The material removed contains all of the osmotic fluids on this hull. Next step is to apply the HotVac system and lower moisture content of the hull.
For detailed information and more photos scroll down this page.
Thai-Kiwi Marine Company Limited |
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Professional boat building in
Thailand Building power boats, catamarans, yachts in composites and steel Chris Craft replicas, Coastworker 28 |
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This photo shows a member of our team
using the GelPlane to remove outer layers of chopped
strand mat to a depth of 4mm.
The material removed contains all of the osmotic fluids on this hull. Next step is to apply the HotVac system and lower moisture content of the hull. For detailed information and more photos scroll down this page. |
Initial Diagnosis.Budget for the planned work normally needs to be determined as accurately as possible prior to work commencing. The vessel should be slipped and test peels done in several places. A professional surveyor with sound knowledge of osmosis problems and repair should be contracted to report. The boat owner will then have a realistic view as to the degree of osmosis repair required. |
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Peeling the hull using a Gelplane.This hand-held tool will cut to 1.25mm deep by 75mm wide and is a fast, efficient means of removing affected gel-coat, chopped strand or woven roving. The photos below show the hull of a 90' power boat undergoing the process. Total peeled area for the vessel amounted to 7,500 square feet and this phase of the work was completed in 5 weeks.Photos show peeling in progress, a blister void at 3rd peel, 4 layers removed and a section for repair.
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Drying and post-cure.The object is to get the moisture content of the hull down to an acceptable level for relaminating. Post-cure is also desirable to dry/remove any uncured resin and osmotic fluids. The HotVac system which uses a combination of heat and vacuum is an efficient method of drying and post-cure. All internal moisture must be removed from the hull as soon as the vessel is slipped. Floors are lifted and air-flow through the interior is maximized by opening hatches, use of fans etc.The HotVac system is fast but a stabilisation period is recommended whereby the hull is allowed to air dry inside and out for up to a month. Sometimes, when moisture has penetrated stringers and other foam-filled structural areas, penetrating infra-red heat will be required. These photos show moisture from internal stringers and the HotVac system in operation.
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Preparing the work area.Working on a covered slipway presents problems such as lack of height and space, difficulty moving equipment etc. To improve workspace the whole area under the vessel must be floored with plywood sheets. A preparation [wetting-out etc] room is made under the stern of the boat.Sand-blasting.In order to remove all dried, potentially reactive material from the original lay-up the hull is sand-blasted with garnet grit. This process also gives an ideal 'keying' surface for any epoxy to be applied.
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Water-blasting.The hull is high pressure washed several times after sand-blasting to remove any acidic material. Ph level is tested and water washing continues until Ph is the same as the water being used for washing. The hull is then left to dry for 24-48 hours.
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Tenting for environment control.If local temperature and humidity are not within the accepted limits for epoxy application the hull must be tented so dehumidifiers and air conditioning may be used for environment control. A tent is initially built for sand-blasting to control emissions. To help control temperature and humidity a 2nd tent is built inside the 1st to provide double insulation. Humidity readings outside in HK at this time range from 84% to 100%, temperature is normally around 32C. Ideal working conditions for applying epoxy and laminate are humidity below 70% and temperature 23-25C. With current outside conditions a partitioned room 30' x 25' needs four 20,000 Btu air conditioners and two dehumidifiers to maintain ideal working environment.
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Relaminating and vacuum baggingA wetting-out machine makes relaminating easier and much faster. The triaxial cloth is 50" wide and sheets up to 14' in length were applied when laminating the boat in the pictures. Photos show our laminating team in action; laying up 10-14' lengths over 2 chines takes skill and co-ordination. Peel ply was applied on top of the laminate and vacuum bagging was used to get maximum bond. Advantages with use of peel-ply are:- superior finish is attained and additional layers of cloth or resin can be applied upon removal of the peel-ply, after initial cure, without any further surface preparation.
The hull being repaired requires 4 lay-ups of 750gm triaxial cloth to replace material removed by peeling. Each lay-up is overlapped along the hull and on alternative sides at the keel. The previous days work has the forward edges lightly sanded Photos below show laminate layers, peel ply and the vacuum bag set up.
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