Rebuilding a rotten wooden mast [Sea Japan-Ep25]

When we originally bought Tiare she had varnished masts

Which looked fantastic, but being in the tropics, with all the high UV were just too much maintenance.

Each year a new coat of varnish had to be applied, meaning going up the mast to sand and varnish. Just too much hassle

After a couple of years living onboard we discovered that the aft sail collar had worn through  the covering of glass that protects the mast from hard knocks.

This had allowed the tropical rains to run down the mast and into the wood.

It didn’t take long for the heat and humidity of the tropics  to turn the wood to mush.

The damage was bad enough that we really needed to pull the masts out   and rebuild the first 6 feet

I also wanted to paint them white, no more varnish and no more sanding!

We couldn’t do this in Thailand due to visa limits , so we carefully sailed down to Lumut, in Malaysia.

Once the masts were out, we found the Masthead had also rotted out .

Bottom of the mast was rebuilt with wood, the masthead we replaced with aluminium.

Once the work was done we re-stepped and continued cruising.


After cruising for a while we noticed that cracks started to appear in the aft mast, first on the paint, then the fiberglass.

Initially at the top, then further down.

But we were cruising remote places well away from the  resources needed to either drop or lift out the masts.

So we filled, or covered the cracks trying to stop any more water getting in, and  kept an eye on them and hoped for the best.

Had been ten years since we had bought her, and really done almost no major maintenance, other than to keep her, and us,  safe.

Well last year we were finally in a position where I could give Tiare her much needed maintenance / overhaul.

and could finally crane the masts out and  assess the damage, and perhaps have a good cry.

And yes, it wasn’t pretty.

Looked like the fibreglass had not stuck to the wood. It just peeled off. Water had gotten underneath and rot had set in. Only this time the main damage was to the top 6 meters. The masthead, now being aluminium had no issues.

The forward mast appeared fine, no cracks and I didn’t want to jinx myself by disturbing what wasn’t a problem. 

So the forward mast just got a cosmetic overhaul, new primer and top paint. plus a fancy streaming light and deck-light.


The damage to the to top 6 meters was fairly extensive. 

Luckily the mast is made using a birds-mouth construction technique, and where the lengths of wood were glued together the damage had not moved from one length to the next due to the glue between the two pieces of wood.

I could save half existing mast wood, but needed to replace the rotten lengths.

But, suitable spar wood is very expensive in Japan, So I looked at alternatives.
replacing the mast with aluminium would be nice, but thick walled aluminium of the right diameter were not cheap and shipping to me in Japan, made it even  less so.

We simply couldn’t afford either new wood, and definitely not a new mast

The only option left was to use the some rot and insect resistance wood that I had bought for the office deck.

This is Hinoki, or Japanese cypress, very rot resistance, which sounded good to me.

I also had  enough lengths available to do the Job, finishing the office deck would have to wait.

Removing the damaged wood, was scary, hoping that the remaining wood would hold the weight and not break, If that had happened the whole job would have become seriously more difficult and my trust in the repair would be undermined. I didn’t want to be in rough seas wondering if the mast was going to break.


I applied Ethyl glycol, or antifreeze, to stop any further spread of dry rot or fungi, It also has the benefit of showing up areas where water had penetrated the mast.


After selecting the lengths that had the least amount of knots making the replacement strips was fairly straight forward. Simple calculation based on the diameter of the mast, and the number of pieces. Tiare’s mast has eight sections, I needed to replace four of them.

The wood I had wasn’t long enough for some, so it they needed to be joined with health 12:1  scarf.

My youngest son was down for the holidays and helped out with the scarf joints.

Once I had this done I could cut out the birds-mouth,. 

Miso the Bernese Mountain dog we were looking after enjoyed the time too. Like most dogs, being close by was the best possible place to be.

There was also some stiffeners to make that fit inside the mast, I think here you can see why its called a birds-mouth joint. The joint increases the surface area of the glue bond.


Once the rotten sections in the mast had been removed and scarfs made, and the new wood cut and then scarfed to length. It was time to glue the new wood into place.

Getting a close fit with new wood to the old hadn’t been easy, Seeing the epoxy squeeze out as I tightened the clamps up was a big relief. As it meant the joints were a good fit.

Looping then twisting the ropes around the mast really put the pressure on the joints.  I was surprised at how well this worked.

After that it was waiting a couple of days for the epoxy to set before I could roll the mast around and start rounding off the new wood to match the circumference of the mast. 

Any low parts were made up with epoxy filler.


After the mast has been rounded, filled and sanded smooth.  

It was time to prep it for a layer of fiber glass. 

This layer of glass is really there to stop any hard objects from making holes and damaging the protective paint layer and letting in water.

This time instead of very light weight layer of glass, and keeping in mind that the mast is supposed to flex, I opted to use S-glass, which is around 30% better in everything over standard, or normal, e-glass. 

It’s stronger, more flexible and also more expensive.

How ever I did manage to find a very good price for a roll of 8.95oz cloth. 


This our oldest son Sam, who unlike me, is a boat builder, and  actually knows what he is doing.

Once the glass is all on and cut to size, the peel ply is ripped off, which an incredibly satisfying experience! not unlike peeling off dead sunburnt skin, but with the added pleasure of extra noise.

Next is to add 3 coats of high build epoxy primer, sanded down to a smooth finish.

And then a final 3 coats of finish paint.

The paint I used was the same as the hulls, only white. It is a flouropolymer resin, designed mainly to be used on offshore structures, very hard wearing, long life gloss retention, and anywhere other than Japan, would be out of my budget.

But, being made in Japan it ends up being more affordable than other well known brands of marine paint.

Each coat of paint took an hour, 30 minutes per mast, per side, and only one coat could be applied a day.

Only in the early morning before the sun got too hot.

So six days to apply the primer and another six days to apply the top coat. Can only do one half of the masts at a time.

And I needed a couple of days to let the paint harden before I could roll the mast over to do the other side.

And there was a deadline as I had to have the masts out as the area was booked for a construction project.

It couldn’t rain, or we would have had to step the masts before the final coats of paint were on and hardened.

We made it with a day to spare.


The big day had arrived.

All that work is now falling into place.

The standing rigging, new lights, new wood, new paint, blocks, everything, is ready for the final step.

Im really pleased with the results and more importantly, no longer worried about the mast falling apart.

Another benefit is that I now have the confidence to build a completely new mast should I need to .

It’s not difficult, a new wooden mast really is a low tech, simple step by step process, 

I feel a new build would have be easier than trying to do the repairs I did. 

But money constraints meant that a new mast was never on the cards. 


A decision about what to do with the standing rigging had to be made, whether I put the old wire rigging back on , make up some new wire rigging or were there other options?

Given that our budget is really really tight, perhaps just reusing the old rigging would be the only choice.

But life constantly throws unexpected opportunities, and a chance meeting with an Australian rigger provided the answers.

But that story is for the next episode.