marineSOLUTIONS

Your Marine Surveyors in the Eastern Mediterranean…


REPAIR of BALSA and CORE OSMOSIS

Problem:

The owner of the Contest sailing yacht contacted marineSOLUTIONS because of a broken starboard rubrail and two blisters greater than 10 cm in diameter that had appeared on the hull. These bubbles were about 15mm thick. Two wet water marks running down the side were apparent. When the blisters were opened during our inspection, they were found to contain liquid with a pH in the aceitic range. Salt seawater that is trapped between polyester layers may cause hydrolysis, or as it is also known, osmosis.The well-known tell tale signs of osmosis: are blisters filled with liquid that smells like vinegar. We determined that this liquid was coming from the balsa core and had entered via the delamination on the starboard rubrail.

Procedure:

Repair work would entail a drying out period of at least 4 months. The yacht was first hauled to dry-dock. The paint and epoxy were removed from the necessary areas on the starboard side using our gel plane machine, which exposed the outer layer of the balsa sandwich, and the boat was left to dry out naturally.

Work step 1:

A few balsa samples were taken from a small area on the starboard side of the hull and examined for rot.

Work step 2:

The designer of the yacht was contacted and the problem was explained to him. Information was obtained about the structural details of the balsa and upper layers (paint, filler, thicknesses of balsa etc.)

Work step 3:

The entire area affected by water was cleaned of paint and filler to expose the uppermost layer of the sandwich.

Work step 4:

The sandwich was allowed to dry naturally, and the level of moisture was checked regularly.

Work step 5:

When the moisture had decreased to acceptable levels, the upper layer of the balsa was impregnated with an antifungicide.

Work step 6:

The whole of the exposed area was covered with a coat of epoxy and fibreglass to give reinforcement.

Work step 7:

After this, baxial fibre was applied to the layers that would provide the necessary reinforcement in connection with the boat’s structure.

Work step 8:

The glassed surfaces were covered with epoxy filler, levelled with a gauge and sanded smooth by longboarding.

Work step 9:

The areas that had been repaired were sprayed with gel coat to match the original colour, and the surface was faired and polished.

Work step 10:

Layers of waterproofing epoxy were applied to the hull below the waterline to protect this area.

Work step 11:

The boat topline was painted with two good coats of paint in its original colour.

Work step 12:

Three coats of selfpolishing antifouling paint were applied.

Work step 13:

The yacht was launched and handed over to the owner.

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