Saturday, October 10, 2009

Making a new rudder, part 3

Designing a rudder, part 1
Designing a rudder, part 2
Making a rudder, part 1

After lots of careful shaping of details (mostly with an orbital sander) and filling in the odd accidental gouge (using a mixture of epoxy and colloidal silica - which sets into a very tough and water-impervious substance), I was nearly ready to laminate.

From Laminating new rudder
Hardwood inserts epoxied in place, ready to take bolts

The final pre-lamination step was to drill big holes where the bolts connecting rudder to yacht will later sit, out to a radius of 5 times the bolt size: since Corecell is too soft to hold stainless steel bolts, I fixed hardwood inserts (chiseled from the remains of my old rudder) in place with lots of epoxy/colloidal silica mix to fill the gaps (actually, the wood was not technically necessary - but cheaper than epoxy, and a nice link with the old rudder, so in it went). Now, my rudder is a wood/corecell/epoxy/colloidal silica composite - and we've not even started with the glass fibre yet.

From Laminating new rudder
Rudder core, fully shaped, smoothed, faired, and ready for lay-up

Next step was to cut glass cloth to size; this is beautiful stuff - layers of four-harness satin alternating with heavy unidirectional fabric. It isn't that easy to cut, especially the 500g/metre stuff - glass is really hard. Also, the material looks almost too beautiful to use.

From Laminating new rudder
Unidirectional glass fabric, 500g/square metre

Before laminating, I need to don my protective gear - epoxy is great stuff, but not for the human body. I always wear eye protection in case of silly accidents, nitrile gloves (I'm now using cheap disposables instead of the heavy duty items pictured - latex won't do, by the way), rubber boots (because there are always drips and spatters), overalls (well, duh!) and an apron (because I tend to lean against the workbench, and my overalls nearly soaked through once).

From Laminating new rudder
Ready for Fun with Chemicals

From Laminating new rudder
Wet fabric (transparent) draped over the rudder core

My first couple of layups went pretty well - except I laid the epoxy on way too thick; extra does not add extra strength, only weight - and it is pricey stuff to be wasting. In the picture above, note the puddles of excess epoxy sitting on top of the cloth, and the messy ends at the rudder head (beside the squeegee) that I had to grind off after the resin had set. Hard to see, but important: the plywood workbench has been covered in white-faces hardboard (cheap enough to bin later) which in turn has been covered with a transparent polyethelene sheet (does not stick to epoxy).

Miscellaneous tips:
  • Clean your squeegee straight after use, while the resin is still soft
  • Buy a set of cheap brushes from Tesco for dabbing on resin wherever dry spots show up (€1.25 gets you 3 brushes in our local). Ditch after use (too hard to clean).
  • Disposable nitrile gloves give great tactile feedback - actually better than the heavy kind (plus, no clean-up). Very, very cheap at B&Q - and insanely cheap on E-bay.
  • It is much easier to use too much resin than too little
  • ...but you still need to keep an eagle eye for dry spots.
  • take your time and do careful work - resin sets fast, but not crazy fast
  • use peel ply - leaves a lovely smooth easy-to-work with surface, helps remove excess resin, well worth the money
  • an ounce of preparation (masking tape, polyethylene sheets, etc.) saves a ton of fixing up later

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