Logboats are the most prevalent form of water transport to be found in the ancient world, and can be found in nearly every continent. As the name suggests, a log boat is a craft fashioned from a single tree, the most common wood used for construction being oak, at least in Northern Europe. Antiquarians believed that logboats, with their simplistic form, were a purely primitive creation, only used by peoples lurking in the mists of time. However, from a study conducted in the 1970's by the National Maritime Museum of the UK, it was discovered that logboats from Britain dated up to at least the 14th Century, and so it is much more likely that this simple but effective mode of transport was used well into the middle ages.

What does a logboat look like?
Logboats, as mentioned above, are fashioned from a single tree trunk. The trunk is normally cut off above the buttresses, the thick, flared base of the tree, and stops just below the bole where the branches begin to spread out. The size of the tree will, therefore, determine the size of the boat. Boats can be anything from two metres to fifteen metres in length, despite logboat criteria suggesting that the minimal size is three metres.
Some trees, oaks in particular, suffer from a disease called heart rot, which rots the tree from the inside out, making it hollow. Although this means less work for those hollowing out the log to form a boat, (90% of the wood has to be removed, quite an undertaking!) it also means that one or both end are open. Transoms are normally found fitted to boats that have suffered from this disease, which are boards slotted into the ends to make the boat watertight.
Logboats are normally hollowed out of a single tree trunk, but that trunk may be split in half first, and then hollowed out, or several tree trunks may be fitted together to form a log catamaran!

A logboat survey of the British Isles was conducted by Sean McGrail, then the Director of the Greenwich National Maritime Museum, during the 1970's. Although many logboats had been discovered in Britain, they had never been examined in detail and many had no record at all being part of antiquarian collections. This appears to be a pretty global trend. Due to the unexpected prevalence of logboats in the British Isles, the study was limited to just examining the logboats of England and Wales, but even with this smaller catchment area it still took over five years to compile. The study came up with six different criteria for the identification of a logboat. If a wooden object suspected of being a logboat complied with two or more of the criteria, then it was included in the survey. The criteria are as follows:

These criteria are now accepted worldwide in archaeological circles, as defining a logboat. The survey itself can be found in BAR (British Archaeological Record) 51, which covers two volumes and was published in 1978.

Please do /msg me with examples of logboats outside of the British Isles, as I'm afraid my own knowledge is limited to examples in McGrail's books, which are rather biased to the UK, but good examples from Britain are: