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Tom W. Clark prepared this on-line version of the repair instructions provided by Boston Whaler with their hull patch kits. This information prints to standard 8.5 X 11 paper without cropping.

INSTRUCTIONS -- HULL PATCH KITS

(Note: These instructions are a reproduction of Boston Whaler's printed instructions, Dwg. #15000201, Rev. "E," pages 1-4, print date 4/94. They were originally included with their Hull Patch Kits.)

These instructions first give important information on the preparation, mixing and catalyzing of the gelcoat supplied (colored polyester resin) and then information on the use of the gelcoat and other materials for repairs of increasing magnitude (scratches, punctures, and structural repairs both small and large).

  1. Preparation, mixing and catalyzing the gelcoat

    1. First, to ensure complete hardening of the gelcoat, remove cover and immerse the can to within 1/4" of the top in water as hot as your hand can stand (120° - 140°F) for approximately five minutes while stirring thoroughly. This guarantees that a wax added to prevent "tacky" surfaced patches is in solution.

    2. Allow gelcoat to cool down to room temperature before proceeding.

    3. Catalyze gelcoat only after preparing the area to be repaired and just prior to performing the repair to ensure sufficient working time.

      Do not work at temperatures below 60°F!

      Mix in catalyst at the rate of 1/2 graduation (2 1/2 cubic centimeters) on the plastic bottle per 1/2 8 oz. cup of gelcoat or 1 graduation (5 cubic centimeters) per full 8 oz. cup of gelcoat. If the catalyst is in an ungraduated plastic tube use the ratio of 1 teaspoon per full 8 oz. cup. On an average cool day this will harden in the cup in 20-30 minutes. A thin layer on cool work will take longer. At higher temperatures hardening in the cup will be faster therefore catalyst may be reduced to no less than half the amount specified above.

  2. Scratches

    Most small scratches not through the gelcoat can be removed by wet sanding with #600 paper and rubbed down with auto body compound.

    If scratches require filling:

    1. Rough area with sandpaper.

    2. Clean area with lacquer thinner.

    3. Measure out required amount of gelcoat.

    4. Mix in the required amount of catalyst per step 1-c.

    5. Paint on gelcoat over the entire sanded area. Allow to harden.

    6. Wet sand to desired finish, using progressively finer grades of sandpaper. To duplicate original finish, wind up with auto buffing compound.

      NOTE: If you sand through the gelcoat in steps 2-f, scuff the area with #100 paper and repeat step 2.5.

  3. Punctures

    All areas to be repaired must be clean and dry before proceeding. Areas that have salt water in them should be first flushed with fresh water to remove salt and then allowed to dry.

    Small punctures or holes up to 3/8" in diameter may be simply filled with chopped fibers and resin (or resin alone if it doesn't run out).

    Larger punctures or holes up to the size of a dime should be repaired as in the structural repair instructions, but the tapering of the main skin as in step 4-d of Structural Repairs need only be 1/2" away all the around the hole.

  4. Structural Repairs (Holes larger than a dime)

    Neglected punctures or repairs that fail on the boat bottom can "scoop" water with enough pressure to burst the fiberglass skin away from the foam!

    The object of this repair method is to grip both sides of the original skin with the repair to make a strong joint unlikely to pull apart.

    1. If necessary, clean and dry areas to be repaired as in Punctures.

    2. Cut away all cracked & broken fiberglass with a fine toothed hack saw blade. Snap off or grind away the end so it will slip into the foam easier.

      modified hacksaw blade

    3. Fashion a hook from an old file or a piece of heavy steel wire,

      bent file tail

      and clean the foam from under the skin about 1".

      foam carved out

    4. Taper the skin with a disc grinder to a knife edge at the hole starting about 2" away all around the hole.

      tapered edges

    5. Catalyze the gelcoat supplied if a small repair, or regular general purpose resin if a large repair, for about a 1/2 hour gel time (see step 1-c for gelcoat) and then mix in the chopped fibers from the patch kit to a stiff mash.

    6. Stuff this mash into the hole with a stick and tamp well in under the skin. Spread out over the foam and build up the level to the underside of the skin. Before mash is hard, cover repair and tapered original skin with no less than two layers of 2 oz. mat as shown. Note: on dime size or smaller holes skip the mat and simply build up the level of the mash slightly higher than and overlapping the taper of the original skin. Allow to cure.

      mash covered with mat

    7. Wrap some #50 sandpaper onto a block of wood about 3" wide and 8" long and sand the repair down to grade in long strokes overlapping onto the original skin a bit. (Just barely into the outer gelcoat)

    8. Measure out enough gelcoat to cover the entire sanded area, catalyze per step 1-c, and paint over the area. Allow to harden.

    9. Wet sand to desired finish, using progressively finer grades of sandpaper. To duplicate original finish, wind up with auto buffing compound.

      NOTE: If you sand through the gelcoat in step 4-i, scuff the area with #100 paper and repeat step 4-h.

  5. Large Structural Repairs (rebuilding of crushed or ripped away sections)

    In brief, repairs are accomplished by fitting blocks of foam into the damaged areas, carving to original shape and covering with an appropriate thickness of fiberglass. Finally the fiberglass is ground and sanded smooth and sprayed with colored resin for finish.

    1. Use only polyurethane foam since it is not affected by the resin used in "laying-up" the fiberglass for the covering "skin" (Styrofoam will dissolve in contact with resin). Polyurethane foam is obtainable in ready made blocks or in a two-part liquid which when mixed in the recommended proportions and poured into a cardboard box of the required size will yield a good carving foam in a short time. Two pound per cubic foot density foam is recommended in either case. (Isocyanate Product's Isofoam PW-2 or PPG's 6403/6564 are two good foams available in small quantities).

    2. If several blocks must be used, fasten them together with toothpicks, pencils, or even splinters of wood forced into each foam block. Do not glue-up blocks of foam to the required size. The glue line (since it is harder) does not sand down as easily as the foam thereby leaving a high spot or ridge. It becomes very difficult to obtain a smooth looking surface. It is not necessary to achieve a complete absence of voids. The main purpose is to have a surface on which to lay new glass.

    3. After carving and sanding foam to shape (foam should be lower than the surrounding fiberglass skin by the thickness of the skin) undercut and taper the surrounding skin as in steps 4-c and 4-d of Structural Repairs. Stuff mash, prepared as in step 4-e, all around the repair under the existing skin as shown below:

      intersection of replacement-foam and hull-foam

    4. Before mash is hard, cover repair and tapered original skin with no less than two layers of 2 oz. fiberglass mat on large "panel" areas and no less than four layers on areas of severe wear.

    5. Finally grind and sand the fiberglass to a smooth surface flush with the original skin and paint as in steps 4-h and 4-i of Structural Repairs.

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