Sailors need to look up, not just for the wind vane and the weather, but also for things that can entangle, electrify, or simply snap off the mast. Even if you are confident that there will always be plenty of water beneath your hull in your local waters, you cannot ignore the tide tables when it comes to overhead obstructions.
Overhead power lines and bridges are marked on large scale charts with their vertical clearance above mean high water. Donít assume, however, that you can proceed without worries if your mast is a few feet less than the vertical clearance. To be sure of clearing the overhead obstruction, you should know exactly what the mean high-water level is for that location, what the tidal range at the location is for that time of year, the state of the tide at the time when you want to pass under the obstruction, and the distance between the waterline and the top of your mast. In the case of overhead wires, assume that they have sagged since the vertical clearance was last measured. Then factor in the lift from waves and wakes.
When lacking that assurance, there are two options. Set a different course, or unstep the mast.
When faced with the choice of sailing an extra 80 miles to get around Montauk Point, or unstepping Kirstenís 23-foot mast to get through Shinnecock Canal and its 22 feet of vertical clearance, I chose the canal.
The county has small, manually operated cranes at either end of the canal for sailors to do their own work in unstepping and stepping their masts. But it seemed unlikely that a small army could have managed to do the job with one of them, situated as it was high above a concrete seawall with nothing for a boat to tie up to.
The shipyard crews and their equipment helped carry out the work in less than an hour at each end of the canal. Even with arrangements made in advance, however, the shipyard wonít necessarily be available as soon as you are ready. Expect to add half a day or more to your schedule.
Bridges and overhead cables are not the only enemies of masts. Maneuvering in close quarters with another sailboat can easily get spreaders and shrouds entangled with dismaying results. And there are numerous tales of woe from sailors at sea who came alongside large ships for a gam, mail, or supplies, and soon found that the ocean swell and waves were bashing their mast against the other vesselís topsides. Even trees and buildings set close to a narrow, crowded channelís seawalls can suddenly become disastrously intimate.
Overhead obstructions are one of the very good reasons why every sailor should read absolutely everything on the charts for the area. Otherwise, a sudden squall forcing you to head for shelter in an unfamiliar cove can arrange an unexpected meeting between your aluminum mast and some nearly invisible wires carrying enough electricity to power a small city. It should also be noted that more sailors are electrocuted by raising the mast near powerlines than by any other activity.
Visually judging the clearance from the deck of your boat as you approach the overhead obstruction is nearly impossible. Perspective will make your mast look much taller than the opening it needs to pass through. Unless the water and wind are calm enough to come up very slowly under power and back off quickly if contact is made, you need to know with absolute confidence that there is clearance.
Tidal ranges are critical when the clearance is a close call. Knowing the time of high tide is not enough. Tidal ranges vary constantly as different forces come into play. Spring tides, which come at every full and new moon when the sun and moon are aligned with the earth, result in tidal ranges averaging about 20 percent greater than normal. Conversely, with neap tides, when the moon is in its first or third quarter and thereby at right angles to the position of the sun in relation to the earth, tidal ranges are about 20 percent less than normal.
In addition to these monthly variations of the tidal range, there are annual variations based on how near or far the sun is from the earth. The tidal range is remarkably greater during the fall and winter, for example, in the bays where I sail. At low tide, this makes running aground in unexpected locations much more likely during that time of year, but also provides for a greater margin of vertical clearance.
These variations can be seen at a glance in tidal calendars, where the time and height of the tides are given for each day and are graphically depicted by a line that rises and falls across a grid. Your local marine supply store is likely to have these calendars available as freebies at the counter. A little forethought regarding vertical clearance before slipping the lines can quite literally save the day.
|Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)|
|Thread||Thread Starter||Forum||Replies||Last Post|
|When up is down and down is up||PBzeer||Politics, Current Affairs, Guns & HOT Topics||8||04-12-2011 07:44 AM|
|Man beat up his ex after break-up (Hartlepool Mail)||NewsReader||News Feeds||0||11-03-2006 10:15 AM|
|Olympic sailing runner-up Yin tuning up for 2008 Olympics (People's Daily)||NewsReader||News Feeds||0||08-29-2006 09:17 PM|
|Re: Follow Up to the Follow Up re: Spectacle Isl. this weekend||NewsReader||Mass Bay Sailors||0||07-20-2006 01:15 PM|
|Follow Up to the Follow Up re: Spectacle Isl. this weekend||NewsReader||Mass Bay Sailors||0||07-20-2006 10:15 AM|