A Little About Rot
by Alistair Wasey

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? Apparently not.

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 damage.

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).

The 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 badly.

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 than that!

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: al_a_man@yahoo.co.uk