Well, the title was sure to get your attention, and you won't be disappointed because this one really is about going topless.

Some people have qualms about removing their tops, perhaps understandably, especially if summer hasn't quite started yet. But here in France it's just another part of life on the canals. And yes, Liz and I both sailed topless yesterday.

Curb your enthusiasm; we don't do it every day of course, but sometimes it's just necessary. Like yesterday. Having decided to leave Colombiers and head for a wee town called Argeliers, we checked in the canal guide book and discovered we'd be going under some of the lowest bridges on the Canal du Midi. This meant dropping Liberty's top in order to be able to get under.

What? You didn't really think we personally would be topless when the temperature's only 16 degrees, it's windy and cloudy did you? Get real. Sorry if we gave you that impression :-)

Before continuing the story though, a bit of background to Buying a Boat 101. When choosing a craft to cruise the French waterways there are two key measurements you need to be aware of. In French these are the 'tirant d'eau' and the 'tirant d'air' - basically the measurements of how deep your hull sits in the water and how high the highest point of your boat is above the water.

The first measurement - the boat's draft - is important because in some places the canal depth is as little as 1.4 metres, so if your draft is one metre then you can find yourself with only 40cms of water beneath your keel. If your draught is already 1.4 then you can find yourself horribly, embarrassingly stuck. Mayday, mayday!

Height-wise, your tirant d'air needs to be lower than the lowest bridge you're likely to encounter. If it's not you can easily demolish your mast, wheelhouse windows and lose all your superstructure equipment such as radio aerials, horn, navigation lights - or worse - your expensive radar dome. You can also bang your head rather nastily and suffer excruciating embarrassment if people are watching. Pride will be bruised.

Many boats are designed therefore with droppable tops. Liberty, for example, has a stainless steel equipment rack carrying the forward mast light, aerials, horn and two NZ flags, but flip a couple of levers and the whole thing drops down on hinges. Likewise, the canvas Bimini top unclips and folds down, and, for the lowest of the low, we can unhinge the flying bridge windows to sneak under the really challenging spans. It means that Liberty enjoys 'Access All Areas' status on the French waterways, and all we have to remember is to duck as we go under low bridges.

Yesterday we had to drop everything to squeeze beneath three particularly low arches, which was a bit of a challenge. We know there are more to come too, but the canal book includes the measurements of every bridge so we have plenty of warning. We got through without bruising heads, egos, or anything else.

One of the other joys of yesterday's four-hour sail was going through the Malpas Tunnel, the oldest canal tunnel in Europe. In itself it isn't particularly challenging; it's short (160m), high enough for us to leave our top on, and wide enough that we could get through without banging the sides of the boat. What is remarkable about it is that canal-builder P Riquet, on encountering a hill in the way of his canal work in 1679, was ordered to stop tunneling as the excavation was considered a health and safety risk (this some-400 years before anyone actually knew what H&S meant, and way before fluoro safety vests or hard-hats).

But Riquet was on a mission, and the finishing line was - figuratively at least - within sight, so he quietly instructed his chief mason to continue the tunnel in secret. Eight days later - EIGHT DAYS! - the workers were through, and all Riquet's objectors, nay-sayers and governmemt worry-mongers had to shut up and watch him carry on creating what is today regarded as one of the world's engineering marvels.

So we raised a metaphorical glass to Paul-Pierre Riquet as we slid majestically through his anarchic excavation. In 1679 it was another engineering feat that couldn't be topped. It was - in a word - topless.