Friday, April 25, 2008

Challenges when not using vacuum - bubble trouble part II

On my recent 40th birthday my soon 5 years old son gave me this masterpiece to be kept in the workshop. It's a boat and a dangerous rock in a red ocean (acryl on canvas). Tusen takk, Eilert!

As covered in an earlier post I ran in to problems with the vacuum integrity when trying to infuse the outer hull skins and kind of gave it all up, converting to hand lay up for the float outer skins. It is, however, not so sure you can get away with this method without trouble either, at least I didn't (nor did Jay).

I've been trying not to think about it, hoping this would fix the problem. Unfortunately, this head in the sand approach didn't lead to any solution, and now this is the only float side not faired and I had to face the problem.

With glass it is usually very obvious where an air bubble in the laminate is (clearly visible), but with these un-see-through fibers I use it is harder. I put up a lot of lightsources and used my hand to localize the bubbles, then marked them with a marker. I found a few more later on, even though I went over the whole float quite thoroughly.

Bow view. Close to 30 bubbles all together....

I started in the aft part, using a 30.000 rpm grinder with 50 grit paper (aramid (Kevlar®) is definately resistant to mechanical wear) and worked my way in until I met the foam core. Tapering off the circumference and laminating a layer of hybrid covered with a bigger piece of carbon as the carbon cloth is thinner and I suspected this would give a smoother transition between the repair and the hull. I took no chances this time and let it cure under vacuum.

It turned out the vacuum was very effective in minimizing the bumps from overlapping and I continued with the rest (and more visible parts) of the float inner side using the same approach.
Close up of one of the patches:

It actually looks like the float caught some kind of nasty disease....

The rest of the lesions under cure:


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