Making a “air-core” FibreGlass oar – part 1

My oar design on paper and plywood for the mould

It is my personal belief that all cruising yachtsmen (and yachtswomen) needs to learn the skill of fibreglassing. Who knows where you will be when you need to quickly whip up some fitting to safely do the next leg of journeying across the seas? Lets just hope that we will even find the resin still useable when we need.. yeah right..

Moulds.. made of plywood

Use a Fb/G working suit if you have one...

Let me try to describe this process in the proper sequence.

  1. Design the oar, get the numbers right
  2. Build the moulds, calculate the materials needed
  3. Buy the materials… in my case, I bought almost everything from Wee Tee Tong.. 10m2 3oz Fb/G cloth, 10m2 Fb/G matt, 1x20kg tin polyester resin, 1kg MEKP(hardener), 1l Liquid wax, 4l Acetone … and then gather some other stuff like disposable gloves, paint brushes, vinyl sheets and car wax (mould release). Get a good 3M respiratory with charcoal filter for lungs protection from the fumes.
  4. Prepare the mould by covering with vinyl sticker sheetins and then rub on generous amount of car wax. This picture shows our moulds, made of plywood and covered with leftover gloss vinyl sticker sheet and waxed for mould release.

    Cutting the rolls of fibreglass to the right size.

    From left, the bottom of blade, the upface of blade and the half oar (top half and bottom half is the same).

  5. Cut the Fb/G to size, adding 1inch to every edge. My plan was to lay in the sequence of cloth, matt, cloth, matt. Plan and cut all the neccessary pieces for the job. Wear a protection suit and gloves if you wish to not get that Fb/G itch.
  6. Mix polyester resin, note the formula. Dont be too ambitious to mix a big patch for the whole job… it will set before you can finish. I made my resin in batches of 300ml to 450ml and I found that I had just enough time before they become gluey jelly like.

    Painting on the resin, get as much on as possible

  7. Paint the mould surface with resin. Add cloth to the mould, try to straighten out the cloth and let the wet resin hold it down. Paint more resin onto the cloth and tap it with the brush to make sure it soak thru the cloth. Cloth becomes transparant when throughly wet. Add matt and drench more resin until throughly soaked. Excess resin will drip down onto table… some waste is unavoidable.. Repeat the process, add cloth layer, wet out and then add final matt layer.
  8. Repeat step 7 for the other moulds. Mix up more resin as needed. Let the layers and resin dry overnight.
  9. Fb/G shell should come off easily from the waxed and vinyl mould

  10. The Fb/G is ready for popping when dry and hard. Its only a little tacky in some areas on the top surface. We found that Liquid wax was not neccessary to make it less tacky and more handleable.
  11. Saw off 1 edge of the Fb/G on the mould, and lift from this edge. The shells should lift quite easily from the vinyl. Wear gloves when doing this as the insides may still be quite tacky and the edges or some loose strands of fibres are very sharp.   
  12. Cut off the excess Fb/G edges.. Tada! My shells are ready. This picture shows the blade top and blade bottom put together before the excess edges are cut off.

cut off the excess on the sides

Wrinkly surface from the vinyl

This is my 1st Fb/G doings and I think it went pretty well… I didnt get much of itch despite not putting on the suit, only had 2 piercings by the loose strands (and then I decided to wear gloves :p) .. after 3hrs of dabbing and tapping with the brush, my right hand and fingers were crampped for the whole night and so no games for me…  As we were working outdoors, the fumes werent too bad..

This is roughly the shape of the oar blade

Opps, the wrinkly shells. A result of chemical reaction between the resin and the vinyl. Not a problem for me as there are still 8 more layers to be added to the shells.

So we did this and then we were out of time.. more fibreglassing next weekend. .. TBC..


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Sailing 2015: Port Townsend(WA, US) -> Costes Island (BC, Canada)

Sailing 2013: Singapore -> Okinawa -> Kobe

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February 2010
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