Before techniques are considered, the question of logistical support and obligations should be addressed. If the new FRP boatyard is the only one in the country and particularly if it is set up using scarce government resources, then it will have an obligation to look after the national interest and investment by taking on FRP repair work no matter how difficult or distant from the yard.
It takes considerable courage on the part of an owner to spend borrowed money on a vessel built of an unfamiliar material. He deserves to be supported by the national repair facility even if considerable effort is needed. In the case of a small boat this will not prove too difficult, but if a 15 m vessel is hauled and immobilized 150 km away, then these obligations need to be addressed seriously.
Figure 38 Hauling out a fishing vessel
Small vessels can be considered as those which can be manouvered by a reasonable amount of manual force into a position in which they can be repaired. These include canoes, outboard powered boats and others which are brought ashore daily. Repair work on the beach is not unusual but vessels which have been severely damaged and require much repair are preferably moved to the yard where a more comprehensive range of skills and equipment will be available. In a remote location it is unlikely that there will be any source of electrical power so all work will be manual. If a large vessel has to be repaired at a distant village then a small team may have to live and work at that village for several weeks. Logistics should not be underestimated but neither should the owner be exploited by any monopoly held by the yard.
Once a survey has been carried out and a price has been agreed between owner and repairer, then the work can begin. The boat should be manouvered into a position away from the water and arranged so that good working access is available. Shade will keep temperatures reasonable for both men and materials. The environment should be as clean, tidy and dry as possible and kept so.
Maintaining the skin of an FRP vessel in good condition means keeping the surface gelcoat sound so that it protects the reinforcement layers below. “Maintenance free” is often seen in advertising FRP products and this is true within limits. An FRP boat left unused and unattended for a number of years will remain unchanged except for some dulling of the gelcoat shine which may be restored by polishing. Depending on the type of gelcoat and colour pigment used an otherwise sound gelcoat may require spray painting when polishing no longer restores a shine. Further than this, regular checking for damage due to abrasion, impact damage, or attack from fuels or chemicals is all that is required. Anti-fouling paint is applied in a similar to wooden boats but new boats may need de-waxing and etch priming. Burners should not be used to remove old paint and any scraping must not damage gelcoats.
Repairs to FRP vessels all have in common the necessity of removing old, damaged material back to areas of sound FRP to which a bond can be made. Beginning at the outside of the vessel, the gelcoat can have the following faults, most of which can be repaired simply by sanding back the gelcoat and painting new on.
WRINKLING this is caused by the heat released by the following laminate immediately attacking an undercured thin gelcoat (Figure 39).
PINHOLING small air bubbles trapped during the cure show up on release (Figure 40).
POOR ADHESION occurs when a gelcoat is left unreinforced for too long. A weekend is long enough (Figure 41).
SPOTTING all over the gelcoat layer small spots will indicate poor mixing of one of the components.
STRIATIONS indicate inadequate mixing of the colour pigment.
FIBRE PATTERNS if the gelcoat is thin or the reinforcement is applied before the gelcoat is sufficiently cured the roving pattern may “print through” and be visible in the gelcoat when the hull is released (Figure 42).
FISH EYES caused by the gelcoat “de-wetting” from the polished mould surface in spots. Occurs mainly when silicone based waxes are used. These, in particular car waxes, should be avoided (Figure 43).
BLISTERS an indication of delamnation between layers on older vessels. Of various causes and potentially the most serious of problems (Figure 44).
CRAZING usually indicates a gelcoat which is too thick and has crazed during flexing of the hull (Figure 45).
STAR CRACKING once again due to an overthick gelcoat but this time it must have received an impact from the inside (Figure 46).
INTERNAL DRY PATCHES areas where resin has not penetrated (Figure 47).
LEACHING a serious fault. Severe weathering can remove a poor resin from surface of a laminate (Figure 48).
YELLOWING discoloration of clear or light gelcoats.
It is apparent fro this list that great care must be taken in the formulation and application of the gelcoat and that it is the barrier between the environment and the structural laminate of the hull and not simply the shiny coloured surface of mouldings. Wearing away of the gelcoat is caused by abrasion. This occurs when materials harder than cured polyester consistently rub on the same area. This may be the anchor chain or heavy gear being hauled over the side of a fishing boat. It does not take long to scratch the thin gelcoat below which the laminate will be revealed. At this point, particularly if the damage is below the waterline, corrective action should be taken as descpite FRP being a plastic material, water can slowly penetrate the laminate and render it “rotten” by seeping along pathways created by the fibres of the reinforcement. A correctly designed vessel should have adequate protection in areas where abrasion can be predicted but problems can occur when a boat is inexpertly converted from one fishing method to another.
Accidental damage is relatively easy to repair by the hand lay-up or contact moulding methods. If the vessel is locally built then the technicians performing the repair can be expected to be familiar with its construction and be able to put back the rquired reinforcement. If the vessel is imported and unique to the country, then samples may have to be cut out to ascertain exactly what the hull is made of. A sample is taken by drilling with a hole saw and burned to remove the cured resin to reveal the reinforcement it contains. If it is found to contain a core such as balsa, then a suitable replacement must be found. In an emergency, a solid laminate can be used but would be heavier and more expensive.
Figure 39 Gelcoat fault - wrinkling
Figure 40 Gelcoat fault - pinholing
Figure 41 Gelcoat fault - poor adhesion
Figure 42 Gelcoat fault - fibre patterns
Figure 43 Gelcoat fault - fish eyes
Figure 44 Gelcoat fault - blisters
Figure 45 Gelcoat fault - crazing
Figure 46 Gelcoat fault - star cracking
Figure 47 Gelcoat fault - internal dry patches
Figure 48 Gelcoat fault - leaching
Some typical damages of vessel hulls are shown in Figures 52, 53, 54 and 55.
Hacksaw, chisel, file, mallet, grinder/sander, wet-and-dry paper, wax and polishing cloth, plastic sheeting, plastic bucket and small mixing containers, laminating brushes, sharp knife, tape measure, paint scraper, acetone, catalyst measuring bottle.
Figure 49 Repair technique for impact fracture
These appear as a crack which may extend as far as the reverse side of the laminate.
The fracture should be enlarged from the surface of the impact into a V-shaped groove, ensuring that all the damaged area is removed to the full depth of the crack. It may be necessary to penetrate the slot fully.
Abrade the back surface of the original laminate for about 75 mm in all directions from the slot and remove loose material.
Cut four strips of CSM each 20 mm larger than the previous. The smallest should be 20 mm larger then the repair.
Prepare resin 2.5 × weight of CSM.
Apply resin and CSM to the back of the repair area starting with the smallest piece. Caution not to push the CSM through the slot when consolidating. Allow to cure.
From the gelcoat side fill the slot with overlapping strips of CSM to just below gelcoat level. Allow to cure.
Sand smooth and fill with pigmented gelcoat. Sand and polish smooth when cured.
Holes (Access to Both Sides)
Figure 50 Repair technique for punctures
All jagged edges and damaged laminate must be cut out to leave a clear hole in sound FRP.
Edges must be filed down to form a wedge with the fine edge towards the outside. The interior surrounding area is sanded down and dust, grease and damp removed.
Reinforcement equal to the original laminate is cut to shape and layered and the correct weight of resin is prepared. Further layers are prepared to cover the patch and surrounding sanded area on the inside.
The essence of obtaining a good repair is to arrange a smooth surface flush with the gelcoat on which to work. For small repairs a piece of formica, aluminium, hardboard as well as a thin laminate offcut can be used and secured firmly to the gelcoat side of the repair with self tapping screws. For larger holes the curvature of the hull complicates the process and may require a facia board or “splash” to be moulded from an identical vessel to achieve a compound curved surface which will fit the repair area exactly. The facia board, no matter what size, must fit exactly over the edges of the repair area with no gaps. Fastener spacing should suit the application and for large holes with a heavy FRP facia board bolts may need to be used. If the required area of a sister vessel is not available because of a skin fitting for example, then an area immediately adjacent might be used to lift a splash which, with a little persuading, can be fastened flush with the hole. This is possible as hull shape usually changes only gradually along the length of the hull. The opposite side of the same vessel cannot be used.
Before fixing over the hole the facia board should be well waxed. If PVA release agent is used also to aid release of the facia board after the repair is complete, then care should be taken that it does not contaminate any prepared surface to which a strong bond is to be made.
The repair is then continued as if a hull were being laid up in a mould, which is what the facia board is providing. The join line on the inside should be overlaid as in the previous repair once the board and any fastenings are removed.
If the board was tightly fastened around the join line little gelcoat repair will be required. Any remaining gelcoat imperfections and fastening holes should be hand finished and polished.
Repairs to Blind Panels (One Side Access)
In some cases it will be impossible to reach the reverse side of a laminate.
The hole should be cut out as before and the blind (unseen) side cleaned and sanded as much as possible by reaching through the hole. The edges are beveled with the fine edge innermost.
THE NEXT 3 STAGES REQUIRE GOOG TIMING. A small laminate the size of the sanded surrounding area is prepared comprising of two layers of light CSM and no gelcoat. A third piece of light CSM is prepared but not used at this stage.
At the gel stage the double layer is released from its formica sheet mould and with some speed, the third previously prepared piece of CSM is applied to the double layer's rough side with an over-catalysed or “hot mix”. A screw or wire is then inserted side to form a grip or handle protruding through the rougher wet side. WORK FAST!
Utilizing the flexibility of the double layer at its gel stage, it is slightly folded and pushed through the smaller hole. When it springs back into shape, the screw or wire handle is used to hold it against the inaccessible sanded area until the hot mix is cured and the patch adheres to the inside face. Grip can then be released (Figures 24–25).
The screw is then removed or sawn flush or the wire withdrawn or clipped and the repair continued as previously described. This method requires that the accessible side receive heavier overlaying than simpler methods.
Where the hole is larger, the laminate very heavy and the panel has little curvature, the method illustrated above may be used. In this case a rectangular hole is cut and a ply pad used instead of the thin flexible CSM panel. It can be only very slightly larger than the hole as it must pass through diagonally.
FRP vessels have a lifespan proportional to the amount of care and attention that is given to them. However, a recent development in some older FRP vessels is the blistering of under water gelcoat surfaces. This is referred to as osmosis.
No gelcoat is entirely waterproof and it is possible for water to collect in small air bubbles which are formed during the moulding process. Water in contact with soluble substances in the gelcoat forms an acidic solution and an osmotic process then attracts seawater through the outer gelcoat membrane which leads to a blister on the hull surface. Water can also be drawn down glass strands which are too close to the surface also causing blisters as does a gelcoat which has been over mixed and aerated before application to the mould. Both of these can be confused with osmosis. To remove any offending gelcoat requires either grit or slurry blasting the underwater surfaces. A solventless epoxy paint should then be applied in its place. Use of an Iso-NPG resin gelcoat (Isophthalic neopentyl glycol) during original manufacture should prevent osmosis.
Figure 51 Repair technique for blind panels
Figure 52 Hole due to grounding on anchor
Figure 53 Collision damage to bow
Figure 54 Abrasion damage to gelcoat and laminate
Figure 55 Severe impact damage to side
Twenty years is often quoted as the lifespan of an FRP vessel. However, there are many vessels older than this still very sound and in service. It is also obvious that an FRP pleasure boat which is well maintained and rarely used will have a longer service life than an FRP trawler in daily use and repaired only when something breaks. The fact is that an FRP trawler is more likely to become worn out through rough handling, lack of maintenance and breakages than any sudden structural failure of the hull laminate after a fixed period of time.
It is tempting to sheath an old, planked wooden boat in FRP to stop persistent leaks, prevent rot or extend its life but this is generally not recommended. In this form and condition the many pieces of wood which make up the hull have varying moisture contents both from the inside to the outside and particularly from deck level to keel. A sheathed hull may appear an improvement when first coated but it is only a matter of time before it begins to del aminate. Rot can be accelerated by the sealing in of moisture.