Archive for October, 2009

The ABC of Scend = D

Friday, October 23rd, 2009

First, for those people who don’t know what scend is, here is a definition:

Scend is the distance from sea level to the bottom of the trough of a wave. The trough can be taken as being equal to the height of the wave above sea level, or more simply as half the height of the wave. This means that, with a 3m sea running over a bar, the depth available to you may be 1.5m less than you would have in a flat sea.

So how does a navigator deal with it? You need to think of the charted level of the sea, the average height of the waves and swells combined. To this you add your calculation of the relevant state of tide and estimate the scend with the above definition in mind. Call that ‘A’.

‘B’ is the depth of the keel and the amount of scend. Subtract ‘B’ from ‘A’ to get ‘C’. If ‘C’ is negative there isn’t enough water. Even if it is positive there has to be a reasonable safety margin.

Then, depending how frightened you are, add a second safety margin. Call that ‘D’.

Offshore wind farms – another sailing hazard?

Tuesday, October 20th, 2009

If, like me, you’ve sailed through areas where oil rigs are located, you will know that they are easy to see, both during the day and at night. In fact, overnight they are lit up like well-decorated Christmas trees. Navigating to avoid them is, therefore, not difficult except perhaps when there’s fog.

But, after reading about a new wind farm development, I’ve been wondering what it would be like sailing through or near one, if that’s permitted.

The world’s largest offshore wind farm will be built in the UK off the Kent and Essex coasts. Located 12 miles offshore, it will be out of sight of land.

There will be 341 wind turbines generating 1,000 megawatts of electricity – enough to power all 750,000 homes in Kent and East Sussex and save 1.9million tonnes of carbon dioxide per annum.

Read the full article on this wind farm.

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Monday, October 5th, 2009
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Rules of the Road

Friday, October 2nd, 2009

Whether racing or cruising, you need to know which is the burdened boat, i.e. which boat must give way, in many different circumstances.

Giving way to boats on starboard may seem obvious but what about when you see a yacht running downwind towards you? Can you be sure which side the wind is crossing her deck? In fact, COLREGS state in Rule 12:

(iii) If a vessel with the wind on the port side sees a vessel to windward and cannot determine with certainty whether the other vessel has the wind on the port or on the starboard side, she shall keep out of the way of the other.

This is just one of the rules you can learn from our interactive Rules of the Road quiz, which is one of five comprising our brand new download, Nautical Knowledge.