'Will there be an overhead bridge or cable in this voyage?'
There are some dangers on inland waterways that don't occur in an open ocean. Look over any larger scale chart and you sometimes may see overhead power cables that span a narrow channel. Take care to make sure that your mast will clear the cable--before you attempt to pass beneath! Use these sailing tips for safety.
Correct Your Mast Height
Determine a total, corrected and conservative mast height for your sailing boat. For example, let's say your boat has a mast 38 feet above the water. If you installed a VHF whip antenna, masthead wind fly, or tri-color navigation light, that additional height would need to be added. Let's say two feet of antenna had been added to the original mast.
This would make the overall mast height 40 feet. As a final measure, I recommend an additional 10% or more, so add another four feet or so. Total mast height to clear would be 38 feet + two feet (antenna) = 40 feet (overall mast height) + four feet (10% additional safety factor) = 44 feet of clearance for safety.
Know These Overhead Power Cable Symbols and Abbreviations
Overhead Cables - potentially dangerous if ignored when planning your voyage - but how much height allowance is enough? - .. .
International charts often show cable vertical clearances inside brackets, but NOAA (US) charts, for instance, write cable vertical clearance within the descriptive note. Make sure you know how the chart you are consulting works. Check the chart notes (particularly if you are away from your home waters) to find out if this number indicates feet or meters.
The second and third illustrations show cable strung between pylons with the vertical clearance shown in brackets. This symbol will often be found on International charts. NOAA charts show the vertical height clearance written on the side of the river bank along with the rest of the description (as shown in the first illustration). Heights are shown in feet or meters for clearances at high water. Always check your chart near the title block for the datum used for heights.
The fourth chart illustration shows a magenta height clearance between the brackets. This means that the power company or regulating authority has verified the indicated height clearance. Realize that vertical cable clearances are for the center of the waterway.
Look at the first chart illustration. The towers on each side of the waterway show a dot surrounded by a circle and are abbreviated in all Capital letters. This means the positions are highly accurate and the towers prominent.
The cable itself may or may not be as visible. In certain atmospheric conditions, it could be difficult to see from a distance. Always check your chart near the title block for the datum used for heights. In this case, heights are given in feet above mean high water.
Allow for Extreme or Unusual Circumstances
In places with extreme tides, take care to allow extra room at maximum high tide. Storm surge or heavy rainfall can add a lot to tidal height, as can spring tides--higher high tides and lower low tides than normal--twice a month at the new and full stages of the moon. If in doubt, find an alternative route to avoid a dangerous encounter that could result in costly damage or injury.
Nigel Calder, in his book 'How to Read a Nautical Chart', warns that some power transmission lines can have extreme voltages. These cables can discharge current without direct contact. Allow an additional clearance of two to five meters (Seven to 17 feet) or more if you see this warning on your nautical chart.
Use these sailing navigation tips to avoid the danger of overhead power cable contact with your sailing boat's mast. Keep your sailing crew or partner and boat safe on the inland waterways of the world--wherever in the world you choose to sail.
Captain John Jamieson (Captain John) shows you the no-nonsense cruising skills you need for safer sailing. Visit his website at Skipper Tips. Sign up for the free, highly popular weekly 'Captain John's Sailing Tip-of-the-Week'. Discover how you can gain instant access to hundreds of sailing articles, sailing skills videos, sailing tips newsletters and Free sailing topic e-Books!
by John Jamieson
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7:14 PM Thu 6 Feb 2014GMT
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