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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 600g biaxial cloth with 45/45 degree strands from Composite24 and West System 105 epoxy with 206 fast hardener at a local marine store.

Cutting fabric

The work was done in sections, we started with the bilge bottom/floor while the keel nuts and washers were removed. It got 4 layers that come up 10cm at the bilge sides. This area gets most of the loads and we wanted to reinforce it by connecting the fabric on the bottom to the one to be layed on the sides.

4 layers on the bottom

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.

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.

Section around the mast step

In the biggest 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 larger bilge pump and can access all the keel nuts with a torque wrench.

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

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

Covered with peel-ply

Floor beam glassed down to the bottom

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 corners to have a more smooth curve and avoid air bubbles.

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 over it.

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

Cutting fabric for the new structural member

Now glassed in

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

Fairing around the mast step

Two layers of fairing compound on

Second coat of Danboline

Finished new structural member

Finished middle section with the glassed down floor beam and opened drain hole

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)    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    350 kr
Total: 15026kr (~1600 USD)


  1. Azért ez elég jó kis összegbe fájt.

    1. Hát minden viszonyítás kérdése. Valóban nem volt olcsó, de a hajó értékéhez vagy egy műhely munkadíjához képest igazából elenyésző. Viszont rengeteg időt is rá kellett áldozni 🙂


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