SJ23 Tech Tip B28, (Issued 2011-08-16) Rich Lowe

Index

Repair a Hull Damaged by Trailer Rollers.

I bought an SJ23 that hadn't been licensed in 18 years and apparently spent all of them resting on a trailer equipped with rollers.  The hull was also partially filled with water.  Predictably this caused large indentations in the hull.  I hope nobody else is confronted with this abuse but if you are, there is a method to remove the "dimples."

Notice the dark roller marks on the hull and the general depressed area around them.  The dimples did not pop out on their own after this roller was pulled back.  Dimples this deep will slow the boat.

SOLUTION

  1. Support the hull with jacks under the keel.  I also used a steel framework attached to the toe rail to keep the hull upright while keeping the damaged dimple area clear.  You must have access to both sides of a dimple, inside and outside the hull, to remove them.

  2. The chain plate bulkheads were rotten so they were replaced.

  3. Find a technique to apply and hold pressure to the dimples from inside the hull.  I used a (2x4)" and a bottle jack to push between the cabin liner and the hull liner.  At the top I used plywood pads backed up with Styrofoam bead board against the hull.  At the bottom I used inner tubes between the hull liner and the hull.  In both cases the inner tubes and the foam were used to spread the forces evenly.  The bottle jack can apply force with total control.

  4. Heat the hull to 1500F with a radiant propane heater and verify the temperature with an infrared spot reading thermometer.

  5. Apply pressure to the inside of a dimple till there is about 1/2" displacement (outward).  Hold the pressure while the hull cools.  If necessary, reposition the pressure, reheat the hull and push a little bit again.

  6. When the original hull shape is restored (or it won't bend any further) heat the affected and surrounding area uniformly with pressure applied and then let it cool completely while holding the pressure.  Remove the pressure the next day or when the hull has cooled to room temperature.

The 1500F temperature made the FRP flexible enough to bend without sign of stress cracking, odour or chemical change.   There was very little spring back when the pressure was removed.   Afterwards I applied epoxy barrier coating as per WEST Systems instructions.  She is sailing again, apparently none the worse for the experience. 

Rich Lowe
Sandpoint, Idaho
 
"With full credit given to one of my boat builder mentors, tooling professional, and pretty much anything fibreglass, Dick Williams was the fibreglass wizard at Clark.  A great teacher, the best damned gel coat color matching person I have ever seen (he is color blind), and he taught me a trick about easing dimples out of a boat.  Dick said that a tooled shape will always seek to return to that shape once the offending stress is relieved.  His approach was to use a heat lamp on the deformed region.  Not a heat gun, to be clear: just a flood-light style of gentle heat.  His method was one of patience and persistence, gently relaxing the laminate to allow it to become pliable and compliant, reawakening the memory of the laminate to the original position.

If you consider how this dimple got there in the first place, Dick's method is exactly the same, but in reverse.  A suction cup lightly loaded can also assist as the laminate softens.

Dick is getting up there in years, and I hope he remains in good health.   What a guy.  Clark Boat would have been in a world of hurt without his leadership."   Glen Moore.
 

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