Carbon Fibre Mast Repair.

[Trevor]

Does anybody have a preferred method to fix split masts. I know I should probably replace the tubes but these are very old C1, C2 and C3 rigs and the sails are not worth spending much on.  I have one in particular that has come apart between the lower sections leaving half a dozen splits at the end of the bottom bit.  Would injecting epoxy into the cracks and binding with CF Tow or Tape be OK?  Other masts have splits at the gooseneck (particularly where screw have been used!). Same technique I assume?

Cheers

Trevor

[Richard98]

Hi Trevor,  Carbon unidirectional (Uni) masts are very easily split. Carbon tows work and so do sleeves.  I keep short lengths of woven epoxy carbon tubes for that purpose. A 14mm Uni mast sleeved with a 10mm long piece of 16mm woven, epoxied over the splits and wherever a fitting is placed; plus at the mast top where the backstay crane places a huge splitting load.  Gooseneck, of course. Spreaders, shrouds etc etc.  The sleeves are so easy and clean to fit and I resort to CF tows for the gooseneck.

Injecting epoxy may make things worse; however no reason not to "wipe" epoxy where the splits extend beyond any sleeves.  Lastly: some cheaper CF uni tubes are polyester bound and are not worth the trouble. Ensure any tubes are Epoxy bound, any decent supplier will confirm this.

Good luck.

Richard

[Trevor]

Thanks Richard.  I have ordered unidirectional tubes (epoxy bound) so I can use them for both replacing and sleeving (internal) but think I might use them so quickly I need both sorts! I also got tow and tape for local reinforcement as you say around the backstay.  I am wondering about a technique for applying tow by attaching the end to the tube with a spot of cyano, winding around a wetted tube, holding down with another spot of cyano before wetting out and taping.  Some winding might be done on my lathe.

When I say injecting epoxy I just mean opening up the splits and wiping resin in and letting it cure as with three or four splits it may be difficult to hold the tube round while winding.

Cheers

Trevor

[Richard98]

Hi again Trevor, Your technique for applying tow works. I wind a couple of turns to achieve a single layer of flattened tow. No need to cyano the free end, just cyano the start, wet out, wind on and tape over with electrical tape.  The woven sleeve is cleaner, simpler and less bulky where a run of reinforcement is necessary; say 10-20mm or more.  Bulk may impact on the sail to mast clearance unless very careful. Sleeves are 1mm wall and this is very easily exceeded with tow. 

Sorry if this sounds repetitive, but there is no need to over wind tows. A single thickness winding is sufficient. Also adds weight. I peel ply to remove excess epoxy, but this is a bit paranoid !

Sounds like you have a serious amount of splitting and I possibly see why you would want to wind on with a lathe.  You must have a "proper" workshop. 

Richard

[Trevor]

Hi I wouldn't call it a proper workshop but it's fine for models and small engineering jobs.  Two masts are being rebuilt with new lower tubes and one that split at the first joint is being bandaged! The lathe is useful for removing tow applied in the pregnant snake style!  I can take it back to the tube and reapply.

I was contemplating using Dyneema to bind the goosenecks on but think it will look better with a couple of wraps of 1" wide woven tape.

Final decision is whether to use epoxy glue or resin?  I'm thinking glue is thicker and may be more controllable but will need to be "massaged" into the CF but resin will "wet" better.

Cheers

Trevor

[tiggy_cat]

To avoid splitting on the bottom end on my c/f tube masts, I buy a piece of suitable sized wood dowel and epoxy that inside. Gives the screws from the gooseneck something to bite into.

[Mike Ewart]

resin will definitely wet out the tow much better and if you wind around with tape or I use a cling film it comes out quite tidy

[Trevor]

Thanks I'll try the cling film.

[tiggy_cat]

15 hours ago, Mike Ewart said:

resin will definitely wet out the tow much better and if you wind around with tape or I use a cling film it comes out quite tidy

I have some shrink wrap silicon tube that I put over the tow to tidy things up when finished.

[Trevor]

So far so good I have the C1 mast fixed.  I have learnt not to use masking tape to retain resin as it's a fiddle to get it off!

Currently struggling with mast measurements as I forgot to measure the limit marks! The measurements on the certificate don't seem to add up either but I'll ask that question in another post.

T

[Trevor]

All fixed now and the measurement problem turned out to be a typo!

Things learnt from the CF mast repair.

1.  Cyano tack the tow to the mast, wind on required amount and cyano tack again.  Wet the tow with resin and massage into the tow. 

2. Wrapping with tape is fine on a cylindrical repair/reinforcement but masking tape or kitchen cling film sticks.

3. Wrapping a tow reinforced gooseneck with anything makes a mess!

4. Cutting CF tube to length in a lathe is OK but don't go all the way through!  If you do the last few fibres don't cut and twist together into a very strong rope!

5. Reducing the outer diameter of a tube so it telescopes nicely is best done in a lathe with a file.  Turning with even a very sharp tool is difficult.

T