Thursday, 22 October 2009

DIY - Batten Repair

Here is a simple Do-It-Yourself repair of a glass or carbon tube / rod batten.

The most common area(I have found) for batten damage & breakage is the join between the middle and tail tube rods on the cross batten. This joint is under enormous load when sailing & when rotating the sail(on water or land). Another common cause of damage is when carrying the sail and you happen to catch the end of the cross batten overhanging the clew on something solid.

A break in the batten is easy to spot with the sail rigged. There will be a kink in the batten that is usually a smooth transition (with a small step) between the batten tubes. The degree of the break can vary from a crack in the batten which appears as only a small kink in the sail profile right up to a full break where the batten halves flex easily and a sharp kink in the profile can be seen. It is possible to sail with a cracked batten but more damage can possibly occur by doing so and the draft will move around more than usual.


Batten Construction

Tube rod battens are usually constructed in 3 parts:
  1. The first part of the batten is a solid pultruded fibreglass rod that is about 8.4mm in diameter. The sides(windward and leeward) are tapered towards the tip that is inserted into the camber inducer. This allows the leading edge of the sail to have a nice progressive curve towards the tip.
  2. The second part of the batten is the middle tube rod. This is a pultruded fibreglass tube that is lighter and stiffer than a fibreglass rod of the same geometry. It has an outer diameter of 10.4mm(1mm wall) and fits neatly over the solid batten tip. This area of the foil still has some shape but is much stiffer than the tapered area of the batten tip.
  3. The third part of the batten is the tail tube rod. This is also a pultruded fibreglass(or carbon) tube that is stiffer again than the middle tube as it is 12.75mm in diameter and a slightly thicker wall. This part of the batten forms the trailing edge of the profile and helps to lock the draft and deepest part of the profile forward in the sail.
Each of these batten section are glued and pinned together. The joint is then reinforced with fibreglass tape and covered with a head shrink plastic coating to smooth the layup while wet. The heat shrink also reduces the wearing on the inside of the batten pocket and protects hands from fibreglass splinters. It pays to remove your camber battens once in a while to check for cracking of the heat shrink as this is a sure sign that the fibreglass reinforcement has fractured beneath. If this has occured and the batten joint seems to be ok, remove the heatshrink and fibreglass tape with a chisel and re-apply some more glass tape with epoxy. See the final stages of the repair below for details on applying the tape.

Below is an exploded view of the standard tube rod joint(between the middle and tail tube)

Inspecting the Damage

To repair the batten we first need to inspect what type of damage has occured. As mentioned above if the heat shrink is cracked and you can see the fibreglass reinforcement has fractured(white furry looking cracks) then at the very least the glass will need to be re-applied. The batten might be completely broken and once removed from the pocket it may only be held together by a web of heatshrink. In either case the heatshrink needs to be removed and the batten prepaired for the repair.

  1. Peel the heat shrink off after scoring it lightly with a sharp knife. Be sure not to damage the section of the batten that in not reinforced.
  2. Remove the fibreglass with a chisel. With the batten placed genly in a vice(with a rag protecting the batten from the jaws) guide the chisel by placing the underside on the carbon tube and the cutting edge towards the glass reinforcement. Gently remove the glass in narrow strips being sure not to damage the end of the larger tube. The stainless steel joint pins will now be visible.
  3. Flex the smaller rod lightly to see firstly if there is movement and the joint seperates from the large tail tube, and secondly if there are any cracks that open under load. If neither of these occur will not need to remove the pins in step 4 . Place some tape around the middle batten and butt it up to the edge of the tail batten to show how far the tube is sleeved. Place a ring of tape on the end of the tail batten(but not over the pins) and draw a line on both pieces of tape on the top along the centreline to show the way the rods should be aligned when the pins are removed.
  4. Removed the joint pins by knocking them out with the point of a small nail or a pin punch. The pins will still need to be removed if the middle batten tip is broken and is sitting inside the tail tube because we need to place a rod down the centre that spans the joint.


Repairing the Joint
The cheapest and easiest way to repair the break is by placing a small piece of rod batten inside of the joint. Pryde wave sails use rod battens constructed from the same material as the tapered tip on the tube rod battens. This means they are great to use for the repair and your local shop may have one that they can spare, if not a piece of one.
Cut a piece of rod 70mm long and lightly sand the outside to remove any release agend that may be left from the manufacturing process. Add a 1mm chamfer to both ends to aid insertion and to allow glue stay on the contact surfaces. Check that the rod fits easily into the end of the middle tube rod. If the rod is too tight or doesn't fit keep sanding the outside in even strokes until it does.

With everything sanded to fit you can start gluing the components together in stages. Use 5 minute araldite(epoxy adhesive) and glue the rod inside the middle tube rod, leaving the ends flush. Once the adhesive has cured, drill out the pin holes through the inner rod using the outer rod holes to guide the drill. Check that the joint pins fit in the drilled holes.

Now glue the middle tube to the tail tube rod using the tape & markings to correctly align the pin holes. Re-fit the pins before the adhesive has cured and allow it to set.
Once the adhesive has cured it is time to reinforce the joint. The easiest and cleanest reinforcement to use is glass tape(20mm) or ribbon but if you have worked with composites before plain weave carbon or glass cloth will do. The advantage of the tape is the ease of which it can be wound and its thickness varied. It is also easier to get a high glass content as excess resin is forced out in the winding motion.
Lightly sand the rod 40mm either side of the joint and mix up a small batch of epoxy resin. You will need a small brush (or spatula if proficient) and some electrical tape. If possible leave the glass tape on the roll in case you need more during the wetting out process. If you don't have the glass on a roll you can wind it around a piece of dowel and have a handle making it easier to put tension on the tape. You will need 30cm or so per repair and it is handy to have some spare in case you have to repair another batten.
Start by wetting out the first 10cm of tape. Wind the tape onto the middle rod end of the join with the dowel or centre of the roll on the opposite side of the tape to the batten. This allows you to keep tension on the roll. Wind the tape onto itself until you feel it gripping and then proceed to wind towards the join wetting the tape out as you go. Overlap by about a half tape width so that you have 2 layers of glass minimum over the joint. You might want to wind the tape around the middle rod just as it meets the tail rod to reduce the step up to the larger rod. Continue winding over the join until you reach the other end of the sanded area. Cut the glass of at a point which is still dry and wrap it around the batten with the brush to wet out.
With the electrical tape(preferably black) attach it to the batten just before the area you started winding the tape and proceed to wrap it over the glass tape with a small amount of pressure to remove and trapped air and excess resin. Finish the tape past the wetout glass tape and allow it to cure for 24 hrs. Dont worry about the excess resin sitting on the tape as this will crack off when the tape is removed.

When the resin has cured remove the tape and if there are any lumps lightly sand them out. It is a good idea to wrap the join in electrical tape again to protect the batten pocket from damage due to wear over time. Your batten is repaired and you are good to go. You can use the above method to replace broken batten sections with new ones if you can get your hands on the right diameter glass or carbon pultrusion. This would maintain the exact batten curve but is obviously a more expensive option.

2 comments:

  1. You have made everything out of fibreglass, how many fibreglass moulds did you have to make

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  2. I assume that a good extra layer of cloth + epoxy is far more durable than electrical tape.

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