Sunday, January 3, 2016

October 2007: Repairs begin -- Adventures in "Delignification"

As I mentioned earlier, Compadre is scheduled to return to the yard soon for our planned engine swap.  Target time is now the first week in February.  As that time draws closer, I thought it might be useful to review the work done in earlier trips to Port Townsend in 2007, 2010, and 2013.  I'll start with the earliest work in this post, then devote separate posts to the later two projects.

During our pre-purchase survey in mid 2007 it was noted that the wooden blocks supporting the rudder posts were badly deteriorated and required replacement.  The cause was something called delignification, caused by too much zinc.  For those of you non-boaters, sacrificial zinc anodes typically are attached to the propeller shafts and rudders to prevent corrosion from damaging these expensive components.  Corrosion instead attacks the zincs, which are periodically replaced.  With fiberglass boats, owners don't have to worry about putting on too much zinc, and not much thought goes into selecting the size of zincs and how many to use.  In wooden boats, however, the situation is quite different:  Use too little zinc and the bronze props or rudders corrode; use too much and the wood near these metal parts is attacked by sodium hydroxide (lye), and the hard parts of the wood basically dissolve, leaving a spongy mess.

So after suffering from too much zinc for who knows how long, in October of 2007 Compadre made the trip to the yard in Port Townsend to have the rudder blocking replaced.  No big deal; just a few days on the hard, a little marine carpentry, then we'd be back in the water and good to go.  Well, as with most wooden
boat projects, we didn't know the full extent of the problem until we started removing parts.

Plank sections removed, where rudders used to be.

Inside looking aft with rudders and planks removed.
We quickly learned that not only were the rudder blocks shot, the planks beneath them were also mushy, as were the floor timbers and frames adjacent to them.  In a matter of a few minutes our short trip to the yard turned into an extended stay.  After some consultation with Brian Wentzel, our shipwright at Freyja Boat Works, we decided it made sense to do whatever work was needed in the lazarette area while we had things taken apart.  Thus the project grew to include replacing four floor timbers, sistering three pairs of frames, and replacing the bad plank sections above each rudder.
Old floor timbers damaged by rot and delignification.
Once the old wood was removed, Brian went to work fashioning the replacement floors and frames -- the floors from purple heart (a hard, dense, rot-resistant wood) and the frames from steam-bent white oak.  Soon the work inside was finished, and all that remained was to replace the plank sections, plane them fair, and prepare for new bottom paint.
Four new floor timbers.
Brian planing the replacement plank.
Next we replaced the rudders, put a new coat of white paint on the topsides, and had the bottom painted.
Rudders back in place and new bottom paint.
Looking good and ready to go.

Before relaunching, Brian and I discussed Compadre's general condition and made a list of things that would need attention in the future.  This was my first experience with a wooden boat project, and I was very pleased with the outcome.  Brian and his partners at Freyja were very professional and the workmanship was first rate.  Needless to say when it came time for future work, we knew where to turn.

Having done all this work, the last thing we wanted to do was put on too much zinc again.  We consulted with two marine electricians to learn as much as we could about electrolysis and zinc protection.  Where that took us will be the subject of a later post.  Suffice it to say that we have learned a lot, and the solution involved more than just bolting on new zincs from time to time.  Stay tuned.

Sadly, Freyja Boat Works is no more, the three partners having gone their separate ways over the years, with Brian moving on to producing fine wooden furniture.  Fortunately Arren Day, one of the Freyja partners, has recently joined the Port Townsend Shipwrights Coop, and Compadre continues under his expert care.  He will be heading up the engine replacement project next month.

In our next post Arren does major repairs in the forward section during our trip to the yard in 2010.

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