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I have struggled converting a carbon fiber mast for use on a modified Cataproa. I think the failures and successes are informative for those interested in carbon spars. I used to do this kind of work in my carreer, first as a fabricator and later as a Materials and Process Engineer. So I am embarressed by the failures. I have had successes in the past. For example, here is a cutt-off from a custom carbon mast that was a success:

You can read more about this on my blog:
http://gator2002.temp.domains/~mancegns/2021/09/13/davids-cataproa-2/

David M

Hi Philip
Interesting that you have also built a carbon mast.?
Besides David, there are sure more folks here who are interested.
If you don't mind send your file to the group too.

Cheers

Bernd

I enjoyed reading about Phil's infused carbon mast building. He took a different path than I did with my infusion. My infusion failed because my mandrel was not airtight. But I have used the method successfully with airtight molds. So how is my method different?

I use staged infusion. This means placing resin supply lines every meter. For a small laminate like a mast, I use 4mm ID, hard, polyethylene tubing for resin supply. It supplies plenty of resin for infusing a mast and does not allow the infusion front to race too fast. If you look at my picture, you can see the resin supply tubes and the vacuum tube (same tubing material) nearest the camera. One advantage of this particular tubing material is that I can seal it by simply kinking it and taping the kink until I want resin flow. This is effective and very inexpensive compared to clamps.

Resin supply lines every meter or less for staged infusion.


Infusion set-up from other end. You can see the kinked tubes instead of clamps to seal the tubes. Note also, the ends of the resin supply tubes are cut at an angle so they cannot seal against the bottom of the resin bucket.

As Phil noted, a key element of infusion is to prevent wrinkles in the laminate. In my infusion there are at most 4-layers of reinforcement. Each layer is tightly rolled using Super 77 adhesive to keep them in place. This was not as difficult as a full length mast because, for this job, reinforcements are only added to the bottom 3.6 meters of the spar. Also, with at most 4-layers, tightly wrapped, previous experience has shown impression resulting from the spiral tubing resin distribution lines will be minimal. For this process I never wrap one layer multiple times around the mast because I believe doing so can increase the chance of inducing wrinkles.

My infusion setup is: laminate; peel ply; infusion flow media; vacuum bag. My resin distribution lines are 10mm id polyethylene spiral wrap fed by 4mm id resin supply lines. They are placed at most 1-meter apart. The infusion flow media stops about 50mm from the vacuum line. There is a "brake" between the flow fabric and the vacuum line to slow the resin. The brake I use for masts is a single layer of 200 g/m^2 balanced glass cloth with peel ply on top.?

To infuse this part, I would have first pulled a vacuum for at least 4-hours. Next I would do a pressure drop test by closing the valve on the second resin trap. If after an hour, I had not lost more than 2 psi (on the gauge of the first resin trap), I would be ready to infuse. I would have started the infusion at the butt of the mast (away from the vacuum line) and allowed the resin front to pass the second resin supply tube. I would then close (kink and tape) the first resin supply line and open the second resin supply line. This process would continue until the resin front reaches the "brake" before the vacuum line. I would then close the valve on the second resin trap (i.e. disconnect the vacuum pump from the laminate). I usually don't need to engage the vacuum pump again but would briefly if the vacuum fell more than 4 psi.

David M

Great stuff Phil.

Comment about pre-preg: One difficulty with pre-preg is related to Phils struggle with wrinkles on his infused mast test. The pre-preg must be very tightly "wound" around the mandrel. Typically this is done by laying the pre-preg patterns out on a table. The mandrel is then forced onto the pre-preg and very tightly rolled. The tack of the pre-preg holds it in position on the mandrel. Heat shrink tape can then be spiral wound around the outside of the prepreg. The whole system is then put into an oven. The oven shrinks the tape, applying pressure to the laminate and the heat cures the resin in the pre-preg. It is extremely diifficult to maintain even pressure the full length of a long mast when rolling the pre-preg. Any uneven areas of pressure are subject to wrinkles. Also, a thick laminate needs intermediate de-bulking steps. This means applying a release ply, then a breather and then a vacuum bag. After the vacuum bag removes excess air, it is removed along with the breather and release ply and more pre-preg plies can then be rolled onto the laminate.

Hope this helps.
David M