki/Stress_concentration

You can see in the photo the prepared surface with a crack and prevention holes is ready for the carbon.

Cut the carbon fiber to measure and be careful to prevent the ends from fraying.

Step 4: Epoxy Time!

ow for the epoxy..

Measure out the correct parts according to the manufacturer's instruction, usually 2:1 or 4:1 by volume.
You can do things like use two syringes, or little party cups.
With the cups, let's say you have a 4:1 mix - mark 1 cup for part A, and then mark it at the same level on 4 cups for part B.

Don't use too much! Especially in one go! I once mixed too much to see what it would do :(
It got so hot it melted the container and almost caught alight.
For this project, you should only need 30mL or so of one part (a shot glass or so).

Mix into the take-away container and stir well. Paint across the tape that has been taped to the balloon.

Make sure that the carbon fiber doesn't look dull, this means it hasn't been wet out sufficiently. More is better in this case (not for a superlight bicycle though!)

Once the epoxy is 'tack' dry, remove the blue tape (otherwise it will stick and you can't remove it!). Add more layers if you want a stronger bond. The key is to make the carbon wet with epoxy and form a bond between the first and subsequent layers of carbon. In this example repair I used one piece of cloth only on a surf ski which had a fatigue crack. The single piece has held up for a year of weekly ocean paddling (to date). I also used the film release taped to the boat to prevent dust landing on it while it cured. This method won't make the boat any lighter, but you can look at removing epoxy by 'vacuum bagging' it for high performance and cost.

http://www.westsystem.com/ss/assets/HowTo-Publications/Vacuum-Bagging-Techniques.pdf

Using more layers, you are building up an epoxy / carbon fiber 'composite matrix' which is the principle behind the strength and light weight of carbon fiber.

Step 5: Finishing

Once the epoxy is dry and all of the tape and film are removed, use the Dremel to get rid of any 'dags' or protrusions. This is especially important on a kayak or surfski where your skin, clothes or wetsuit could catch and ruin your day.

Spray with waterproof (or other) varnish to provide some UV protection, otherwise you may find the epoxy will discolour and gradually lose its strength.

Try the repair out in shallow water and wear a PFD.

Enjoy! Happy boating....