BuiltWithNOF
Dragon Fly

Health Care Reform, Insurance Reform, Quality

Roger H Strube, MD

Tom Anderson, one of my friends on the multihull news group at Steam Radio recently purchased a fixed ama Dragonfly that was in the end stages of restoration. When he picked up the boat he noted the Dagger Board “sloshed”. This page is an account of the repair of the board.

The work was done at my Hobby Work Shop (a.k.a., “Dr. Strube’s Museum of Unfinished Projects” or “The Taj Garage”). Initially the board was placed on horses outside with the trailing edge down to allow drainage of the internal water. A simple resurfacing of the trailing edge to stop the leaks was anticipated. Mean Ol’ Mr. Gravity worked but not very well. After a week out in the sun lots of water remained as the drips fell out of the board slowly. The board was returned inside, jigged trailing edge down and a 1/4” hole drilled in a skin about 3” from the trailing edge. An air hose nozzle was applied using about 45# of pressure. The water flowed a little faster, the board “swelled”, creaked and ten “POP”. Actually it was more of a “BANG”. All the water dumped on the floor. This fortuitous accident actually was beneficial as it opened up about 3 feet of the trailing edge bond that was weak and leaking in places. The edge was wedged open and lots of fresh water and detergent flushed out the inside of the hollow board.

A second benefit of this long narrow split was that it allowed us to inspect the inside of the board. The board had swelled under air pressure as the bond between the skins and an internal longitudinal strut had failed on the starboard side. Although the strut is only minimally structural in a stiffening sense, it does provide separation and bonds the two sides of the board together providing the strength of a “sandwich” like a foam core. I believe this separation failure decreased the board’s resistance to flex and, after many cycles, the trailing edge began to fail.

Following the clean out and drying, the trailing edge was wedged open and a mix of epoxy (West 105 / 206), cotton fibers and chopped glass was applied to the surfaces of the skin and strut. The mix was made with the viscosity of cold syrup so it would hang in an area for a while before sagging down. The syrup was applied at and above the failed joint, the board was clamped (see pics below) and Mean Ol’ Mr. Gravity was allow to do his work pulling the excess above the joint down onto the strut. The edge was wedged again and another mix was poured into the board. The strut is short of the bottom by several inches so this pour was allowed to flow over the strut (top of the board tilted way up) down to the leading edge of the board at the forward lower corner. The board was then tilted back and forth to allow the mix to flow along the entire leading edge to assure strengthening of this bond. A second pour was applied to the strut and the board tilted up and down so the mix would flow across the entire joint. Finally, a looser mix of epoxy, cotton fibers and chopped glass was applied to the inside of the trailing edge and down several inches into the void. The edge was then clamped and the board turned over so the clamped trailing edge was down. More tilting to allow Mr. Gravity to do his job.

The board was now structurally restored but I decided to foam the interior using Great Stuff available at any Home Depot (the high density, low expansion stuff). This would keep any water out and provides a very ridged foam interior that should provide a little more resistance to bend. Several entry holes were drilled and several smaller pressure release holes drilled near the trailing edge. The board was foamed until some foam came out of the relief holes. When you tap the board it now sounds like a solid oak door. The holes were ground out with a countersink and undercut then filled with “All Metal” a polyester/aluminum power water resistant body filler. The board was then faired.

BTW, I don’t want to hear any crap about the use of Great Stuff foam. If you have a chance to repair a hollow board, you can do it any way you feel will work best.

The rudder was also chipped by the OB propeller and was repaired using “All Metal” and a coat of “Gel Paste”. Both parts are now in Tom’s garage collecting dust until he can get to painting them.

Roger H Strube, MD

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