I am a recent graduate of Chapman's School of Seamanship Marine
Surveyor course. One of the things I was looking forward to learning
about was the treatment of rot in wooden hulls. The school didn't
spend much time on it because (and it's true) the majority of the
hulls I survey are FRP. But! I own two beautiful 35 foot wooden motor
yachts that I am restoring. I didn't want to do all this work and then
have things go wrong in the "basement". So, after months of study,
this is the treatment that I believe will keep these two old beauties
sound for another 15 years. After opening up the boat and installing
access to most of the interior of the hull, I pressure washed the
whole interior. Pumped the water out and let it dry. Then I boiled up
on the stove a mixture of antifreeze, boric acid, and borax. I spent
about $50 to make about 10 gallons, of which sells for around $90 a
gallon at the marine supply. The glycol in the antifreeze LOVES water
and absorbs into any wet surface, carrying the boric acid/ borax mix
into and wet or moist wood. Oils and epoxies will not go into damp
wood. Thinking it out, this is the only way I could think of to take a
strong anti-fungus to any wet parts. After drying it out (summertime)
I am now cooking boric acid into raw linseed oil and maybe getting a
little packets of anti fungus that the paint store sells to add also.
Fungus and rot LOVE linseed oil to eat. I am going to take this
mixture of raw linseed oil, paint thinner, and boric acid/anti-fungus
and spray it into the inside of the hull where the glycol/boric acid
mixture has already absorbed into the wood, sealing it in there for
all time. The last spraying will be with boiled linseed oil
substituted for the raw. Boiled doesn't absorb as much, but does leave
a final barrier.
I know this sounds like a lot of work. But it really isn't. I fill
industrial spray bottles from Costco with my mixture and it takes
about 3 minutes to empty each one. Once everything is in the spray
bottles , I just put on my gasmask and empty a couple into the wood
before I leave the boat for the day, or the week. It really doesn't
take any time at all.
I was going to paint the bilge and all the inside of the hull, but all
my studies showed me that it wasn't a good idea. Paint goes on the
outside of the boat to keep moisture out, and the inside of the boat
gets a treatment that lets moisture evaporate back out.

The whole cost of this for two 35 foot boats is about $100. These
boats are worth near $60,000 together. A small price for a little
peace of mind about wood rot.

Contact me if you would like my recipe's.

My next adventure is to see if the old cresote roofing tar that a
local roofing company gave me from the back of their warehouse can be
mixed with paint thinner and substituted for the pine tar sold by the
wooden boat companies!!!

Please let me know if there are any other folks out there that have
tried to preserve their classic boats on a budget!