Hull Inspection/Osmosis Check - Marine Surveyor, John Cherry Yacht Surveys AMYDSA

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Hull Inspection/Osmosis Check

Types of Boat Survey


There are several stages of inspection used to assess osmotic damage to a hull.

  • Moisture meter readings are taken using the Sovereign Quantum Marine (Moisture Meter), which will take both shallow and deep readings. Low readings usually rule out the possibilities of any ongoing problems and whilst it is hard to draw conclusions from just high moisture readings alone, recommendations to investigate further would be based other influencing factors

  • Looking for cracks, crazing and pin holes as these may be letting water into the laminate and accelerating hydrolysis.

  • Identify the size and frequency of any blisters if present as the diameter is often associated with the depth of the blister and is a rough gauge of the depth of the hydrolysis. It is risky to place too much emphasis on blister size but generally bigger blisters mean bigger problems.

  • Looking for sediment piles as these would indicate active hydrolysis, even though there may be no blisters visible.

  • The hull is then tapped over at random with a small hammer to check for any serious delamination.

Osmosis Treatment:

Following on from the initial inspection and with further investigation being recommended it will be necessary to open up the laminate in order to inspect the surface below the gelcoat to access the full extent of the problem:

  • Firstly an area about 300-600mm below the water line will be chosen and an area of 200 x 200mm will be ground out to expose the blisters.

  • Moisture and hardness readings are again taken with the process of grinding and inspection will continue until a layer is reached which is in good condition and unaffected by water.

  • Following a further inspection, full recommendations will be made:

  • This will involve the removal of gelcoat and quite possibly laminate/s back to the unaffected surface.

  • The hull will then need to be pressure washed with fresh water and steam cleaned, this is to remove salts and other contaminates which are present in the laminate due to osmosis. The boat will then either need to be moved into a shed or the hull tented up.

  • The laminate must be allowed to dry out to an acceptable level before the paint treatment system can be applied and this can take from 1 to 3 months.

  • Once the laminate is dry, the right temperature, humidity and surface temperature will have to be achieved before the treatment can begin.


For a quotation you can fill in the questionaire form, click on this link Quotation Request or alternatively telephone me on either 07982 239039 or 02392 598084.

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