In Australia we have to spend a lot more money on plywood. So the boats are much more expensive than the average (but not all) Duckworks boats. This means that we tend to go the full coating epoxy method. Three coats wet on wet before varnishing or painting.
The result is that many builders go for a more "yacht" type finish, quite commonly the boats are painted outside, but gunwales and interiors are fully varnished. Not always by any means, but probably the majority.
You probably know about our ozone hole! Lots of Northern Hemisphere spar varnishes (SPAR varnishes are always higher UV resistant) just don't cut it and fall to bits pretty quick. However, if the boat is epoxy sealed and it is small enough to keep under a good cover then we find varnish can last very well.
This is a photo of Peter Hyndman's goat island skiff. At the time of the photo it was 13 years old. Full three coats of epoxy on everything and then two pot polyester paint but six coats of a single pot spar varnish from an Australian manufacturer.
Remember that epoxy is much less laborious than varnish as you can apply one coat, wait for it to go tacky and then apply the next coat until you have three in one day.
A real downside of paint as opposed to epoxy is that it can take quite a few coats to fill the grain of some plywoods. A Quick Canoe I did in Australia and decided not to epoxy was at coat six without the grain being filled yet. And I would expect maybe three coats of any sort of paint that gives a decent finish to take three coats.
The boat was stored outside and often had water inside for extended periods. Also, in a tropical steamy area. But it did have a cover of good quality tarpaulin fabric that fitted quite closely. About year 15 it needed a recoat of the varnish only, the outside was still quite okay.
So what about bigger boats that are hard to cover or on a mooring. I"ve done that type of job professionally over many years. In general, in our harsh ozone hole sun, a boat on a mooring unprotected will need yearly recoats. UV filters are consumed as they do their job.
So, no covers, six to 8 coats of varnish with no epoxy means a light sand at the end of the year and another coat or two. But still, it may not quite manage to make out the year.
With epoxy under the varnish I would be expecting that the year will be totally fine with no problems and do the yearly recoat.
On a mooring with good covers and epoxy under the paint you can look at maybe three or four years before the boat needs a light sand and a couple more coats.
I hope this gives some idea of the different performance we get over the long term. Many of the boats we did were around here for several years so we got to see how the maintenance cycles went.
My theory about varnish is very close to the argument I make about epoxy. This is an argument on a statistical base, because when wooden boats were common for racing in Australia and New Zealand it was rare to see any boats that were completely painted. All boats almost without exception had varnished interiors and decks. The external hull was either varnished or painted. We are talking thousands of boats, mostly built by experienced home builders. This continued into the early days of fibreglass production where decks were still ply and would also be clear finished.
It all depends on the cost of the ply and the mindset. If cheap good ply is unavailable (everywhere except north America) then you have to use the good expensive, beautiful stuff. Then people are reluctant to cover it with paint. This is also true in the UK for their plywood boat era.
A second professional reason is that for complex surfaces like the cockpit of a ply dinghy it is by far easier to get a nice looking job in varnish compared to paint. One or two small paint runs look terrible. The same runs in varnish can be hard to spot. So the last varnish coat will be the last coat rather than some small problem in paint forcing a resand (ugh) and recoat.
The sanding to get an excellent paint finish is hugely time consuming. There is always the risk that you'll go through to, or get too close to, a dark colour of plywood under the upper layer so shadows appear. But varnish needs about half or less of the sanding and there's no chance of going through to something of a different shade.
This wass the Oz tradition up to about 1960. Maybe part was the working class showing the yacht people (who excluded them) that they can do just as well.
A more modern 1970s shot above - probably 60 boats at this regatta. It was this way until composites finally took over with more skiff type shapes in the mid '80s.
The feeling to me, being from Oz (and going back that far), is that this is utterly familiar and normal.
Same deal in the UK above. Varnished decks and some varnished hulls.
In the rest of the world the varnish tradition remained strong until the mid 1980s, at least for classes of boat that can be stored out of the sun. These are Italian above.
I think part of it too was that North America strongly embraced fibreglass (selling points were "lower maintenance" and lighter and cheaper, the second and third ones were wrong in retrospect).
The rest of the world had a strong plywood homebuilt boat revival in the early '60s which America only got a little bit of in comparison. Lightning, Snipe, Blue Jay, Windmill, 110 - with only few (Windmill) taking some of the advantages of lightweight ply construction), but many classes were designed around glass production. Beat the drum about "low maintenance" and people start to believe it.
In Australia, NZ, UK, South Africa the bulk of this size of boat would have been lightweight ply construction with substantial areas of varnish, all before epoxy .
Varnish is okay providing the boat is small enough to covered or keep under a roof.
UV distribution 2010, why northern hemisphere varnish doesn't hang in well in the Southern Hemisphere.
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We really gave the old ozone a fair (unfair) whacking. When I was young even a fair bloke like me could go out in the sun for an hour or so in summer without too much worry. Now it is down to 15 minutes or less and you are fried.