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Bilge reinforcement - Part 2

After careful surface preparation, the bilge reinforcement project continued with laying the new laminate. I consulted with West System on what fabric to use and they suggested biaxial cloth without chopped strand matting. The biaxial cloth is very strong and CSM would just add weight. We bought a 600g biaxial cloth with 45/45 degree strands from Composite24 and West System 105 epoxy with 206 fast hardener at a local marine store.

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Cutting fiberglass fabric

The work was done in sections. We started with the bilge bottom, while the keel nuts and washers were removed. It got 4 layers, which goes up 10cm at the bilge sides. This area gets most of the load and we wanted to reinforce it by overlapping the fabric on the bottom with the fabric layed on the sides.

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4 layers on the bottom of the bilge

In theory these types of reinforcements are suggested to be done either with the keel dropped or while the keel is hanging so it's not compressing the joint while the boat is standing on the keel. The idea is to avoid building in stress into the laminate.

After the bilge floor cured and the keel washers and nuts were reinstalled we launched the boat and continued the work in the water, so the keel is hanging and there is no stress built in.

The second section was the area around the mast step. It has the most difficult access, but we managed to lay up laminate on both sides of the mast step without cutting up the floor.

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Section around the mast step

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Another angle of the mast step area

In the largest middle area we added 4 layers of fiberglass on the sides, then re-connected the floor beams to the hull with 6 more layers. We decided to add one new half-height structural member and glass down one of the floor beams till the bottom of the bilge, so it can act as a second structural member. This way we can still have enough room aft of this beam to fit in a bilge pump, and can access all the keel nuts with a torque wrench.

The side of the floor beam got 8 layers and some extra strips to bond it to the hull. We used a bonocell piece wrapped in a plastic foil as a backing plate while laying the glass to the "open area" of the floor beam. Epoxy doesn't stick to plastic foil, so the backing could be easily removed after it cured.

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4 layers on the sides and 4-6 more layers on the floor beam attachments

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Covered with peel-ply

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Floor beam glassed down to the bottom of the bilge

In the galley we added 3 layers as it's not a structural area. At this point we ran out of fabric and epoxy and we couldn't find any 600g biaxial fabric readily available so we decided to go with 800g triaxial (0/45/45 degree strands) which we bought at Epotex. As this is a more thick fabric, we applied thickened epoxy to all the corners, to have a more smooth curve and to avoid trapping air bubbles.

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Reinforced between the galley and the engine

The new structural member got a 15cm bonocell core based on cardboard templates, which we glued in place with thickened epoxy. Then we laid 6 layers of 800g cloth over it.

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Three 5cm thick bonocell foam core glued together and into place

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Cutting fabric for the new structural member, to fit onto the bonocell core.

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New structural member glassed in

After it cured, we sanded everything, then faired the whole bilge with West System's 407 low density filler in two layers (sanded it between layers), then applied 3 layers of white Danboline paint as a final finish.

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Fairing compound around the mast step

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Two layers of fairing compound on

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Second coat of Danboline bilge paint

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Finished middle section with the glassed down floor beam, extra structural member and opened drain hole

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Finished aft section

This was our most difficult boat project so far but we managed to do it!

A professional repair at a boatyard would cost at least 100.000 SEK for a job like this and it's not sure they would cover all the areas that we did. We spent a little over 15.000 SEK in materials, plus lots of our time.

Here are the detailed costs (in Swedish Crowns):

  • Keel bolt washers, laser cut 65x65x6mm (8pcs) 1100 kr
  • Fiberglass biaxial 600g 15m2 1000 kr
  • Fiberglass biaxial 800g 5m2 500 kr
  • Peelply 5m2 300 kr
  • West System Epoxy (3x6kg) 5600 kr
  • 406 colloidal silica 300 kr
  • 407 low density filler 350 kr
  • Distansmaterial (bonocell) 700 kr
  • Epoxy rollers 300 kr
  • Protective suit (4pcs) 400 kr
  • Nirtile gloves (lots of them) 400 kr
  • Mask dust filters 300 kr
  • Infrared termometer 399 kr
  • Epoxy pumps 300 kr
  • Scissors 80 kr
  • 1/2" breaker bar 179 kr
  • Vacuum cleaner with HEPA filter 500 kr
  • Torque wrench 40-210Nm 399 kr
  • Sander (mouse type) 350 kr
  • Thin belt sander 500 kr
  • M20 30mm long socket 150 kr
  • Sanding paper (lofs of various types) 500 kr
  • Papercovers 69 kr
  • Danboline paint 350 kr
  • Total: 15026kr (~1600 USD)