7/3/17 - Lapstrake Repair

 


        

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In continuing my effort to get caught up on the Dunphy project status... today I'll write about the work done to the lapstrake planks this past spring.  On the exterior side of the hull the lapstrakes looked to be in good shape.  They were made of 3/8" marine plywood (from the 1962 era of marine plywood). The inner plies were made of fir, and the exterior plies were made of mahogany. However, on the inside of the hull the lapstrakes had some damage.  On the very bottom of the boat, a lot of the outer most ply easily peeled away. This was not apparent until I removed the paint. The boat had been spray-painted at the factory, after the frames had been installed. After removing the frames, I found various places of rot in the lapstrakes, most notably behind the frames that were void of paint or any other coating to protect them. The most drastic areas were on each side of the dashboard. The top most three planks on the port side of the dashboard were severely damaged, and the all the planks on the starboard side of the dashboard were severely damaged. Again the severity of the damage was not apparent until the paint was removed... these sections would have to be replaced. For the remaining damaged areas I choose to just replace the veneer as the damaged areas were small and confined. I felt the bottom was still in good enough condition to use the boat even with the outer most veneer delaminated in a lot of places (just on the inside of the boat).... scraping off the peeling veneer, some sanding, followed with an application of penetrating epoxy ought to be enough to keep this boat usable for the foreseeable future. Otherwise I'd end up replacing the entire boat piece-by-piece.

      

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I started with the easier port side and cut out the three damaged planks. I choose the locations of the cuts so that they where staggered and so that they would be scarf jointed (Lou makes it look easy) back together fell over a frame in order to securely fasten them back together.  Next I proceeded with the starboard side, leaving a concerning gapping hole in the side of the boat.

        

        

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I carefully cut away the damaged section so that they could be used for templates in making the new pieces, making the long enough to allow me to plane a scarf joint.  The new pieces were made from 3/8" Okoume marine grade plywood (BS1088 Hydrotek). After shaping the new piece, I carefully planed a 12:1 scarf joint on both the new piece and the adjourning ends of the planks on the boat. Once fitted, they were epoxied into place and clamped, one end at-a-time, to help ensure a fair plank (no hollows, or bulges along the plank line were the new piece fitted to the existing plank). Doing this one end at a time made for long process of repairing these planks.  The planks, where they overlapped each other, were glued with 3M 5200 Sealant/Adhesive.

        

        

        

(click on an image to zoom in)


 

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