The log ship (see Figure 11.3) is nothing more than a board weighted so that when thrown overboard it stands upright and sits still in the water as it drags line off a reel.
Once the spare line took the log clear of the ship, knots were tied in it every 14.5 metres (47 feet 3 inches). The number of knots that run out in 28 seconds is the speed through the water.
The rotator log was introduced in the 19th century but the log ship was still used on some US Navy ships as late as 1917. It is probably the best DIY log you could make.
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