There is no boat more beautiful in my opinion than a varnished wooden boat. But I can understand why some people paint their wood another colour, especially if they are travelling in the tropics.

Tropical climatic conditions are probably the harshest conditions for a varnished wooden boat. In the tropics you have a high humidity and constant high temperatures.

During the day the surface of the wood heats up from the glaring sun. All wood has a certain amount of moisture in it and because you are in the tropics the wood will have a higher than average moisture level. The moisture in the wood heats, expands and comes to the surface. When this moisture comes to the surface of the wood, tension is applied to the varnish. At night the surface cools down again and the humidity level drops and the wood grain tightens. This constant process of expanding and shrinking is very hard for your wood and very hard on your varnish.

The only other weather conditions that could be more severe on a varnished wooden boat are rainforest conditions such as you would find up the Kinabatangan River in North East Borneo. We spent six weeks cruising up this beautiful river but it was hard climate conditions for our 11 metre varnished wooden yacht Petima.

The humidity in this area is so high that in the morning you wake up to a dense fog and the entire boat is dripping wet. The fog is so thick that you can’t see another boat anchored in front of you.

It doesn’t take long for the sun to come up, the fog disappears and the wood is steaming with the focus of the intensely hot sun shining down on it. At the end of our six weeks cruising up the Kinabatangan River we could easily see the destructive nature of these climatic conditions on the wood.

In the tropics, moisturising wood is a big problem and must be dealt with at an early stage otherwise you will have rotting wood on your hands and this is a bigger problem. The trick with wooden boat maintenance is to keep up with it. Never let it go. A varnished wooden boat looks beautiful when it’s well maintained but if you don’t keep up with the maintenance then a wooden boat can look ugly very fast. There is no in between.

Our wooden yacht Petima is a custom built boat by Knut Olsen. She was built in Denmark. People don’t believe us when we tell them she is 26 years old, they always say she looks new and that is because she is very well maintained.

Petima’s main structural beams are solid oak and her hull is made from Norwegian pine. Her pilot house is teak and so is her deck.

The interior is constructed from a mix of pine, teak and plywood.

We often get other cruisers coming to us saying “you have a beautiful boat but I wouldn’t fancy doing the maintenance”.

Cruisers never believe us but we always reply saying “the maintenance on a varnished wooden boat is the same as the maintenance on a steel or fibreglass boat”.

When they find out that we actually sail with a 13m steel yacht as well they look at us in complete horror. We know what maintenance is all about and a steel boat produces her fair share of work as well.

In all of Petima’s 26 years she has spent the last 10 years in the tropics. Her hull is varnished once a year and above deck is maintained twice a year. The interior is completely stripped every ten years.

Of course in the meantime there are areas that require attention.

Oh and did I mention we have a 2.6m varnished wooden dinghy as well? Put it this way we are never short of something to do!

Where to start the maintenance?

Before you start any job you should always have the proper tools to tackle the job, good quality tools.

You can’t start to sand and varnish a wooden boat and suddenly find that you don’t have enough sandpaper or the correct varnish brush.

So what do you need? Sandpaper of various grits: rough sandpaper (60 grit) for the areas that you want to completely sand down to the bare wood; higher grit sandpaper (120) for areas that just require a light sanding.

An electric ex-centre sander for the open flat areas is better than a normal sander as it doesn’t focus on one area giving more of an even sand. A wood scraper is very handy for quickly taking off old varnish.

When it comes to buying varnish, cruising the world we have to change our brand of varnish as you can’t find the same brand everywhere.

We always choose a polyurethane varnish because it is normally more flexible. A two pack varnish is harder. You can tell if the varnish is good quality by shaking it, make sure it’s not too watery and it has some body to it.

If you are choosing a varnish for interior wood you will notice the clear varnish is very clear - you can see easily to the bottom of the tin. However if you are buying a clear varnish for exterior wood there must be a certain amount of dark pigment in the varnish, this helps to protect your varnish from UV rays. If it doesn’t have it, don’t buy it. Don’t forget the turpentine as well.

You must get good quality brushes of different sizes. Make sure the hair doesn’t come out when you pull on them. A foam roller for larger areas such as the hull.

Plenty of clean jars are required for cleaning your brushes and storing old varnish.

Elbow grease

So now you have the tools you are ready to start your maintenance.

Maintenance can be done anywhere. You do not need to have your boat out of the water to sand or varnish. All our sand and varnish work is done on the water. We sometimes sand and varnish while we are under sail in good conditions.

If you have areas on your boat where the wood looks black this is a good place to start your maintenance. If it is black it means water has got underneath the varnish so you must strip all the varnish off (using a wood scraper) and get down to the bare wood.

Always scrape and sand in the direction of the wood grain never in the opposite direction, otherwise the wood will look like a cat got its claws into your wood and you will never get the scratches out. You will still be able to see the scratch marks even when covered in varnish.

Once all the varnish is scraped off, sand around to make sure there are no high areas of varnish around. Then let this area dry before applying varnish. This can take a couple of days it all depends on your drying conditions and humidity in the air.

If you don’t let it dry out properly and apply a coat of varnish you will eventually have the same dark spots again.

If you are finished work for the day and the wood is still not dry, cover it with plastic to protect it from moisture for the night.

Get cracking

If you have areas on your boat where the varnish is cracking then this is the next area you should attack.

Once the varnish is cracked you have left your maintenance too long and you must scrape all the varnish off. Once all the varnish is scraped off, lightly sand until the surface feels smooth to the touch.

If you see light colour spots while sanding, these are areas where air and humidity have got underneath the varnish. You must sand these areas out until these light spots are gone and the wood looks the same colour all over.

The corners on a boat are very important, make sure you sand right into the corner. It is important that you get the right connection between the old and the new varnish. If you are not careful with your sanding then the new varnish will peel off because it has not got the correct grip to the old surface.

Sanding is far more important than varnishing. It is easy to apply a fresh coat of varnish but not so easy to
sand correctly.

Varnishing trick

We always say varnishing is the reward for sanding.

In the tropics before you start to varnish make sure the area that you want to varnish is clean. Wipe it over with a damp cloth that will not leave fluff.

Stir your varnish well before using it, don’t shake it. The first coat of varnish is the most important coat. If this is the first application of varnish make sure the varnish is thin and runny. Many coats of thin varnish are better than a few coats of thick varnish.

If the varnish is too thick or gets thick in the process of varnishing keep adding turpentine. The reason for thin varnish is to give the wood a chance to suck the varnish into itself and then the varnish will hold better.

Always varnish the areas that have no varnish first. In a day under good drying conditions you should be able to apply two coats of varnish.

You will find after the first few coats of varnish that the grains in the wood start to swell with varnish and you will have a rough surface. Lightly sand the area to get a smooth surface before applying the next coat.

After this there is no more sanding required. Unless of course a coat of varnish has been on for more than 24 hours without the next application, then you must sand again before applying more varnish.

If you are just touching up an area and you have only lightly sanded it then it’s enough with one thin coat and one thick coat of varnish. If you start to varnish on bare wood then you need six coats at least.

Apply the varnish evenly. Make sure you get the same amount of varnish everywhere on the straight surface and in the corners.

You will see the best result from your varnishing if you apply the varnish against the grain of the wood and straighten the varnish with the grain. If you can see brush marks then your varnish is too thick.

Using a foam roller for the hull or large areas, you will apply the varnish faster and more evenly.

Take a small section of the hull to varnish each time. Roll on liberally thin varnish in vertical and horizontal strokes, to make sure that you apply the same thickness of varnish everywhere.

You will find you have bubbles from the roller on your hull. Take your brush and in a strong horizontal motion brush out the bubbles and even out your varnish.

With every new section that you varnish always overlap the varnish into the next section. In doing this you won’t be able to see any lines from each section that you varnish once it has dried.

Depending on your drying conditions, you need to be fast varnishing the hull. It always helps to have two people: one person who can prep the brush, roller and varnish and one person to do the varnishing.

If you find the varnish is drying too quickly then take a smaller section of your hull to varnish.

Remember, if your varnish is getting thick add turpentine. Sometimes you find it states on the varnish tin “don’t add turpentine in last coat of varnish”. In the tropics you always need to thin your varnish with turpentine.

You will also find the spots that you have varnished will look a lighter colour than the rest of the varnish. Don’t worry. The sun will eventually darken these areas and you won’t even notice it.

At the end of the day if you are finished varnishing but still have more coats to apply then place your brush in a jar with some turpentine at the bottom. Close the jar with a rag so the turpentine doesn’t evaporate and you will be able to use the brush the next day.


Fibreglass boats have osmosis, steel boats have corrosion and wooden boats have threadworms.

Thread worms need moisture to survive so you will only find them below the waterline. They thrive in the tropics so you can be nearly guaranteed you will have some of these in your hull.

It depends on what kind of wood you have below the waterline whether you will have worms. We have Norwegian pine and they love it. The boat needs to come out of the water in order to get rid of these very smelly creatures.

If you have your boat on the hard, just by drying the boat out the worms will naturally die. But be careful, a wooden boat cannot be on the hard in the tropics for too long. After about ten days on the hard in tropical conditions a wooden boat will start to dry out. A quicker solution to get rid of thread worms once you are on the hard is by using a small hand held propane gas burner. Apply the gas burner about five centimetres off the area infected with worms (if the wood starts to smoke you know you are too close). This will not only dry out the infected area but also kill the threadworms.

If you have damaged areas in your antifoul this is normally where you will find the threadworms. The wood has lost its protection, gets wet and rots providing ideal eating grounds for threadworms. Last year we had very hungry threadworms below the waterline that had eaten through the complete hull.

Wood that has threadworms in it needs to be cut out immediately and replaced with new wood.

You will recognise the areas that have threadworm by smell. Threadworms give off a bad odour and you will smell them before you see them. If you can’t smell them then with a hammer and chisel dig away at any areas with round holes about the size of a worm.

A good way to protect your hull from thread worms is to apply six layers of epoxy primer. This is not a 100% guarantee but it does greatly reduce the amount of threadworms.

- Aideen Henry

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