The trailing log

These mechanical devices, still used by some yachts (including my own), are a major step up from the old 'log chip' arrangement. They work by towing a 'fish' shaped so that it will rotate at a known rate, from a simple analogue measuring device attached to the aft part of the vessel. Distance run is usually measured, realistically, to the nearest !4 mile. These instruments are reliable and accurate. If yours over-reads or under-reads it will at least be consistent, so that once this is known, you can correct its readings as easily as you would a watch that reads fast.

The fact that you must actively stream such a log, and haul it in again, is no nuisance at all. If you are piloting in good weather and you can see where you are, you don't need a log anyway, so you can leave it in the box. Bring it out when land fades away astern, or when the mist thickens. The very act of streaming a trailing log forms a punctuation mark in any passage which says, 'From now on, we take the navigation seriously.'

Don't wrap the log-line around your propeller, watch out for weed on the fish, and beware of its readings if it is in direct line astern of the propeller and you are under power. With these provisos, no better system has yet been devised for the cruising yacht. Inexpensive and reliable, a quality trailing log such as the 'Walker Excelsior' may not supply the data required to run linked functions, but it remains a joy to use.

Electronic logs offer the advantage of no moving parts except for the tiny, spinning impeller. Some don't even have one of those, operating by measuring Doppler effect instead. The majority of yachts nowadays have an electronic log of some sort. For the most part they work well. Some are better than others, some seem prone to weed attacking their impellers, but they all give you a lovely big dial to tell you what you rarely need to know: your water speed. They do read distance in tenths of a mile, though, which is handy. Some of them purport to read in hundredths, which is of no use to anyone except 'electronic man' - who is so misinformed about the real world that he wants to know where he is to the nearest 20 yds (18 m) while on passage. Even for close-in pilotage, such promise of accuracy can be a snare. The log can only read distance through the water, so if you rely on it amongst the rocks in a tideway, you are bilged for certain.

If you have an electronic log, for goodness sake study the instruction book. I could tell you of a number of navigators who have dumped their all-important distance run at the punch of a wrong button. If a shark chomps off your trailing log you will at least know where you were when it happened, because the beast doesn't generally flop aboard and zero your log dial to complete the job.

Calibrating a log

Some logs can be calibrated to remove error. If yours cannot, there is no cause for concern, so long as you know what's going on. In cither case, you should be empirically aware of its performance.

The traditional way to calibrate the log is to take a two-way run down a measured mile at slack water. Divide the results in half and compare the answer with the charted distance. The difference is the log error. Either correct it out, or note it in your log book and apply it in the future.

The hard reality is that with the added security of GPS, few yacht skippers actually do this any more, but the subject must not be ignored. The main reason for having a log is to provide data for cross-checking GPS, and to look after us should it fail. In either case, we need to know what it's doing, so calibrate it we still must.

Fortunately, any GPS receiver will read out 'SOG' or 'Speed over the ground'. Choose a calm day, wait for slack water (note that no current is running past a handy buoy), motor steadily ahead at a moderate speed, then read the log manual and twiddle the knobs until its reading coincides with the SOG. Nothing is simpler, yet many people don't take the trouble and some silly boat speeds arc recorded as a result.

A final balance is to compare logged passage distances with the charted or GPS distances over an extended period. Having taken due account of any tide or current, does it over-read consistently, or under-read, or neither? Whatever the case, so long as you see a noticcable pattern, you can adjust your future log readings with a confident sense of realism.


The third essential navigational input is depth. We have already discussed something of the meaning of 'depth' as it relates to tidal height, but the reality of how much water you have underneath you is only truly revealed by some sort of measuring device.

How To Have A Perfect Boating Experience

How To Have A Perfect Boating Experience

Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.

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