A Little About Rot
For any wooden boat owner, there are two great certainties in
life. One is death, and the other is rot. The latter, in common
with the former, may successfully be avoided by a combination
of exercise, attention to chemical intake, and by protection from
the worst of the elements.
Rot, in common with all living things, requires three conditions
to be met for it to survive. It must have food, water and oxygen.
Remove any of the three, and it will become dormant. An easy task?
In a boat constantly in the water, my understanding is that rot
is limited because the wood is constantly saturated, meaning that
rot is severely inhibited by a lack of oxygen. The extent to which
this effect may be witnessed is dependant on the chemical composition
of the water. For example, sea water tends to be somewhat kinder
to wood than freshwater (although it's a killer for metal work).
I didn't fully appreciate this until I read John Leather's Clinker
Boatbuilding. The back of the book contains a chapter briefly
outlining woods that may be used in boatbuilding work. In the
same way that salty air inhibits plant growth on cliff tops, salty
water inhibits rot growth in timber. It is also worth noting that
any boat kept in water most of the time will also be subject to
an annual haul out and inspection, at which point any rot is dealt
with before it can cause any damage.
An alternative is to epoxy cover the outside and have open bilges
such that the water that gets in to the wood by osmosis has some
way out on the other side. Alternatively, epoxy encapsulate the
whole hull, which will prevent air from getting at the wood...
although at some point that epoxy will crack and then... Suffice
to say, epoxy encapsulation is best kept to the experts.
There is also a vast range of wood preservatives from Linseed
oil (which has it's own, spontaneous combustion dangers) through
to high performance, designer preservatives, with commercial pressure
treatments somewhere in the middle (remember, when using pressure
treated wood, wear a good quality dust mask, gloves for preference,
and try to keep work areas free from dust. Wood is a carcinagen,
preservatives are worse). I would only use these preservatives
after considerable research, and appropriately to the boat being
built. (In other words, I don't).
However, for us mere mortals, our boats are rather more amphibian
than piscatorial, spending more time in the air than the water.
In my opinion, the best route to take is just to paint the hull,
and leave it in the garage between uses. The wood dries out (it
should never get wet in the first place, if it does, you need
to paint again...) and rot doesn't occur because there is no water.
If you have to keep your boat outside, it's well worth investing
in a polytarp and tying that over the boat. Here in the horrendously
expensive land of Her Majesty, I can pick up 40 square metres
(VERY approximately 360 square feet) of polytarp for five of my
very English pounds sterling at B&Q (Our equivalent to Home
Depot). I bought mine from their website (www.diy.com),
and they may ship internationally. A Polytarp over a boat will
not only protect your boat from rain (and permanently wet bilges),
but also from checking caused by sunlight and to an extent, frost
A slightly unhappy looking elegant punt
I wouldn't lose too much sleep even without these measures. I
built an elegant punt (Bolger) from a Gaboon (Okoume) faced exterior
ply with Southern Yellow Pine stringers and left it out in the
English weather for three years with a single coat of primer on
it. It's just started to show the first furs of rot and will still
be structurally sound for several years to come (except for my
workmanship). For the £80 that boat owes me, most people
would consider that pretty fair return on investment. (And all
I have to do is sand it back to bare, clean wood and refinish
it to extend it's life indefinitely).
best way to inhibit rot is to use the highest quality, rot resistant
materials available. Select your timber carefully for example
(white oak being a reasonable one off the top of my head, southern
yellow pine being an appalling one that will rot if it looks at
water). Okoume/Gaboon timber is not necesairily very rot resistant,
despite being considered one of the higher grades of marine ply.
According to my HMSO handbook of hardwoods, it is used in plywood
because you get a high yield of good quality veneers (without
checks). If you're going to bust a gut over the rot issue, build
the boat from the outset to last, and that means hardwood timber
of the highest quality, with best quality fastenings, very high
standards of craftsmanship, and the best quality coatings and
tender loving care every time the craft is used.
At right: Two years in
a leaky garage can cause havoc in the wrong woods, like this Southern
Yellow Pine plank. Note how the areas that have remained dry are
totally rot free
But I don't believe that that is what we're aiming for in our
boats. You don't save money building a boat, so I guess if you
build a boat, you do it because you enjoy the process. If you
have to build again eight or nine years down the line, so what?
To illustrate this, I'd like to talk about a clinker (lapstrake)
built wooden pair (rowing boat rowed by two oarsmen, with one
"sweep" oar each) that I handled as part of a summer
job cosmetically restoring boats for the display trade. This boat
was between 30 and 50 years old and all original timber. It was
a built like a tank and therefore took the abuse it received as
a club rowing boat throughout it's life with good grace. It had
been stored under cover when off the water, and given an annual
coat of varnish. We left it out in the sun one day for about twenty
minutes, when we came back the old varnish had started bubbling,
but covering it with a simple polytarp protected it. In other
words, even a craft which will always have leaked, has survived
perfectly intact because the right materials methods and care
were used on it.
By contrast, my Dad's boat was built about 15 years ago from
marine ply and mahogany, and originally had a little polyester
resin based fibreglass on the chines. For a lot of it's life it
was stored outside, and it very rarely saw the varnish brush.
Over time it accumulated bits of fibreglass where damage had occured,
over the mahogany keel to protect it. Now there's rot in the keel,
and rot in the ply, and the common factor seems to be that polyester
fibreglass. If I'd known five years ago what I know now, that
boat would still be healthy, but as I look at it now, it's tricky
to see how to resurrect it.
British Railways ran, for a long
time, on timber sleepers treated periodically with creosote (a
preservative). This did an excellent job of preserving the top
side. However, when you turn it over, the areas that weren't creosoted
and which weren't exposed to the air to help them dry, rotted
So, in other words, I'd say that three factors govern rot in
a home built boat. One is the raw materials from which you make
the boat, another is the finish you place on your boat, and the
final factor, is the use and care you take of the boat.
I will leave you with one thought however, because I don't want
everyone to have rot-related nightmares. Rot is a very slow process.
A 3x2 timber that is left embedded
in the ground will still retain much of it's structural integrity
after several years. Think how much more care your boat receives
Take care, and always remember, we do this stuff for fun!
Mr. Wasey will soon be writing
a regular monthly column for Duckworks in which he will discuss
rot and many other subjects. He requests that you contact him
with your thoughts on this subject at: email@example.com